Cloning and sequence analysis of a novel β2related integrin transcript from T lymphocytes: homology of integrin cysteine-rich repeats to domain III of laminin B chains

Publisher Website
Google Scholar
Abstract
The integrins have been grouped into three subfamilies based on the utilization of three distinct beta chain subunits, β1, β2 and β3. The recent discovery of β4 and β5 subunits, and the sharing of a subunits between β subfamilies reflects a greater structural and functional diversity of the Integrin supergene family than first anticipated. We exploit integrln gene sequence homology for the Identification of a new integrin β chain. Oligonucleotide probes designed from the highly conserved Arg-Gly-Asp (RGD)-bindlng domain were used to amplify related transcripts from phytohaemagglutlnin-activated human peripheral blood lymphocytes using the polymerase chain reaction (PCR). Five PCR products encoding β1, β2, β3, β4, and a new β clone, designated β7, were identified. Full-length β7 cDNA was isolated from an activated human T lymphocyte library, using an oligonucleotide probe constructed from the β7 PCR product. The β7 cDNA contains a long open reading frame of 2391 bp which encodes a protein sequence consisting of 797 amino acids. The encoded sequence revealed a typical signal peptide, a predominantly hydrophllic 707 amino acid residue domain with 8 N-glycosylatlon sites, a transmembrane domain, and a C-termlnal domain of 52 amino acids. The β7 sequence showed homology to known β1, β2, β3, β4, and β5 sequences of 43, 46, 38, 32, and 37% respectively. Four cysteine-rlch homologous repeat sequences were found in β7 and were homologous to sequences In other integrin β subunits, and to domain III of the laminln B chains. Part of this cysteine-rlch region is homologous to proteins that contain epidermal growth factor-like repeat sequences. Northern analysis revealed that mature β7 mRNA is ∼3.5 kb in size, and expression was restricted to T and B lymphocytes in the small panel of cell types examined. We conclude that β7 may be a new member of the leukocyte cell adhesion molecule subset of integrins, and is a candidate immunoregulatory molecule.