Career Narrative of Dr. Timothy A. Springer

Dr. Springer's CV

I majored in Biochemistry at the University of California, and graduated Phi Beta Kappa with Distinction and the Departmental Citation. I received my Ph.D. in biochemistry working with Jack Strominger on the isolation, protein chemistry, and organization in the membrane of major histocompatibility complex antigens. Realizing the power of monoclonal antibodies for the characterization of proteins on the cell surface, I did postdoctoral work with César Milstein. I started as an Assistant Professor at Harvard Medical School in 1977 where I have been ever since, moving a few blocks down the street to the Dana-Farber Cancer Institute in 1981 and to the CBR Institute for Biomedical Research in 1988.

In the 1970’s, little was known about how cells of the immune system recognized other cells, although cell-cell communication was known to be important for immune responses. In cell biology, little was known about how cells adhered to one another to form the specific architecture of organs; specific adhesion molecules were one possibility but simple sorting out by nonspecific physicochemical properties was also proposed. Immunologists envisioned that the only important receptor for foreign antigen-bearing cells would be the T lymphocyte receptor for antigen; however, conjugation of killer lymphocytes to target cells was found to require Mg2+. Based on what was known of antigen recognition by antibodies, it did not seem likely that Mg2+ would be required by a T cell antigen receptor. Therefore, I hypothesized that cell adhesion molecules might be present on lymphocytes, and sought to find them using monoclonal antibodies. The idea was to screen for antibodies able to block antigen-specific killing of target cells by lymphocytes, and therefore to focus discovery on the small subset of surface molecules important in cell recognition.

In collaboration with the lab of Eric Martz, I discovered lymphocyte function-associated antigen-1 (LFA-1) in the mouse (1-3). Subsequently, in a collaboration that used human cytolytic cell lines provided by Steve Burakoff and Jack Strominger’s labs, Francisco Sanchez-Madrid and I immunized mice, prepared hybridomas, and screened for inhibition by the hybridoma supernatants of T cell-mediated killing, and cloned the relevant hybridomas and identified their target antigens by immunoprecipitation. In two remarkably productive fusions, we identified in the human what we called the lymphocyte function-associated antigens LFA-1, LFA-2 (CD2), and LFA-3 (4). Later, Bob Rothlein and I discovered a counter-receptor for LFA-1 that we called intercellular adhesion molecule-1 (5). Our initial work suggested that LFA-1 must also have other counter-receptors; subsequently, ICAM-2 was discovered by functional cloning with Don Staunton (6) and ICAM-3 was discovered by antibodies with Tony de Fougerolles (7, 8).
In a collaboration with Steve Shaw’s lab we discovered that CD2 and LFA-3 participated in an adhesion pathway distinct from that in which LFA-1 functioned (9). Using purified molecules in suspension or reconstituted in lipid bilayers, Dustin and Selvaraj in my laboratory directly demonstrated binding of CD2 to LFA-3 (10-12). Thus CD2 and LFA-3 functioned as cell adhesion molecules, and this was the first heterophilic adhesive interaction demonstrated in cell biology, coming after the first homophilic interaction between NCAM molecules identified in the Edelman lab.

Using purified molecules, Marlin and Dustin in my lab demonstrated that LFA-1 was a receptor for ICAMs, and that recognition required Mg2+, explaining the Mg2+ requirement for adhesive interactions by lymphocytes (13). After discovering LFA-1, I noticed that its polypeptides were remarkably similar to a macrophage differentiation antigen I had been working on termed Mac-1 (14). Based on the functional relevance of LFA-1 on lymphocytes, we sought in collaboration with Emil Unanue’s lab a function for Mac-1 on macrophages, and found it was a receptor for the complement component iC3b (15). My lab found that Mac-1 and LFA-1 were each noncovalently associated ab heterodimers, and had identical b subunits and distinct a subunits (16-19). Later, using protein purified in my lab, and N-terminal amino acid sequencing in Bill Dreyer’s lab, we found that the Mac-1 aM and LFA-1 aL subunits were 35% identical, and thus evolved by gene duplication and divergence (20). The above studies were the first evidence for the integrin family, which rapidly expanded when N-terminal sequence became available on fibronectin, vitronectin, and fibrinogen receptors from other labs (21, 22), and subsequently when integrin a and b subunit cDNA sequences were determined in this and other labs (22-29).

