Cloning and characterization of alternatively spliced isoforms of rat tenascin. Platelet-derived growth factor-BB markedly stimulates expression of spliced variants of tenascin mRNA in arterial smooth muscle cells.

To understand the alteration of extracellular matrix composition evoked by chemotactic factors, we have studied the expression of adhesive (fibronectin) and anti-adhesive (tenascin) proteins in response to platelet-derived growth factor-BB (PDGF-BB), a potent chemoattractant for rat aortic smooth muscle cells (ASMC). PDGF-BB markedly induced two major tenascin mRNA transcripts, whereas fibronectin mRNA levels did not change. The results of immunoprecipitation studies paralleled Northern blot data. Since alternative splicing is responsible for the generation of multiple tenascin mRNAs in other cell types, we studied the effect of chemotactic factors on the relative abundance of tenascin isoforms. The alternatively spliced region of ASMC-derived rat tenascin was amplified and the identity of the products confirmed by sequencing. Three major polymerase chain reaction products were detected: a 1727-base 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 PDGF-BB or angiotensin II. Functional studies showed that the unspliced isoform of human tenascin inhibited attachment of both human and rat ASMC to fibronectin. These results suggest that PDGF-BB markedly up-regulates the expression of tenascin variants, which may lead to destabilization of cell-matrix interactions and promotion of cell migration.