Deficiency of GRP94 in the hematopoietic system alters proliferation regulators in hematopoietic stem cells

MEK1 activation enhances the ex vivo proliferation of haematopoietic stem/progenitor cell

Haematopoietic stem/progenitor cell (HSPC) integrates intracellular signal network from growth factors (GFs) and utilizes its proliferation feature to generate high yields of transplantable cells upon ex vivo culture. However, the molecular basis for HSPC activation and proliferation is not completely understood. The goal of this study was to investigate proliferation regulator in the downstream of GFs and develop HSPC expansion strategy. Microarray and Ingenuity Pathway Analysis were performed to evaluate differentially expressed genes in cytokine-induced CD34⁺ cells after ex vivo culture. We identified that MEK1 was a potential HSPC proliferation regulator, which represented indispensable roles and MEK1 silence attenuated the proliferation of HSPC. Notably, 500 nM MEK1 agonist, PAF C-16, increased the numbers of phenotypic HSPC and induced cell cycling of HSPC. The PAF C-16 expanded HSPC demonstrated comparative clonal formation ability and secondary expansion capacity compared to the vehicle control. Our results provide insights into regulating the balance between proliferation and commitment of HSPC by targeting the HSPC proliferation-controlling network. This study demonstrates that MEK1 critically regulates HSPC proliferation and cell production in the ex vivo condition for transplantation.

Heat shock proteins in cancer stem cell maintenance: A potential therapeutic target?

Cancer stem cells (CSCs) are a subpopulation of tumor cells with unlimited self-renewal capability, multilineage differentiation potential and long-term tumor repopulation capacity. CSCs reside in anatomically distinct regions within the tumor microenvironment, called niches, and this favors the maintenance of CSC properties and preserves their phenotypic plasticity. Indeed, CSCs are characterized by a flexible state based on their capacity to interconvert between a differentiated and a stem-like phenotype, and this depends on the activation of adaptive mechanisms in response to different environmental conditions. Heat Shock Proteins (HSPs) are molecular chaperones, upregulated upon cell exposure to several stress conditions and are responsible for normal maturation, localization and activity of intra and extracellular proteins. Noteworthy, HSPs play a central role in several cellular processes involved in tumor initiation and progression (i.e. cell viability, resistance to apoptosis, stress conditions and drug therapy, EMT, bioenergetics, invasiveness, metastasis formation) and, thus, are widely considered potential molecular targets. Furthermore, much evidence suggests a key regulatory function for HSPs in CSC maintenance and their upregulation has been proposed as a mechanism used by CSCs to adapt to unfavorable environmental conditions, such as nutrient deprivation, hypoxia, inflammation. This review discusses the relevance of HSPs in CSC biology, highlighting their role as novel potential molecular targets to develop anticancer strategies aimed at CSC targeting.

Glucose-Regulated Protein 94 Modulates the Response of Osteosarcoma to Chemotherapy

Background

Osteosarcoma (OS) is the most common and most aggressive primary solid malignant bone tumor in children and young adults and has high rates of recurrence and metastasis. The endoplasmic reticulum (ER) stress pathway is important in regulating the chemo-responsiveness of cancer. However, the role of glucose-regulated protein 94 (GRP94) in regulating the response of OS to chemotherapy has never been explored.

Methods

In this study, two OS cell lines, MG63 and 143B cells, were used to evaluate the mechanism by which GRP94 modulates the response of osteosarcoma to chemotherapy. GRP94-knockdown (GRP94-KD) OS cells were generated using short hairpin RNAs, and the response to chemotherapy was assessed using an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Cell apoptosis was quantified with propidium iodide (PI) staining and flow cytometry.

Results

Silencing of GRP94 in MG63 and 143B cells did not influence the growth and migration of the cells, but reduced the colony formation. GRP94-KD OS cells were more resistant to paclitaxel, gemcitabine, and epirubicin treatments than cells transfected with the scrambled control, and more cells transfected with the scrambled control underwent apoptosis after paclitaxel, gemcitabine, and epirubicin treatments than GRP94-KD cells.

Conclusions

Therefore, GRP94 silencing may increase the resistance of MG63 and 143B cells to paclitaxel, gemcitabine, and epirubicin treatments by inhibiting the induction of apoptosis. Thus, GRP94 may be a key biomarker for the chemotherapeutic response of OS.

Infection-resistant MRI-visible scaffolds for tissue engineering applications

Tissue engineering utilizes porous scaffolds as template to guide the new tissue growth. Clinical application of scaffolding biomaterials is hindered by implant-associated infection and impaired in vivo visibility of construct in biomedical imaging modalities. We recently demonstrated the use of a bioengineered type I collagen patch to repair damaged myocardium. By incorporating superparamagnetic iron oxide nanoparticles into this patch, here, we developed an MRI-visible scaffold. Moreover, the embedded nanoparticles impeded the growth of Salmonella bacteria in the patch. Conferring anti-infection and MRI-visible activities to the engineered scaffolds can improve their clinical outcomes and reduce the morbidity/mortality of biomaterial-based regenerative therapies.