How could adhesion molecules function in antigen-specific recognition? Dustin and I discovered that the integrin LFA-1 was basally inactive, and that activation of lymphocytes through the T cell receptor initiated intracellular pathways that fed into the cytoplasmic domains of LFA-1, and activated adhesiveness of its extracellular domain, a process we termed inside-out signaling (30).

Our earliest studies had shown that antigen-specific recognition by the T cell receptor was highly cooperative with the CD2 : LFA-3 and LFA-1 : ICAM adhesion pathways, since blocking either of these pathways greatly decreased the efficiency of antigen-specific recognition (31). This has led to important therapeutics for autoimmune disease. Dustin and I purified the LFA-3 protein, and in a collaboration with Biogen, protein sequence was used to identify a LFA-3 cDNA clone (32). Biogen subsequently developed a fusion between the extracellular domain of LFA-3 and the Fc portion of IgG1 as a therapeutic that blocks the CD2 : LFA-3 adhesion pathway and also depletes ~ 35% of the memory T lymphocyte subset, which express more CD2 than naïve T cells. This therapeutic was approved in January 2003 by the FDA for treatment of patients with moderate to severe psoriasis. It is marketed by Biogen with the proprietary name Amevive, and has the generic name alefacept (LFA-cept). Although we were the first to make antibodies to both mouse and human LFA-1(3, 4), we never patented them. Shortly after us, Hildreth and McMichael made an anti-human LFA-1 antibody (33), and subsequently licensed it to Genentech , which with XOMA, “humanized” it. This therapeutic antibody, which is directed to the aL subunit’s I domain, blocks the LFA-1 : ICAM adhesion pathway, and down-modulates the amount of LFA-1 expressed on lymphocyte surfaces, and does not deplete lymphocytes. Known as Raptiva or generically as efalizumab, this therapeutic was approved by the FDA for moderate and severe psoriasis in October 2003.

With Don Anderson, I discovered that mutations in the integrin b subunit common to LFA-1 and Mac-1 caused leukocyte adhesion deficiency, a life-threatening inherited disease in which leukocyte binding to endothelium and subsequent migration into infected tissues is defective (34, 35). My interest and work on leukocyte-endothelial interactions (36) led Lawrence and I to discover that adhesion through selectins mediates transient, rolling interactions that constitute the first step in leukocyte surveillance of endothelium (37). Furthermore, we reconstituted with purified components in vitro the rolling and firm adhesion steps that had been demonstrated more than a 100 years earlier to occur on endothelium in vivo when leukocytes accumulated at inflammatory sites. When leukocytes in a parallel wall flow chamber were exposed to P-selectin and ICAM-1 on the lower wall, they accumulated and rolled on the P-selectin; however, no interaction with the ICAM-1 occurred. When a chemoattractant was added to the flow stream that was known to bind to a G-protein coupled receptor on the leukocytes, the integrins on the leukocytes immediately became activated, enabling the leukocytes to become firmly adherent to the ICAM-1. The “inside-out” activation of the integrin in response to signals received by other receptors on the cell resembled the activation of LFA-1 we had previously observed after antigen recognition by lymphocytes. Thus, we demonstrated the three-step model of leukocyte localization at inflammatory sites, in which selectin-mediated rolling on endothelium exposes leukocytes to chemoattractants, which bind to G protein-coupled receptors and activate firm adhesion through integrins (37, 38). The subsequent emigration out of the blood stream into tissues is also mediated by integrins. Independently and working in vivo, von Andrian, Arfors, Butcher and colleagues demonstrated that rolling through L-selectin preceded firm adhesion through integrins, and proposed a similar model (39).

There have been additional intersections of my basic research with important clinical problems. Along with another group, we found that ICAM-1 was the receptor for rhinoviruses, the most predominant of the common cold viruses (40, 41). We subsequently showed that the binding sites for LFA-1 and rhinovirus on ICAM-1 are distinct but overlapping (42). Based on the blockade by Pertussis toxin of lymphocyte exit from the bloodstream, I hypothesized that there should be G protein-coupled receptors on lymphocytes for chemoattractants that regulated lymphocyte recirculation and tissue localization (38). Subsequently, Bleul and I identified SDF-1 as a primordial chemoattractant for lymphocytes and other cells (43). The search for its receptor led us and colleagues to fusin, now known as CXCR4 (44, 45). We showed that the major co-receptor on T lymphocytes for human immunodeficiency virus was identical to CXCR4, the receptor for SDF-1, and that SDF-1 would block HIV infection in vitro. Recently Shimaoka and I investigated the mechanism of action of small molecule antagonists of LFA-1, and discovered a previously unsuspected, third mechanism of antagonism of integrins (46).

