The expression of p53-target genes in the hypoxia-tolerant subterranean mole-rat is hypoxia-dependent and similar to expression patterns in solid tumors.
The tumor suppressor gene, p53, in response to DNA damage/hypoxia, induces growth arrest and/or apoptosis. Inactivation of p53, by mutations and/or overexpression of the mdm2 gene, confers a selective advantage to tumor cells under hypoxic microenvironment during tumor progression. The mole rat, Spalax, spends its life underground at low-oxygen tensions and hence has developed a wide range of respiratory/molecular adaptations to hypoxic stress. We previously reported that the highly conserved p53 Arg(R)-174 is substituted by lysine (K) in Spalax, identical to a tumor-associated mutation. Functionality assays revealed that Spalax p53 and human R174K-mutated p53 were unable to induce human/Spalax apaf1, an apoptotic target gene, while over-activating the mdm2 gene. Moreover, cells transfected with human p53 underwent more extensive apoptosis (44.8%) as compared to Spalax p53 (23.2%) transfected cells. To support our hypothesis that the pattern of activity in Spalax is related to hypoxia tolerance, we quantified apaf1 and mdm2 mRNA levels under normoxia (21% O(2)), short-acute hypoxic stress (5 h at 6% O(2)) and long-mild hypoxic insult (44 h at 10% O(2)). Results were compared to those of rats under similar conditions. Following hypoxia, Spalax apaf1 mRNA levels decreased significantly, but increased in rats. apip mRNA levels, a negative regulator of apaf1, increased in Spalax and decreased in rats. mdm2 mRNA levels under hypoxia were significantly higher in Spalax. We conclude that, similar to our previous in-vitro work, two parallel hypoxia-adaptive mechanisms evolved in Spalax: mutated p53 and p53 response element leading to a bias against apoptosis and increased mdm2, which are analogous to observations in tumor development.
Band
Mark
M
The W.M. Keck Center for Comparative and Functional Genomics, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
Ashur-Fabian
Osnat
O
Avivi
Aaron
A
D000595:Amino Acid Sequence; D000818:Animals; D053477:Apoptotic Protease-Activating Factor 1 / Q000235:genetics / Q000378:metabolism; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D046308:Spalax; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
C506594:Apaf1 protein, rat; D053477:Apoptotic Protease-Activating Factor 1; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D051736:Proto-Oncogene Proteins c-mdm2; C506435:Casp9 protein, rat; D053453:Caspase 9