Cloning and Characterization of a Novel Integrin β3Subunit*
- Chandrika S. Kumar‡§,
- Ian E. James¶,
- Angela Wong¶,
- Vincent Mwangi‡,
- John A. Feild‡,
- Parvathi Nuthulaganti‡,
- Janice R. Connor¶,
- Christopher Eichman‖,
- Fadia Ali**,
- Shing Mei Hwang¶,
- David J. Rieman¶,
- Fred H. Drake¶ and
- Maxine Gowen¶
- From the Departments of ‡Molecular Genetics,¶Cellular Biochemistry, ‖Molecular Immunology, and**Medicinal Chemistry, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406
Abstract
We have identified a novel integrin β3 subunit, termed β3C, from a human osteoclast cDNA library. The COOH-terminal sequence and 3′-untranslated region of the β3C subunit differs from the previously reported β3A (platelet) and β3B (placenta) sequences, while the regions coding for the transmembrane and extracellular domains are identical. The β3C cytoplasmic domain contains 37 amino acids, the last 17 of which are encoded by a novel exon located about 6 kilobase pairs downstream of exon 14 of the β3A gene. HEK 293 cells were stably co-transfected with αV and either β3C (HEKβ3C) or β3A(HEKβ3A). The viability of HEKβ3C cells was lower than that of HEKβ3A cells, and HEKβ3Ccells in culture grew as clusters rather than as a monolayer. The novel cytoplasmic domain did not affect receptor binding affinity; both αVβ3A and αVβ3Cisoforms exhibited high affinity binding to 125I-echistatin and cyclic and linear RGD peptides. However, in contrast to HEKβ3A, HEKβ3C cells failed to adhere to osteopontin, an αVβ3 matrix protein. The data provide further support for the key role of the cytoplasmic domain of the β3 integrin in cell adhesion and suggest a potential role for the β3C integrin subunit in modulating cell-matrix interactions.
Footnotes
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ To whom correspondence should be addressed: SmithKline Beecham Pharmaceuticals, R&D, 709 Swedeland Rd., P.O. Box 1539, King of Prussia, PA 19406. Tel.: 610-270-7626; Fax: 610-270-5093.
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↵1 For the sake of uniformity with other β3 variants, we refer to this novel β3subunit as β3C to distinguish it from the β3A (platelet/endothelial cell) and β3B(placenta) subunits.
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↵2 The abbreviations used are: PCR, polymerase chain reaction; RT, reverse transcriptase; UTR, untranslated region; kb, kilobase pair(s); bp, base pair(s).
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- Received November 22, 1996.
- Revision received March 18, 1997.
