Protein kinase RNA/FADD/caspase-8 pathway mediates the proapoptotic activity of the RNA-binding protein human antigen R (HuR).
The RNA-binding protein human antigen R (HuR) has been implicated in apoptosis in multiple ways. Several studies have shown that in response to a variety of stresses HuR promotes the expression of proapoptotic mRNAs, whereas others reported its regulatory effect on antiapoptotic messages. We recently showed that in response to severe stress, HuR is cleaved to generate two cleavage products (CPs), HuR-CP1 (24 kDa) and HuR-CP2 (8 kDa), by which it promotes apoptotic cell death. Here, we show that this cleavage event is dependent on protein kinase RNA (PKR). Surprisingly, although in response to the apoptotic inducer staurosporine PKR itself is not phosphorylated, PKR triggers the cleavage of HuR via its downstream effector FADD that in turn activates the caspase-8/caspase-3 pathway. This effect, however, does not require the phosphorylation of the eukaryotic translation initiation factor 2alpha. Additionally, we observed that these HuR-CPs are sufficient to trigger cell death in the absence of activation of the PKR pathway. Therefore, our results support a model whereby in response to lethal stress, PKR, without being phosphorylated, activates the FADD/caspase-8/caspase-3 pathway to trigger HuR cleavage, and the HuR-CPs are then capable of promoting apoptosis.
von Roretz
Christopher
C
Biochemistry Department and Rosalind and Morris Goodman Cancer Center, McGill University, Montreal, Ontario H3G 1Y6, Canada.
Gallouzi
Imed-Eddine
IE
D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism*; D017209:Apoptosis; D053181:Caspase 8 / Q000378:metabolism*; D002460:Cell Line; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D010766:Phosphorylation; D011485:Protein Binding; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D019892:eIF-2 Kinase / Q000737:chemistry*
D000954:Antigens, Surface; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D016601:RNA-Binding Proteins; D019892:eIF-2 Kinase; D053181:Caspase 8