PERK (eIF2α kinase) is required to activate the stress-activated MAPKs and induce the expression of immediate-early genes upon disruption of ER calcium homoeostasis

Abstract

The eIF2alpha (eukaryotic initiation factor-2alpha) kinase PERK (doublestranded RNA-activated protein kinase-like ER kinase) is essential for the normal function of highly secretory cells in the pancreas and skeletal system, as well as the UPR (unfolded protein response) in mammalian cells. To delineate the regulatory machinery underlying PERK-dependent stress-responses, gene profiling was employed to assess global changes in gene expression in PERK-deficient MEFs (mouse embryonic fibroblasts). Several IE (immediate-early) genes, including c-myc, c-jun, egr-1 (early growth response factor-1), and fra-1 (fos-related antigen-1), displayed PERK-dependent expression in MEFs upon disruption of calcium homoeostasis by inhibiting the ER (endoplasmic reticulum) transmembrane SERCA (sarcoplasmic/ER Ca2+-ATPase) calcium pump. Induction of c-myc and egr-1 by other reagents that elicit the UPR, however, showed variable dependence upon PERK. Induction of c-myc expression by thapsigargin was shown to be linked to key signalling enzymes including PLC (phospholipase C), PI3K (phosphatidylinositol 3-kinase) and p38 MAPK (mitogen-activated protein kinase). Analysis of the phosphorylated status of major components in MAPK signalling pathways indicated that thapsigargin and DTT (dithiothreitol) but not tunicamycin could trigger the PERK-dependent activation of JNK (c-Jun N-terminal kinase) and p38 MAPK. However, activation of JNK and p38 MAPK by non-ER stress stimuli including UV irradiation, anisomycin, and TNF-alpha (tumour necrosis factor-alpha) was found to be independent of PERK. PERK plays a particularly important role in mediating the global cellular response to ER stress that is elicited by the depletion of calcium from the ER. We suggest that this specificity of PERK function in the UPR is an extension of the normal physiological function of PERK to act as a calcium sensor in the ER.

Upregulated expression of PERK in spinal ligament fibroblasts from the patients with ossification of the posterior longitudinal ligament

“…Fibroblasts cells can differentiate into osteoblasts or osteocytes [4,8,9,12,24,28]. This differentiation should be accompanied by an upregulation of several marker genes related to bone formation, such as OCN, ALP and COL I.…”

“…These two processes might differ in terms of the speed of bone formation [6,31]. Although several studies have investigated the osteogenetic characteristic of the spinal ligament fibroblasts from OPLL patients, the intracellular signaling pathways still remain unclear [4,8,9,12,24,28].…”

“…PERK is negatively regulated by the ER chaperones 78 kDa glucose-regulated protein/Immunoglobulin heavy chain-binding protein (GRP78/BIP) and 94 kDa glucoseregulated protein (GRP94). The high concentration of calcium within the ER lumen promotes binding of PERK to these ER chaperones and inhibits PERK's dimerization and activation [12,13]. However, PERK is activated during ER stress when the folding capacity of the ER is compromised by Ca 2?…”

Differential expression of prohibitin is correlated with dual action of Vitamin D as a proliferative and antiproliferative hormone in breast epithelial cells

“…In silico analysis identified two potential VDR binding sites and multiple putative EGR and GR binding sites in the promoter region of prohibitin. EGR and GR are also involved in cell stress [11,12]. The combination of these binding sites in promoter region provides a basis for dual regulation of prohibitin by vitamin D. Initially, the siRNA experiments were designed to evaluate the function of prohibitin in relation to cell proliferation and not stress.…”

Physiological/pathological ramifications of transcription factors in the unfolded protein response

“…The activities of additional TFs, including NFκB, increase due to a reduction in inhibitor levels as a consequence of translational attenuation mediated by eukaryotic initiation factor 2α (eIF2α) phosphorylation (Jiang et al 2003;Deng et al 2004). Some TFs, including c-JUN, c-FOS, EGR-1, and c-MYC, known as immediate early genes, are induced at very early time points after eIF2α phosphorylation, but their functions and induction mechanisms are unknown (Liang et al 2006b). …”