Overexpression of molecular chaperons GRP78 and GRP94 in CD44(hi)/CD24(lo) breast cancer stem cells

Introduction: Breast cancer stem cell with CD44^hi/CD24^lo phonotype is described having stem cell properties and represented as the main driving factor in breast cancer initiation, growth, metastasis and low response to anti-cancer agents. Glucoseregulated proteins (GRPs) are heat shock protein family chaperons that are charged with regulation of protein machinery and modulation of endoplasmic reticulum homeostasis whose important roles in stem cell development and invasion of various cancers have been demonstrated. Here, we investigated the expression levels of GRP78 and GRP94 in CD44^hi/CD24^lo phenotype breast cancer stem cells (BCSCs).

Methods: MCF7, T-47D and MDA-MB-231 breast cancer cell lines were used. CD44^hi/CD24^lo phenotype cell population were analyzed and sorted by fluorescence-activated cell sorting (FACS). Transcriptional and translational expression of GRP78 and GRP94 were investigated by western blotting and quantitative real time PCR.

Results: Results showed different proportion of CD44^hi/CD24^lo phenotype cell population in their original bulk cells. The ranking of the cell lines in terms of CD44^hi/CD24^lo phenotype cell population was as MCF7<T-47D<MDA-MB-231. Our results also indicated that CD44^hi/CD24^lo phenotype cells exhibited higher mRNA and protein expression level of GRP78 and GRP94 compared to their original bulk cells.

Conclusion: Our results show a relationship between overexpression of GRP78 and GRP94 and exhibiting CD44hi/CD24lo phenotype in breast cancer cells. We conclude that upregulation of GRPs may be an important factor in the emergence of CD44hi/CD24lo phenotype BCSCs features.

Targeted deletion of ER chaperone GRP94 in the liver results in injury, repopulation of GRP94-positive hepatocytes, and spontaneous hepatocellular carcinoma development in aged mice

Hepatocellular carcinoma (HCC) often results from chronic liver injury and severe fibrosis or cirrhosis, but the underlying molecular pathogenesis is unclear. We previously reported that deletion of glucose regulated protein 94 (GRP94), a major endoplasmic reticulum chaperone, in the bone marrow and liver leads to progenitor/stem cell expansion. Since liver progenitor cell (LPC) proliferation can contribute to liver tumor formation, here we examined the effect of GRP94 deficiency on spontaneous liver tumorigenesis. Utilizing liver-specific Grp94 knockout mice driven by Albumin-Cre (cGrp94(f/f)), we discovered that while wild-type livers are tumor free up to 24 months, cGrp94(f/f) livers showed abnormal small nodules at 15 months and developed HCC and ductular reactions (DRs) by 21 months of age, associating with increased liver injury, apoptosis and fibrosis. cGrp94(f/f) livers were progressively repopulated by GRP94-positive hepatocytes. At 15 months, we observed expansion of LPCs and mild DRs, as well as increase in cell proliferation. In examining the underlying mechanisms for HCC development in cGrp94(f/f) livers, we detected increase in TGF-β1, activation of SMAD2/3, ERK, and JNK, and cyclin D1 upregulation at the premalignant stage. While epithelial-mesenchymal transition (EMT) was not evident, E-cadherin expression was elevated. Correlating with the recurrence of GRP94 positive-hepatocytes, the HCC was found to be GRP94-positive, whereas the expanded LPCs and DRs remained GRP94-negative. Collectively, this study uncovers that GRP94 deficiency in the liver led to injury, LPC expansion, increased proliferation, activation of oncogenic signaling, progressive repopulation of GRP94-positive hepatocytes and HCC development in aged mice.

Connexins: Intercellular Signal Transmitters in Lymphohematopoietic Tissues

Life-long hematopoietic demands are met by a pool of hematopoietic stem cells (HSC) with self-renewal and multipotential differentiation ability. Humoral and paracrine signals from the bone marrow (BM) hematopoietic microenvironment control HSC activity. Cell-to-cell communication through connexin (Cx) containing gap junctions (GJs) allows pluricellular coordination and synchronization through transfer of small molecules with messenger activity. Hematopoietic and surrounding nonhematopoietic cells communicate each other through GJs, which regulate fetal and postnatal HSC content and function in hematopoietic tissues. Traffic of HSC between peripheral blood and BM is also dependent on Cx proteins. Cx mutations are associated with human disease and hematopoietic dysfunction and Cx signaling may represent a target for therapeutic intervention. In this review, we illustrate and highlight the importance of Cxs in the regulation of hematopoietic homeostasis under normal and pathological conditions.

