Small Glutamine-rich Tetratricopeptide Repeat-containing Protein Alpha Research Articles

PLPP2: Potential therapeutic target of breast cancer in PLPP family

PLPPs (Phospholipid phosphatases) are widely expressed in different human tissues, regulate cell signal transduction, and are overexpressed in cancers such as gliomas, pancreatic adenocarcinoma, lung adenocarcinoma, and so on. As a member of the PLPP family, PLPP2 (phospholipid phosphatase 2) plays a vital role in the occurrence and development of breast cancer, but its mechanism is still unclear. Our research found that PLPP2 was overexpressed in breast cancer, and the higher expression level of PLPP2 showed a worse prognosis for breast cancer patients. Further analysis showed that overexpression of PLPP2 affected the expression of CDC34 (cell-division cycle 34), LSM7 (Like-Smith 7), and SGTA (small glutamine-rich tetratricopeptide repeat-containing protein alpha) through EMT (epigenetic-mesenchymal transition) related pathways to promote the occurrence and development of breast cancer. In vitro, silencing PLPP2 significantly reduced the proliferation, invasion, and migration abilities of human breast cancer cells MDA-MB-231. ER+ is a common subtype of breast cancer. Furthermore, we found that the overexpression of PLPP2 was significantly related to the poor prognosis of ER+ breast cancer. These results indicate that PLPP2 has value as a potential therapeutic target for breast cancer, especially for ER+ breast cancer.

Structural complexity of the co-chaperone SGTA: a conserved C-terminal region is implicated in dimerization and substrate quality control

BackgroundProtein quality control mechanisms are essential for cell health and involve delivery of proteins to specific cellular compartments for recycling or degradation. In particular, stray hydrophobic proteins are captured in the aqueous cytosol by a co-chaperone, the small glutamine-rich, tetratricopeptide repeat-containing protein alpha (SGTA), which facilitates the correct targeting of tail-anchored membrane proteins, as well as the sorting of membrane and secretory proteins that mislocalize to the cytosol and endoplasmic reticulum-associated degradation. Full-length SGTA has an unusual elongated dimeric structure that has, until now, evaded detailed structural analysis. The C-terminal region of SGTA plays a key role in binding a broad range of hydrophobic substrates, yet in contrast to the well-characterized N-terminal and TPR domains, there is a lack of structural information on the C-terminal domain. In this study, we present new insights into the conformation and organization of distinct domains of SGTA and show that the C-terminal domain possesses a conserved region essential for substrate processing in vivo.ResultsWe show that the C-terminal domain region is characterized by α-helical propensity and an intrinsic ability to dimerize independently of the N-terminal domain. Based on the properties of different regions of SGTA that are revealed using cell biology, NMR, SAXS, Native MS, and EPR, we observe that its C-terminal domain can dimerize in the full-length protein and propose that this reflects a closed conformation of the substrate-binding domain.ConclusionOur results provide novel insights into the structural complexity of SGTA and provide a new basis for mechanistic studies of substrate binding and release at the C-terminal region.

Expression of small glutamine-rich tetratrico peptide repeat-containing protein alpha and clinical significance in breast cancer

