Regulation of the Ring Finger E3 Ligase Siah2 by p38 MAPK

Abstract

The RING finger ubiquitin ligase Siah2 controls the stability of various substrates involved in stress and hypoxia responses, including the PHD3, which controls the stability of HIF-1␣. In the present study we determined the role of Siah2 phosphorylation in the regulation of its activity toward PHD3. We show that Siah2 is subject to phosphorylation by p38 MAPK, which increases Siah2-mediated degradation of PHD3. Consistent with these findings, MKK3/MKK6 double-deficient cells, which cannot activate p38 kinases, exhibit impaired Siah2-dependent degradation of PHD3. Phosphopeptide mapping identified T24 and S29 as the primary phospho-acceptor sites. Phospho-mutant forms of Siah2 (S29A or T24A/S29A) exhibit impaired degradation of PHD3, particularly after hypoxia. Conversely, a phospho-mimic form of Siah2 (T24E/S29D) exhibits stronger degradation of PHD3, compared with wild type Siah2. Whereas phospho-mutant Siah2 exhibits weaker association with PHD3, phospho-mimic Siah2 associates as well as wild type and is localized within the perinuclear region, suggesting that phosphorylation of Siah2 affects its subcellular localization and, consequently, the degree of its association with PHD3. In all, our findings reveal the phosphorylation of Siah2 by p38 and the implications of such phosphorylation for Siah2 activity toward PHD3.

Seven in Absentia Proteins Affect Plant Growth and Nodulation inMedicago truncatula

“…The name of the protein family is derived from the first member that was characterized, the Drosophila melanogaster SINA that regulates photoreceptor differentiation by targeting the transcription factor Tramtrack for proteasomal degradation (Carthew and Rubin, 1990;Li et al, 1997;Cooper, 2007). The human SINA homologs Siah1 and Siah2 are involved in synaptic transmission, apoptosis, tumor suppression, and stress and hypoxia responses among others (Wheeler et al, 2002;Franck et al, 2006;Khurana et al, 2006;Fukuba et al, 2007).…”

Novel Function of E3 Ubiquitin Ligase Siah2 to Regulate ROS Metabolism

“…S29 and T24 are major phosphorylation sites of Siah2. The phosphorylation of Siah2 by p38 MAPK results in stabilization and subsequent activation of the Siah2 protein in the cytoplasm [26] . In addition, the expression of Siah2 is up-regulated by estrogen in estrogen-receptor (ER)-positive breast cancer cells, in which Siah2 degrades the repressor of ER signaling, N-CoR, resulting in resistance to apoptosis induction and affecting mitochondrial function [18] .…”

Siah: A Promising Anticancer Target

“…If this is a Siah1-specific effect, inversely correlated or independent results for Siah2 need to be investigated as well. Importantly, posttranslational modifications of Siah proteins have also been shown to change the activity, substrate specificity, and subcellular localization of Siah (10,27,31). Therefore not only the abundance, but also the extent of modifications and function of Siah proteins as a result need to be taken into consideration.…”

“…phosphorylates Siah2 under hypoxic conditions, causing it to relocalize to the cytoplasm and subsequently increases its ubiquitin-targeted degradation activity (10). In addition, the deubiquitinating enzyme USP13 reduces the substrate degradation activity of Siah proteins (11).…”