Biochemical and molecular analysis of the interaction between ERK2 MAP kinase and hypoxia inducible factor-1α

The mitogen activated protein kinase (MAPK) signaling pathways play significant roles in fundamental cellular processes, such as cell growth and differentiation. It has been shown that the specificity and efficacy of phosphorylation by MAP kinases rely upon distinct MAPK-docking domains (D-domains) found in a wide range of MAPK substrates including the ETS-transcription factor Elk-1. Importantly, the MAPK signaling cascade converges with the hypoxia-induced signaling pathway. The key regulator of hypoxia signaling is the heterodimeric transcription factor hypoxia inducible factor-1 (HIF-1). The a-subunit of HIF-1 (HIF-1a) is a substrate for the ERK2 MAP kinase. Unraveling the interplay of these main signaling systems is a prerequisite for understanding their role in tumor growth, a situation sustained by simultaneous mitogenic and hypoxic signals. In this work, we investigated the molecular cues that direct HIF-1a recognition and phosphorylation by ERK2. We showed that HIF-1a possesses a MAPK docking domain. Utilizing surface plasmon resonance (SPR) methodologies we demonstrated efficient binding between HIF-1a and ERK2, with a K(D) value in the low micromolar range. Although, the D-domain did not contribute to the above interaction significantly, it could act in trans by recruiting ERK2 and conferring responsiveness to poor ERK substrates. These results indicate that, via its conserved D-domain, HIF-1a could serve as a platform for ERK2 in the nucleus of the cell, thus potentially facilitating phosphorylation of other ERK2 substrates. The identification of an ERK2 recognition domain on HIF-1a opens new avenues for the analysis of HIF-1a-related ERK2 signaling and may allow designing of interfering compounds.