Synuclein γ protects Akt and mTOR and renders tumor resistance to Hsp90 disruption

Cancer Cells Enter an Adaptive Persistence to Survive Radiotherapy and Repopulate Tumor

Repopulation of residual tumor cells impedes curative radiotherapy, yet the mechanism is not fully understood. It is recently appreciated that cancer cells adopt a transient persistence to survive the stress of chemo- or targeted therapy and facilitate eventual relapse. Here, it is shown that cancer cells likewise enter a "radiation-tolerant persister" (RTP) state to evade radiation pressure in vitro and in vivo. RTP cells are characterized by enlarged cell size with complex karyotype, activated type I interferon pathway and two gene patterns represented by CST3 and SNCG. RTP cells have the potential to regenerate progenies via viral budding-like division, and type I interferon-mediated antiviral signaling impaired progeny production. Depleting CST3 or SNCG does not attenuate the formation of RTP cells, but can suppress RTP cells budding with impaired tumor repopulation. Interestingly, progeny cells produced by RTP cells actively lose their aberrant chromosomal fragments and gradually recover back to a chromosomal constitution similar to their unirradiated parental cells. Collectively, this study reveals a novel mechanism of tumor repopulation, i.e., cancer cell populations employ a reversible radiation-persistence by poly- and de-polyploidization to survive radiotherapy and repopulate the tumor, providing a new therapeutic concept to improve outcome of patients receiving radiotherapy.

Multiomics characterization implicates PTK7 in ovarian cancer EMT and cell plasticity and offers strategies for therapeutic intervention

Most patients with ovarian cancer (OC) are diagnosed at a late stage when there are very few therapeutic options and a poor prognosis. This is due to the lack of clearly defined underlying mechanisms or an oncogenic addiction that can be targeted pharmacologically, unlike other types of cancer. Here, we identified protein tyrosine kinase 7 (PTK7) as a potential new therapeutic target in OC following a multiomics approach using genetic and pharmacological interventions. We performed proteomics analyses upon PTK7 knockdown in OC cells and identified novel downstream effectors such as synuclein-γ (SNCG), SALL2, and PP1γ, and these findings were corroborated in ex vivo primary samples using PTK7 monoclonal antibody cofetuzumab. Our phosphoproteomics analyses demonstrated that PTK7 modulates cell adhesion and Rho-GTPase signaling to sustain epithelial-mesenchymal transition (EMT) and cell plasticity, which was confirmed by high-content image analysis of 3D models. Furthermore, using high-throughput drug sensitivity testing (525 drugs) we show that targeting PTK7 exhibited synergistic activity with chemotherapeutic agent paclitaxel, CHK1/2 inhibitor prexasertib, and PLK1 inhibitor GSK461364, among others, in OC cells and ex vivo primary samples. Taken together, our study provides unique insight into the function of PTK7, which helps to define its role in mediating aberrant Wnt signaling in ovarian cancer.

Emerging Link between Tsc1 and FNIP Co-Chaperones of Hsp90 and Cancer

Heat shock protein-90 (Hsp90) is an ATP-dependent molecular chaperone that is tightly regulated by a group of proteins termed co-chaperones. This chaperone system is essential for the stabilization and activation of many key signaling proteins. Recent identification of the co-chaperones FNIP1, FNIP2, and Tsc1 has broadened the spectrum of Hsp90 regulators. These new co-chaperones mediate the stability of critical tumor suppressors FLCN and Tsc2 as well as the various classes of Hsp90 kinase and non-kinase clients. Many early observations of the roles of FNIP1, FNIP2, and Tsc1 suggested functions independent of FLCN and Tsc2 but have not been fully delineated. Given the broad cellular impact of Hsp90-dependent signaling, it is possible to explain the cellular activities of these new co-chaperones by their influence on Hsp90 function. Here, we review the literature on FNIP1, FNIP2, and Tsc1 as co-chaperones and discuss the potential downstream impact of this regulation on normal cellular function and in human diseases.

EPDR1, Which Is Negatively Regulated by miR-429, Suppresses Epithelial Ovarian Cancer Progression via PI3K/AKT Signaling Pathway

Epithelial ovarian cancer (EOC) is the main pathological type of ovarian cancer. In this study, we found that ependymin-related 1 (EPDR1) was remarkably downregulated in EOC tissues, and low EPDR1 expression was associated with International Federation of Gynecology and Obstetrics (FIGO) stage, metastasis, and poor prognosis. We confirmed that EPDR1 overexpression dramatically suppressed EOC cell proliferation, migration, and invasion in vitro and in vivo. Mechanistically, EPDR1 inhibited EOC tumorigenesis and progression, at least in part, through the repression of the PI3K (Phosphoinositide 3-kinase)/AKT (AKT Serine/Threonine Kinase 1) signaling pathway. Furthermore, the expression and function of EPDR1 were regulated by miR-429, as demonstrated by luciferase reporter assays and rescue experiments. In conclusion, our study validated that EPDR1, negatively regulated by miR-429, played an important role as a tumor-suppressor gene in EOC development via inhibition of the PI3K/AKT pathway. The miR-429/EPDR1 axis might provide novel therapeutic targets for individualized treatment of EOC patients in the future.

