GRP78, also referred to as 'immunoglobulin heavy chain-binding protein'
(BiP), is a member of the heat-shock protein-70 (HSP70) family and is involved in the folding and assembly of proteins
in the endoplasmic reticulum (ER). Because so many ER proteins interact with GRP78 transiently, it may play a key
role in monitoring protein transport through the cell.
NCBI Summary:
The protein encoded by this gene is a member of the heat shock protein 70 (HSP70) family. This protein localizes to the lumen of the endoplasmic reticulum (ER) where it operates as a typical HSP70 chaperone involved in the folding and assembly of proteins in the ER and is a master regulator of ER homeostasis. During cellular stress, as during viral infection or tumorogenesis, this protein interacts with the transmembrane stress sensor proteins PERK (protein kinase R-like endoplasmic reticulum kinase), IRE1 (inositol-requiring kinase 1), and ATF6 (activating transcription factor 6) where it acts as a repressor of the unfolded protein response (UPR) and also plays a role in cellular apoptosis and senescence. Elevated expression and atypical translocation of this protein to the cell surface has been reported in viral infections and some types of cancer cells. At the cell surface this protein may facilitate viral attachment and entry to host cells. This gene is a therapeutic target for the treatment of coronavirus diseases and chemoresistant cancers. [provided by RefSeq, Jul 2020]
Expression and Impact of Vaspin on In Vitro Oocyte Maturation through MAP3/1 and PRKAA1 Signalling Pathways. Kurowska P et al. (2020) Oocyte maturation is a critical stage in embryo production and female reproduction. The aims of this study were to determine: (i) the mRNA and protein expression of vaspin and its receptor 78-kDa glucose-regulated (GRP78) in porcine cumulus-oocyte complexes (COCs) by real-time PCR and Western blot analysis, respectively, and their localisation by immunofluorescence; and (ii) the effects of vaspin on in vitro oocyte maturation (IVM) and the involvement of mitogen ERK1/2 (MAP3/1)- and AMPKα (PRKAA1)-activated kinases in the studied processes. Porcine COCs were matured in vitro for 22 h or 44 h with vaspin at a dose of 1 ng/mL and nuclear maturation assessed by Hoechst 33342 or DAPI staining and the measurement of progesterone (P4) level in the maturation medium. We showed that vaspin and GRP78 protein expression increased in oocytes and cumulus cells after IVM. Moreover, vaspin enhanced significantly porcine oocyte IVM and P4 concentration, as well as MAP3/1 phosphorylation, while decreasing PRKAA1. Using pharmacological inhibitors of MAP3/1 (PD98059) and PRKAA1 (Compound C), we observed that the effect of vaspin was reversed to the control level by all studied parameters. In conclusion, vaspin, by improving in vitro oocyte maturation via MAP3/1 and PRKAA1 kinase pathways, can be a new factor to improve in vitro fertilisation protocols.//////////////////Role of vaspin in porcine ovary: effect on signaling pathways and steroid synthesis via GRP78 receptor and protein kinase A. Kurowska P et al. (2020) Vaspin, visceral adipose tissue-derived serine protease inhibitor, is involved in the development of obesity, insulin resistance, inflammation and energy metabolism. Our previous study showed vaspin expression and its regulation in the ovary; however, the role of this adipokine in ovarian cells has never been studied. Here, we studied in vitro the effect of vaspin on various kinase signaling pathways: mitogen-activated kinase (MAP3/1), serine/threonine kinase (AKT), signal transducer and activator of transcription 3 (STAT3) protein kinase AMP (PRKAA1), protein kinase A (PKA) and on expression of nuclear factor kappa B (NFKB2) as well as on steroid synthesis by porcine ovarian cells. By Western blot, we found that vaspin (1 ng/ml), in a time-dependent manner, increased phosphorylation of MAP3/1, AKT, STAT3, PRKAA1 and PKA, while it decreased expression of NFKB2. We observed that vaspin, in a dose-dependent manner, increased basal steroid hormones secretion (progesterone and estradiol), mRNA and protein expression of steroid enzymes using real-time PCR and Western blot, respectively, and the mRNA of gonadotropins (FSHR, LHCGR) and steroids (PGR, ESR2) receptors. The stimulatory effect of vaspin on basal steroidogenesis was reversed when ovarian cells were cultured in the presence of a PKA pharmacological inhibitor (KT5720) and when GRP78 receptor was knocked down (siRNA). However, in the presence of insulin-like growth factor type 1 and gonadotropins, vaspin reduced steroidogenesis. Thus, vaspin, by activation of various signaling pathways and stimulation of basal steroid production via GRP78 receptor and PKA, could be a new regulator of porcine ovarian function.//////////////////
