Sigma-2 Receptors-From Basic Biology to Therapeutic Target: A Focus on Age-Related Degenerative Diseases.

There is a large unmet medical need to develop disease-modifying treatment options for individuals with age-related degenerative diseases of the central nervous system. The sigma-2 receptor (S2R), encoded by TMEM97, is expressed in brain and retinal cells, and regulates cell functions via its co-receptor progesterone receptor membrane component 1 (PGRMC1), and through other protein-protein interactions. Studies describing functions of S2R involve the manipulation of expression or pharmacological modulation using exogenous small-molecule ligands. These studies demonstrate that S2R modulates key pathways involved in age-related diseases including autophagy, trafficking, oxidative stress, and amyloid-ß and α-synuclein toxicity. Furthermore, S2R modulation can ameliorate functional deficits in cell-based and animal models of disease. This review summarizes the current evidence-based understanding of S2R biology and function, and its potential as a therapeutic target for age-related degenerative diseases of the central nervous system, including Alzheimer's disease, α-synucleinopathies, and dry age-related macular degeneration.

Inhibition of MAC30 exerts antitumor effects in nasopharyngeal carcinoma via affecting the Akt/GSK-3ß/ß-catenin pathway.

Meningioma-associated protein 30 (MAC30) is a vital modulator of malignant transformation in numerous cancers. Yet, the involvement of MAC30 in nasopharyngeal carcinoma (NPC) is undetermined. This study was devoted to the study of the function of MAC30 in NPC, along with the molecular mechanism of its involvement in disease progression. This study showed an elevated level of MAC30 in NPC tissues and cell lines. MAC30 silencing impeded the proliferation, colony formation, and invasion of NPC cells, while MAC30 upregulation had the opposite effects. MAC30 regulated the Wnt/ß-catenin pathway via affecting the protein kinase B (Akt)/glycogen synthase kinase-3ß axis. Akt inhibition markedly abrogated the MAC30-mediated activation of the Wnt/ß-catenin pathway. Restoration of ß-catenin reversed MAC30 silencing-induced tumor-inhibiting effects. Knockdown of MAC30 weakened the tumorigenic potential of NPC cells in vivo. This study elucidates the fact that inhibition of MAC30 produces antitumor effects in NPC via affecting the Akt/Wnt/ß-catenin pathway.

Meningioma-associated protein 30 accelerates the proliferation and invasion of hepatocellular carcinoma by modulating Wnt/GSK-3ß/ß-catenin signaling.

Meningioma-associated protein 30 (MAC30) has been recently identified as a new tumor-associated protein that is implicated in multiple tumor types. However, the role of MAC30 in hepatocellular carcinoma (HCC) has not been studied. In the current study, we explored the expression, biological function and underlying mechanism of MAC30 in HCC. We found that MAC30 expression was significantly elevated in HCC tissues and cell lines. Functional in vitro assays demonstrated that the knockdown of MAC30 inhibited the proliferation and invasion of HCC cells, while MAC30 overexpression facilitated these biological behaviors. Moreover, the knockdown of MAC30 decreased glycogen synthase kinase (GSK)-3ß phosphorylation level and ß-catenin expression, leading to the inactivation of Wnt/ß-catenin signaling in HCC cells. The inhibition of GSK-3ß or reactivation Wnt/ß-catenin signaling markedly reversed MAC30 knockdown-mediated inhibitory effects on the proliferation and invasion of HCC cells. Notably, the inhibition of Wnt/ß-catenin signaling abrogated the MAC30-evoked oncogenic role in HCC cells. In addition, the knockdown of MAC30 impeded tumor formation and the growth rate of HCC cells in vivo. Taken together, our data recognized MAC30 as a potential tumor-promotion factor in HCC, which accelerated the proliferation and invasion of HCC through the up-regulation of Wnt/ß-catenin signaling. Our study suggests MAC30 as a potential anticancer target for HCC.

