Hsp70 (HSP70A1A) downregulation enhances the metastatic ability of cancer cells.

Heat shock protein 70 (Hsp70; also known as HSP70A1A) is one of the most induced proteins in cancer cells; however, its role in cancer has not yet been fully elucidated. In the present study, we proposed a hypothetical model in which the silencing of Hsp70 enhanced the metastatic properties of the HeLa, A549 and MCF7 cancer cell lines. We consider that the inability of cells to form cadherin­catenin complexes in the absence of Hsp70 stimulates their detachment from neighboring cells, which is the first step of anoikis and metastasis. Under these conditions, an epithelial­to­mesenchymal transition (EMT) pathway is activated that causes cancer cells to acquire a mesenchymal phenotype, which is known to possess a higher ability for migration. Therefore, we herein provide evidence of the dual role of Hsp70 which, according to international literature, first establishes a cancerous environment and then, as suggested by our team, regulates the steps of the metastatic process, including EMT and migration. Finally, the trigger for the anti­metastatic properties that are acquired by cancer cells in the absence of Hsp70 appears to be the destruction of the Hsp70­dependent heterocomplexes of E­cadherin/catenins, which function like an anchor between neighboring cells.

Loss of p14(ARF) confers resistance to heat shock- and oxidative stress-mediated cell death by upregulating ß-catenin.

The p14(ARF) is a key tumor suppressor induced mainly by oncogenic stimuli. Although p14(ARF) does not seem to respond to DNA damage, there are very few data regarding its role in other forms of stress, such as heat shock (HS) and oxidative stress (OS). Here, we report that suppression of p14(ARF) increased resistance to cell death when cells were treated with H(2) O(2) or subjected to HS. In this setting, protection from cell death was mediated by elevated levels and activity of ß-catenin, as downregulation of ß-catenin alleviated the protective role of p14(ARF) silencing. Moreover, Hsp70 was shown to regulate ß-catenin protein levels by interacting with p14(ARF) , suggesting that Hsp70, p14(ARF) and ß-catenin form a regulatory network. This novel pathway triggers cell death signals when cells are exposed to HS and OS.

Mutant p53 enhances nuclear factor kappaB activation by tumor necrosis factor alpha in cancer cells.

Mutations in the p53 tumor suppressor are very frequent in human cancer. Often, such mutations lead to the constitutive overproduction of mutant p53 proteins, which may exert a cancer-promoting gain of function. We now report that cancer-associated mutant p53 can augment the induction of nuclear factor kappaB (NFkappaB) transcriptional activity in response to the cytokine tumor necrosis factor alpha (TNFalpha). Conversely, down-regulation of endogenous mutant p53 sensitizes cancer cells to the apoptotic effects of TNFalpha. Analysis of human head and neck tumors and lung tumors reveals a close correlation between the presence of abundant mutant p53 proteins and the constitutive activation of NFkappaB. Together, these findings suggest that p53 mutations may promote cancer progression by augmenting NFkappaB activation in the context of chronic inflammation.

deltaEF1 repressor controls selectively p53 family members during differentiation.

The discovery of two new p53 homologs, p73 and p63, has defined a family of transcription factors heavily involved in the control of growth suppression, apoptosis, differentiation and development. While p53-deficient mice undergo spontaneous tumors, p73 and p63 knockout mice exhibit severe developmental defects. We demonstrate here that p73 gene is an in vivo transcriptional target of the muscle regulatory factors MyoD, myogenin, Myf5 and Myf6. Ectopic expression of the transcriptional repressor deltaEF1/ZEB/zfhx1a counteracts MyoD/Myf5- or MyoD/Myf6-mediated transcriptional activation of p73. A distinct pattern of in vivo recruitment of muscle regulatory factors and deltaEF1 on p73 regulatory regions was found between proliferating and differentiating muscle cells. We also found that deltaEF1 plays a role in the transcriptional regulation of p53 family members during keratinocytic differentiation. Mouse embryo fibroblasts derived from deltaEF1-deficient mice exhibit unbalanced expression of DeltaNp63, TAp73 and DeltaNp73 but not of TAp63 and p53. The analysis of tissues derived from deltaEF1+/- mice exhibit a selective enrichment of DeltaNp63 in skin.

