CLONING AND CHARACTERIZATION OF ALTERNATIVELY SPLICED ISOFORMS OF RATTENASCIN - PLATELET-DERIVED GROWTH FACTOR-BB MARKEDLY STIMULATES EXPRESSION OF SPLICED VARIANTS OF TENASCIN MESSENGER-RNA IN ARTERIAL SMOOTH-MUSCLE CELLS

To understand the alteration of extracellular matrix composition evoke d by chemotactic factors, we have studied the expression of adhesive ( fibronectin) and anti-adhesive (tenascin) proteins in response to plat elet-derived growth factor-BB (PDGF-BB), a potent chemoattractant for rat aortic smooth muscle cells (ASMC). PDGF-BB markedly induced two ma jor tenascin mRNA transcripts, whereas fibronectin mRNA levels did not change. The results of immunoprecipitation studies paralleled Norther n blot data. Since alternative splicing is responsible for the generat ion of multiple tenascin mRNAs in other cell types, we studied the eff ect of chemotactic factors on the relative abundance of tenascin isofo rms. The alternatively spliced region of ASMC-derived rat tenascin was amplified and the identity of the products confirmed by sequencing. T hree major polymerase chain reaction products were detected: a 1727-ba se pair unspliced form which was maximal at 2 h and 635- and 362-base pair products which were more abundant at 8 h after treatment with PDG F-BB or angiotensin II, Functional studies showed that the unspliced i soform of human tenascin inhibited attachment of both human and rat AS MC to fibronectin. These results suggest that PDGF-BB markedly up-regu lates the expression of tenascin variants, which may bad to destabiliz ation of cell matrix interactions and promotion of cell migration.