At one stage in my career, I cloned and determined the amino acid sequences of many of the proteins I had discovered, including the integrin aL, aM, aX, and b2 subunits (27, 29, 47, 48), LFA-3 (32), and ICAM-1, ICAM-2, and ICAM-3 (6, 49, 50). We then carried out structure and function studies to define ligand binding and other functionally important sites on these molecules, and transfection or knockout studies to examine biological function.

More recently in my career, I have been seeking to understand, at the atomic level in three dimensions, the structure of these molecules, and how change in three dimensional structure, termed conformational change, can be communicated across membranes and regulate protein functions such as ligand binding. I have predicted b-propeller domains in two families of extracellular proteins, a seven-bladed propeller in integrins (51) and six-bladed YWTD propellers in endocytic/signaling receptors (52) and related seven-bladed propellers in Archaea (53). We have determined crystal structures of three different predicted b-propellers, in the low density lipoprotein receptor in collaboration with Takagi, Eck, and Blacklow (54), in an archaeal surface layer protein with Jing, Takagi, and Wang (53), and in nidogen in complex with laminin, with Takagi and Wang (55). We have determined atomic crystal structures of ICAM-2, ICAM-1, and MAdCAM-1 (56-58) with Casasnovas and Wang. With Lu, Shimaoka, Xiao, and Wang, we mutated I domains to stabilize them in different conformational states that varied 10,000-fold in affinity for ligand (59-62), and determined the structure of aL I domains in three distinct conformations termed open, intermediate, and closed, and in complex with the ligand ICAM-1 (63). In the LFA-1 I domain : ICAM-1 complex, a Mg2+ ion in the I domain ligates a Glu residue in ICAM-1, demonstrating at the atomic level why Mg2+ is required for leukocyte binding to other cells. An NMR structure of two domains in the integrin b2 subunit was determined with Beglova, Takagi, and Blacklow (64), and electron microscope structures of the extracellular domain of integrin aVb3 and the headpiece of integrin a5b1 bound to a module in fibronectin were determined with Takagi and Walz (65, 66). These structures and associated biochemical and functional assays have demonstrated a dramatic, switchblade-like opening of the extracellular domain of integrins that is associated with activation, and that a change in angle between the b subunit I-like and hybrid domains is linked to a change in affinity at the ligand binding site at the opposite end of the I-like domain. Further studies demonstrate that in both the I-like domain of integrin b subunits, and the I domain of integrin a subunits, conformational changes are transmitted by similar helix piston motions between the “top” of the domain where ligand is bound, and the “bottom” of the domain that connects to other domains.

A major focus of my current work is defining how conformational change is transmitted in integrins across the lipid bilayer in which they are embedded. With Kim and Carman, I have demonstrated that movement apart of integrin a and b subunit cytoplasmic domains is directly linked to the switchblade-like opening of their extracellular domains (67).

Another aspect of my research is concerned with how receptor: ligand bonds can withstand the substantial forces that are applied when they mediate adhesion of leukocytes to the blood vessel wall in flowing blood. We have measured how koff values for both selectin and integrin bonds are increased by the forces applied in shear flow, to understand their mechanical properties (68-70). We demonstrated a surprising phenomenon, that shear flow actually enhances receptor-ligand bond formation (71), and with Chen that the increased number of bonds that form at higher flow rates compensates for their increased rate of breakage by the increased applied force (72). This “automatic braking system” is essential to yield the observed relative insensitivity of leukocyte rolling velocity to the shear stress (flow rate) in vitro and in vivo. Post capillary venules differ markedly from one tissue to another in flow rates, and the automatic braking system gives rolling leukocytes a similar amount of time, independent of flow velocity, to survey endothelium for other signs of inflammation such as chemoattractants. Receptor : ligand bonds that resist force require distinctive specializations that are not required in the more typical receptors that bind soluble ligands, and we are defining the molecular basis for this specialization.

