IDENTIFICATION OF THE ALPHA-IIB-BETA-3 INTEGRIN IN MURINE TUMOR-CELLS

Previously, we have identified an alpha(IIb)beta-3-like integrin in tumor cells by using antibodies against platelet alpha(IIb)beta-3. However, alpha(IIb)beta-3 was considered to be expressed strictly in megakaryocyte lineage cells. In order to resolve this controversy, the alpha(IIb)beta-3-like integrin in murine B16 amelanotic melanoma (B16a) cells was characterized at DNA, RNA, and protein levels. The presence of alpha-5, alpha(v), alpha(IIb), beta-1, and beta-3 genes in B16a cells was confirmed by Southern analysis. mRNAs for all these integrins except alpha(v) were detectable by Northern blotting. The alpha(IIb)beta-3 protein was identified by Western blotting using subunit-specific antibodies and by immunoprecipitation using complex-specific antibody. The alpha(IIb)beta-3 integrin was localized intracellularly by immunocytochemistry. Finally, alpha(IIb) and beta-3 mRNAs were amplified by reverse transcription-polymerase chain reaction and the identity of alpha(IIb) was verified by sequencing. Partial DNA and deduced amino acid sequence analysis showed that B16a alpha(IIb) shares approximately 80% homology with the human alpha(IIb) and approximately 90% homology with the rat alpha(IIb), whereas B16a alpha(IIb) shares only approximately 26% homology with the human alpha(v). These experiments indicate that the alpha(IIb)beta-3-like protein in B16a cells is the authentic alpha(IIb)beta-3 and demonstrate, for the first time, that integrin alpha(IIb)beta-3 is not confined to megakaryocyte lineage cells.