NF-κB Signaling Activation Induced by Chloroquine Requires Autophagosome, p62 Protein, and c-Jun N-terminal Kinase (JNK) Signaling and Promotes Tumor Cell Resistance

Abstract

Edited by George N. DeMartinoMacroautophagy (hereafter autophagy) is a catabolic cellular self-eating process by which unwanted organelles or proteins are delivered to lysosomes for degradation through autophagosomes. Although the role of autophagy in cancer has been shown to be context-dependent, the role of autophagy in tumor cell survival has attracted great interest in targeting autophagy for cancer therapy. One family of potential autophagy blockers is the quinoline-derived antimalarial family, including chloroquine (CQ). However, the molecular basis for tumor cell response to CQ remains poorly understood. We show here that Macroautophagy (hereafter autophagy) is an evolutionarily conserved cellular self-eating process, in which proteins or organelles are delivered to lysosomes for degradation (1, 2). Autophagy can inhibit or promote tumor development depending on the context (3-6). Autophagy deficiency has been reported to increase genome instability induced by oxidative stress or DNA damage, a well known factor for cancer initiation and progression (2,7,8). However, autophagy has been shown to promote cell survival and adaptation by protecting cells against various stress conditions such as anticancer treatment and unfavorable tumor microenvironments such as anoikis, starvation, and hypoxic or oxidative conditions (9, 10). Increasing evidence has indicated that inhibition of autophagy suppresses tumor growth, invasion, and metastasis (11-13). These findings suggest autophagy inhibition as an attractive new strategy to prevent and treat cancer.One of the representative autophagy inhibitors is chloroquine (CQ), 2 a lysosomotropic drug approved by the United States Food and Drug Administration for the prophylactic treatment of malaria (14, 15) and the management of lupus erythematosus and rheumatoid arthritis (16,17). Although it has several side effects such as skin rash, muscle damage, and vision problems (18,19), and an overdose can be lethal (20, 21), CQ has recently attracted considerable attention as an antitumor drug due to the potential biological effects on blocking autophagy in tumor cells (22)(23)(24). However, recent studies have shown that CQ exhibits its antitumor activity independent of autophagy inhibition (25), including normalizing the tumor vasculature (26). Several phase I and II clinical trials with CQ suggest that CQ can moderately improve the clinical activity of radiation therapy and several chemotherapeutics (22)(23)(24). In contrast, another antimalarial quinacrine is shown to induce cancer cell death through autophagy inhibition and p53-dependent inhibition of the oxidative pentose phosphate pathway (27).It is possible that the limited anticancer efficacy of CQ is caused by the induction of resistance pathways in tumor cells. However, how CQ induces resistance is unknown. In this study, we found that CQ induced NF-B activation through autophagosome accumulation, p62, and JNK signaling, which mediated CQ resistance in both squamous cell carcinoma (SCC) and melanoma cells. To determi...

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“…Additionally, it has been suggested that autophagy, like the proteasomal system, is closely related to the complex network of NF-κB and Nrf2 transcription factors [ 66 ]. Autophagy could be required for the full activation of NF-κB [ 67 ]. Therefore, several elements of the NF-κB system, including all IKK, NIK, and p62SQSTM1 subunits, are simultaneously autophagic substrates.…”

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“…Notably, CQ creates a positive feedforward loop between p62 and NF-κΒ, the CQ-induced upregulation of p62 actives NF-κΒ, which, in turn, induces p62 expression. Nevertheless, blocking either p62 or NF-κΒ pathway sensitized cancer cells to CQ-mediated apoptotic cell death, suggesting the important role of p62/NF-κΒ axis in mediating cell survival and resistance to CQ in cancer 84 . In keeping with the role of autophagy in drug resistance, Jia and collaborators reported that Bortezomib, a novel anticancer agent used for the treatment of MM, induced autophagy of IκBα in DLBCL, thus promoting cell drug resistance.…”

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“…3). 166 Nevertheless, in normal cells, coordinated proteostatic feedback is beneficial for the host tissue. 165 Figure 2.…”

“…In melanoma cells, 25 lM CQ suffices to cause accumulation of the autophagy adaptor protein p62, inducing NF-jB activity and thereby leading to expression of survival genes and p62 itself, culminating in cell resistance to apoptosis. 166 Nevertheless, in normal cells, coordinated proteostatic feedback is beneficial for the host tissue. An example of such a beneficial function of the proteostatic feedback is seen when NF-jB promotes mitophagy through induction of p62 expression in macrophages, thereby preventing the accumulation of damaged mitochondria and limiting excessive IL-1b-dependent inflammation.…”