Abstract 1814: Claudin-3 and claudin-4 regulate sensitivity to cisplatin by controlling expression of the copper and cisplatin influx transporter CTR1

Abstract

Abstract Cell adhesion complexes play a central role in controlling the behavior of epithelial cells, and loss of cell-cell adhesion is a characteristic of virtually all epithelial malignancies. Claudin-3 (CLDN3) and claudin-4 (CLDN4) are the major structural molecules that form tight junctions between epithelial cells. We found that knockdown of the expression of either CLDN3 or CLDN4 produced marked changes in the phenotype of ovarian cancer cells including an increase in in vivo growth rate and metastatic potential. However, the role of claudins in controlling sensitivity of ovarian cancer cells to the platinum-containing drugs, and the mechanisms by which they regulate the sensitivity, remain largely unknown. The effect of CLND3 and CLDN4 on cisplatin cytotoxicity, cellular accumulation and DNA adduct formation was compared in the CLDN3- and CLDN4-expressing parental human ovarian carcinoma 2008 cells and CLDN3 or CLDN4 knockdown sublines (CLDN3KD and CLDN4KD, respectively). CLDN3KD cells were 3.1-fold resistant to cisplatin whereas CLDN4KD cells were 8.0-fold resistant compared to the parental 2008 cells. The net accumulation of platinum in CLDN3KD and CLDN4KD cells was reduced to 66% and 49% of that in the parental cells after exposure to 30 μM cisplatin for 1 h. Likewise, the DNA adduct levels dropped to 65% and 41% of control when CLDN3 and CLDN4 were knocked down. Given that transporters and chaperones that manage copper homeostasis regulate platinum drug accumulation and efflux, their expression was measured by qRT-PCR. Among these, only the expression of CTR1 was significantly reduced (p<0.01) in the knockdown cells while there was no appreciable change in CTR2, ATP7A, ATP7B or ATOX1 mRNA levels. Consistent with the decrease in CTR1 level, the average steady-state copper level in the 2008 cells was 6.4 ± 1.26 ng Cu/μg S whereas the CLDN3KD and CLDN4KD cells contained only 4.2 ± 0.87 and 4.0 ± 0.74 ng Cu/μg S resulting in a 34% (p=0.008) and 38% (p=0.004), respectively, loss of intracellular copper. Copper-dependent tyrosinase activity was also markedly reduced in those CLDN knockdown cells when incubated with the substrate L-DOPA. These results indicate that CLDN3 and CLDN4 affect sensitivity to the cytotoxic effect of cisplatin by regulating expression of the copper transporter CTR1 that we have previously shown to play a central role in the influx of cisplatin. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1814. doi:1538-7445.AM2012-1814