While continuing my academic work, I founded as an outside consultant a company called LeukoSite in 1992. Two drugs that were already in development by LeukoSite at the time of its acquisition by Millennium Pharmaceuticals in 1999 were subsequently approved by the FDA, an antibody called CamPath (alemtuzumab) for the treatment of chronic lymphocytic leukemia in 2001, and a proteosome inhibitor called Velcade (bortezomib) in 2003 for treatment of multiple myeloma.

My academic work has been widely recognized. Since 1989 I have held a chair endowed by the Latham family at Harvard Medical School. My research work is funded by NIH grant R01 CA31798 (1981-2014) “Lymphocyte function-associated antigens”; NIH grant R01 CA31799 (1981-2006) “Leukocyte adhesion receptors Mac-1 and p150,95”; and a program project grant that I lead, NIH grant P01 HL48675 (1992-2005) “Integrins and modular surface proteins in vasculature.” I received a MERIT NIH grant award in 1988 and will begin another one in 2004 when CA31798 will be renewed for 10 years. I received faculty awards from the American Cancer Society in 1981 and 1984. Many keynote addresses, distinguished lectureships, visiting professorships, and meetings I have organized are listed on my CV. I received the Basic Research Prize from the American Heart Association in 1993, the William B. Coley Medal for Distinguished Research in Fundamental Immunology from the Cancer Research Institute in 1995, and the highest award of the Society for Leukocyte Biology in 1995. In 1996 I was elected to the National Academy of Science, and in 2001 to the American Academy of Arts and Sciences. In 2000 I moved from Section 43, Immunology and Microbiology, at the National Academy of Sciences to the newly created Section 29, Biophysics. I was elected to be the chair of Section 29 for a three year term beginning in 2004.

The publications describing my research have been widely cited, showing that other scientists value my work. An analysis by ISI (ScienceWatch.com) of “high impact” publications in immunology – the 300 most cited papers in each of the years 1990-1994 - ranked me first, both in total citations to high impact papers, 2,801, and citations per high impact paper, 700. In an analysis by ISI of the most-cited researchers in all fields of science in the twenty year period 1983-2002, I was found to rank eleventh, with 54,737 citations by other authors to 438 of my publications.

References:

