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Selective inhibition of tumor cell associated Vacuolar-ATPase 'a2' isoform overcomes cisplatin resistance in ovarian cancer cells.

ABSTRACT: Development of resistance to platinum compounds significantly hinders successful ovarian cancer (OVCA) treatment. In tumor cells, dysregulated pH gradient across cell membranes is a key physiological mechanism of metastasis/chemo-resistance. These pH alterations are mediated by aberrant activation of key multi-subunit proton pumps, Vacuolar-ATPases (V-ATPases). In tumor cells, its 'a2' isoform (V-ATPase-V0a2) is a component of functional plasma-membrane complex and promotes tumor invasion through tumor-acidification and immuno-modulation. Its involvement in chemo-resistance has not been studied. Here, we show that V-ATPase-V0a2 is over-expressed in acquired-cisplatin resistant OVCA cells (cis-A2780/cis-TOV112D). Of all the 'a' subunit isoforms, V-ATPase-V0a2 exhibited an elevated expression on plasma membrane of cisplatin-resistant cells compared to sensitive counterparts. Immuno-histochemistry revealed V-ATPase-V0a2 expression in both low grade (highly drug-resistant) and high grade (highly recurrent) human OVCA tissues indicating its role in a centralized mechanism of tumor resistance. In cisplatin resistant cells, shRNA mediated inhibition of V-ATPase-V0a2 enhanced sensitivity towards both cisplatin and carboplatin. This improved cytotoxicity was mediated by enhanced cisplatin-DNA-adduct formation and suppressed DNA-repair pathway, leading to enhanced apoptosis. Suppression of V0a2 activity strongly reduced cytosolic pH in resistant tumor cells, which is known to enhance platinum-associated DNA-damage. As an indicator of reduced metastasis and chemo-resistance, in contrast to plasma membrane localization, a diffused cytoplasmic localization of acidic vacuoles was observed in V0a2-knockdown resistant cells. Interestingly, pre-treatment with monoclonal V0a2-inhibitory antibody enhanced cisplatin cytotoxicity in resistant cells. Taken together, our findings suggest that the isoform specific inhibition of V-ATPase-V0a2 could serve as a therapeutic strategy for chemo-resistant ovarian carcinoma and improve efficacy of platinum drugs.

SUBMITTER: Kulshrestha A

PROVIDER: S-EPMC5423172 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Selective inhibition of tumor cell associated Vacuolar-ATPase 'a2' isoform overcomes cisplatin resistance in ovarian cancer cells.

Kulshrestha Arpita A Katara Gajendra K GK Ginter Jordyn J Pamarthy Sahithi S Ibrahim Safaa A SA Jaiswal Mukesh K MK Sandulescu Corina C Periakaruppan Ramayee R Dolan James J Gilman-Sachs Alice A Beaman Kenneth D KD

Molecular oncology 20160129 6

Development of resistance to platinum compounds significantly hinders successful ovarian cancer (OVCA) treatment. In tumor cells, dysregulated pH gradient across cell membranes is a key physiological mechanism of metastasis/chemo-resistance. These pH alterations are mediated by aberrant activation of key multi-subunit proton pumps, Vacuolar-ATPases (V-ATPases). In tumor cells, its 'a2' isoform (V-ATPase-V0a2) is a component of functional plasma-membrane complex and promotes tumor invasion throug ...[more]

