Cytoplasmic polyadenylation-element-binding protein (CPEB)1 and 2 bind to the HIF-1α mRNA 3′-UTR and modulate HIF-1α protein expression

The heterodimeric HIF (hypoxia-inducible factor)-1 is a transcriptional master regulator of several genes involved in mammalian oxygen homoeostasis. Besides the well described regulation of the HIF-1 alpha subunit via hydroxylation-mediated protein stability in hypoxia, there are several indications of an additional translational control of the HIF-1 alpha mRNA, especially after growth factor stimulation. We identified an interaction of CPEB (cytoplasmic polyadenylation-element-binding protein) 1 and CPEB2 with the 3'-UTR (untranslated region) of HIF-1 alpha mRNA. Overexpression of CPEB1 and CPEB2 affected HIF-1 alpha protein levels mediated by the 3'-UTR of HIF-1 alpha mRNA. Stimulation of neuroblastoma SK-N-MC cells with insulin and thus activation of endogenous CPEBs increased the expression of a luciferase reporter gene fused to the 3'-UTR of HIF-1 alpha as well as endogenous HIF-1 alpha protein levels. This could be abrogated by treating the cells with CPEB1 or CPEB2 siRNAs (short interfering RNAs). Injection of HIF-1 alpha cRNA into Xenopus oocytes verified the elongation of the poly(A)(+) (polyadenylated) fail by cytoplasmic polyadenylation. Thus CPEB1 and CPEB2 are involved in the regulation of HIF-1 alpha following insulin stimulation.