MAC30 knockdown involved in the activation of the Hippo signaling pathway in breast cancer cells.

Down-regulation of the meningioma-associated protein (MAC30) gene has been found in many solid cancers. This study was carried out to determine the roles and the mechanisms of MAC30 in breast cancer. We used our own data and a public database to analyze the MAC30 mRNA and protein levels in breast cancer tissues. In addition, we established MAC30 knockdown breast cancer cells using MAC30 siRNA. The roles of MAC30 were detected by using the Soft agar assay, Annexin-V-FITC/PI double staining and the Transwell assay. Western blotting was used to analyze the potential mechanism(s) of MAC30 in these cells. We found that MAC30 mRNA and protein were higher in the cancer tissues compared to the matched normal tissues. MAC30 expression was associated with tumor size, tumor differentiation and estrogen receptor (ER) status. Overall survival rate of the patients with low MAC30 expression was obviously higher than the ones with high expression. The apoptotic ratio was lower in MDA-MB-231 and MDA-MB-157 cells with MAC30 expression. By Western blot analysis, we found that increased levels of phosphorylated YAP1, MST1 and LATS1 after MAC30 siRNA transfection in these two cells. In summary, we demonstrate that MAC30 knockdown is involved in the activation of the Hippo signaling pathway.

The prognostic role of MAC30 in advanced gastric cancer patients receiving platinum-based chemotherapy.

AIM: We aimed to investigate a practical profile of MAC30 on chemotherapeutic response in gastric cancer (GC). PATIENTS & METHODS: We elected 87 GC patients receiving platinum-based chemotherapy in this study. MAC30 levels in tumor and adjuvant nontumor tissues were confirmed via reverse transcription-PCR to identify the clinical profile in GC and the correlation with therapeutic response. RESULTS: We found elevated MAC30 in GC compared with the matched adjacent nontumor tissues. GC with enhanced MAC30 exhibited poorer survival by Kaplan-Meier analysis and poor response to adjuvant platinum-based chemotherapy. A multivariate analysis showed that MAC30 was an independent prognostic factor of overall survival in GC receiving platinum-based chemotherapy. CONCLUSION: MAC30 could play as a potential biomarker for prognosis of GC with platinum-based chemotherapy.

Histatin-1 is an endogenous ligand of the sigma-2 receptor.

The Sigma-2 receptor (S2R) (a.k.a TMEM97) is an important endoplasmic reticular protein involved in cancer, cholesterol processing, cell migration, and neurodegenerative diseases, including Niemann-Pick Type C. While several S2R pharmacologic agents have been discovered, its recent (2017) cloning has limited biological investigation, and no endogenous ligands of the S2R are known. Histatins are a family of endogenous antimicrobial peptides that have numerous important effects in multiple biological systems, including antifungal, antibacterial, cancer pathogenesis, immunomodulation, and wound healing. Histatin-1 (Hst1) has important roles in epithelial wound healing and cell migration, and is the primary wound healing agent in saliva. Little is understood about the downstream machinery that underpins the effects of histatins, and no mammalian receptor is known to date. In this study, we show, using biophysical methods and functional assays, that Hst1 is an endogenous ligand for S2R and that S2R is a mammalian receptor for Hst1.

The Biological Function of Sigma-2 Receptor/TMEM97 and Its Utility in PET Imaging Studies in Cancer.

