Cytoplasmic polyadenylation element binding protein (CPEB)1 and 2 bind to the HIF-1α mRNA 3’UTR and modulate HIF-1 α protein expression
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The heterodimeric hypoxia-inducible factor (HIF)-1 is a transcriptional master regulator of several genes involved in mammalian oxygen homeostasis. Besides a well described regulation of the HIFα-subunit via hydroxylation-mediated protein stability in hypoxia, there are several indications for an additional translational control of the HIF-1α mRNA especially after growth factor stimulation. We identified an interaction of the cytoplasmic polyadenylation element binding protein (CPEB) 1 and 2 with the 3'-UTR of the HIF-1α mRNA. Overexpression of CPEB1 and 2 affected HIF-1α protein levels mediated by its mRNA 3'-UTR. Stimulation of neuroblastoma SK-N-MC cells with insulin and thus activation of endogenous CPEBs increased the expression of a luciferase reporter gene that was fused to the 3'-UTR of HIF-1α as well as endogenous HIF-1α protein levels. This could be abrogated by treating the cells with CPEB1 or CPEB2 siRNAs. Injection of HIF-1α cRNA in Xenopus oocytes verified the elongation of the polyA tail by cytoplasmic polyadenylation. Thus, CPEB1 and 2 are involved in the regulation of HIF-1α following insulin stimulation.