1. Kürzinger, K., T. Reynolds, R. N. Germain, D. Davignon, E. Martz, and T. A. Springer. 1981. A novel lymphocyte function-associated antigen (LFA-1): cellular distribution, quantitative expression, and structure. J. Immunol. 127:596.
2. Davignon, D., E. Martz, T. Reynolds, K. Kürzinger, and T. A. Springer. 1981. Monoclonal antibody to a novel lymphocyte function-associated antigen (LFA-1): Mechanism of blocking of T lymphocyte-mediated killing and effects on other T and B lymphocyte functions. J. Immunol. 127:590.
3. Davignon, D., E. Martz, T. Reynolds, K. Kürzinger, and T. A. Springer. 1981. Lymphocyte function-associated antigen 1 (LFA-1): A surface antigen distinct from Lyt-2,3 that participates in T lymphocyte-mediated killing. Proc. Natl. Acad. Sci. U.S.A. 78:4535.
4. Sanchez-Madrid, F., A. M. Krensky, C. F. Ware, E. Robbins, J. L. Strominger, S. J. Burakoff, and T. A. Springer. 1982. Three distinct antigens associated with human T lymphocyte-mediated cytolysis: LFA-1, LFA-2, and LFA-3. Proc. Natl. Acad. Sci. U.S.A. 79:7489.
5. Rothlein, R., M. L. Dustin, S. D. Marlin, and T. A. Springer. 1986. A human intercellular adhesion molecule (ICAM-1) distinct from LFA-1. J. Immunol. 137:1270.
6. Staunton, D. E., M. L. Dustin, and T. A. Springer. 1989. Functional cloning of ICAM-2, a cell adhesion ligand for LFA-1 homologous to ICAM-1. Nature 339:61.
7. de Fougerolles, A. R., S. A. Stacker, R. Schwarting, and T. A. Springer. 1991. Characterization of ICAM-2 and evidence for a third counter-receptor for LFA-1. J. Exp. Med. 174:253.
8. de Fougerolles, A. R., and T. A. Springer. 1992. Intercellular adhesion molecule 3, a third adhesion counter-receptor for lymphocyte function-associated molecule 1 on resting lymphocytes. J. Exp. Med. 175:185.
9. Shaw, S., G. E. G. Luce, R. Quinones, R. E. Gress, T. A. Springer, and M. E. Sanders. 1986. Two antigen-independent adhesion pathways used by human cytotoxic T cell clones. Nature 323:262.
10. Dustin, M. L., M. E. Sanders, S. Shaw, and T. A. Springer. 1987. Purified lymphocyte function-associated antigen-3 (LFA-3) binds to CD2 and mediates T lymphocyte adhesion. J. Exp. Med. 165:677.
11. Selvaraj, P., M. L. Plunkett, M. L. Dustin, M. E. Sanders, S. Shaw, and T. A. Springer. 1987. The T lymphocyte glycoprotein CD2 (LFA-2/T11/E-Rosette receptor) binds the cell surface ligand LFA-3. Nature 326:400.
12. Plunkett, M. L., M. E. Sanders, P. Selvaraj, M. L. Dustin, and T. A. Springer. 1987. Rosetting of activated human T lymphocytes with autologous erythrocytes: Definition of the receptor and ligand molecules as CD2 and lymphocyte function-associated antigen 3 (LFA-3). J. Exp. Med. 165:664.
13. Marlin, S. D., and T. A. Springer. 1987. Purified intercellular adhesion molecule-1 (ICAM-1) is a ligand for lymphocyte function-associated antigen 1 (LFA-1). Cell 51:813.
14. Springer, T. A., G. Galfre, D. S. Secher, and C. Milstein. 1979. Mac-1: a macrophage differentiation antigen identified by monoclonal antibody. Eur. J. Immunol. 9:301.
15. Beller, D. I., T. A. Springer, and R. D. Schreiber. 1982. Anti-Mac-1 selectively inhibits the mouse and human type three complement receptor. J. Exp. Med. 156:1000.
16. Kürzinger, K., M. K. Ho, and T. A. Springer. 1982. Structural homology of a macrophage differentiation antigen and an antigen involved in T-cell-mediated killing. Nature 296:668.
17. Kürzinger, K., and T. A. Springer. 1982. Purification and structural characterization of LFA-1, a lymphocyte function-associated antigen, and Mac-1, a related macrophage differentiation antigen. J. Biol. Chem. 257:12412.
18. Sanchez-Madrid, F., P. Simon, S. Thompson, and T. A. Springer. 1983. Mapping of antigenic and functional epitopes on the a and b subunits of two related glycoproteins involved in cell interactions, LFA-1 and Mac-1. J. Exp. Med. 158:586.
