Soluble collagen VI drives serum-starved fibroblasts through S phase and prevents apoptosis via down-regulation of bax

We previously showed that soluble, pepsin-solubilized collagen VI increases de novo DNA synthesis in serum-starved HT1080 and 3T3 fibroblasts up to 10 0-fold compared with soluble collagen I, reaching 80% of the stimulation ca used by 10% fetal calf serum. Here we show that collagen VI also inhibits a poptotic cell death in serum-starved cells as evidenced by morphological cr iteria, DNA laddering, complementary apoptosis assays (terminal deoxynucleo tidyl transferase-mediated dUTP nick end labeling, enzyme-linked immunosorb ent assay, and fluorescence-activated cell sorting), and quantification of apoptosis-regulating proteins. In the presence of starving medium alone or collagen I, the proapoptotic Bar was up-regulated 2-2.5-fold, compared with soluble collagen VI and fetal calf serum, whereas levels of the antiapopto tic Bcl-2 protein remained unaffected. In accordance with its potent stimul ation of DNA synthesis, soluble collagen VI carries serum-starved HT1080 an d Balb 3T3 fibroblasts through G(2) as shown by fluorescence-activated cell sorting analysis, whereas cells exposed to medium and collagen I where arr ested at G(1)-S. This was accompanied by a 2-3-fold increase in cyclin A, B , and D1 protein expression. Collagen VI-induced inhibition of apoptotic ce ll death may be operative during embryogenesis, wound healing, and fibrosis when elevated tissue and blood levels of collagen VI are observed, thus in itiating a feedback loop of mesenchymal cell activation and proliferation.