Piwil2 Inhibits Keratin 8 Degradation through Promoting p38-Induced Phosphorylation To Resist Fas-Mediated Apoptosis

Abstract

bThe piwi-like 2 (piwil2) gene is widely expressed in tumors and protects cells from apoptosis induced by a variety of stress stimuli. However, the role of Piwil2 in Fas-mediated apoptosis remains unknown. Here, we present evidence that Piwil2 inhibits Fasmediated apoptosis. By a bacterial two-hybrid screening, we identify a new Piwil2-interacting partner, keratin 8 (K8), a major intermediate filament protein protecting the cell from Fas-mediated apoptosis. Our results show that Piwil2 binds to K8 and p38 through its PIWI domain and forms a Piwil2/K8/P38 triple protein-protein complex. Thus, Piwil2 increases the phosphorylation level of K8 Ser-73 and then inhibits ubiquitin-mediated degradation of K8. As a result, the knockdown of Piwil2 increases the Fas protein level at the membrane. In addition to our previous finding that Piwil2 inhibits the expression of p53 through the Src/ STAT3 pathway, here we demonstrate that Piwil2 represses p53 phosphorylation through p38. Our present study indicates that Piwil2 plays a role in Fas-mediated apoptosis for the first time and also can affect p53 phosphorylation in tumor cells, revealing a novel mechanism of Piwil2 in apoptosis, and supports that Piwil2 plays an active role in tumorigenesis.

Phosphorylation Impacts N-end Rule Degradation of the Proteolytically Activated Form of BMX Kinase

“…Notably, phosphorylation can regulate protein ubiquitination and degradation machinery via regulating the activity of E3-ubiquitin ligases, as reported previously (39). Alternatively, the coordinated targeting of a protein substrate by phosphorylation and ubiquitin-dependent degradation provides another avenue of cross-regulation (40). Although there are a number of examples of how phosphorylation impacts, either positively or negatively, target protein substrate degradation by the ubiquitin-proteasome system (40,41), herein we describe, to the best of our knowledge, the first clear example of phosphorylation regulating recognition of a caspase proteolytic product by the N-end rule degradation pathway, which was discovered about 3 decades ago (42).…”

“…Alternatively, the coordinated targeting of a protein substrate by phosphorylation and ubiquitin-dependent degradation provides another avenue of cross-regulation (40). Although there are a number of examples of how phosphorylation impacts, either positively or negatively, target protein substrate degradation by the ubiquitin-proteasome system (40,41), herein we describe, to the best of our knowledge, the first clear example of phosphorylation regulating recognition of a caspase proteolytic product by the N-end rule degradation pathway, which was discovered about 3 decades ago (42). Although the impact on degradation is clear, the mechanism of how phosphorylation at this internal residue inhibits recognition and proteasome targeting by UBR1 and UBR2 has yet to be determined.…”

HILI destabilizes microtubules by suppressing phosphorylation and Gigaxonin-mediated degradation of TBCB

“…Our previous researches showed that HILI can promote cell proliferation2932. Based on our findings above, we studied whether TBCB is implicated in HILI-regulated tumor cell proliferation, migration and invasion.…”

“…Our previous researches have shown that HILI regulates microfilaments and intermediate filaments of tumor cells29303132, these findings prompt us to shift our attention to the roles of HILI in microtubule dynamics of tumor cells.…”

“…PIWIL2, aka HILI, is a member of PIWI subfamily containing PIWI and PAZ domains, plays crucial roles in self-renew of stem and germ cells, RNA silencing and translational regulation in different organisms during evolution and is ectopically expressed in different cancer cells1617181920212223242526272829303132. Our previous researches have shown that HILI regulates microfilaments and intermediate filaments of tumor cells29303132, these findings prompt us to shift our attention to the roles of HILI in microtubule dynamics of tumor cells.…”