Expression of new prognostic markers, peripheral-type benzodiazepine receptor and carbonic anhydrase IX, in human breast and ovarian carcinoma cell lines
Abstract:
Peripheral benzodiazepine receptor (PBR), a mitochondrial protein involved in cell proliferation and differentiation, and carbonic anhydrase IX (CA IX), an intrinsic marker of hypoxia, have been studied in the panel of human breast (MCF-7, BT- 20, MDA-MB-453, MDA-MB-231) and ovarian (A2780, A2780/CP, A2780/ADR, CH1, SKOV-3) carcinoma cell lines that differ by malignant progression. The expression of both antigens was detected by staining with the PBR-specific 8D7 and CA IX-specific M75 monoclonal antibodies and quantitated by flow cytometry. PBR was related to mitochondrial mass and CA IX to the cell density. Breast carcinoma cell lines showed higher relative fluorescence intensity of PBR expression than ovarian cell lines, with the exception of A2780/CP cisplatin-resistant subline that was comparable to highly invasive MDA-MB-231 breast line. Among the breast cell lines, PBR expression increased with their invasive potential. The ovarian cell lines showed greater variability in fluorescence intensities and the expression of PBR did not correlate with the amount of mitochondria. Mitochondrial PBR density disclosed significant difference between cisplatin-sensitive (low PBR density) and -resistant (high PBR density) ovarian cell lines. MTT test showed higher sensitivity of 2 breast cell lines MCF-7 and MDA-MB-231 (IC50 90 μM, in chemo- and radio- resistant lines IC50 > 110 μM). Growth inhibitory effect of PK 11195 did not correlate with the amount of PBR and was mediated probably by another, PBRindependent mechanisms. The expression of CA IX was only marginal in majority of tested cell lines in subconfluent conditions and was inducible by high cell density. More than 5% of positive cells in sparse culture have been found in MDA-MB-231 and MDA-MB-453 breast cell lines while more than 15% of A2780/ADR adriamycin-resistant ovarian cells were positive for CA IX expression under the same conditions. Our data indicate that PBR expression in breast and ovarian carcinoma cell lines is not proportional to the amount of mitochondria and should be expressed relatively to the cell mitochondrial mass. This assessment allows establishing high PBR density as a measure of aggressiveness (invasion in breast and resistance in ovarian cancer). Observation of relatively high CA IX expression in A2780/ADR cells evokes the assumption that multidrug resistance might be connected with selection advantage towards CA IX expressing cells.