Glucose-Regulated Protein, 78-Kilodalton as a Modulator of Luteinizing Hormone Receptor Expression in Luteinizing Granulosa Cells in Rats. Kogure K et al. Glucose-Regulated Protein, 78-kilodalton (GRP78) is a molecular chaperone that exists in the endoplasmic reticulum and is involved in the assembly, transportation, and folding of proteins. Previously, GRP78 was reported to associate with gonadotropin receptors. However, little is known about how GRP78 is involved in the regulation of LH receptor (LHR). Thus, in this study we investigated the significance of GRP78 for the induction of LHR in rat luteinizing granulosa cells. Western blot analysis of rat LHR expressed in HEK293 cells revealed that the protein levels of LHR were increased, depending on the increment of GRP78 protein. In both in vivo and in vitro experiments, the GRP78 mRNA level peaked while LHR mRNA was down-regulated by hCG. To examine the time-dependent localization of GRP78 in vivo, immunohistochemistry was performed. GRP78 was expressed mainly in granulosa cells, and the GRP78 protein peaked 18 h after the ovulatory dose of hCG injection in pregnant mare serum gonadotropin-primed immature rats. To ascertain the role of GRP78 in LHR after down-regulation, siGRP78 was transfected to cultured rat granulosa cells, demonstrating that knockdown of the GRP78 protein level impaired the recovery of cell surface LHR from down-regulation that negatively affected the progesterone synthesis. Moreover, luciferase assays showed that CRE mediated the hCG-induced promoter activity of GRP78 in rat luteinizing granulosa cells. These results reveal a novel mechanism of LHR by GRP78 in the early stage of corpus lustrum formation, which may be an important factor in the recovery of LHR after the down-regulation.
Expression regulated by
LH, mir376a
Comment
MicroRNA-376a regulates 78-kilodalton glucose-regulated protein expression in rat granulosa cells. Iwamune M et al. (2014) The 78-kilodalton glucose-regulated protein (GRP78) is a molecular chaperone that assists in protein assembly, folding, and translocation. Recently, our laboratory reported that GRP78 regulates the expression of luteinizing hormone-human chorionic gonadotropin receptor (LHR) in the early stage of corpus luteum formation. In this study, we investigated whether microRNAs (miRNAs), which post-transcriptionally regulate mRNA, are involved in the regulation mechanism of GRP78 in the ovary. A miRNA microarray was performed to analyze the overall miRNA expression profile, and the results indicated that 44 miRNAs were expressed highly after ovulation was induced. The results from a bio-informative database analysis and in vitro granulosa cell culture studies led us to focus on rno-miR-376a for further analysis. In both in vivo and in vitro studies, rno-miR-376a levels increased 12 h after human chorionic gonadotropin (hCG) administration. To elucidate whether rno-miR-376a induced mRNA destabilization or translational repression of GRP78, rno-miR-376a was transfected into cultured granulosa cells, resulting in decreased GPR78 protein levels without an alteration in GRP78 mRNA levels. To confirm that rno-miR-376a binds to GRP78 mRNA, we cloned the 3'-end of GRP78 mRNA (nucleotides 2439-2459) into a reporter vector that contained a Renilla luciferase coding region upstream of the cloning site. The luciferase assays revealed that rno-miR-376a bound to the 3'-end of GRP78 mRNA. From these data, we conclude that rno-miR-376a potentially negatively regulates GRP78 protein expression through translational repression at an early stage transition from the follicular phase to luteinization.//////////////////
Ovarian localization
Oocyte, Cumulus, Granulosa
Comment
