Abstract 306: KRas mediated induction of HIF-1α in normoxia promotes tumorigenesis and identifies HIF-1α as a therapeutic target

Abstract

Abstract Oncogenic mutation of the KRas enzyme occurs frequently in human tumors and results in the constitutive activation of multiple signaling pathways. KRas mutation occurs in three specific codons, 12, 13, or 61, and involves the substitution of multiple amino acids. We observed in cancer cell lines containing activating mutations in KRas but not wild type KRas, that the Hypoxia Inducible Factor 1 α (HIF-1α) is expressed and functional under normoxic conditions. HIF-1α itself has been implicated in multiple aspects of tumorigenesis, including survival and invasion. We have found that exogenous expression of wild type KRas or the introduction of oncogenic KRas into transformed cells, causes the expression of HIF-1α in normoxia, but has little or no effect on HIF-1α induction by hypoxia. Additionally, in cancer cells, the deletion of the oncogenic KRas allele, while preserving the wild type allele, silenced the normoxic expression of HIF-1α. To determine the mechanisms by which KRas elicits the expression of HIF-1α, we quantitated the expression of 176 phospho or total proteins utilized a Reverse Phase Protein Array (RPPA) of 74 highly characterized non small cell lung cancer lines (NSCLC's) including 22 NSCLS with oncogenic KRas under three different culture conditions (with serum, without serum and starved then stimulated with serum for 30 minutes). From this RPPA, we found that NSCLC lines containing oncogenic KRas expressed active serine 473 Akt at differing levels, dependent upon which amino acid substitution was present in KRas. Additionally, we found that the KRas activation of Akt signaling, along with other KRas dependent signals, was responsible for HIF-1 stabilization in a hypoxia independent manner. As previously suggested we find that through KRas and Akt driven signaling, KRas is able to overcome the oxygen driven mechanisms responsible for HIF-1α degradation by increased HIF-1α protein translation However, we additionally found that aerobic glycolysis driven by KRas and Akt, specifically the accumulation of the products of glycolysis, also contribute to HIF-1α expression in normoxia. Finally, genome wide mRNA profiling of a KRas transformed line with a stable shRNA mediated knockdown of HIF-1α compared it a vector control showed that under normoxic conditions, knockdown of HIF-1α down regulates several genes important to transformation, including growth factors previously associated with KRas induced transformation. This data suggests inhibitors of HIF-1α may be effective in tumors harboring the KRas oncogenes. Additionally, Akt and HIF-1α inhibitors may be more active when combined with other agents targeted to other signaling pathways activated by KRas in order to bypass resistance mediated by redundant KRas driven signaling pathways. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 306.