The Phorbol Ester TPA Regulates Collagen Gene Expression at the Transcriptional Level

Previously, we reported that growth activation of quiescent 3T3-L1 cells by TPA led to a rapid increase of pro-α2 (I) collagen mRNA and protein, while induction of pro-α2 (I) was not observed in VT-1 cells, a line non-mitogenic in the presence of TPA (26). Here, we further examine the expression of pro-α2 (I) collagen during mitogenic stimulation at the molecular level. In addition to pro-α2 (I) mRNA, TPA treatment increased mRNA production of other collagen family members, pro-α1 (I) and pro-α1 (III) although in reduced amounts relative to pro-α2 (I). In contrast to pro-α2 (I), the mRNA expression profiles of several protooncogenes were regulated in both VT-1 and 3T3-L1 cells. Consistent with increased mRNA levels, TPA treated 3T3-L1 cells produced a matrix abundant in collagen type I protein. In vitro nuclear "run-on" transcription assays demonstrated a 4-fold increase in pro-α2 (I) mRNA that was maximal within 10 min of TPA treatment. Using a chloramphenicol-acetyl transferase (CAT) assay, we identified a TPA sensitive domain within the promoter of the COL1A2 gene. These results establish COL1A2 as an early growth responsive gene, and that its regulation is PKC dependent. Additionally, the increased expression of protooncogenes and transin during TPA stimulation of non-mitogenic VT-1 cells indicated that the regulation of these genes is independent of PKC, indicating the existence of multiple regulatory mechanisms amongst early response genes.