Table 3.

Summary of cited proteins involved in ER stress

SYMBOL	FULL NAME	DETAILS
ER stress
AMPK	AMP-activated protein kinase	Metabolite sensing serine/threonine kinase that has been termed the master regulator of cellular energy metabolism due to its numerous roles in the regulation of glucose, lipid, and protein metabolism
APAF1	apoptotic peptidase activating factor 1	Cytoplasmic protein that initiates apoptosis: if cytochrome c is released into the cytosol, in the presence of ATP or dATP it mediates the allosteric activation and hepta-oligomerization of APAF1, generating the complex known as apoptosome. The apoptosome recruits and processes caspase-9 to form a holoenzyme complex, which in turn recruits and activates the effector caspases, thus beginning the proteolytic cascade that results in the morphological features of apoptosis
ATF-6	Activating transcription factor 6	Endoplasmic Reticulum stress-regulated transmembrane transcription factor required for activating many UPR target genes
CaMKKβ	Ca2+/calmodulin-dependent kinase kinase-β	CaMKKβ belongs to the Serine/Threonine protein kinase family, and to the Ca2+/calmodulin-dependent protein kinase subfamily. Ca2+-mediated autophagy depends on CaMKKβ-dependent activation of AMPK that ultimately leads to the inhibition of mTORC signaling complex 1
eIF2α	eukaryotic translation initiation factor 2α	Phosphorylated eIF2α interferes with the formation of the 43S translation initiation complex, leading to overall translational repression in UPR-induced cells presumably to alleviate ER stress by reducing the influx of the newly synthesized proteins into the ER
GRP78/BiP	78-kDa glucose-regulated protein GRP78, also referred to as the immunoglobulin binding protein BiP	see Table 2
IRE1	Inositol-requiring enzyme 1	ER-resident transmembrane protein kinase and endoribonuclease that induces the non-conventional splicing of XBP1 mRNA and so transmits an ER stress signal to the cytoplasm and mediates the UPR
mTOR	mammalian target of rapamycin	Serine/threonine kinase that controls many aspects of cellular physiology, including transcription, translation, cell size, cytoskeletal organization and autophagy. Recent advances in the mTOR signaling field have found that mTOR exists in two heteromeric complexes, mTORC1 and mTORC2. The activity of mTORC1 is regulated by the integration of many signals, including growth factors, insulin, nutrients, energy availability and cellular stressors such as hypoxia, osmotic stress, reactive oxygen species, viral infection and ER stress
PERK	Protein kinase-like ER kinase	ER-transmembrane kinase that phosphorylates the a subunit of eIF2α thereby reducing cellular protein synthesis and with it the load of proteins entering into the ER
Sig-1R	Sigma-1 receptor	see Table 2
XBP1	X-box DNA binding protein 1	XBP1 pre-mRNA is converted to spliced mRNA (by activated IRE1) in response to UPR, leading to the production of an activated/spliced XBP-1 (XBP-1s), a potent transcription factor responsible for UPR