DIFFERENTIAL TRANSACTIVATION OF HUMAN METALLOTHIONEIN-IIA IN CISPLATIN-RESISTANT AND CISPLATIN-SENSITIVE CELLS

Cells with acquired anticancer drug resistance frequently exhibited br oad cross-resistance to other anticancer agents. Increased human metal lothionein (hMT) IIa transcription has been found in some cells with a cquired resistance to cisplatin (CP). A panel of 5'-hMT-Ila promoter d eletions linked to the chloramphenicol acetyl transferase gene ((5'-hM T-IIaCAT) were used to demonstrate that certain cia-elements are impor tant for the increased hMT-IIa transcription in CP-resistant cells (SC C25/CP) compared to CP-sensitive cells (SCC25). We further identified trans-acting factor differences between SCC25 and SCC25/CP cells using gel mobility shift assays. Significant increases in binding of specif ic factors to the -286 to -160 and -96 to -51 region were seen in CP-r esistant SCC25/CP cells compared to sensitive SCC25 cells. Using cross -competition and super gel shift analyses, we identified enhanced Sp1 and AP-2 binding activity in SCC25/CP cells. By Western blot analysis and immunoprecipitation, we demonstrated that the level of Sp1 was unc hanged between the two cell types whereas AP-2 was elevated twofold in SCC25/CP cells. Our results indicated that the selection of CP-resist ant phenotype in SCC25/CP was accompanied by increased Sp1 and AP-2 DN A binding activities, which are likely not only to enhance hMT-IIa tra nscription but could also alter expression of other genes responsible for a broader anticancer drug cross-resistance. Thus, altered trans-ac ting factors could account for the complex cross-resistant phenotype f ound in some anticancer drug-resistant cells.