CYCLIC-AMP-DEPENDENT PROTEIN-KINASE TYPE-I IS INVOLVED IN HYPERSENSITIVITY OF HUMAN BREAST CELLS TO TOPOISOMERASE-II INHIBITORS

Topoisomerase II (Topo II) is an essential enzyme that catalyzes the b reakage of double-strand DNA and is the target of several effective an ticancer drugs, including the epipodophyllotoxins, The regulatory subu nits of the cyclic AMP-dependent protein kinase are differentially exp ressed in normal and cancer cells, The RIa subunit is overexpressed in cells transformed by transforming growth factor-alpha (TGF-alpha) or Ha-ras oncogene, It has been shown that murine cells transformed by Ha -ras become hypersensitive to Topo II-targeting anticancer drugs, In t his report we have tested whether any correlation exists between the e xpression of RI alpha protein and cellular sensitivity of Topo II-targ eting drugs, Normal human breast MCF-10A cells and their derivatives o verexpressing TGF-alpha, Ha-ras, or the different protein kinase subun its were treated with either Topo II inhibitors, such as etoposide, te niposide, or amsacrine, or with drugs which act independently of Topo II, such as bleomycin, Here we show that MCF-10A TGF-alpha and MCF-10A Ha-ras cells overexpress the RIa protein and become hypersensitive to epypodophyllotoxins and amsacrine but not to bleomycin, Direct introd uction of the RI alpha gene into MCF-10A induces hypersensitivity to T opo II inhibitor drugs. In contrast, the overexpression of the other p rotein kinase subunits, RII beta or C alpha, does not modify the drug sensitivity of MCF-10A cells, No differences in the mRNA/protein conte nt or in the activity of Topo II were found between hypersensitive cel ls and parental MCF-10A cells, suggesting that RI alpha may influence drug sensitivity via modulation of events downstream of the Topo II-DN A cleavable complex.