TENASCIN-C IS SYNTHESIZED AND SECRETED BY MEGAKARYOCYTES, WHOSE ADHERENCE TO INTACT TENASCIN IS MEDIATED BY THE INTEGRIN SUBUNIT BETA(1)

Bone marrow megakaryocytes reside on a complex extracellular matrix, p roduced by stromal cells, as well as by megakaryocytes themselves. Usi ng immunofluorescence microscopy we have determined the distribution o f tenascin-C in guinea-pig bone marrow, finding that it has a prominen t fibrillar distribution in association with megakaryocytes. Western b lot analysis of CHRF-288 cells, a human megakaryocytic cell line and i solated purified guineapig megakaryocytes, with polyclonal and monoclo nal antibodies, demonstrate the presence of three tenascin isoforms (2 10, 220 and 250 kDa). Immunoprecipitation of radiolabelled isolated gu inea-pig megakaryocytes cultured on a type I collagen gel, demonstrate that these three tenascin isoforms were present in megakaryocytes, wh ereas only two isoforms were secreted into the media (210 and 220 kDa) . Analysis of rat bone marrow by in situ hybridisation reveals that tr anscripts for tenascin-C are present in megakaryocytes. Integrin regul ation of CHRF cell adhesion to intact tenascin was shown to be mediate d solely by the beta(1) integrin.