Testis-specific HMG-domain protein alters the responses of cells to cisplatin.

Cisplatin is an effective agent for the treatment of testicular cancer. In the present study with mouse testicular teratocarcinoma cell extracts, we observed a deficiency in nucleotide excision repair (NER) of a DNA probe bearing a cisplatin 1,2-d(GpG) intrastrand cross-link. In contrast, repair of the cisplatin 1,3-d(GpTpG) intrastrand cross-link was still active in these cell extracts. A current working hypothesis is that complexes of HMG-domain proteins with the major cisplatin 1,2-intrastrand cross-links could enhance cisplatin cytotoxicity by blocking repair of these lesions on the genome. The family of HMG-domain proteins include a testis-specific protein, tsHMG, which might account for the altered NER in testicular cells. To test this possibility, a human cervical carcinoma cell line (HeLa) was constructed which ectopically expressed tsHMG under the control of an inducible promoter. Microscopic examination of tsHMG expression and cisplatin-induced apoptosis on a cellular level revealed that the nuclear protein did indeed modulate the cytotoxic consequences of cisplatin treatment. Also, tsHMG enhanced transcription inhibition by cisplatin. These results reveal that an HMG-domain protein can affect cellular responses to cisplatin and may be relevant to the clinical observation that cancer cells in specific tissues are particularly sensitive to cisplatin.