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The transcription factor EB (TFEB) was identified as a master regulator of autophagy and lysosomal biogenesis. We recently demonstrated that TFEB is aberrantly regulated in pancreatic cancer (PDAC) cells. Interference with TFEB impairs PDAC cell growth supporting an important role for TFEB in maintaining PDAC cell phenotype. Given the limited impact of chemotherapeutic drugs in the context of PDAC, we aimed at testing whether the aberrantly regulated TFEB in PDAC cells could confer resistance to DNA damage agents, commonly used in PDAC therapeutic regimens. Methods: Experiments were performed in PDAC cells (MIA PaCa2, PANC1). The DNA damage agents gemcitabine, 5-FU, cisplatin and doxorubicin were used. Autophagic flux was measured upon 4-hours treatment with bafilomycin A1. Results: Treatment with DNA damage agents 1) increased the autophagic flux in PDAC cells. This autophagic signal was associated with 2) the dephosphorylation and nuclear accumulation of TFEB. The mTORC1 pathway is well-known to regulate TFEB phosphorylation and nuclear localization of TFEB. 3) However, the impact of the DNA damage agents on TFEB appeared independent of the mTORC1 pathway since no modulation in the phosphorylation of the mTORC1 target S6K1 was observed. To delineate whether TFEB influenced the response to DNA damage agents, we generated stable populations of PDAC cells expressing a non-targeting or shRNA targeting TFEB. Interfering with TFEB function 4) prevented the autophagic response upon treatment with DNA damage agents. This correlated with 5) increased accumulation of DNA damage and 6) increased sensitivity to the DNA damage agents. Conclusion: Our results suggest that DNA damage agents can induce a pro-survival autophagic response involving TFEB. Interfering with TFEB function limits the autophagic response and leads to increased sensitivity to DNA damage agents. Altogether, our results suggest that the aberrantly expressed TFEB in PDAC cells could confer resistance to DNA damage agents by, among others, promoting autophagy and limiting DNA damage accumulation. Citation Format: Benoit Marchand, Marie-Josée Boucher. DNA damage agents promote TFEB function and induce pro-survival autophagy signals [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2619.

We recently demonstrated that prolonged inhibition of GSK3 activity induces JNK-dependent cell death in human pancreatic cancer cells. Surprisingly, we observed that, concomitant to apoptosis, GSK3 inhibition also induces autophagy. Preventing this autophagic response sensitizes pancreatic cancer cells to the GSK3 inhibition-induced apoptosis suggesting a protective role for autophagy against cell death caused by prolonged inhibition of GSK3. Nevertheless, the mechanisms underlying the control of autophagy by GSK3 remain unknown. The aim of this study was to determine the molecular mechanism involved in the regulation of autophagy by GSK3 in pancreatic cancer cells. Methods: Experiments were performed in pancreatic cancer cells (PANC1, MIA PaCa2 and BxPC3), and HEK293T cells. GSK3 activity was inhibited using shRNA directed against GSK3beta and/or GSK3alpha or by using the GSK3 specific inhibitors CHIR99021 and SB216763. The JNK inhibitor SP600125 and the mTOR specific inhibitor Torin1 were also used. Results: 1) Inhibition of the JNK-cJun pathway prevented the apoptotic response but not the autophagic response upon GSK3 inhibition excluding a contribution of the JNK-cJUN pathway in the autophagy induced by GSK3 inhibition. We therefore analyzed the activity of the mTOR pathway since this pathway is well known to modulate autophagy. 2) Inhibition of GSK3 activity reduced the activity of S6K1, a direct substrate of the mTOR complex suggesting an inhibition of the mTOR pathway upon GSK3 inhibition. The mTOR pathway was recently shown to regulate autophagy through its impact on the transcription factor TFEB, a master regulator of an autophagic/lysosomal gene network. 3) Interestingly, treatment of cells with GSK3 inhibitors or a mTOR inhibitor both led to the nuclear translocation of TFEB, 4) and correlated with the expression of a lower molecular weight TFEB protein. 5) Pre-treatment of cells with the serine/threonine phosphatase inhibitor calyculin A prevented the molecular weight shift of TFEB induced upon GSK3 inhibition suggesting that GSK3 impacts on TFEB phosphorylation. 6) Furthermore, either GSK3 or mTOR inhibition correlated with increased activity of a TFEB-luciferase reporter gene, 7) and with an increased staining of lysosomes (lysotracker). 8) Interestingly, shRNA-mediated reduction of TFEB expression sensitized pancreatic cancer cells to the apoptosis induced upon GSK3 inhibition. Conclusion: Our results demonstrate that GSK3 inhibition promotes the dephosphorylation of TFEB that correlates with increased transcriptional activity of this master regulator of autophagy and lysosomal biogenesis. Furthermore, our results support a protective role against cell death assumed by TFEB upon GSK3 inhibition. Citation Format: Benoît Marchand, Alexandre Raymond-Fleury, Marie-Josée Boucher. Regulation of the transcription factor TFEB and the autophagic/lysosomal network by GSK3 in pancreatic cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 315. doi:10.1158/1538-7445.AM2014-315