Objective To study the expression of small glutamine-rich tetratrico peptide repeat-containing protein alpha (SGTA) in human breast cancer and its relationship with clinicopathological features. Methods The SGTA expression in breast cancer was detected by Western blotting in 8 paired fresh tissues and immunohistochemistry on 128 parffin-embedded slices, and the relationship of SGTA and proliferating cell nuclear antigen (Ki-67) with the clinical parameters was analyzed. Serum starvation and refeeding was performed on MG-132 cells to study the role SGTA played in cell cycle. Results SGTA was highly expressed in breast cancer. The results showed that the expression of SGTA was low in well-differentiated breast cancer tissues, which was consistent with the Ki-67 expression. Multivariate analysis showed that SGTA protein in breast cancer was significantly correlated with histological grade (P=0.000), pTNM staging (P=0.000) as well as Ki-67 (P=0.021), but not with other parameters such as age, estrogen receptor (ER), progesterone receptor (PR), human epidermalgrowth factor receptor-2 (Her-2), histological type, lymph node metastasis and tumor size. Cox’s proportional hazards model showed that SGTA [Hazard ratio (HR)=2.410, 95% confidence interval (CI): 1.075-5.408, P=0.033] might be an independent indicator for breast cancer. Besides, survival curve analysis also showed that high SGTA expression was correlated with a poor prognosis (42.9% vs. 84.5%, P=0.000). Conclusion SGTA may play a role in breast cancer cell proliferation. The abnormal expression of SGTA may be closely related to the initiation and progress of breast cancer. Key words: Breast cancer; Small glutamine-rich tetratrico peptide repeat-containing protein alpha; Prognosis; Proliferation

Small Glutamine-Rich Tetratricopeptide Repeat-Containing Protein Alpha (SGTA) Ablation Limits Offspring Viability and Growth in Mice.

Small glutamine-rich tetratricopeptide repeat-containing protein α (SGTA) has been implicated as a co-chaperone and regulator of androgen and growth hormone receptor (AR, GHR) signalling. We investigated the functional consequences of partial and full Sgta ablation in vivo using Cre-lox Sgta-null mice. Sgta+/− breeders generated viable Sgta−/− offspring, but at less than Mendelian expectancy. Sgta−/− breeders were subfertile with small litters and higher neonatal death (P < 0.02). Body size was significantly and proportionately smaller in male and female Sgta−/− (vs WT, Sgta+/− P < 0.001) from d19. Serum IGF-1 levels were genotype- and sex-dependent. Food intake, muscle and bone mass and adiposity were unchanged in Sgta−/−. Vital and sex organs had normal relative weight, morphology and histology, although certain androgen-sensitive measures such as penis and preputial size, and testis descent, were greater in Sgta−/−. Expression of AR and its targets remained largely unchanged, although AR localisation was genotype- and tissue-dependent. Generally expression of other TPR-containing proteins was unchanged. In conclusion, this thorough investigation of SGTA-null mutation reports a mild phenotype of reduced body size. The model’s full potential likely will be realised by genetic crosses with other models to interrogate the role of SGTA in the many diseases in which it has been implicated.

Structural and Functional Insights into Small, Glutamine-Rich, Tetratricopeptide Repeat Protein Alpha.

The small glutamine-rich, tetratricopeptide repeat-containing protein alpha (SGTA) is an emerging player in the quality control of secretory and membrane proteins mislocalized to the cytosol, with established roles in tail-anchored (TA) membrane protein biogenesis. SGTA consists of three structural domains with individual functions, an N-terminal dimerization domain that assists protein sorting pathways, a central tetratricopeptide repeat (TPR) domain that mediates interactions with heat-shock proteins, proteasomal, and hormonal receptors, and viral proteins, and a C-terminal glutamine rich region that binds hydrophobic substrates. SGTA has been linked to viral lifecycles and hormone receptor signaling, with implications in the pathogenesis of various disease states. Thus far, a range of biophysical techniques have been employed to characterize SGTA structure in some detail, and to investigate its interactions with binding partners in different biological contexts. A complete description of SGTA structure, together with further investigation into its function as a co-chaperone involved quality control, could provide us with useful insights into its role in maintaining cellular proteostasis, and broaden our understanding of mechanisms underlying associated pathologies. This review describes how some structural features of SGTA have been elucidated, and what this has uncovered about its cellular functions. A brief background on the structure and function of SGTA is given, highlighting its importance to biomedicine and related fields. The current level of knowledge and what remains to be understood about the structure and function of SGTA is summarized, discussing the potential direction of future research.

Expression and prognostic role of SGTA in human breast carcinoma correlates with tumor cell proliferation.

