Laminin, a major
structural glycoprotein complex of basement membranes has been found to be modulated by
angiotensin II in vitro and in vivo. In cultures of aortic organoids and vascular smooth muscle cells, expression of
laminin was stimulated by exogenous
vasoconstrictor peptide. Stimulation of
laminin protein and
mRNA expression was observed for both
laminin B1/B2-chains and an unknown
laminin heavy chain. Compared with PYS-2 cells, a mouse
teratocarcinoma cell line which constitutively expresses a 10-kb
mRNA transcript for 'classical'
laminin A-chain, cultured vascular smooth muscle cells (VSMC) did not express a corresponding
mRNA. However, cultured VSMC were found to express
laminin A-chain-related mRNAs of approximately 1.8 kb and approximately 3.8 kb, respectively. The 1.8-kb species of transcript was expressed in a constitutive manner, whereas the 3.8-kb
mRNA was found to be regulated by
angiotensin II.
Laminin complexes secreted by cultured cells contained a approximately 300 kD heavy chain which did not immunoreact with immunoreagents raised against either the classical
laminin complex secreted by
EHS tumor cells or the
merosin heavy chain. The putative A-chain analogue possibly represents a new form of a tissue-specific
laminin heavy chain, distinct from the A- and M-chains thus far described. Translation products encoded by the A-chain-related transcripts of cultured smooth muscle cells could not be specified using currently available
antibodies. The putative
protein(s) is speculated to contain the
biological features of the N-terminus of the
laminin A-chain, namely self-assembly and association with
collagen type IV.