Down-regulation of epidermal growth factor receptor-signaling pathway by binding of GRP78/BiP to the receptor under glucose-starved stress conditions

Abstract

GRP78/BiP, a molecular chaperone in the endoplasmic reticulum, is induced under such adverse conditions for cell survival as glucose starvation. Induction of GRP78 has been shown to coincide with G1 cell cycle arrest, which is an important cellular defense system. In this study, we investigated involvement of GRP78 in the mechanism of growth arrest by using human epidermoid carcinoma A431 cells. Under a chemical stress condition with 2-deoxyglucose, GRP78 was induced 3-4-fold. In the stressed cells, an underglycosylated form of epidermal growth factor receptor (EGFR) was produced and the mature form was decreased. We found that the molecular chaperone GRP78 in the endoplasmic reticulum formed a stable complex with the underglycosylated EGFR but did not with the mature form. This complex formation occurred specifically under the stress conditions, and the complex was dissociated upon removal of the stress. Treatment of the GRP78-underglycosylated EGFR complex with ATP resulted in a release of the underglycosylated EGFR from GRP78, indicating that the complex could be formed through the chaperone function of GRP78. In accordance with the complex formation with endoplasmic reticulum-resident GRP78, the underglycosylated EGFR could not be translocated to the cell surface. As a result, EGF could not induce expression of cyclin D3, a G1 cyclin, in the stressed cells, whereas it did in non-stressed cells. These results indicated that, in the stressed cells, GRP78 participated in down-regulation of EGF-signaling pathway by forming a stable complex with EGFR and inhibiting EGFR translocation to the cell surface.

GRP78 haploinsufficiency suppresses acinar-to-ductal metaplasia, signaling, and mutant Kras -driven pancreatic tumorigenesis in mice

“…EGFR activity is essential for metaplastic duct formation and initiation of KRAS-induced pancreatic tumorigenesis (33). GPR78 was reported to directly complex with EGFR in the ER (34,35) and to cooperate with activated α2-macroglobulin to facilitate the interaction between EGFR and c-Src on the cell surface (43). Thus, GRP78 could regulate the synthesis, transport, and stability of EGFR, thereby affecting its activation and downstream signaling, which impacts ADM and PDAC development.…”

“…EGFR signaling has been reported to play an important role in ADM in KRAS-induced pancreatic tumorigenesis (33). As EGFR is a client protein of GRP78 in the ER (34,35), we examined whether GRP78 haploinsufficiency affected EGFR expression, thus providing an explanation for the reduction of ADM in the PKC78 f/+ pancreas. Indeed, PKC pancreata expressed about fivefold more EGFR than control pancreata, and this increase was reduced by 60% in the PKC78 f/+ pancreata based on Western blot analyses (Fig.…”

Treatment of murine collagen‐induced arthritis by the stress protein BiP via interleukin‐4–producing regulatory T cells: A novel function for an ancient protein

“…The delay in the initiation of arthritis suppression could be explained by the absence of exogenous BiP in the BiP-primed T cells at the onset of disease. Although BiP is ubiquitously expressed, as an intracellular protein under stressful conditions, the transcription of BiP is increased (27) and cell-surface expression and secretion of BiP are seen (Brownlie RJ, et al: unpublished observations). Such conditions are found in the inflamed joint (28) and BiP has been detected in the synovial fluid of patients with inflammatory joint disease (14).…”

Mammalian unfolded protein response inhibits cyclin D1 translation and cell-cycle progression

“…Conversely, growth factor withdrawal prevents cyclin D1 gene expression, and the relative instability of the protein ensures that cyclin D1 levels fall precipitously, thereby enabling mitogen-deprived cells to exit the cycle quickly. Although agents that interfere with protein biogenesis in the ER might conceivably hinder maturation of growth factor receptors, thereby compromising mitogenic signaling and braking the cell cycle (11,24), several lines of evidence suggest that this interference is not the mechanism responsible for rapid growth arrest during the UPR. First, mitogen-dependent activation of ERKs was not inhibited by tunicamycin.…”

“…In principle, ER-stress conditions could indirectly impede cell-cycle progression by interfering with the proper maturation of growth factor receptors or other modulators of mitogenic signaling (11). Alternatively, ER stress may directly induce a checkpoint response that prevents cells from completing their cell division cycle under conditions that compromise the proper folding and assembly of proteins.…”