Glucose-regulated protein 94 is a novel glioma biomarker and promotes the aggressiveness of glioma via Wnt/β-catenin signaling pathway

Malignant glioma is the most common type of primary brain tumor and represents one of the most aggressive and lethal human cancer types. Glioma recurrence is a common event; however, the relevant molecular mechanisms in this setting are not well-understood. In this study, we investigated glucose-regulated protein 94 (GRP94) expressions in human glioma and aimed to determine the roles of GRP94 expression affects cell proliferation, invasion, and regulatory signaling in human glioma U87 cells. Our results showed that GRP94 was overexpressed at both mRNA and protein levels in high-grade glioblastoma as compared with normal brain tissues. High GRP94 levels also predict shorter overall survival of glioma patients. RNAi-mediated silencing of GRP94 suppressed cellular proliferation, colony formation ability in glioma cells. Depletion of GRP94 also inhibited cell migration and invasion ability in glioma cell. Furthermore, gene microarray analysis revealed that GRP94 depletion caused the dysregulation of critical pathway, Wnt/β-catenin signaling pathway. We next demonstrated GRP94 regulates Wnt/β-catenin signaling pathway to promote the proliferation of glioblastoma cells. Conclusion, our findings establish GRP94 as progression markers and druggable targets in glioblastoma, relating their oncogenic effects to activation of the Wnt/β-catenin signaling pathway.

Role of the unfolded protein response, GRP78 and GRP94 in organ homeostasis

The endoplasmic reticulum (ER) is a cellular organelle where secretory and membrane proteins, as well as lipids, are synthesized and modified. When cells are subjected to ER stress, an adaptive mechanism referred to as the Unfolded Protein Response (UPR) is triggered to allow the cells to restore homeostasis. Evidence has accumulated that the UPR pathways provide specialized and unique roles in diverse development and metabolic processes. The glucose regulated proteins (GRPs) are traditionally regarded as ER proteins with chaperone and calcium binding properties. The GRPs are constitutively expressed at basal levels in all organs, and as stress-inducible ER chaperones, they are major players in protein folding, assembly and degradation. This conventional concept is augmented by recent discoveries that GRPs can be actively translocated to other cellular locations such as the cell surface, where they assume novel functions that regulate signaling, proliferation, apoptosis and immunity. Recent construction and characterization of mouse models where the gene encoding for the UPR components and the GRPs is genetically altered provide new insights on the physiological contribution of these proteins in vivo. This review highlights recent progress towards the understanding of the role of the UPR and two major GRPs (GRP78 and GRP94) in regulating homeostasis of organs arising from the endoderm, mesoderm and ectoderm. GRP78 and GRP94 exhibit shared and unique functions, and in specific organs their depletion elicits adaptive responses with physiological consequences.

Glucose-regulated proteins in cancer: molecular mechanisms and therapeutic potential

The glucose-regulated proteins (GRPs) are stress-inducible chaperones that mostly reside in the endoplasmic reticulum or the mitochondria. Recent advances show that the GRPs have functions that are distinct from those of the related heat shock proteins, and they can be actively translocated to other cellular locations and assume novel functions that control signalling, proliferation, invasion, apoptosis, inflammation and immunity. Mouse models further identified their specific roles in development, tumorigenesis, metastasis and angiogenesis. This Review describes their discovery and regulation, as well as their biological functions in cancer. Promising agents that use or target the GRPs are being developed, and their efficacy as anticancer therapeutics is also discussed.

Liver-specific knockout of GRP94 in mice disrupts cell adhesion, activates liver progenitor cells, and accelerates liver tumorigenesis

Liver cancer is one of the most common solid tumors, with poor prognosis and high mortality. Mutation or deletion of the tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is strongly correlated with human liver cancer. Glucose-regulated protein 94 (GRP94) is a major endoplasmic reticulum (ER) chaperone protein, but its in vivo function is still emerging. To study the role of GRP94 in maintaining liver homeostasis and tumor development, we created two liver-specific knockout mouse models with the deletion of Grp94 alone, or in combination with Pten, using the albumin-cre system. We demonstrated that while deletion of GRP94 in the liver led to hyperproliferation of liver progenitor cells, deletion of both GRP94 and PTEN accelerated development of liver tumors, including both hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC), suggestive of progenitor cell origin. Furthermore, at the premalignant stage we observed disturbance of cell adhesion proteins and minor liver injury. When GRP94 was deleted in PTEN-null livers, ERK was selectively activated.

CONCLUSION

GRP94 is a novel regulator of cell adhesion, liver homeostasis, and tumorigenesis.