Considering that a tumor promoting role for GSK3 has been suggested in pancreatic cancer (PC) cells and that GSK3 inhibitors are currently under clinical trials for treatment of different disorders, inhibition of GSK3 activity might represent an attractive therapeutic option for PC patients. However, mechanisms under the control of GSK3 activity in PC cells need to be clarified. We have previously demonstrated that prolonged inhibition of GSK3 activity induces JNK-dependent cell death in human PC cells. Recently, autophagy was proposed to be required for pancreatic tumor growth and inhibition of autophagy was shown to sensitize diverse cancer cells to a wide array of stress conditions. The JNK pathway has now well established roles in both apoptosis and autophagy positioning this pathway at the crossroad of these two processes. Furthermore, inhibition of GSK3 was shown to induce autophagy in prostate cancer and neuroblastoma cells suggesting a link between GSK3 activity and the regulation of autophagy. The AIM of this study was to evaluate whether GSK3 controls autophagy in PC cells and to determine whether inhibition of autophagy sensitizes pancreatic epithelial cells to GSK3 inhibition-induced cell death. METHODS Experiments were performed using the human PC cell lines PANC1 and MIAPaCa2 and the non-tumorigenic HPDE cells. GSK3 activity was inhibited by treatment with GSK3 inhibitors SB216763 and CHIR99021 or by specific shRNA targeting GSK3alpha/beta. Apoptosis was measured by assessment of PARP and caspase-7 cleavages. Autophagy was evaluated by the detection of the membrane-bound LC3B-II isoform and was inhibited by treatment with 3-methyladenine or transfection of a siRNA targeting ATG5. RESULTS 1) Prolonged inhibition of GSK3 (48-72h) induced an apoptotic response in PC cells. 2) Moreover, inhibition of GSK3 in pancreatic epithelial cells triggered an autophagic response and increased the autophagic flux. 3) The inhibition of autophagy sensitized pancreatic epithelial cells to the GSK3 inhibition-induced cell death. 4) The inhibition of GSK3 correlated with activation of the JNK-cJun signaling and reduced levels of phosphorylated p70S6K (Thr389) and S6 (Ser235/236). 5) As opposed to what was observed for the GSK3 inhibition-induced apoptosis, activation of the JNK-cJun pathway was not required for the autophagy response following GSK3 inhibition. Also, downregulation of cJun by shRNA did not prevent the reduced levels of phosphorylated p70S6K following GSK3 inhibition. These results suggest that GSK3 acts on other targets then JNK/cJun to modulate autophagy. CONCLUSION Our results provide evidence that GSK3 inhibition induces autophagy in pancreatic epithelial cells and suggest a protective role of autophagy against GSK3 inhibition-induced cell death. Finally, our observations suggest a potential role for the mTOR/p70S6K signaling in the GSK3-dependent regulation of autophagy. Citation Format: Benoit Marchand, Marie-Josée Boucher. Inhibition of GSK3 reduces p70S6K activity and promotes autophagy independently of the JNK-cJun pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1674. doi:10.1158/1538-7445.AM2013-1674

Pancreatic cancer (PC) is the fourth leading cause of cancer-related death worldwide and has the highest fatality rate of all cancers. The chemoresistance of PC cells contributes to the poor prognosis of PC patients which raises the need for the identification and development of new effective therapy. Studies have revealed that the glycogen synthase kinase 3 (GSK3) is overexpressed in human pancreatic adenocarcinoma as compared to normal pancreas and its inhibition leads to the growth arrest of established tumor xenografts thus suggesting a tumor promoting role for GSK3 in PC cells. Considering that GSK3 inhibitors are currently under clinical trial for treatment of different disorders such as neurodegenerative diseases and diabetes, inhibition of GSK3 activity might represent an attractive therapeutic option for PC patients. However, mechanisms under the control of GSK3 activity in PC cells need to be clarified. We have previously demonstrated that prolonged inhibition of GSK3 activity induces JNK-dependent cell death in human PC cells. Recently, it was suggested in prostate cancer cells that GSK3 promotes both apoptosis and autophagy, the latter playing a protective role against cell death. Interestingly, inhibition of autophagy was shown to sensitize diverse cancer cells to a wide array of stress conditions. The AIM of the study was to evaluate whether GSK3 controls autophagy in PC cells and determine the role of autophagy with regard to PC cell survival. METHODS. Experiments were performed using the human PC cell lines PANC1 and MIAPaCa2. GSK3 activity was inhibited by treatment with a specific GSK3 inhibitor SB216763 (20μM). Apoptosis was measured by assessment of PARP cleavage and caspase 3 and 7 activities. Autophagy was evaluated by the detection of the membrane-bound LC3B-II isoform. The autophagy inhibitor 3-methyladenine 3-MA (10mM) and the JNK inhibitor SP600125 (25μM) were also used. RESULTS. 1) Prolonged inhibition of GSK3 activity (48-72h) in PC cells induced both an apoptotic and autophagic responses. Treatment with 3-MA 2) elicited an apoptotic response and 3) strongly promoted the SB216763-induced apoptosis. 4) Mechanistically, inhibition of GSK3 activity led to a rapid and persistent activation of the JNK-cJun pathway. 5) Interestingly, blockade of the JNK pathway prevented the SB216763-induced apoptosis but not the SB216763-induced autophagy. CONCLUSION. Our results provide evidences that GSK3 regulates both apoptosis and autophagy in PC cells. On one hand, inhibition of GSK3 activity triggers apoptosis through JNK-dependent mechanisms. On the other hand, inhibition of GSK3, independently of the JNK pathway, promotes autophagy, a process that appears to protect PC cells against cell death. Inhibition of autophagy might represent an attractive avenue to promote cytotoxic activity of potential therapeutic agents such as GSK3 inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2874. doi:10.1158/1538-7445.AM2011-2874