ANGIOTENSIN-II-INDUCED EXPRESSION OF LAMININ COMPLEX AND LAMININ A-CHAIN-RELATED TRANSCRIPTS IN VASCULAR SMOOTH-MUSCLE CELLS

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, ex pression of laminin was stimulated by exogenous vasoconstrictor peptid e. Stimulation of laminin protein and mRNA expression was observed for both laminin B1/B2-chains and an unknown laminin heavy chain. Compare d with PYS-2 cells, a mouse teratocarcinoma cell line which constituti vely expresses a 10-kb mRNA transcript for 'classical' laminin A-chain , cultured vascular smooth muscle cells (VSMC) did not express a corre sponding mRNA. However, cultured VSMC were found to express laminin A- chain-related mRNAs of approximate to 1.8kb and approximate to 3.8 kb, respectively. The 1.8-kb species of transcript was expressed in a con stitutive manner, whereas the 3.8-kb mRNA was found to be regulated by angiotensin II. Laminin complexes secreted by cultured cells containe d a approximate to 300 kD heavy chain which did not immunoreact with i mmunoreagents raised against either the classical laminin complex secr eted by EHS tumor cells or the merosin heavy chain. The putative A-cha in analogue possibly represents a new form of a tissue-specific lamini n heavy chain, distinct from the A- and M-chains thus far described. T ranslation products encoded by the A-chain-related transcripts of cult ured smooth muscle cells could not be specified using currently availa ble antibodies. The putative protein(s) is speculated to contain the b iological features of the N-terminus of the laminin A-chain, namely se lf-assembly and association with collagen type IV.