6th ESACP Congress, Heidelberg, April 7-11, 1999

A155
MULTIDRUG-RESISTANCE IN HUMAN OVARIAN CARCINOMA CELLS IS ASSOCIATED WITH NUCLEAR TEXTURE CHANGES AND DNASE I HYPERSENSITIVITY
Yatouji S, Trentesaux C, Dufer J

Unité médian, EA2063, IFR53, UFR Pharmacie, University of Reims, Reims, France

Alterations in nuclear morphology have long been recognised as a hallmark of cancer cells, but the molecular bases of these alterations remain sometimes to be established. We showed previously that multidrug-resistant cancer cells displayed nuclear texture changes. In this work, two tumoral cell line variants were studied: the human ovarian carcinoma cell line IGROV1 and the multidrug-resistant subline OV1-VCR selected with vincristine. We confirmed by immunocytochemistry, RT-PCR, and Southern blot that OV1-VCR cells overexpress P-glycoprotein and its corresponding mRNA without mdr1 gene DNA amplification. Cell smears of these two cell populations were stained with Feulgen method and analysed by image cytometry. As compared to drug-sensitive cells, OV1-VCR display a chromatin global decondensation as assessed by textural features analysis. In order to correlate this decondensation with alterations in chromatin structure, genomic DNA was extracted from both cell lines nuclei after treatment with various con centrations of DNase I. OV1-VCR cells DNA displayed an increased (about 5 fold) DNase I sensitivity, suggesting an increased chromatin accessibility. To investigate further the presence of putative DNase I hypersensitive (HS) sites in the vicinity of the mdr1 gene promoter, genomic DNA from both cell lines was analysed by Southern blot after digestion with DNase I and restriction enzymes (Hind III, BamH1, EcoR1, and Kpn1). According to the mdr1 probe (1.3kb) and enzymes used, no change in DNase HS sites could be visualised.