Evidence of the activation of unfolded protein response in granulosa and cumulus cells during follicular growth and maturation. Harada M et al. (2015) The objective of the present study is to investigate whether unfolded protein response (UPR), activated by endoplasmic reticulum (ER) stress, in granulosa cells (GC) and cumulus cells (CC) is involved in the process of follicular growth and maturation. First, to examine the presence of UPR in growing follicles, the expression of spliced form of X-box-binding protein 1 (XBP1(S)) and heat shock 70 kDa protein 5 (HSPA5) mRNA, typical UPR genes, in mice ovaries were examined by in situ hybridization. GC of later stage than large secondary follicles expressed both XBP1(S) and HSPA5 mRNA, which was accompanied with the activation of ER stress sensor proteins, inositol-requiring enzyme 1 (IRE1) and double-stranded RNA-activated protein kinase-like ER kinase (PERK), confirmed by immunohistochemistry. Next, to examine the association between the fertilization capacity of oocytes and the expression levels of UPR genes in surrounding CC, human CC were collected from patients undergoing ICSI. The expression levels of XBP1(S) mRNA, quantified by RT-PCR, in CC enclosing human oocytes achieving fertilization were two-fold higher, than those in CC enclosing oocytes without fertilization capacity. In conclusion, UPR is activated during follicular growth and suggested to be involved in the process of follicular growth and maturation.//////////////////
Protein patterns of pig oocytes during in vitro maturation. Ellederova Z et al. In vitro maturation (IVM) of fully grown mammalian oocytes is characterized by initial germinal vesicle (GV) breakdown and rearrangement of microtubule network during the first meiosis (MI), followed by extrusion of the first polar body and block of the oocytes in metaphase of the second meiosis (MII). Only fully matured oocytes are capable of undergoing fertilization and the initiation of zygotic development. These observations are mostly based on morphological evaluation; however, the molecular events responsible for these processes are not known. In this study, we have launched the analysis of pig oocytes during in vitro maturation using a proteomics approach. First, oocyte proteins have been separated by two-dimensional gel electrophoresis and identified by mass spectrometry. Remarkably, several proteins, including peroxiredoxins, ubiquitin carboxyl-terminal hydrolase isozyme L1, and spermine synthase, are even more abundant than actin, usually the most abundant protein in somatic cells. Furthermore, we have initiated comparative analysis of the oocytes at different stages of maturation to characterize candidate proteins, which are differentially expressed during in vitro maturation. To date, we have identified antiquitin (D7A1), the member of aldehyde dehydrogenase family7 that has been significantly increased in MI and MII stages compared with GV oocytes. To our knowledge, this is the first pig oocyte proteome available so far that may be used as a reference map. The proteins that are differentially regulated during IVM may present potential biomarkers of oocyte maturation and quality. It is a useful inventory toward a deeper understanding of the mechanisms underlying reproduction and development.
Follicle stages
Antral, Preovulatory
Comment
Liu HC, et al 2001 reported tha application of complementary DNA microarray (DNA chip) technology in the study of gene expression profiles during
folliculogenesis.
They used oligonucleotide microarray (DNA chip)-based hybridization
analysis to gain a comprehensive view of gene expression and regulation
involved in folliculogenesis.
Preantral follicles isolated from day 14 B6D2F-1 mice
were stimulated in vitro to form Graafian follicles. Total RNA extracted from
the mouse preantral and Graafian follicles were reverse transcribed, labeled
with digoxigenin-11-dUTP, and then hybridized with Clontech Atlas mouse cDNA
expression arrays for comparison. Of 588 known studied genes, 39 and 61 were detected in preantral follicles and in Graafian follicles, respectively, and 17 were highly
expressed consistently in both preantral and Graafian follicles. Performing
clustering analysis, 46 were upregulated as the follicles advanced to mature stages.
The HSPA5 gene is up-regulated in the Graafian follicles.
Phenotypes
Mutations
1 mutations
Species: mouse
Mutation name: Grp78-/-
type: null mutation fertility: embryonic lethal Comment: The Grp78+/- mice, which express 50% of the wild-type level of the GRP78 protein, are viable. The heterozygous Grp78 cells up-regulate the ER proteins GRP94 and protein disulfide isomerase at both the transcript and protein levels, while other UPR targets such as CHOP and XBP-1 are not affected. Mouse embryonic fibroblasts from Grp78+/- mice are capable of responding to ER stress. However, Grp78-/- embryos that are completely devoid of GRP78 lead to peri-implantation lethality. These embryos do not hatch from the zona pellucida in vitro, fail to grow in culture, and exhibit proliferation defects and a massive increase in apoptosis in the ICM, which is the precursor of embryonic stem cells.