β1D Integrin Inhibits Cell Cycle Progression in Normal Myoblasts and Fibroblasts*
- From the ‡Department of Biochemistry, American Red Cross, Rockville, Maryland 20855, the ¶Institute of Biology, University of Palermo, 90133 Palermo, and the Department of Biology, Genetics and Medical Chemistry, University of Torino, 10126 Torino, Italy
Abstract
Integrins are αβ heterodimeric transmembrane receptors involved in the regulation of cell growth and differentiation. The β1 integrin subunit is widely expressed in vivo and is represented by four alternatively spliced cytoplasmic domain isoforms. β1D is a muscle-specific variant of β1 integrin and a predominant β1 isoform in striated muscles. In the present study we showed that expression of the exogenous β1D integrin in C2C12 myoblasts and NIH 3T3 or REF 52 fibroblasts inhibited cell proliferation. Unlike the case of the common β1A isoform, adhesion of β1D-transfected C2C12 myoblasts specifically via the expressed integrin did not activate mitogen-activated protein kinases. The β1D-induced growth inhibitory signal was shown to occur late in the G1 phase of the cell cycle, before the G1-S transition. Ha-(12R)Ras, but not (Δ22W)Raf-1 oncogene, was able to overcome completely the β1D-triggered cell growth arrest in NIH 3T3 fibroblasts. Since perturbation of the β1D amino acid sequence in β1A/β1D chimeric integrins decreased the growth inhibitory signal, the entire cytoplasmic domain of β1D appeared to be important for this function. However, an interleukin-2 receptor-β1D chimera containing the cytoplasmic domain of β1D still efficiently inhibited cell growth, showing that the ectodomain and the ligand-binding site in β1D were not required for the growth inhibitory signal. Together, our data showed a new specific function for the alternatively spliced β1D integrin isoform. Since the onset of β1D expression during myodifferentiation coincides with the timing of myoblast withdrawal from the cell cycle, the growth inhibitory properties of β1D demonstrated in this study might reflect the major function for this integrin in commitment of differentiating skeletal muscle cells in vivo.
Footnotes
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↵* This work was supported by National Institutes of Health R29 Grant CA77697 (to A. M. B.) and National Institutes of Health Grant GM29860 (to Dr. Keith Burridge).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: Dept. of Biochemistry, American Red Cross, 15601 Crabbs Branch Way, Rockville, MD 20855. Tel.: 301-738-0725; Fax: 301-738-0794; E-mail: belkina{at}usa.redcross.org.
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↵1 The abbreviations used are: MAP, mitogen-activated protein; ECM, extracellular matrix; BrdUrd, bromodeoxyuridine; MBP, myelin basic protein; mAb, monoclonal antibody; IL2R, interleukin-2 receptor; DMEM, Dulbecco’s modified Eagle’s medium; CHO, Chinese hamster ovary; FBS, fetal bovine serum.
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↵3 M. Brancaccio, S. Cabodi, A. M. Belkin, G. Collo, V. E. Koteliansky, D. Tomatis, F. Altruda, L. Silengo, and G. Tarone, manuscript in preparation.
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↵2 A. M. Belkin, unpublished observations.
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- Received October 24, 1997.
- Revision received February 28, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
