Human laminin: cloning and sequence analysis of cDNAs encoding A, B1 and B2 chains, and expression of the corresponding genes in human skin and cultured cells.

A human placental lambdagt11 expression cDNA library was probed for laminin cDNAs by a combination of immunoscreening using polyclonal anti-human laminin antibody, and plaque hybridizations using a mouse laminin A chain cDNA. A total of 36 recombinant clones were isolated and characterized. Northern blot hybridizations with poly(A)+RNA, isolated from cultured human skin fibroblasts, revealed hybridization either to (a) a single 10 kb transcript consistent with A chain; (b) a single 5.7 kb transcript consistent with B1 chain; or (c) polymorphic 5.6 and 8.2 kb transcripts consistent with B2 chain of human laminin. Nucleotide sequencing of representative cDNA clones (approximately 2.5 kb in size) confirmed that these three groups of cDNAs encoded C-terminal sequences of laminin A, B1 and B2 chains, respectively. Deduced amino acid sequences for both B1 and B2 chains contained epidermal growth factor-like sequences and alpha-helical heptad repeats, as found previously for mouse laminin. Partial laminin A chain cDNA encoded 680 amino acid residues characterized by several internal repeats. This portion of the peptide accounted for a large part of the globular domain (fragment 3), the whole length of a second (T2) and portions of a third (T1) globular domain. The human A chain also contained an Arg-Gly-Asp sequence, a potential cell-binding site, which is not found in the same segment of mouse laminin. The newly isolated cDNAs were also utilized to analyze expression of laminin mRNAs by cultured human cells and tissues. The results demonstrated that the laminin A, B1, and B2 chain genes were expressed in an uncoordinate manner in both cultured cells and tissues, with a particularly low level of the A chain mRNA being present.