Vacuolar ATPase (V‐ATPase) is an ATP‐dependent H+‐transporter that pumps protons across intracellular and plasma membranes. It consists of a large multi‐subunit protein complex and influences a wide range of cellular processes. This review focuses on emerging evidence for the roles for V‐ATPase in cancer. This includes how V‐ATPase dysregulation contributes to cancer growth, metastasis, invasion and proliferation, and the potential link between V‐ATPase and the development of drug resistance.

Prostate cancer is critically dependent on androgen receptor (AR) signaling. Despite initial responsiveness to androgen deprivation, most patients with advanced prostate cancer subsequently progress to a clinically aggressive castrate-resistant prostate cancer (CRPC) phenotype, typically associated with expression of splicevariant or mutant AR forms. Although current evidence suggests that the vacuolar-ATPase (V-ATPase), a multiprotein complex that catalyzes proton transport across intracellular and plasma membranes, influences wild-type AR function, the effect of V-ATPase inhibition on variant AR function is unknown. Inhibition of V-ATPase reduced AR function in wild-type and mutant AR luciferase reporter models. In hormone-sensitive prostate cancer cell lines (LNCaP, DuCaP) and mutant AR CRPC cell lines (22Rv1, LNCaP-F877L/T878A), V-ATPase inhibition using bafilomycin-A1 and concanamycin-A reduced AR expression, and expression of AR target genes, at mRNA and protein levels. Furthermore, combining chemical V-ATPase inhibition with the AR antagonist enzalutamide resulted in a greater reduction in AR downstream target expression than enzalutamide alone in LNCaP cells. To investigate the role of individual subunit isoforms, siRNA and CRISPR-Cas9 were used to target the V 1 C1 subunit in 22Rv1 cells. Whereas transfection with ATP6V1C1-targeted siRNA significantly reduced AR protein levels and function, CRISPR-Cas9mediated V 1 C1 knockout showed no substantial change in AR expression, but a compensatory increase in protein levels of the alternate V 1 C2 isoform. Overall, these results indicate that V-ATPase dysregulation is directly linked to both hormone-responsive prostate cancer and CRPC via impact on AR function. In particular, V-ATPase inhibition can reduce AR signaling regardless of mutant AR expression.

Graphical abstract

<p>Figure S6 shows bafilomycin-A1 impact on AR signalling in LNCaP cells</p>

<p>Figure S1 shows concanamycin-A effect on AR signalling</p>

<p>Figure S3 shows V-ATPase inhibition in DuCaP cells</p>

<div>Abstract<p>Prostate cancer is critically dependent on androgen receptor (AR) signaling. Despite initial responsiveness to androgen deprivation, most patients with advanced prostate cancer subsequently progress to a clinically aggressive castrate-resistant prostate cancer (CRPC) phenotype, typically associated with expression of splice-variant or mutant AR forms. Although current evidence suggests that the vacuolar-ATPase (V-ATPase), a multiprotein complex that catalyzes proton transport across intracellular and plasma membranes, influences wild-type AR function, the effect of V-ATPase inhibition on variant AR function is unknown.</p><p>Inhibition of V-ATPase reduced AR function in wild-type and mutant AR luciferase reporter models. In hormone-sensitive prostate cancer cell lines (LNCaP, DuCaP) and mutant AR CRPC cell lines (22Rv1, LNCaP-F877L/T878A), V-ATPase inhibition using bafilomycin-A1 and concanamycin-A reduced AR expression, and expression of AR target genes, at mRNA and protein levels. Furthermore, combining chemical V-ATPase inhibition with the AR antagonist enzalutamide resulted in a greater reduction in AR downstream target expression than enzalutamide alone in LNCaP cells. To investigate the role of individual subunit isoforms, siRNA and CRISPR-Cas9 were used to target the V₁C1 subunit in 22Rv1 cells. Whereas transfection with ATP6V1C1-targeted siRNA significantly reduced AR protein levels and function, CRISPR-Cas9–mediated V₁C1 knockout showed no substantial change in AR expression, but a compensatory increase in protein levels of the alternate V₁C2 isoform.</p><p>Overall, these results indicate that V-ATPase dysregulation is directly linked to both hormone-responsive prostate cancer and CRPC via impact on AR function. In particular, V-ATPase inhibition can reduce AR signaling regardless of mutant AR expression.</p></div>

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