Role of Apollon in Human Melanoma Resistance to Antitumor Agents That Activate the Intrinsic or the Extrinsic Apoptosis Pathways

Abstract

Purpose To assess the role of Apollon in melanoma resistance to intrinsic and extrinsic pathways of apoptosis and to identify strategies to reduce its expression. Experimental Design Apollon expression was assessed in melanoma cells in vitro and in vivo. Apollon modulation and melanoma apoptosis were evaluated by Western blot and/or flow cytometry in response to cytotoxic drugs, mitogen-activated protein/extracellular signal–regulated kinase (MEK)-, BRAFV600E-, and mTOR-specific inhibitors, TRAIL and anti-HLA class II monoclonal antibodies (mAb). Mitochondrial depolarization, caspase activation, apoptosis assays, and gene expression profiling were used to test effects of Apollon silencing, by siRNA, on melanoma response to antitumor agents. Results Apollon was constitutively expressed by melanoma cells, in vitro and in vivo, and at higher levels than in benign melanocytic lesions. Melanoma apoptosis correlated significantly with Apollon protein downmodulation in response to cytotoxic drugs, MEK, or BRAFV600E-specific inhibitors. Combinatorial treatment with MEK and mTOR inhibitors and HLA class II ligation, by a specific mAb, promoted Apollon downmodulation and enhanced melanoma apoptosis. Apollon downmodulation induced by antitumor agents was caspase independent, but proteasome dependent. Knockdown of Apollon, by siRNA, triggered apoptosis and/or significantly enhanced melanoma cell death in response to cytotoxic drugs, MEK- and BRAFV600E-specific inhibitors, and soluble or membrane-bound TRAIL. Apollon silencing promoted mitochondrial depolarization and caspase-2, caspase-8, caspase-9, and caspase-3 activation in response to different antitumor agents and altered the profile of genes modulated by MEK or BRAFV600E-specific inhibitors. Conclusions Targeting of Apollon may significantly improve melanoma cell death in response to antitumor agents that trigger the intrinsic or the extrinsic apoptosis pathways.

Overcoming chemotherapy drug resistance by targeting inhibitors of apoptosis proteins (IAPs)

“…Esophagus, tonsil, testis, thyroid, skin, lung, and brain etc. [43]API2Colo rectal cancer [56]Regulation of tumor necrosis factor-mediated signaling pathway [55]Multiple myeloma [64]Regulator of innate immune signaling [62]Breast carcinoma [65]Pancreatic carcinoma [66]Involved in MAPK signaling [60]BIRC 3RING domain with E3 ubiquitin ligase activityBladder cancer [67]Chronic lymphocytic leukemia [68]Ts-IAP (testis-specific IAP)hlLP21 BIR domainFound in normal and cancerous testisBIRC 81 RING domainRestricted specificity for caspase 9 [69]ILP-2Suppess apoptosis induced by Bax but not Fas-mediated apoptosis [69]BRUCE (BIR-containing ubiquitin conjugating enzyme)ApollonHigh levels in brain,testis and lymphatic cells [70]Suppression of apoptosis by facilitating the degradation of SMAC and caspase-9 [71] and promotion of cytokinesis [72]1 BIR domainBIRC61 UBA doma nColorectal cancer [73], neuroblastoma, melanoma [74], prostrate cancer [75]DNA damage repair and genome stability [76]SurvivinTIAP (murine homologue of human survivin)Some of the normal adult human tissues, including colonic mucosa, placenta, bone marrow and keratinocytes of the basal layer of the skin. In embryonic tissues [77]Regulation of physiological functions of haematopoietic stem cells, neuronal stem cells or intestinal stem cells [78, 7...…”

BIRC6 (Baculoviral IAP repeat-containing 6)

“…Moreover, targeting of BIRC6, by siRNA, significantly enhanced caspasedependent melanoma apoptosis in response to cytotoxic drugs, MEK, and BRAFV600E inhibitors and soluble or membrane-bound TRAIL (Tassi et al, 2012).…”

“…BIRC6 and treatment resistance. Silencing of BIRC6 has been shown to sensitize cancer cells to various anticancer agents, including 5-fluorouracil (in cervical, fibrosarcoma and breast cancer cells) (Chu et al, 2008), oxaliplatin and cisplatin (in colonospheres) (Van Houdt et al, 2011), MEK inhibitor, BRAFV600E-specific inhibitor and soluble or membrane-bound TRAIL (in melanoma cells) (Tassi et al, 2012), cisplatin (in non-small cell lung cancer and glioma) (Dong et al, 2013;Chen et al, 1999), camptothecin (glioma) (Chen et al, 1999) and sorafenib (in hepatoma) . Essential in embryonic development.…”

Targeting the intrinsic apoptosis pathway as a strategy for melanoma therapy

“…However, this latter observation may also be explained by the immunogenic nature of ML‐IAP, which can result in immune‐mediated destruction of ML‐IAP + melanoma cells (Schmollinger et al., ). Much less is known about NAIP (Damiano et al., ), apollon (Tassi et al., ) and ILP2 (Richter et al., ) in melanoma but as their contribution to the inhibition of apoptosis becomes clearer it may reveal novel potential for therapeutic intervention.…”