Small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA) was reported to be implicated in various cellular processes and involved in control of cell cycle regulation and transcription. It may play a critical role in oncogenesis. In this study, to investigate the potential roles of SGTA in breast cancer, expression patterns, interaction and the correlation with clinical/prognostic factors of SGTA and Ki-67 were examined among patients with breast cancer. Immunohistochemistry and Western blot analysis were performed for SGTA in 100 breast carcinoma samples. The data were correlated with clinicopathological features. The univariate and multivariate survival analyses were also performed to determine the prognostic significance. We found that SGTA was overexpressed in breast carcinoma compared with the adjacent normal tissues. High expression of SGTA was positively associated with histological grade (P=0.002) and Ki-67 (P=0.001). Univariate analysis showed that SGTA expression was associated with a poor prognosis (P=0.002). Kaplan-Meier survival curves of the study population showed that high expression level of SGTA significantly correlated with short-term survival. While in vitro, SGTA depletion by small interfering RNA inhibited cell proliferation and cell cycle in breast cancer cell lines. Western blot analyses showed that SGTA depletion decreased cyclin A, cyclin B and CDK2, whereas increased p27 levels. Additionally, treatment of phosphatidylinositol 3-kinase inhibitor LY294002 could arrest cells growth and diminish SGTA expression. These results suggested that SGTA overexpression was involved in the pathogenesis of breast cancer which might serve as a future target for novel treatment in breast cancer.

The Cochaperone SGTA (Small Glutamine-rich Tetratricopeptide Repeat-containing Protein Alpha) Demonstrates Regulatory Specificity for the Androgen, Glucocorticoid, and Progesterone Receptors

Steroid hormone receptors are ligand-dependent transcription factors that require the ordered assembly of multichaperone complexes for transcriptional activity. Although heat shock protein (Hsp) 90 and Hsp70 are key players in this process, multiple Hsp70- and Hsp90-associated cochaperones associate with receptor-chaperone complexes to regulate receptor folding and activation. Small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA) was recently characterized as an Hsp70 and Hsp90-associated cochaperone that specifically regulates androgen receptor activity. However, the specificity of SGTA for additional members of the steroid hormone receptor superfamily and the mechanism by which SGTA regulates receptor activity remain unclear. Here we report that SGTA associates with and specifically regulates the androgen, glucocorticoid, and progesterone receptors and has no effect on the mineralocorticoid and estrogen receptors in both yeast and mammalian cell-based reporter assays. In both systems, SGTA knockdown/deletion enhances receptor activity, whereas SGTA overexpression suppresses receptor activity. We demonstrate that SGTA binds directly to Hsp70 and Hsp90 in vitro with similar affinities yet predominately precipitates with Hsp70 from cell lysates, suggesting a role for SGTA in early, Hsp70-mediated folding. Furthermore, SGTA expression completely abrogates the regulation of receptor function by FKBP52 (52-kDa FK506-binding protein), which acts at a later stage of the chaperone cycle. Taken together, our data suggest a role for SGTA at distinct steps in the chaperone-dependent modulation of androgen, glucocorticoid, and progesterone receptor activity.

High Expression of SGTA in Esophageal Squamous Cell Carcinoma Correlates With Proliferation and Poor Prognosis

Receptor tyrosine kinases (RTKs) expression and the growth factor such as platelet-derived growth factor (PDGF) and their receptors have been considered relevant in the process of angiogenesis and dissemination in esophageal squamous cell carcinoma (ESCC). Small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA) downstream of RTK signaling was a critical regulator of PDGF receptors (PDGFR) stability. The aim of the present study was to examine the expression of SGTA and to elucidate its clinicopathologic significance in ESCC. Immunohistochemistry and western blot analysis were performed for SGTA in ESCC samples. SGTA was up-regulated in ESCC as compared with the adjacent normal tissue. High expression of SGTA was associated with tumor grade (P < 0.01), and SGTA was positively correlated with proliferation marker Ki-67 (P < 0.05). Univariate analysis showed that SGTA expression did has a remarkable prediction for poor prognosis (P = 0.016). Knockdown or overexpression of SGTA affected ESCC cells proliferation and cell cycle. Additionally, after ESCC cells silenced for SGTA were treated with cisplatin (an anti-ESCC agent), the cell growth was down-regulated. These findings suggested that SGTA was involved in the pathogenesis of ESCC and might indicate a poor prognosis for ESCC patients.

