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ß₁ Integrin Expression on Human Small Cell Lung Cancer Cells¹

Simpson Memorial Research Institute, Department of Internal Medicine, Division of Hematology and Oncology, The University of Michigan Medical School, Ann Arbor, Michigan 48109

The integrins are a supergene family of cell surface glycoproteins that promote cellular adhesion. Each member of the family is an /ß heterodimer composed of a distinct subunit noncovalently linked to one of at least six common ß subunits. These include the six ß₁ integrins (_1–6/ß₁) which represent receptors for extracellular matrix proteins and the three ß₂ integrins (_L, _M, _x/ß₂ that are expressed by leukocytes and which bind to C3bi and/or endothelial ligands. Recently, it was reported that certain human tumor cells express the ß₁ integrins and that small cell lung cancer (SCLC) cell lines express the ß₂ integrin Mo1 (_M/ß₂). To extend these initial observations, we examined SCLC cell lines for integrin expression at the glycoprotein and mRNA levels and assessed the potential function of these integrins in promoting SCLC adhesion. An indirect immunofluorescence analysis of five SCLC cell lines (NCI-H187, H345, H146, H209, and N417) using and ß subunit-specific monoclonal antibodies demonstrated the uniform expression of ß₁ (ß₁ >> ß₂ ß₃ ß₄). Among the ß₁-associated subunits, ₃ was uniformly expressed at high surface density by all five cell lines (as confirmed in H345 cells by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of anti-ß₁ and anti-₃ immunoprecipitates), while 5 was not detected. The leukocyte (ß₂-associated) _M and _L subunits were also variably expressed by the five lines. Consistent with the surface expression of ß₁ integrin gene products, ß₁ (but not ß₂) mRNA was detected in SCLC cells by Northern blot analysis. That ß₁ integrin expression was involved in SCLC adhesion was suggested by the adherence of H345 cells to laminin, a known ligand for the ₃ß₁ integrin. Moreover, an antibody specific for the ß₁ subunit inhibited this adhesion, indicating that the ß₁ subunit promotes adhesion to laminin. We conclude that ß₁ integrin molecules are expressed by human SCLC cells (with uniform expression of ₃/ß₁) and promote their adhesion to laminin.

¹ This work was supported by NIH Grants R01CA39064 (R. F. T.) and National Research Service Award IF32CA08873-01 (L. E. F.).

² To whom requests for reprints should be addressed, at Simpson Memorial Research Institute, The University of Michigan, 102 Observatory Street, Ann Arbor, MI 48109.

Received 7/10/90. Accepted 12/ 3/90.

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