GRP78

The 78 kDa glucose-regulated protein (GRP78) is the eukaryotic orthologue to the prokaryotic heat shock 70 kDa protein 5 (HSPA5). GRP78 is also sometimes referred to as BiP. GRP78 is a member of the HSP70 family and plays dynamic roles in protein regulation within the endoplasmic reticulum. GRP78 is the most abundant chaperone in the ER and plays an important role in regulating the unfolded protein response (UPR) (1). GRP78 forms a multiprotein chaperone complex with DNAJB11, HSP90B1, HYOU, PDIA2, PDIA4, PDIA6, PPIB, SDF2L1, UGT1A1, and ERP29.

C/EBP homologous protein (CHOP) is a transcription factor that regulates apoptosis in response to cellular stress. CHOP also known as growth arrest and DNA damage 153 (GADD153) was first cloned because of its induction in response to genotoxic stress such as UV irradiation. CHOP has now been shown to be induced mainly by ER-stress (1). CHOP is normally expressed at low levels and localizes to the cytoplasm. Cellular stress triggers an upregulation of CHOP levels and accumulation in the nucleus where it can act as either a transcriptional repressor or activator (1).

The protein ATF6 is a constitutively expressed transcription factor that is a key mediator of the unfolded protein response (UPR) that allows mammalian cells to maintain cellular homeostasis under conditions of environmental and physiological stress. ATF6 is endoplasmic reticulum (ER) membrane-anchored in its inactive form, and under certain stress conditions, translocates to the Golgi where it is processed into its active form through action of the S1P and S2P proteases.

HSP70 family member GRP78 (78 kD glucose-regulated protein) is an abundant protein cofactor commonly known as a molecular chaperone. Found in most eukaryotes, Hsp genes are members of a heat-inducible multigene family.