Expression and clinical role of small glutamine-rich tetratricopeptide repeat (TPR)-containing protein alpha (SGTA) as a novel cell cycle protein in NSCLC

A small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA) is a 35kDa protein involved in a number of biological processes. However, the role of SGTA in non-small-cell lung cancer (NSCLC) tumorigenesis has never been elucidated. The purpose of this study was to determine whether SGTA could serve as a biomarker for stratification and prediction of prognosis in NSCLC. Small glutamine-rich tetratricopeptide repeat-containing protein alpha expression was evaluated by Western blot in 8 paired fresh lung cancer tissues and immunohistochemistry on 83 paraffin-embedded sections. The effect of SGTA was assessed by RNA interference in A549 cells. Serum starvation and refeeding, flow cytometry, CCK-8, and tunnel assays were performed. Small glutamine-rich tetratricopeptide repeat-containing protein alpha was highly expressed in NSCLC and significantly correlated with NSCLC histological differentiation, clinical stage, and Ki-67. Multivariate analysis indicated that SGTA was an independent prognostic factor for NSCLC patients' survival. The present investigation demonstrated that suppression of SGTA expression resulted in a significant decline of proliferation in A549 cells. Besides, SGTA could abolish the toxicity of cisplatin in A549 cells. These findings suggested that SGTA might play an important role in promoting the tumorigenesis of NSCLC, and thus be a promising therapeutic target to prevent NSCLC progression.

The Association of BAG6 with SGTA and Tail-Anchored Proteins

BackgroundThe BAG6 protein is a subunit of a heterotrimeric complex that binds a range of membrane and secretory protein precursors localized to the cytosol, enforcing quality control and influencing their subsequent fate.Methodology and Principal FindingsBAG6 has an N-terminal ubiquitin-like domain, and a C-terminal Bcl-2-associated athanogene domain, separated by a large central proline-rich region. We have used in vitro binding approaches to identify regions of BAG6 important for its interactions with: i) the small-glutamine rich tetratricopeptide repeat-containing protein alpha (SGTA) and ii) two model tail-anchored membrane proteins as a paradigm for its hydrophobic substrates. We show that the BAG6-UBL is essential for binding to SGTA, and find that the UBL of a second subunit of the BAG6-complex, ubiquitin-like protein 4A (UBL4A), competes for SGTA binding. Our data show that this binding is selective, and suggest that SGTA can bind either BAG6, or UBL4A, but not both at the same time. We adapted our in vitro binding assay to study the association of BAG6 with an immobilized tail-anchored protein, Sec61β, and find both the UBL and BAG domains are dispensable for binding this substrate. This conclusion was further supported using a heterologous subcellular localization assay in yeast, where the BAG6-dependent nuclear relocalization of a second tail-anchored protein, GFP-Sed5, also required neither the UBL, nor the BAG domain of BAG6.SignificanceOn the basis of these findings, we propose a working model where the large central region of the BAG6 protein provides a binding site for a diverse group of substrates, many of which expose a hydrophobic stretch of polypeptide. This arrangement would enable the BAG6 complex to bring together its substrates with potential effectors including those recruited via its N-terminal UBL. Such effectors may include SGTA, and the resulting assemblies influence the subsequent fate of the hydrophobic BAG6 substrates.

Androgen receptor protein levels are significantly reduced in serous ovarian carcinomas compared with benign or borderline disease but are not altered by cancer stage or metastatic progression.