19. Sanchez-Madrid, F., J. Nagy, E. Robbins, P. Simon, and T. A. Springer. 1983. A human leukocyte differentiation antigen family with distinct a subunits and a common b subunit: The lymphocyte function-associated antigen (LFA-1), the C3bi complement receptor (OKM1/Mac-1), and the p150,95 molecule. J. Exp. Med. 158:1785.
20. Springer, T. A., D. B. Teplow, and W. J. Dreyer. 1985. Sequence homology of the LFA-1 and Mac-1 leukocyte adhesion glycoproteins and unexpected relation to leukocyte interferon. Nature 314:540.
21. Charo, I. F., L. A. Fitzgerald, B. Steiner, S. C. Rall, Jr., L. S. Bekeart, and D. R. Phillips. 1986. Platelet glycoproteins IIb and IIIa: Evidence for a family of immunologically and structurally related glycoproteins in mammalian cells. Proc. Natl. Acad. Sci. U.S.A. 83:8351.
22. Suzuki, S., R. Pytela, H. Arai, W. S. Argraves, T. Krusius, M. D. Pierschbacher, and E. Ruoslahti. 1986. cDNA and amino acid sequences of the cell adhesion protein receptor recognizing vitronectin reveal a transmembrane domain and homologies with other adhesion protein receptors. Proc. Natl. Acad. Sci. U.S.A. 83:8614.
23. Fitzgerald, L. A., B. Steiner, S. C. Rall, Jr., S. Lo, and D. R. Phillips. 1987. Protein sequence of endothelial glycoprotein IIIa derived from a cDNA clone. Identity with platelet glycoprotein IIIa and similarity to "integrin". J. Biol. Chem. 262:3936.
24. Fitzgerald, L. A., M. Poncz, B. Steiner, S. C. Rall, Jr., J. S. Bennett, and D. R. Phillips. 1987. Comparison of cDNA-derived protein sequences of the human fibronectin receptor and vitronectin receptor a-subunits and platelet glycoprotein IIb. Biochemistry 26:8158.
25. Poncz, M., R. Eisman, R. Heidenreich, S. M. Silver, G. Vilaire, S. Surrey, E. Schwartz, and J. S. Bennett. 1987. Structure of the platelet membrane glycoprotein IIb: Homology to the alpha subunits of the vitronectin and fibronectin membrane receptors. J. Biol. Chem. 262:8476.
26. Argraves, W. S., S. Suzuki, H. Arai, K. Thompson, M. D. Pierschbacher, and E. Ruoslahti. 1987. Amino acid sequence of the human fibronectin receptor. J. Cell Biol. 105:1183.
27. Corbi, A. L., L. J. Miller, K. O'Connor, R. S. Larson, and T. A. Springer. 1987. cDNA cloning and complete primary structure of the a subunit of a leukocyte adhesion glycoprotein, p150,95. EMBO J. 6:4023.
28. Tamkun, J. W., D. W. DeSimone, D. Fonda, R. S. Patel, C. Buck, A. F. Horwitz, and R. O. Hynes. 1986. Structure of integrin, a glycoprotein involved in the transmembrane linkage between fibronectin and actin. Cell 46:271.
29. Kishimoto, T. K., K. O'Connor, A. Lee, T. M. Roberts, and T. A. Springer. 1987. Cloning of the b subunit of the leukocyte adhesion proteins: Homology to an extracellular matrix receptor defines a novel supergene family. Cell 48:681.
30. Dustin, M. L., and T. A. Springer. 1989. T cell receptor cross-linking transiently stimulates adhesiveness through LFA-1. Nature 341:619.
31. Springer, T. A. 1990. Adhesion receptors of the immune system. Nature 346:425.
32. Wallner, B. P., A. Z. Frey, R. Tizard, R. J. Mattaliano, C. Hession, M. E. Sanders, M. L. Dustin, and T. A. Springer. 1987. Primary structure of lymphocyte function associated antigen-3 (LFA-3): The ligand of the T-lymphocyte CD2 glycoprotein. J. Exp. Med. 166:923.
33. Hildreth, J. E. K., F. M. Gotch, P. D. K. Hildreth, and A. J. McMichael. 1983. A human lymphocyte-associated antigen involved in cell-mediated lympholysis. Eur. J. Immunol. 13:202.
34. Springer, T. A., W. S. Thompson, L. J. Miller, F. C. Schmalstieg, and D. C. Anderson. 1984. Inherited deficiency of the Mac-1, LFA-1, p150,95 glycoprotein family and its molecular basis. J. Exp. Med. 160:1901.
35. Kishimoto, T. K., N. Hollander, T. M. Roberts, D. C. Anderson, and T. A. Springer. 1987. Heterogenous mutations in the b subunit common to the LFA-1, Mac-1, and p150,95 glycoproteins cause leukocyte adhesion deficiency. Cell 50:193.
36. Dustin, M. L., and T. A. Springer. 1988. Lymphocyte function associated antigen-1 (LFA-1) interaction with intercellular adhesion molecule-1 (ICAM-1) is one of at least three mechanisms for lymphocyte adhesion to cultured endothelial cells. J. Cell Biol. 107:321.
