The p53 codon 72 proline allele is endowed with enhanced cell-death inducing potential in cancer cells exposed to hypoxia

The preferential retention of the arginine allele at the p53 codon 72 locus is commonly observed in tumours from arginine/proline heterozygotes. Considering that cancer cells are harboured in a hypoxic environment in vivo, we here tested the hypothesis that the p53 codon 72 proline allele confers a survival disadvantage in presence of hypoxia. Here, we show that the transient transfection of the proline allele in p53 null cancer cells exposed to low oxygen tension or to the hypoxia-mimetic drug Desferoxamine induces a higher amount of cell death than the arginine allele. Accordingly, proline allele transiently transfected cell lines express lower levels of hypoxia pro-survival genes (HIF-1α, carbonic anhydrase IX, vascular endothelial growth factor, heme oxygenase-I, hepatocyte growth factor receptor, vascular endothelial growth factor receptor 2), compared to those transiently transfected with the arginine allele. Further, we report that the exposure of the arginine/proline heterozygote MCF-7 breast cancer cell line to cytotoxic concentration of Desferoxamine for several weeks, gives raise to hypoxia-resistant clones, carrying the arginine, but not the proline allele. These data indicate that the p53 codon 72 proline allele is less permissive for the growth of cancer cells in a hypoxic environment, and suggest that the preferential retention of the arginine allele in the tumour tissues of arginine/proline heterozygous patients may depend upon its lowered capacity to induce cell death in a hypoxic tumour environment

Inhibition of Hypoxia-Inducible Factor-1α (HIF-1α) Protein Synthesis by DNA damage inducing agents

10.1371/journal.pone.0010522PLoS ONE55

Reciprocal influence of the p53 and the hypoxic pathways

When cells sense a decrease in oxygen availability (hypoxia), they develop adaptive responses in order to sustain this condition and survive. If hypoxia lasts too long or is too severe, the cells eventually die. Hypoxia is also known to modulate the p53 pathway, in a manner dependent or not of HIF-1 (hypoxia-inducible factor-1), the main transcription factor activated by hypoxia. The p53 protein is a transcription factor, which is rapidly stabilised by cellular stresses and which has a major role in the cell responses to these stresses. The aim of this review is to compile what has been reported until now about the interconnection between these two important pathways. Indeed, according to the cell line, the severity and the duration of hypoxia, oxygen deficiency influences very differently p53 protein level and activity. Conversely, p53 is also described to affect HIF-1α stability, one of the two subunits of HIF-1, and HIF-1 activity. The direct and indirect interactions between HIF-1α and p53 are described as well as the involvement in this complex network of their respective ubiquitin ligases von Hippel Lindau protein and murine double minute 2. Finally, the synergistic or antagonistic effects of p53 and HIF-1 on some important cellular pathways are discussed

Proteasomal inhibition attenuates transcriptional activity of hypoxia-inducible factor 1 (HIF-1) via specific effect on the HIF-1 alpha C-terminal activation domain

The ubiquitin-proteasome pathway (UPP) is involved in regulation of multiple cellular processes. Hypoxia-inducible factor 1 alpha (HIF-1 alpha) is a prototypic target of the UPP and, as such, is stabilized under conditions of proteasomal inhibition. Using carbonic anhydrase IX (CAIX) and vascular endothelial growth factor (VEGF) expression as paradigmatic markers of HIF-1 activity, we found that proteasomal inhibitors (PI) abrogated hypoxia-induced CAIX expression in all cell lines tested and VEGF expression in two out of three. Mapping of the inhibitory effect identified the C-terminal activation domain (CAD) of HIF-1 alpha as the primary target of PI. PI specifically inhibited the HIF-1 alpha CAD despite activating the HIF-1 alpha coactivator p300 and another p300 cysteine/histidine-rich domain 1-dependent transcription factor, STAT-2. Coimmunoprecipitation and glutathione S-transferase pull downs indicated that PI does not disrupt interactions between HIF-1 alpha and p300. Mutational analysis failed to confirm involvement of sites of known or putative posttranslational modifications in regulation of HIF-1 alpha CAD function by PI. Our data provide evidence for the counterintuitive hypothesis that inhibition of HIF-1 function could be responsible for at least some of the antitumor effects of proteasomal inhibition. Further studies of the mechanism of the PI-induced attenuation of HIF-1 alpha will provide important, potentially novel insight into regulation of HIF-1 activity and possibly identify new targets for HIF-directed therapy

Acute effects of interferon on estrogen receptor function do not involve the extracellular signal-regulated kinases p42mapk and p44mapk.

Exposure to type I interferons (IFN) increased estrogen receptor (ER) ligand binding and induced protein kinase C (PKC) translocation within 30 min but had no effect on net incorporation of [32P] into ER in Madin Darby bovine kidney (MDBK) cells. Ligand binding was also increased within 30 min by phorbol ester and the protein phosphatase inhibitor okadaic acid. Mitogen-activated protein (MAP) kinase phosphorylation was initially inhibited between 2 and 30 min and subsequently activated between 30 and 60 min after treatment with IFN. The activatory response was blocked by the PKC inhibitor Ro 31-8220. Following transient transfection with an ERE-CAT reporter construct, IFN increased CAT expression after 6 h but decreased ER ligand binding, transcriptional activity and phosphorylation after 48 h, probably as a result of decreased ER concentrations. The results rule out rapid activation of ER ligand binding through phosphorylation at Ser118 by MAP kinase because (1) the increase in ligand binding preceded activation of MAP kinase, and (2) IFN had no short-term effect on [32P]incorporation or ER transcriptional activity. The rapid effect of IFN on ER ligand binding is postulated to reflect phosphorylation of the receptor at Tyr537 by p56lck, a member of the Src family of PKC-activated tyrosine kinases