Pentoxifylline triggers autophagy via ER stress response that interferes with Pentoxifylline induced apoptosis in human melanoma cells

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• 作者：Kapil Sharma ; Mohammad Ishaq ; Gaurav Sharma ; Mohammad Aslam Khan ; Rajesh Kumar Dutta ; Sekhar Majumdar ; ^{majumdar@imtech.res.in" class="auth_mail" title="E-mail the corresponding author} ; ^{sekhar_77054@yahoo.com" class="auth_mail" title="E-mail the corresponding author}
• 关键词：PTX ; Pentoxifylline ; ER stress ; endoplasmic reticulum stress ; CHOP ; C/EBP homologous protein ; GRP78 ; glucose regulated protein 78 ; IRE1-α ; inositol-requiring enzyme 1alpha ; BAPTA-AM ; 1 ; 2-bis(2-aminophenoxy)ethane-N ; N ; N&prime ; N&prime ; -tetraacetic acid tetrakis(acetoxymethyl ester) ; PARP ; poly (ADP-ribose) polymerase ; ROS ; reactive oxygen species ; LC3 ; microtubule-associated protein 1 light chain 3 ; HBSS ; Hank&rsquo ; s Balanced Salt Solution
• 刊名：Biochemical Pharmacology
• 出版年：2016
• 出版时间：1 March 2016
• 年：2016
• 卷：103
• 期：Complete
• 页码：17-28
• 全文大小：4060 K

文摘

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 (Ca²⁺) level. Ca²⁺ is the central player as blocking Ca²⁺ 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 Ca²⁺→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.