JAK2 associates with the erythropoietin receptor and is tyrosine phosphorylated and activated following stimulation with erythropoietin

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Abstract

Erythropoietin (EPO) regulates the proliferation and differentiation of erythroid cells through interaction with its receptor (EPOR). Although EPOR is a member of the cytokine receptor superfamily and lacks a kinase domain, EPO induces tyrosine phosphorylation, which is correlated with gene transcription and mitogenesis. Here we demonstrate that EPO induces tyrosine phosphorylation of JAK2 kinase and activates its in vitro autophosphorylation. Using EPOR mutants, phosphorylation and activation of kinase activity correlate with the induction of mitogenesis. Furthermore, JAK2 physically associates with a membrane-proximal region of the EPOR cytoplasmic domain that is required for biological activity. The results support the hypothesis that JAK2 is the kinase that couples EPO binding to tyrosine phosphorylation and mitogenesis.

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Most cited references 27

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S Hanks, A. Quinn, T. Hunter (1988)

In recent years, members of the protein kinase family have been discovered at an accelerated pace. Most were first described, not through the traditional biochemical approach of protein purification and enzyme assay, but as putative protein kinase amino acid sequences deduced from the nucleotide sequences of molecularly cloned genes or complementary DNAs. Phylogenetic mapping of the conserved protein kinase catalytic domains can serve as a useful first step in the functional characterization of these newly identified family members.

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Single-step purification of polypeptides expressed in Escherichia coli as fusions with glutathione S-transferase

Kevin S. Johnson, Donald Smith (1988)

Plasmid expression vectors have been constructed that direct the synthesis of foreign polypeptides in Escherichia coli as fusions with the C terminus of Sj26, a 26-kDa glutathione S-transferase (GST; EC 2.5.1.18) encoded by the parasitic helminth Schistosoma japonicum. In the majority of cases, fusion proteins are soluble in aqueous solutions and can be purified from crude bacterial lysates under non-denaturing conditions by affinity chromatography on immobilised glutathione. Using batch wash procedures several fusion proteins can be purified in parallel in under 2 h with yields of up to 15 micrograms protein/ml of culture. The vectors have been engineered so that the GST carrier can be cleaved from fusion proteins by digestion with site-specific proteases such as thrombin or blood coagulation factor Xa, following which, the carrier and any uncleaved fusion protein can be removed by absorption on glutathione-agarose. This system has been used successfully for the expression and purification of more than 30 different eukaryotic polypeptides.