37. Lawrence, M. B., and T. A. Springer. 1991. Leukocytes roll on a selectin at physiologic flow rates: distinction from and prerequisite for adhesion through integrins. Cell 65:859.
38. Springer, T. A. 1994. Traffic signals for lymphocyte recirculation and leukocyte emigration: the multi-step paradigm. Cell 76:301.
39. von Andrian, U. H., J. D. Chambers, L. M. McEvoy, R. F. Bargatze, K. E. Arfors, and E. C. Butcher. 1991. Two-step model of leukocyte-endothelial cell interaction in inflammation: Distinct roles for LECAM-1 and the leukocyte b2 integrins in vivo. Proc. Natl. Acad. Sci. U.S.A. 88:7538.
40. Staunton, D. E., V. J. Merluzzi, R. Rothlein, R. Barton, S. D. Marlin, and T. A. Springer. 1989. A cell adhesion molecule, ICAM-1, is the major surface receptor for rhinoviruses. Cell 56:849.
41. Greve, J. M., G. Davis, A. M. Meyer, C. P. Forte, S. C. Yost, C. W. Marlor, M. E. Kamarck, and A. McClelland. 1989. The major human rhinovirus receptor is ICAM-1. Cell 56:839.
42. Staunton, D. E., M. L. Dustin, H. P. Erickson, and T. A. Springer. 1990. The arrangement of the immunoglobulin-like domains of ICAM-1 and the binding sites for LFA-1 and rhinovirus. Cell 61:243.
43. Bleul, C. C., R. C. Fuhlbrigge, J. M. Casasnovas, A. Aiuti, and T. A. Springer. 1996. A highly efficacious lymphocyte chemoattractant, stromal cell-derived factor 1 (SDF-1). J. Exp. Med. 184:1101.
44. Bleul, C. C., M. Farzan, H. Choe, C. Parolin, I. Clark-Lewis, J. Sodroski, and T. A. Springer. 1996. The lymphocyte chemoattractant SDF-1 is a ligand for LESTR/fusin and blocks HIV-1 entry. Nature 382:829.
45. Oberlin, E., A. Amara, F. Bachelerie, C. Bessia, J.-L. Virelizier, A. Arenzana-Seisdedos, O. Schwartz, J.-M. Heard, I. Clark-Lewis, D. F. Legler, M. Loetscher, M. Baggiolini, and B. Moser. 1996. The CXC chemokine, stromal cell derived factor 1 (SDF-1), is the ligand for LESTR/fusin and prevents infection by T-cell-line-adapted HIV-1. Nature 382:833.
46. Shimaoka, M., A. Salas, W. Yang, G. Weitz-Schmidt, and T. A. Springer. 2003. Small molecule integrin antagonists that bind to the b2 subunit I-like domain and activate signals in one direction and block them in another. Immunity 19:391.
47. Larson, R. S., A. L. Corbi, L. Berman, and T. A. Springer. 1989. Primary structure of the LFA-1 a subunit: An integrin with an embedded domain defining a protein superfamily. J. Cell Biol. 108:703.
48. Corbi, A. L., T. K. Kishimoto, L. J. Miller, and T. A. Springer. 1988. The human leukocyte adhesion glycoprotein Mac-1 (Complement receptor type 3, CD11b) a subunit: Cloning, primary structure, and relation to the integrins, von Willebrand factor and factor B. J. Biol. Chem. 263:12403.
49. Staunton, D. E., S. D. Marlin, C. Stratowa, M. L. Dustin, and T. A. Springer. 1988. Primary structure of intercellular adhesion molecule 1 (ICAM-1) demonstrates interaction between members of the immunoglobulin and integrin supergene families. Cell 52:925.
50. de Fougerolles, A. R., L. B. Klickstein, and T. A. Springer. 1993. Cloning and expression of intercellular adhesion molecule 3 reveals strong homology to other immunoglobulin family counter-receptors for lymphocyte function-associated antigen-1. J. Exp. Med. 177:1187.
51. Springer, T. A. 1997. Folding of the N-terminal, ligand-binding region of integrin a-subunits into a b-propeller domain. Proc. Natl. Acad. Sci. U.S.A. 94:65.
52. Springer, T. A. 1998. An extracellular b-propeller module predicted in lipoprotein and scavenger receptors, tyrosine kinases, epidermal growth factor precursor, and extracellular matrix components. J. Mol. Biol. 283:837.
53. Jing, H., J. Takagi, J.-h. Liu, S. Lindgren, R.-G. Zhang, A. Joachimiak, J.-h. Wang, and T. A. Springer. 2002. Archaeal surface layer proteins contain b-propeller, polycystic kidney disease, and b-helix domains, and are related to metazoan cell surface proteins. Structure 10:1453.