The sigma-2 receptor was originally defined pharmacologically and recently identified as TMEM97. TMEM97 has been validated as a biomarker of proliferative status and the radioligand of TMEM97, [18F]ISO-1, has been developed and validated as a PET imaging biomarker of proliferative status of tumors and as a predictor of the cancer therapy response. [18F]ISO-1 PET imaging should be useful to guide treatment for cancer patients. TMEM97 is a membrane-bound protein and localizes in multiple subcellular organelles including endoplasmic reticulum and lysosomes. TMEM97 plays distinct roles in cancer. It is reported that TMEM97 is upregulated in some tumors but downregulated in other tumors and it is required for cell proliferation in certain tumor cells. TMEM97 plays important roles in cholesterol homeostasis. TMEM97 expression is regulated by cholesterol-regulating signals such as sterol depletion and SREBP expression levels. TMEM97 regulates cholesterol trafficking processes such as low density lipoprotein (LDL) uptake by forming complexes with PGRMC1 and low density lipoprotein receptor (LDLR), as well as cholesterol transport out of lysosome by interacting with and regulating NPC1 protein. Understanding molecular functions of TMEM97 in proliferation and cholesterol metabolism will be important to develop strategies to diagnose and treat cancer and cholesterol disorders using a rich collection of TMEM97 radiotracers and ligands.

Down-regulated MAC30 expression inhibits breast cancer cell invasion and EMT by suppressing Wnt/ß-catenin and PI3K/Akt signaling pathways.

Breast cancer (BC) is a leading cause of cancer mortality in women worldwide. MAC30/Transmembrane protein 97 (TMEM97) is aberrantly up-regulated in many human carcinoma cells. However, the function of MAC30 in invasion and EMT of BC cells is uncertain. qRT-PCR was used to determine the level of MAC30 in BC tissues and cell lines. si-MAC30 was transfected into BC cells, and the effects of MAC30 silencing on the invasion and EMT were explored by qRT-PCR as well as transwell and western blot assays. Also, we determined the effects of MAC30 silencing on Wnt/ß-catenin and PI3K/Akt signaling pathways by western blot. We found that MAC30 is significantly up-regulated in BC tissues and cell lines. Down-regulation of MAC30 expression efficiently inhibited the invasion of BC cells. Furthermore, the EMT of BC cells was also inhibited by down-regulation of MAC30. Finally, we found that MAC30 knockdown inhibited Akt phosphorylation, ß-catenin, survivin, and cyclin D1 expressions. To our knowledge, this is the first report investigating the effect of MAC30 on invasion and EMT in BC cells by suppressing Wnt/ß-catenin and PI3K/Akt signaling pathways. MAC30 may be a potential therapeutic target for BC.

Pleural MAC30 as a prognostic marker in NSCLC with malignant pleural effusion.

Over-expressed meningioma-associate protein (MAC30) in tissues was associated with malignant tumor differentiation, metastasis and poor prognosis. However, the attention of MAC30 in pleural effusion from lung tumor is insufficient. Our retrospective study was prepared to explore the clinical values on diagnosis and prognosis of MAC30 from malignant pleural effusion (MPE) in non-small cell lung cancer (NSCLC). Levels of MAC30 were confirmed in MPE from 48 NSCLC patients and in benign pleural effusion (BPE) from 45 controls via enzyme-linked immunosorbent assay (ELISA). The association of MAC30 in MPE with clinical significance was further determined. We found that the levels of MAC30 in MPE were obviously higher than those in BPE (p < 0.05). Moreover, with a cutoff point (17.5 ng/ml), we confirmed the sensitivity and specificity of MAC30 for MPE were 82.7% and 85.3% using ROC curve analysis. Indeed, longer overall survival (OS) was present in NSCLC patients with low MAC30 expression in MPE. Multivariate analysis explicated that elevated MAC30 in MPE was an independent prognostic factor for shorter OS of NSCLC. Our data suggests that MAC30 in pleural effusion could be a potential prognostic marker in NSCLC with MPE.

The Prognostic Effect of MAC30 Expression on Patients With Non-Small Cell Lung Cancer Receiving Adjuvant Chemotherapy.