The transcriptional coactivator Yes-associated protein drives p73 gene-target specificity in response to DNA Damage.

The transcriptional coactivator Yes-associated protein (YAP) has been shown to interact with and to enhance p73-dependent apoptosis in response to DNA damage. Here, we show that YAP requires the promyelocytic leukemia gene (PML) and nuclear body localization to coactivate p73. YAP imparts selectivity to p73 by promoting the activation of a subset of p53 and/or p73 target promoters. Endogenous p73, YAP, and p300 proteins are concomitantly recruited onto the regulatory regions of the apoptotic target gene p53AIP1 only when cells are exposed to apoptotic conditions. Silencing of YAP by specific siRNA impairs p300 recruitment and reduces histone acetylation on the p53AIP1 target gene, resulting in delayed or reduced apoptosis mediated by p73. We also found that YAP contributes to the DNA damage-induced accumulation of p73 and potentiates the p300-mediated acetylation of p73. Altogether, our findings identify YAP as a key determinant of p73 gene targeting in response to DNA damage.

Regulation of p53: intricate loops and delicate balances.

The p53 tumor suppressor protein provides a major anti-cancer defense mechanism, as underscored by the fact that the p53 gene is the most frequent target for genetic alterations in human cancer. Recent work has led to the realization that p53 lies at the hub of a very complex network of signaling pathways that integrate a variety of intracellular and extracellular inputs. Part of this network consists of an array of autoregulatory feedback loops, where p53 exhibits very intricate interactions with other proteins known to play important roles in the determination of cell fate. We discuss two such loops, one involving the beta-catenin protein and the other centering on the Akt/PKB protein kinase. In both cases, the central module is the interplay between p53 and the Mdm2 protein, which inactivates p53 and targets it for rapid proteolysis. Whereas deregulated beta-catenin can lead to Mdm2 inactivation and p53 accumulation, active p53 can promote the degradation and down-regulation of beta-catenin. Similarly, Akt can block p53 activation by potentiating Mdm2, whereas activated p53 can tune down Akt in several different ways. In each case, the actual output of the loop is determined by the delicate balance between the opposing effects of its different components. Often, this balance is dictated by additional signaling processes that occur simultaneously within the same cell. Genetic alterations characteristic of cancer are capable of severely distorting this balance, thereby overriding the tumor suppressor effects of p53 in a manner that facilitates neoplastic conversion.

Regulation of p53: intricate loops and delicate balances.

The p53 tumor suppressor protein provides a major anti-cancer defense mechanism, as underscored by the fact that the p53 gene is the most frequent target for genetic alterations in human cancer. Recent work has led to the realization that p53 lies at the hub of a very complex network of signaling pathways, which integrate a variety of intracellular and extracellular inputs. Part of this network consists of an array of autoregulatory feedback loops, where p53 exhibits very intricate interactions with other proteins known to play important roles in the determination of cell fate. We discuss two such loops, one involving the beta catenin protein and the other centering on the Akt/protein kinase B. In both cases, the central module is the interplay between p53 and the murine double minute 2 (Mdm2) protein, which inactivates p53 and targets it for rapid proteolysis. Whereas deregulated beta catenin can lead to Mdm2 inactivation and p53 accumulation, active p53 can promote the degradation and downregulation of beta catenin. Similarly, Akt can block p53 activation by potentiating Mdm2, whereas activated p53 can tune down Akt in several different ways. In each case, the actual output of the loop is determined by the delicate balance between the opposing effects of its different components. Often, this balance is dictated by additional signaling processes that occur simultaneously within the same cell. Genetic alterations characteristic of cancer are capable of severely distorting this balance, thereby overriding the tumor suppressor effects of p53 in a manner that facilitates neoplastic conversion.