Radiation-induced acid ceramidase confers prostate cancer resistance and tumor relapse
Joseph C. Cheng, … , James S. Norris, Xiang Liu
Joseph C. Cheng, … , James S. Norris, Xiang Liu
Published September 16, 2013
Citation Information: J Clin Invest. 2013;123(10):4344-4358. https://doi.org/10.1172/JCI64791.
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Research Article Oncology

Radiation-induced acid ceramidase confers prostate cancer resistance and tumor relapse

Abstract

Escape of prostate cancer (PCa) cells from ionizing radiation–induced (IR-induced) killing leads to disease progression and cancer relapse. The influence of sphingolipids, such as ceramide and its metabolite sphingosine 1-phosphate, on signal transduction pathways under cell stress is important to survival adaptation responses. In this study, we demonstrate that ceramide-deacylating enzyme acid ceramidase (AC) was preferentially upregulated in irradiated PCa cells. Radiation-induced AC gene transactivation by activator protein 1 (AP-1) binding on the proximal promoter was sensitive to inhibition of de novo ceramide biosynthesis, as demonstrated by promoter reporter and ChIP-qPCR analyses. Our data indicate that a protective feedback mechanism mitigates the apoptotic effect of IR-induced ceramide generation. We found that deregulation of c-Jun induced marked radiosensitization in vivo and in vitro, which was rescued by ectopic AC overexpression. AC overexpression in PCa clonogens that survived a fractionated 80-Gy IR course was associated with increased radioresistance and proliferation, suggesting a role for AC in radiotherapy failure and relapse. Immunohistochemical analysis of human PCa tissues revealed higher levels of AC after radiotherapy failure than those in therapy-naive PCa, prostatic intraepithelial neoplasia, or benign tissues. Addition of an AC inhibitor to an animal model of xenograft irradiation produced radiosensitization and prevention of relapse. These data indicate that AC is a potentially tractable target for adjuvant radiotherapy.

Authors

Joseph C. Cheng, Aiping Bai, Thomas H. Beckham, S. Tucker Marrison, Caroline L. Yount, Katherine Young, Ping Lu, Anne M. Bartlett, Bill X. Wu, Barry J. Keane, Kent E. Armeson, David T. Marshall, Thomas E. Keane, Michael T. Smith, E. Ellen Jones, Richard R. Drake Jr., Alicja Bielawska, James S. Norris, Xiang Liu

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Figure 6

Recurrent PCa after radiation therapy overexpresses AC.

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Recurrent PCa after radiation therapy overexpresses AC. PPC-1 cells were...
PPC-1 cells were subjected to fractionated radiotherapy (40 × 2 Gy) and evaluated (A) for ASAH1 promoter reporter activity (luciferase assay) and (B) for AC protein expression (representative immunoblot) versus nonirradiated control cells. (C) PPC-1 cell subclones grown after a cumulative IR dose of 80 Gy were assessed for AC protein expression by Western blot. (B and C) Mean densitometry of normalized AC expression is shown. (D) The frequencies of clonal repopulation from single-cell cultures of 80 Gy–surviving PCa cells are shown as the combinations of subclones overexpressing (o/e) AC (red) and those not overexpressing AC (white), as determined by immunoblot versus nonirradiated control cells. AC expression in PPC-1 subclones shown in D was quantified based on AC/GAPDH band densitometry and (E) was assessed for Pearson correlation to cellular ceramide content; (F) radiation resistance, as determined by mean inactivation dose from clonogenic survival assays; and (G) doubling rate. Dotted lines indicate mean ceramide content, inactivation dose, and doubling rate, respectively, of IR-naive control PPC-1 cells. (H) AC expression in prostate biopsies of benign, PIN, therapy-naive adenocarcinoma, and biochemical recurrence/failure after definitive radiotherapy (RTF). Representative images of AC expression (brown) against hematoxylin counterstain (blue) are shown for (I) benign, (J) PIN, (K) therapy-naive adenocarcinoma, and (L) RTF tissues. Scale bar: 50 μm. Representative images and immunohistochemistry scores of patient-matched tissues are depicted in K and L and by blue circles connected by dotted lines in H. *P < 0.05, **P < 0.01, ***P < 0.001.