The purpose of this study was to examine the MAC30 expression in non-small cell lung cancer and to evaluate its prognostic value on therapeutic response in patients with non-small cell lung cancer receiving postoperative chemotherapy. Among a total of 218 retrospective Chinese patients with non-small cell lung cancer, 164 patients receiving adjuvant chemotherapy were enrolled in this study. Real-time polymerase chain reaction was performed to confirm the expression of MAC30 messenger RNA in 32 cases of non-small cell lung cancer tumors with the corresponding nontumor lung tissues. The MAC30 protein expression in all specimens was analyzed by immunohistochemical staining. Moreover, we assessed the correlation of MAC30 expression with clinicopathological features, therapeutic response, and survival of patients. Here, we observed the increased expression of MAC30 messenger RNA in patients with non-small cell lung cancer compared to those in control samples. The overexpression of MAC30 was strongly associated with poor tumor differentiation, high tumor-node-metastasis stage, and lymph node metastasis. In addition, we observed that patients with increased MAC30 expression showed gloomy overall survival and disease-free survival. A multivariate analysis explicated that higher MAC30 expression was a valuable independent prognostic factor of poorer tumor differentiation, shorter overall survival, and disease-free survival in patients receiving chemotherapy. MAC30 could be a useful biomarker of tumor differentiation and outcome of patients with non-small cell lung cancer. Overexpression of MAC30 predicts a worse tumor differentiated stage and prognosis in patients with non-small cell lung cancer receiving adjuvant chemotherapy.

Overexpression of MAC30 is Resistant to Platinum-Based Chemotherapy in Patients With Non-Small Cell Lung Cancer.

Adjuvant platinum-based chemotherapy has developed its stability as the first-line treatment in advanced non-small cell lung cancer (NSCLC). The objective of this study was to investigate the prognostic value of meningioma-associated protein (MAC30) on adjuvant platinum-based chemotherapeutic response and survival in patients with NSCLC. A total of 174 retrospective stage III B to IV Chinese patients with NSCLC were enrolled in the study. Among all cases, 85 patients were given platinum-based chemotherapy and another 89 patients received molecularly targeted therapy. The expression of MAC30 in tumor samples was confirmed via immunohistochemical staining to correlate with the therapeutic response and survival of patients. Patients having NSCLC with MAC30 overexpression showed a poorer response to platinum-based chemotherapy, while there was no prognostic value of MAC30 expression on molecularly targeted therapy. Further, patients receiving platinum-based chemotherapy with enhanced MAC30 expression exhibited shorter survival. A multivariate analysis exhibited that increased MAC30 expression was an independent prognostic factor for overall survival in patients having NSCLC with platinum-based chemotherapy. In conclusion, patients having NSCLC with higher MAC30 expression resisted to platinum-based chemotherapy and exhibited worse survival.

TM6SF2 and MAC30, new enzyme homologs in sterol metabolism and common metabolic disease.

Carriers of the Glu167Lys coding variant in the TM6SF2 gene have recently been identified as being more susceptible to non-alcoholic fatty liver disease (NAFLD), yet exhibit lower levels of circulating lipids and hence are protected against cardiovascular disease. Despite the physiological importance of these observations, the molecular function of TM6SF2 remains unknown, and no sequence similarity with functionally characterized proteins has been identified. In order to trace its evolutionary history and to identify functional domains, we embarked on a computational protein sequence analysis of TM6SF2. We identified a new domain, the EXPERA domain, which is conserved among TM6SF, MAC30/TMEM97 and EBP (D8, D7 sterol isomerase) protein families. EBP mutations are the cause of chondrodysplasia punctata 2 X-linked dominant (CDPX2), also known as Conradi-Hünermann-Happle syndrome, a defective cholesterol biosynthesis disorder. Our analysis of evolutionary conservation among EXPERA domain-containing families and the previously suggested catalytic mechanism for the EBP enzyme, indicate that TM6SF and MAC30/TMEM97 families are both highly likely to possess, as for the EBP family, catalytic activity as sterol isomerases. This unexpected prediction of enzymatic functions for TM6SF and MAC30/TMEM97 is important because it now permits detailed experiments to investigate the function of these key proteins in various human pathologies, from cardiovascular disease to cancer.