The role of autophagy in cancer is controversial: Both tumor-suppressing and tumor-promoting functions have been reported. We show that a key regulator of autophagy, autophagy-related protein 5 (ATG5), is often down-regulated in primary melanomas compared to benign nevi, leading to a reduction of basal autophagy as evidenced by a reduced expression of LC3. A follow-up of 158 primary melanoma patients showed that patients with low levels of ATG5 in their tumors had a reduced progression-free survival. In an in vitro model of melanoma tumorigenesis, where the BRAF oncogene was transduced into normal melanocytes, we observed that lowering ATG5 expression promoted proliferation by precluding oncogene-induced senescence. Hence, it appears that down-regulation of ATG5 contributes to tumorigenesis in early-stage cutaneous melanoma, and the expression of ATG5 and LC3 correlates with melanoma diagnosis and prognosis.

Apoptosis is the most common form of neutrophil death under both physiological and inflammatory conditions. However, forms of nonapoptotic neutrophil death have also been observed. In the current study, we report that human neutrophils undergo necroptosis after exposure to GM-CSF followed by the ligation of adhesion receptors such as CD44, CD11b, CD18, or CD15. Using a pharmacological approach, we demonstrate the presence of a receptor-interacting protein kinase-3 (RIPK3)-a mixed lineage kinase-like (MLKL) signaling pathway in neutrophils which, following these treatments, first activates p38 MAPK and PI3K, that finally leads to the production of high levels of reactive oxygen species (ROS). All these steps are required for necroptosis to occur. Moreover, we show that MLKL undergoes phosphorylation in neutrophils in vivo under inflammatory conditions. This newly identified necrosis pathway in neutrophils would imply that targeting adhesion molecules could be beneficial for preventing exacerbation of disease in the neutrophilic inflammatory response.

Melanoma, occurring as a rapidly progressive skin cancer, is resistant to current chemoand radiotherapy, especially after metastases to distant organs has taken place. Most chemotherapeutic drugs exert their cytotoxic effect by inducing apoptosis, which, however, is often deficient in cancer cells. Thus, it is appropriate to attempt the targeting of alternative pathways, which regulate cellular viability. Recent studies of autophagy, a well-conserved cellular catabolic process, promise to improve the therapeutic outcome in melanoma patients. Although a dual role for autophagy in cancer therapy has been reported, both protecting against and promoting cell death, the potential for using autophagy in cancer therapy seems to be promising. Here, we review the recent literature on the role of autophagy in melanoma with respect to the expression of autophagic markers, the involvement of autophagy in chemo-and immunotherapy, as well as the role of autophagy in hypoxia and altered metabolic pathways employed for melanoma therapy.

p73, a member of the p53 tumor suppressor family, is involved in neurogenesis, sensory pathways, immunity, inflammation, and tumorigenesis. How p73 is able to participate in such a broad spectrum of different biological processes is still largely unknown. Here, we report a novel role of p73 in regulating lipid metabolism by direct transactivation of the promoter of autophagy-related protein 5 (ATG5), a gene whose product is required for autophagosome formation. Following nutrient deprivation, the livers of p73-deficient mice demonstrate a massive accumulation of lipid droplets, together with a low level of autophagy, suggesting that triglyceride hydrolysis into fatty acids is blocked owing to deficient autophagy (macrolipophagy). Compared with wild-type mice, mice functionally deficient in all the p73 isoforms exhibit decreased ATG5 expression and lower levels of autophagy in multiple organs. We further show that the TAp73a is the critical p73 isoform responsible for inducing ATG5 expression in a p53-independent manner and demonstrate that ATG5 gene transfer can correct autophagy and macrolipophagy defects in p73-deficient hepatocytes. These data strongly suggest that the p73-ATG5 axis represents a novel, key pathway for regulating lipid metabolism through autophagy. The identification of p73 as a major regulator of autophagy suggests that it may have an important role in preventing or delaying disease and aging by maintaining a homeostatic control. Cell Death and Differentiation (2013) 20, 1415-1424; doi:10.1038/cdd.2013.104; published online 2 August 2013 p73 belongs to the p53 family, a group of transcription factors that have key roles in the regulation of many cellular processes, such as apoptosis, cell cycle, and senescence, especially following DNA damage. 1-3 Whereas p53 is a tumor suppressor and often either deleted or mutated in tumors, p73 is rarely mutated; however, its expression is often deregulated in cancer. 4,5 In p73-deficient mice, unlike in p53-deficient mice, no increase in spontaneous tumorigenesis is observed. 6 It has been demonstrated, however, that p73, in the absence of DNA damage, has a role in neuronal differentiation and development. 6-9 Consequently, p73-deficient mice exhibit neurological defects and, even though no obvious deficiencies in lymphoid or granulocyte populations have been so far detected, such mice show deregulated inflammatory responses and senescence. 6,10 Because of splicing events occurring near the 3 0 end of the coding region and because of an alternative promoter located in the third intron of the gene, p73 exists as multiple protein variants. 11 The isoforms containing a transactivation (TA) domain (TAp73s) generally behave like p53 with respect to overlapping promoters and biological functions. 2,4 For instance, in contrast to p73-deficient mice, TAp73 knockout mice showed spontaneous as well as carcinogen-induced tumors, indicating that TAp73 is a tumor suppressor. 12 The alternative promoter also produces amino-terminal truncated DN isoforms, the so-called ...