The androgen receptor (AR) is expressed in a majority of ovarian carcinomas, but its role in disease development remains unclear. In this study, AR and a novel AR molecular chaperone called small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA) were investigated to assess their potential role in ovarian carcinogenesis. First, an AR and SGTA-positive ovarian cancer cell line was identified to examine whether SGTA influenced AR subcellular localization. Next, relative protein levels of AR and SGTA were measured in two sets of clinical samples: (1) 46 serous ovarian carcinomas (stages I-IV), 9 serous borderline tumors, and 11 benign ovarian tumors; and (2) 24 patient-matched stage III primary and metastatic serous ovarian tumors. Ablation of SGTA protein in OVCAR3 cells significantly increased AR nuclear localization under basal (p ≤ 0.001) and androgen-stimulated (p ≤ 0.001) conditions. In the first clinical set, AR levels were significantly lower in early- (I/II) and late-stage (III/IV) cancers compared with benign (p ≤ 0.001) but not borderline ovarian tumors. SGTA alone did not discriminate between groups but the AR/SGTA ratio was significantly lower in carcinomas and borderline tumors compared with benign tumors (p ≤ 0.001 and 0.015, respectively). In the second clinical set, matched primary and metastatic serous ovarian cancers did not significantly differ for any parameter measured. Collectively, our results suggest that SGTA can influence AR signaling in ovarian cancer cells and that AR signaling capacity may be reduced with the development but not metastatic progression of serous ovarian cancer.

Small glutamine-rich tetratricopeptide repeat–containing protein alpha is present in human ovaries but may not be differentially expressed in relation to polycystic ovary syndrome

To evaluate the expression and function of small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA), an androgen receptor (AR) molecular chaperone, in human ovarian tissues. Examine the effect of SGTA on AR subcellular localization in granulosa tumor cells (KGN) and SGTA expression in ovarian tissues. University-based research laboratory. Archived tissues from premenopausal women and granulosa cells from infertile women receiving assisted reproduction. None. AR subcellular localization and SGTA protein or mRNA levels. SGTA and AR proteins were expressed in the cytoplasm of KGN cells and exposure to androgen stimulated AR nuclear localization. SGTA protein knockdown increased AR nuclear localization at low (0-0.1 nmol/L) but not high (1-10 nmol/L) concentrations of androgen hormone. In ovarian tissues, SGTA was localized to the cytoplasm of granulosa cells at all stages of folliculogenesis and in thecal cells of antral follicles. SGTA protein levels were similar when comparing primordial and primary follicles within core biopsies (n = 40) from women with and without polycystic ovary syndrome (PCOS). Likewise, SGTA mRNA levels were not significantly different in granulosa cells from preovulatory follicles after hyperstimulation of women with and without PCOS. SGTA is present in human ovaries and has the potential to modulate AR signalling, but it may not be differentially expressed in PCOS.

Small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA), a candidate gene for polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a heterogenic, complex common genetic disease. Multiple pathways are involved in its pathogenesis, including the androgen signaling pathway and insulin signaling pathway. Small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA) is a putative member of the androgen receptor-chaperone-co-chaperone complex, and may play a role in androgen signaling as a co-chaperone. Polymorphisms in the SGTA gene have not been evaluated for a role in PCOS. Women with and without PCOS (287 cases, 187 controls) were genotyped for three single nucleotide polymorphisms (SNPs) in SGTA. SNPs and haplotypes were determined and tested for association with PCOS and component traits of PCOS. For SNP rs1640262, homozygotes for the minor allele were protected against PCOS (P = 0.009). Haplotype 1 (G-A-T) was associated with increased risk of PCOS (P = 0.015). In women with PCOS, haplotype 2 (A-G-C) was associated with increased insulin resistance (P = 0.013), consequently resulting in increased insulin secretion (P = 0.014). This study presents genetic evidence suggesting a potential role of SGTA in the pathogenesis of PCOS. SGTA may provide a connection between multiple pathways in PCOS.