PMID: 26899534

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Project description:Osteopontin (OPN) is upregulated in several types of tumor and has been associated with chemoresistance. However, the contribution of OPN splicing isoforms (OPN‑SIs) to chemoresistance requires further investigation. The present study aimed to evaluate the expression patterns of each tested OPN‑SI in cisplatin (CDDP)‑resistant ovarian carcinoma cell lines, focusing on the role of the OPN‑c isoform (OPNc) in drug resistance. ACRP ovarian cancer cells resistant to CDDP, as well as their parental cell line A2780, were used. Analyses of the transcriptional expression of OPN‑SIs, epithelial‑mesenchymal transition (EMT) markers and EMT‑related cytokines were performed using reverse transcription‑quantitative PCR. OPNc was silenced in ACRP cells using anti‑OPNc DNA oligomers and stably overexpressed by transfecting A2780 cells with a mammalian expression vector containing the full length OPNc cDNA. Functional assays were performed to determine cell proliferation, viability and colony formation. The results demonstrated that among the three tested OPN‑SIs, OPNc was the most upregulated transcript in the ACRP cells compared with the parental A2780 cells. In addition, the expression levels of P‑glycoprotein multidrug transporter were upregulated in CDDP‑resistant ACRP cells compared with those in A2780 cells. OPNc knockdown sensitized ACRP cells to CDDP treatment and downregulated P‑gp expression levels compared with those in the negative control group. Additionally, silencing of OPNc impaired cell proliferative and colony formation abilities, as well as reversed the expression levels of EMT markers and EMT‑related cytokines compared with those in the negative control cells. Notably, although stable OPNc overexpression resulted in increased A2780 cell proliferation, it notably increased CDDP sensitivity compared with that in the cells transfected with a control vector. These results suggested that OPNc silencing may represent a putative approach to sensitize resistant ovarian cancer cells to chemotherapeutic agents.

Project description:Ovarian cancer (OVCA) patients often develop tolerance to standard platinum therapy that accounts for extensive treatment failures. Cisplatin resistant OVCA cells (cis-R) display enhanced survival mechanisms to cope with therapeutic stress. In these cells, increased autophagy process assists in chemoresistance by boosting the nutrient pool under stress. To improve the treatment response, both protective autophagy inhibition and its overactivation are showing efficacy in chemosensitization. Autophagy requires a tightly regulated intracellular pH. Vacuolar ATPases (V-ATPases) are proton extruding nanomotors present on cellular/vesicular membranes where they act as primary pH regulators. V-ATPase 'a2' isoform (V0a2), the major pH sensing unit, is markedly overexpressed on the plasma membrane and the early endosomes of OVCA cells. Previously, V0a2 inhibition sensitized cis-R cells to platinum drugs by acidifying cytosolic pH that elevated DNA damage. Here, we examined how V0a2 inhibition affected endosomal function and the autophagy process as a possible factor for cisplatin sensitization. Clinically, V0a2 expression was significantly higher in tissues from drug nonresponder OVCA patients compared to treatment responders. In vitro V0a2 knockdown in cis-R cells (sh-V0a2-cisR) significantly reduced the tumor sphere-forming ability and caused complete disintegration of the spheres upon cisplatin treatment. The apoptotic capacity of sh-V0a2-cisR improved substantially with potentiation of both intrinsic and extrinsic apoptotic pathway when treated with cisplatin. Unlike the chemical V-ATPase inhibitors that acutely induce autophagy, here, the stable V0a2 inhibition dampened the protective autophagy process in sh-V0a2-cisR cells with downregulated expression of proteins beclin-1, ATG-7, and LC3B and low autophagosome numbers compared to control cis-R cells. These cells showed downregulated ERK/MEK pathway that is known to repress autophagy. Interestingly, upon cisplatin treatment of sh-V0a2-cisR, the autophagy initiation proteins (LC3B, ATG7, and Beclin 1) were found upregulated as a stress response compared to the untreated cells. However, there was a concomitant downstream autophagosome accumulation and an enhanced P62 protein levels indicating the overall block in autophagy flux. Mechanistically, V0a2 knockdown caused defects in early endosome function as the transferrin internalization was impaired. Taken together, this study provides a novel insight into the mechanism by which V-ATPase-isoform regulates autophagy that assists in chemoresistance in ovarian cancer. We conclude that V-ATPase-V0a2 is a potent target for developing an effective treatment to enhance patient survival rates in ovarian cancer.

Dataset Information

Selective inhibition of tumor cell associated Vacuolar-ATPase 'a2' isoform overcomes cisplatin resistance in ovarian cancer cells.

Publications

Selective inhibition of tumor cell associated Vacuolar-ATPase 'a2' isoform overcomes cisplatin resistance in ovarian cancer cells.

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