Whether and how autophagy is involved in tumorigenesis is poorly understood. We approached this question by investigating a relatively large cohort of patients with mostly early primary melanoma for their expression of 2 markers for autophagy, the protein ATG5 (autophagy-related 5) and MAP1LC3B/LC3 (microtubule-associated protein 1 light chain 3B). Surprisingly, we discovered that both ATG5 and LC3 levels are decreased in patients with melanomas as compared with those with benign nevi. We wondered why reduced autophagy should facilitate early tumor development. Using an in vitro model of melanoma tumorigenesis, in which a mutated oncogene, BRAF (v-raf murine sarcoma viral oncogene homolog B), had been introduced into normal human melanocytes, we were able to show that downregulation of ATG5 promoted the proliferation of melanocytes because it facilitated bypassing oncogene-induced senescence (OIS). Our work supports previous reports that had argued that autophagy actually suppresses tumorigenesis and explains the possible mechanism. Furthermore, our findings suggest that the status of ATG5 and autophagy could serve as a diagnostic marker for distinguishing benign from malignant tumors of melanocytes.

BCL-2-related ovarian killer (BOK) is a conserved and widely expressed BCL-2 family member with sequence homology to pro-apoptotic BAX and BAK, but with poorly understood pathophysiological function. Since several members of the BCL-2 family are critically involved in the regulation of hepatocellular apoptosis and carcinogenesis we aimed to establish whether loss of BOK affects diethylnitrosamine (DEN)-induced hepatocarcinogenesis in mice. Short-term exposure to DEN lead to upregulation of BOK mRNA and protein in the liver. Of note, induction of CHOP and the pro-apoptotic BH3-only proteins PUMA and BIM by DEN was strongly reduced in the absence of BOK. Accordingly, Bok -/- mice were significantly protected from DEN-induced acute hepatocellular apoptosis and associated inflammation. As a consequence, Bok -/- animals were partially protected against chemical-induced hepatocarcinogenesis showing fewer and, surprisingly, also smaller tumors than WT controls. Gene expression profiling revealed that downregulation of BOK results in upregulation of genes involved in cell cycle arrest. Bok -/- hepatocellular carcinoma (HCC) displayed higher expression levels of the cyclin kinase inhibitors p19INK4d and p21cip1. Accordingly, hepatocellular carcinoma in Bok -/- animals, BOK-deficient human HCC cell lines, as well as non-transformed cells, showed significantly less proliferation than BOK-proficient controls. We conclude that BOK is induced by DEN, contributes to DEN-induced hepatocellular apoptosis and resulting hepatocarcinogenesis. In line with its previously reported predominant localization at the endoplasmic reticulum, our findings support a role of BOK that links the cell cycle and cell death machineries upstream of mitochondrial damage.

Autophagy, a fundamental cellular catabolic process, is involved in the development of numerous diseases including cancer. Autophagy seems to have an ambivalent impact on tumor development. While increasing evidence indicates a cytoprotective role for autophagy that can contribute to resistance against chemotherapy and even against the adverse, hypoxic environment of established tumors, relatively few publications focus on the role of autophagy in early tumorigenesis. However, the consensus is that autophagy is inhibitory for the genesis of tumors. To understand this apparent contradiction, more detailed information about the roles of the individual participants in autophagy is needed. This review will address this topic with respect to autophagy-related protein 5 (ATG5), which in several lines of investigation has been ascribed special significance in the autophagic pathway. Furthermore, it was recently shown that an ATG5 deficiency in melanocytes interferes with oncogene-induced senescence, thus promoting melanoma tumorigenesis. Similarly, an ATG5 deficiency resulted in tumors of the lung and liver in experimental mouse models. Taken together, these findings indicate that ATG5 and the autophagy to which it contributes are essential gatekeepers restricting early tumorigenesis in multiple tissues.

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