Patients with OSCC revealed that 6 of 28 patients had mismatched heteroduplex patterns.
Patients with OSCC revealed that 6 of 28 patients had mismatched heteroduplex patterns. Genomic DNA was extracted from peripheral blood leukocytes and direct sequencing showed that in 5 of the six cases these changes represented polymorphisms while, one case was a somatic mutation. Analyses of TSC1 and TSC2 revealed heteroduplexes in exons: TSC1 exon 17; TSC2 exons 36,40, and 41. The relative levels of HIF-1alpha were significantly greater for tumors possessing a HIF-1alpha polymorphism or mutation within exon 12, whereas tumors possessing a deletion or polymorphism in TSC1/TSC2 displayed a trend for higher levels of HIF1alpha. Western blot analyses for HIF-1alpha, TSC1 and TSC2 in five SCC cell lines revealed high levels of HIF-1alpha in SCC cells possessing TSC1 and/or TSC2 mutations. Wild-type TSC2 cells targeted with siRNA to TSC2 exhibited increased levels of HIF-1alpha. Transfection of a HIF-1alpha mutant produced higher levels of HIF-1alpha in TSC1/TSC2 mutant cell lines than in wild type cells. TSC1/TSC2 mutant cell lines administered Rapamycin blocked S6 phorphorylation and diminished the levels of HIF-1alpha to those observed in cell lines with wild type TSC1/TSC2. Conclusion: Dysregulation of the TSC1/TSC2 complex by mutation compliments HIF-1 polymorphisms in the expression of HIF-1alpha in SCC of the head and neck, and may provide biomarkers to predict responses to specific therapies and overall disease prognosis.Page 1 of(page number not for citation purposes)Molecular Cancer 2006, 5:http://www.molecular-cancer.com/content/5/1/BackgroundHypoxia, a frequent effect of solid tumor growth in head and neck cancer and other PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28499442 cancers, serves to generate a cascade of molecular pathways which include angiogenesis, glycolysis, and various cell-cycle control proteins. These cell-salvaging mechanisms can be carried out rapidly by a transcription factor that reacts to hypoxic conditions, the hypoxia-inducible factor-1 (HIF-1) [1]. HIF-1 is a heterodimer consisting of an subunit and a subunit, both of which are members of the basic helix-loop-helix Per/Arnt/Sim (PAS) H 4065MedChemExpress Deslorelin family [2]. Stability of this dimer is dependent to a large extent on oxygen [3,4]. Thus, in the presence of oxygen HIF family members are hydroxylated on one of two conserved prolyl residues. This is achieved by members of the egg-laying-defective nine (EGLN) family or prolyl hydroxylases (PHD1, PHD2, and PHD3) that achieve hydroxylation, using Fe2+ and ascorbate as cofactors [5,6]. In so doing, prolyl hydroxylation creates a binding site for a ubiquitin ligase complex containing the von Hippel-Lindau (VHL) tumor suppressor protein, which results in HIF destruction [7-10]. Most recently, OS-9, a ubiquitous cellular protein was shown to be a common partner for HIF- and the PHDs, as well as to enhance prolyl hydroxylation and degradation of HIF1 [11]. Conversely, in cells where OS-9 mRNA was targeted for degradation, increased HIF-1 levels and accordingly increased HIF-mediated transcription were observed [11]. HIF transcriptional activation function is also modulated further by asparagine 803 hydroxylation by the asparagine hydroxylase, factor-inhibiting HIF (FIH), which affects recruitment of the coactivators p300/CBP [12-17]. Interestingly, VHL itself has also been implicated in the direct regulation of HIF-1 transcriptional activity, either by recruiting histone deacetylases or by recruiting other transcriptional repressors such as pVHL-associated KRAB-A domain-containi.