title: Pentoxifylline triggers autophagy via ER stress response that interferes with Pentoxifylline induced apoptosis in human melanoma cells.
abstract: Pentoxifylline (PTX), a non-specific phosphodiesterase inhibitor is known to inhibit the growth of various cancer cells including melanoma. Here in this study, we have found that PTX induces autophagy in human melanoma cell lines (A375 and MeWo). Induction of autophagy is associated with the increase in Atg5 expression as knockdown of Atg5 effectively inhibited PTX mediated autophagy. A decrease in mTOR activation was also observed after PTX treatment. We observed that autophagy was activated as a downstream effector mechanism of ER stress induced by PTX. ER stress response was confirmed by upregulation of IRE-1α, GRP78 and CHOP expression. PTX treatment also resulted in an increase in intracellular calcium (Ca(2+)) level. Ca(2+) is the central player as blocking Ca(2+) by intracellular calcium chelator (BAPTA-AM) effectively inhibited the PTX induced ER stress response as well as autophagy. Moreover, silencing of CHOP also resulted in autophagy inhibition with a decrease in Atg5 expression. Collectively, PTX triggers ER stress response followed by induction of autophagy via involvement of Ca(2+)→CHOP→Atg5 signalling cascade. Interestingly, inhibition of intracellular calcium level by BAPTA-AM significantly increased PTX mediated cell death by augmenting intrinsic apoptotic pathway. Inhibition of autophagy by the ATG5 siRNA and pharmacological inhibitor, chloroquine also enhances PTX induced cell death. Taken together, our results clearly indicate that activation of ER stress response and autophagy provides resistance to PTX mediated apoptosis, and thus, interferes with the anticancer activity of PTX in human melanoma cells.
authors.affiliation: Division of Cell Biology and Immunology, CSIR-Institute of Microbial Technology, Chandigarh 160 036, India.
authors.forename: Kapil
authors.initials: K
authors.lastname: Sharma
authors.affiliation: Division of Cell Biology and Immunology, CSIR-Institute of Microbial Technology, Chandigarh 160 036, India.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Ishaq
authors.affiliation: Division of Cell Biology and Immunology, CSIR-Institute of Microbial Technology, Chandigarh 160 036, India.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Sharma
authors.affiliation: Division of Cell Biology and Immunology, CSIR-Institute of Microbial Technology, Chandigarh 160 036, India.
authors.forename: Mohammad Aslam
authors.initials: MA
authors.lastname: Khan
authors.affiliation: Division of Cell Biology and Immunology, CSIR-Institute of Microbial Technology, Chandigarh 160 036, India.
authors.forename: Rajesh Kumar
authors.initials: RK
authors.lastname: Dutta
authors.affiliation: Division of Cell Biology and Immunology, CSIR-Institute of Microbial Technology, Chandigarh 160 036, India. Electronic address: majumdar@imtech.res.in.
authors.forename: Sekhar
authors.initials: S
authors.lastname: Majumdar
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D000071187:Autophagy-Related Protein 5; D002118:Calcium / Q000378:metabolism*; D065096:Calcium Chelating Agents / Q000494:pharmacology; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D008545:Melanoma / Q000473:pathology*; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010431:Pentoxifylline / Q000494:pharmacology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D015398:Signal Transduction; D012878:Skin Neoplasms / Q000473:pathology*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D051742:Transcription Factor CHOP / Q000378:metabolism
chemical_list: C502778:ATG5 protein, human; D000970:Antineoplastic Agents; D000071187:Autophagy-Related Protein 5; D065096:Calcium Chelating Agents; C497249:DDIT3 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D008869:Microtubule-Associated Proteins; D010726:Phosphodiesterase Inhibitors; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D051742:Transcription Factor CHOP; D004533:Egtazic Acid; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D010431:Pentoxifylline; D002118:Calcium
keywords: Autophagy; Calcium; ER stress response; Melanoma; Pentoxifylline