54. Jeon, H., W. Meng, J. Takagi, M. J. Eck, T. A. Springer, and S. C. Blacklow. 2001. Implications for familial hypercholesterolemia from structure of the LDL receptor YWTD-EGF domain pair. Nat. Struc. Biol. 8:499.
55. Takagi, J., Y. Yang, J.-h. Liu, J.-h. Wang, and T. A. Springer. 2003. Complex between nidogen and laminin fragments reveals a paradigmatic b-propeller interface. Nature 424.
56. Casasnovas, J. M., T. A. Springer, J.-h. Liu, S. C. Harrison, and J.-h. Wang. 1997. The crystal structure of ICAM-2 reveals a distinctive integrin recognition surface. Nature 387:312.
57. Casasnovas, J. M., T. Stehle, J.-h. Liu, J.-h. Wang, and T. A. Springer. 1998. A dimeric crystal structure for the N-terminal two domains of ICAM-1. Proc. Natl. Acad. Sci. U.S.A. 95:4134.
58. Tan, K., J. M. Casasnovas, J.-h. Liu, M. J. Briskin, T. A. Springer, and J.-h. Wang. 1998. The structure of immunoglobulin superfamily domains 1 and 2 of MAdCAM-1 reveals novel features important for integrin recognition. Structure 6:793.
59. Lu, C., M. Shimaoka, M. Ferzly, C. Oxvig, J. Takagi, and T. A. Springer. 2001. An isolated, surface-expressed I domain of the integrin aLb2 is sufficient for strong adhesive function when locked in the open conformation with a disulfide. Proc. Natl. Acad. Sci. U. S. A. 98:2387.
60. Lu, C., M. Shimaoka, Q. Zang, J. Takagi, and T. A. Springer. 2001. Locking in alternate conformations of the integrin aLb2 I domain with disulfide bonds reveals functional relationships among integrin domains. Proc. Natl. Acad. Sci. U. S. A. 98:2393.
61. Shimaoka, M., C. Lu, A. Salas, T. Xiao, J. Takagi, and T. A. Springer. 2002. Stabilizing the integrin aM inserted domain in alternative conformations with a range of engineered disulfide bonds. PNAS 99:16737.
62. Shimaoka, M., C. Lu, R. Palframan, U. H. von Andrian, J. Takagi, and T. A. Springer. 2001. Reversibly locking a protein fold in an active conformation with a disulfide bond: integrin aL I domains with high affinity and antagonist activity in vivo. Proc. Natl. Acad. Sci. U. S. A. 98:6009.
63. Shimaoka, M., T. Xiao, J.-H. Liu, Y. Yang, Y. Dong, C.-D. Jun, A. McCormack, R. Zhang, A. Joachimiak, J. Takagi, J.-h. Wang, and T. A. Springer. 2003. Structures of the aL I domain and its complex with ICAM-1 reveal a shape-shifting pathway for integrin regulation. Cell 112:99.
64. Beglova, N., S. C. Blacklow, J. Takagi, and T. A. Springer. 2002. Cysteine-rich module structure reveals a fulcrum for integrin rearrangement upon activation. Nat. Struct. Biol. 9:282.
65. Takagi, J., B. M. Petre, T. Walz, and T. A. Springer. 2002. Global conformational rearrangements in integrin extracellular domains in outside-in and inside-out signaling. Cell 110:599.
66. Takagi, J., K. Strokovich, T. A. Springer, and T. Walz. 2003. Structure of integrin a5b1 in complex with fibronectin. EMBO J. 22:4607.
67. Kim, M., C. V. Carman, and T. A. Springer. 2003. Bidirectional transmembrane signaling by cytoplasmic domain separation in integrins. Science 301:1720.
68. Alon, R., D. A. Hammer, and T. A. Springer. 1995. Lifetime of the P-selectin: carbohydrate bond and its response to tensile force in hydrodynamic flow. Nature 374:539.
69. Chen, S., and T. A. Springer. 2001. Selectin receptor-ligand bonds: Formation limited by shear rate and dissociation governed by the Bell model. Proc. Natl. Acad. Sci. U. S. A. 98:950.
70. de Chateau, M., S. Chen, A. Salas, and T. A. Springer. 2001. Kinetic and mechanical basis of rolling through an integrin and novel Ca2+-dependent rolling and Mg2+-dependent firm adhesion modalities for the a4b7-MAdCAM-1 interaction. Biochemistry 40:13972.
71. Finger, E. B., K. D. Puri, R. Alon, M. B. Lawrence, U. H. von Andrian, and T. A. Springer. 1996. Adhesion through L-selectin requires a threshold hydrodynamic shear. Nature 379:266.
72. Chen, S., and T. A. Springer. 1999. An automatic braking system that stabilizes leukocyte rolling by an increase in selectin bond number with shear. J. Cell Biol. 144:185.