Proteasomes Regulate Erythropoietin Receptor and Signal Transducer and Activator of Transcription 5 (STAT5) Activation

Abstract

Cis is an Src homology 2 domain-containing protein, which binds to the erythropoietin receptor and decreases erythropoietin-stimulated cell proliferation. We show that Cis associates with the second tyrosine residue of the intracellular domain of the erythropoietin receptor (Tyr 401 ). Two forms of Cis with molecular masses of 32 and 37 kDa were detected, and we demonstrate that the 37-kDa protein resulted from post-translational modifications of the 32-kDa form. Anti-ubiquitin antibodies recognized the 37-kDa form of Cis and the proteasome inhibitors N-acetyl-leucyl-leucyl-norleucinal and lactacystin inhibited its degradation, showing that the 37-kDa form of Cis is a ubiquitinated protein, which seems to be rapidly degraded by the proteasome. In erythropoietin-stimulated UT-7 cells, the activation of the erythropoietin receptor and signal transducer and activator of transcription 5 (STAT5) was transient and returned to basal levels after 30 -60 min of erythropoietin stimulation. In contrast, these proteins remained strongly phosphorylated, and STAT5 remained activated for at least 120 min in the presence of proteasome inhibitors. These experiments demonstrate that the proteasomes are involved in the down-regulation of the erythropoietin receptor activation signals. Because the proteasome inhibitors induced the accumulation of both the ubiquitinated form of Cis and the Cis-erythropoietin receptor complexes, our results suggest that the ubiquitinated form of Cis could be involved in the proteasome-mediated inactivation of the erythropoietin receptor.

Differential regulation of SOCS genes in normal and transformed erythroid cells

“…It has been suggested that CIS is involved in the proteasome-mediated inactivation of the Epo receptor (Verdier et al, 1998a).…”

Innate immunodeficiency following genetic ablation of Mcl1 in natural killer cells

“…4c). Enrichment of the well-characterized STAT5 target gene Cish (cytokine-inducible SH2-containing protein) was used as a positive control as this gene has multiple TTC(T/C)N(G/A)GAA motifs in its promoter 36 (Fig. 4c) Fig.…”

The Signal Transduction of the Growth Hormone Receptor Is Regulated by the Ubiquitin/Proteasome System and Continues After Endocytosis

“…The target proteins are first tagged with ubiquitin molecules to form a polyubiquitin chain, which is specifically recognized by the multisubunit proteasome complex, leading to their degradation. Proteasomes were found to be involved in regulating JAK/STAT pathways upon interleukin-2, -3, and erythropoietin stimulation (17)(18)(19). In the presence of specific proteasomal inhibitors, activation of both JAK and STAT molecules was sustained, although neither STAT nor JAK appeared to be ubiquitinated.…”