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.
Highlights
The integrins are a large family of heterodimeric tegrins that arecrucial participants in the inflammatory and cell-surface glycoproteins that play key roles in the immune responses
B7 mRNA was detected in T cDNAs using the polymerase chain reaction (PCR)' and oliand B cell lines and in macrophage-likecell lines, but gonucleotide primers thatrecognize highly conserved integrin not eral in T
Thneovel cDNA is predicted to encode a 97-amino acid fragment of an integrin /3 subunit, designated p7,that is 40-61% identical to the corresponding fragments of the six previouslysequenced /3 subunits.We amplified similar partial cDNAs that presumablyencode the Integrins are a family of heterodimeric cell-surface glycoproteins that mediate adhesion of cells to other cells and to extracellular matrix [1].Leukocytes express a variety of inmouse and rabbithomologs of pi from mouse lymphocyteand macrophage-like lines (WR2.3 and P388D1) and from rabbit leukocytes obtained by bronchoalveolar lavage (>go% macrophages)
Summary
Thesequence of the GC-richregion beginning a t nucleotide 341 andending at nucleotide 370 could not be determined unambiguously with T 7 DNA polymerase and the standard dGTPcontaining sequencing reagent mixture. Both DNA strands were sequenced with Taq polymerase (TaqTrack, Promega Biotec)and with T7 DNA polymerase plus a deoxyinosine triphosphate-contain-. 92% of the cDNA sequence and independent hybridizing clones from each library (Fig. 1). 100% of the sequence of thepredictedopenreadingframe were obtained from both strands of DNA. 100% of the sequence of thepredictedopenreadingframe were obtained from two or more independent clones (see Fig. 1). Human leukocyte lines employedwere HUT78 T cells (ATCC TIB 161),Raji Burkitt lymphomacells (ATCC CCL 86),EBV-B6.1EBV-trans-
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