p73 regulates autophagy and hepatocellular lipid metabolism through a transcriptional activation of the ATG5 gene

Abstract

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 ...

The generation of neutrophils in the bone marrow is controlled by autophagy

“…Interestingly, our work may explain why p73 knockout mice suffer from a general neutrophilic inflammation, 66 since these mice exhibit strongly reduced ATG5 levels in multiple cell lineages. 67 Reduced ATG5 levels in immature neutrophils clearly stimulate neutrophil production as demonstrated in this work. We further show that autophagy is regulated, at least partially, by the p38-mTORC1 signaling pathway.…”

Vascular ageing and endothelial cell senescence: Molecular mechanisms of physiology and diseases

“…Metabolic regulation by p53 family appears a key function for their cancer-related but also ageing-related phenotype. All the three members promote mitochondrial respiration thought regulation of different metabolic enzymes, including the glutaminase 2 (Gls2) (Adamovich et al, 2014;Amelio et al, 2014b;Bellomaria et al, 2010Bellomaria et al, , 2012Giacobbe et al, 2013;He et al, 2013;Hu et al, 2010;Sharif et al, 2015;Simon et al, 2014;Velletri et al, 2013;Viticchie et al, 2015). Gls2 regulates glutamine utilization, supplying anaplerotic flux of substrates resulting in promotion of mitochondrial activity and ATP synthesis (Amelio et al, 2014a;Maniam et al, 2015).…”

p63 threonine phosphorylation signals the interaction with the WW domain of the E3 ligase Itch

“…3,6,14,38. We have previously investigated the molecular mechanism of Itch recognition for the p63 transcription factor 39 in particular, because this powerful transcription factor is crucial for the development of epithelia, 31,[40][41][42][43][44][45] it is involved in cancer, [46][47][48][49][50][51][52][53][54][55][56][57][58][59] and when it is mutated it causes severe genetic diseases.…”