Inhibition by tumor-promoting phorbol esters of procollagen synthesis in promotable JB6 mouse epidermal cells

The JB6 mouse epidermal cell line has been developed to study promotion of neoplastic transformation in vitro. Treatment of JB6 cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) or other tumor promoters resulted in the irreversible acquisition by JB6 cells of tumorigenicity in nude mice and anchorage-independent growth in soft agar. As previously reported, one of the biochemical responses that occurs during TPA treatment is a greater than 75% reduction in a mannose-labeled glycoprotein with an apparent molecular weight of 180,000. This TPA-sensitive glycoprotein has now been identified on the basis of collagenase and pepsin sensitivity as procollagen pro-α1(I) chain. [ ³H]proline labeling also demonstrated a parallel decrease in the 150,000 procollagen pro-α2(I) component. Two nonphorbol promoters, mezerein and epidermal growth factor, were also active in decreasing procollagen synthesis. Promotion-sensitive and promotion-resistant clonal derivatives of JB6 showed similar basal levels of collagen synthesis as well as similar degrees of TPA-dependent procollagen loss indicating that the collagen decrease may be necessary but is not sufficient to produce the promotion response. Comparison of chemically transformed mouse epidermal cell lines with paired nontransformants suggests that reduced procollagen synthesis is a stably acquired phenotypic change and may therefore be involved in maintenance of the transformed phenotype as well as in its induction.