Constitutive overexpression of DNA binding activity to the distal CCAAT box of human thymidine kinase promoter in human tumor cell lines.

We have used the sequence of the cell-cycle regulatory region of human thymidine kinase promoter to study the DNA-protein interaction in human tumor and normal cells. By performing band-shift assays and DNase I footprint analysis, we have demonstrated that human tumor cells exhibited an elevated level of binding activity to the distal CCAAT box of human thymidine kinase promoter. The expression of human thymidine kinase CCAAT-binding activity was serum or independent in human tumor cells but serum dependent in normal human diploid fibroblasts. Our results present the fact that the constitutive interaction of CCAAT-binding factor with the promoter of a cell growth-controlled gene, such as thymidine kinase, is consistent with the loss of stringent cell growth regulation associated with tumorigenic phenotype.