Upon ER stress, BiP releases from the sensors, Ire1 and Perk, leading to activation.
In response to ER stress the translation initiation factor eIF2 α is phosphorylated by PERK leading to attenuation of the translation of most mRNAs.
For example, knockout of Mitofusin 2, a key mitochondrial fusion protein, activates Perk, leading to enhanced reactive oxygen species (ROS) production and reduced respiration (Muñoz et al. 2013).
When cells encounter ER stress or misfolded protein accumulation, an ER-resident chaperone, GRP78, dissociates from PERK, IRE1 and ATF6, leading to autophosphorylation of PERK, IRE1 and mobilization of ATF6 for activation.
Transient cerebral ischemic pre-activation of the ER-stress response has been shown to be associated with a several fold rise in Bip protein levels and less PERK activation, leading to delayed neuronal cell death [19].
In livers from obese mice, administration of LPS or tunicamycin results in IRE1 α and PERK activation, leading to the overexpression of CHOP.
The role of quantitative differences in the pERK response leading to distinct cellular outcomes is well characterized in PC12 neurons (Marshall, 1995), and the transcriptional response to the proliferative program mediated by sustained pERK activation in 3T3 fibroblasts has been reported (Yamamoto et al., 2006).
To support this notion, HDACi have been shown to lead to the acetylation of heat shock protein 90 (hsp90), resulting in the subsequent release of its client poteins like the breakpoint cluster region-abelson fusion protein (Bcr-abl) [ 31], and acetylation of the ER-resident chaperone glucose-regulated protein 78 (GRP78), leading to activation of PERK [ 17].
The results in Figure 6a show that, inactivation of PERK by PERK-DN attenuated eIF2 α phosphorylation and had little effect on cell proliferation, whereas Mar-induced eIF2 α phosphorylation was blunted by PERK-DN, leading to the blocking of LC3BII accumulation and partial restoration of viable cells as well as decreased cell death.
Additionally, a small number of heparin-FGF2 complexes bind to FGFR and initiate signaling complex formation, leading to an increase in pERK response.
