Tumor promotion resistant cells are deficient in AP-1 DNA binding, JunD DNA binding and JunD expression and form different AP-1-DNA complexes than promotion sensitive cells

The JB6 cell culture model is used to identify molecular: determinants of s usceptibility to the promotion of neoplastic transformation. Clonal variant s susceptible to transformation ('P+' cells) form numerous anchorage-indepe ndent colonies in soft agar upon treatment with the phorbol eater tumor pro moter TPA, whereas resistant variants ('P-' cells) do not. We now report th at there is significantly less binding of activator protein-1 (AP-1) to its DNA binding site in P- cells than in P+ cells. Gel supershift assays were performed to detect association of all seven AP-1 family members with their DNA binding site in TPA-treated and -untreated P+ and P- cells. Significan tly lower DNA binding and protein expression of JunD were detected in P- ce lls than in P+ cells, c-Jun was detected in P+, but not P-, AP-I-DNA comple xes, and c-Fos was detected in P-, but not P+, AP-1-DNA complexes. These an d other phenotype-specific differences in abundance and composition of AP-1 -DNA complexes may play a role in the resistance of P- cells to tumor promo ter-induced transformation. (C) 1999 Elsevier Science B.V. All rights reser ved.