Complete amino acid sequence of an integrin beta subunit (beta 7) identified in leukocytes

Abstract

The integrins are a large family of heterodimeric cell-surface glycoproteins that play key roles in the adherence of cells to other cells and to extracellular matrix proteins. We have previously reported the identification of a novel integrin beta subunit partial cDNA from leukocytes. We have now determined the complete sequence of this subunit, designated as beta 7, from overlapping clones obtained from a PEER T leukemia cell library and a peripheral T cell library. The beta 7 cDNA contains a single large open reading frame predicted to encode a 798-amino acid protein precursor (signal peptide plus mature protein). The beta 7 protein, like the other beta subunit proteins, is predicted to contain a large extracellular portion, a transmembrane domain, and a cytoplasmic tail. The deduced beta 7 amino acid sequence is 32-46% identical to the six previously sequenced human integrin beta subunits. beta 7 is most similar to the leukocyte integrin common beta subunit (beta 2, CD18). Analysis of variant beta 7 cDNA clones and reverse transcription-polymerase chain reaction products suggest that alternatively spliced beta 7 mRNAs can be generated by the removal of exons that encode most of the cysteine-rich region of the extracellular portion of beta 7. By Northern blot analysis, beta 7 mRNA was detected in T and B cell lines and in macrophage-like cell lines, but not in any of the nonleukocyte cell lines tested. Peripheral T cells and some lymphoma lines express little beta 7 mRNA before stimulation; but after stimulation with phorbol ester, beta 7 mRNA levels increased markedly. Integrin beta 7 is expected to play a role in adhesive interactions of leukocytes.