SNCG promotes the progression and metastasis of high-grade serous ovarian cancer via targeting the PI3K/AKT signaling pathway

Background

The poor prognosis of patients with ovarian cancer is mainly due to cancer progression. γ-Synuclein (SNCG) has reported as a critical player in cancer metastasis. However, its biological roles and mechanism are yet incompletely understood in ovarian cancer, especially in high-grade serous ovarian cancer (HGSOC).

Methods

This is a retrospective study of 312 patients with ovarian cancer at a single center between 2006 and 2016. Ovarian cancer tissues were stained by immunohistochemistry to analyze the relationship between SNCG expression and clinicopathologic factors. The clinical outcomes versus SNCG expression level were evaluated by Kaplan–Meier method and multiple Cox regression analysis. Next, systematical functional experiments were given to examine the proliferation and metastatic abilities of SNCG both in vitro and in vivo using loss- and gain- of function approaches. Furthermore, the mechanisms of SNCG overexpression were examined by human phospho-kinase array kit and western blot analysis.

Results

Clinically, the expression of SNCG was significantly upregulated in ovarian cancer compared with the borderline and benign tumor, normal ovary, and fallopian tube. Notably, the high level of SNCG correlated with high-risk clinicopathologic features and showed poor survival for patients with HGSOC, indicating an independent prognostic factor for these patients. Functionally, we observed that overexpression of SNCG promoted cell proliferation, tumor formation, migration, and invasion both in vitro and in vivo. Mechanistically, we identified that SNCG promoted cancer cell metastasis through activating the PI3K/AKT signaling pathway.

Conclusions

Our results reveal SNCG up-regulation contributes to the poor clinical outcome of patients with HGSOC and highlight the metastasis-promoting function of SNCG via activating the PI3K/Akt signaling pathway in HGSOC.

Silencing of Synuclein-γ inhibits human cervical cancer through the AKT signaling pathway

BACKGROUND

Synuclein-γ has been demonstrated to be highly expressed in various human cancers including cervical cancer, and has been shown to play a critical role in tumor aggressiveness. We aimed to investigate the role of Synuclein-γ in human cervical cancer in vitro and in vivo.

METHOD

Reverse transcription-quantitative polymerase chain reaction assay and Western blot assay were used to detect the mRNA and protein expression, respectively. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and colony formation assay were performed to measure the viabilities of cancer cells. Flow cytometry assay was used to detect the cell cycle and apoptosis. Moreover, an animal experiment was performed to evaluate the biological behavior of Synuclein-γ in vivo.

RESULTS

In the current study, we found that Synuclein-γ was obviously over-expressed in cervical cancer tissues compared to the adjacent non-cancer tissues. Cervical cancer cells transfected with Synuclein-γ siRNA demonstrated significant inhibition of cancer proliferation (P < 0.01), cell cycle arrest at G0/G1 phase, and cell apoptosis (P < 0.05). Moreover, down-regulation of Synuclein-γ significantly inhibited cervical cancer growth in vivo. In addition, protein levels of AKT, c-Myc and Cyclin D1 were much lower in the Synuclein-γ siRNA-treated groups than that in the control group.

CONCLUSIONS

Synuclein-γ inhibition reduced cervical cancer tumor growth through the AKT pathway. This effect represented a therapeutic opportunity and provided a novel target for cervical cancer treatment.

siRNA Targeting of the SNCG Gene Inhibits the Growth of Gastric Carcinoma SGC7901 Cells in vitro and in vivo by Downregulating the Phosphorylation of AKT/ERK

The aim of the study was to evaluate the effects of synuclein-γ (SNCG) silencing on gastric cancer SGC7901 cells and to elucidate the associated mechanisms. pGCSIL-lentiviral siRNA targeting of the SNCG gene was employed to inhibit SNCG expression. Several experiments such as quantitative real-time PCR, Western blotting, MTT, colony formation, migration assay, and flow cytometry were performed to investigate the biological behavior of infected SGC7901 cells. BALB/c nude mice were used as tumor xenograft models to assess the effects of SNCG silencing on tumor growth. Western blot analysis was carried out to determine the relative levels of AKT, p-AKT, ERK, and p-ERK expression. Our results showed that SNCG was overexpressed in SGC7901 cells as compared to normal gastric mucosal epithelial cells. SGC7901 cells transfected with SNCG siRNA demonstrated significantly decreased gastric cancer growth (p < 0.01), reduced cell migration, cell cycle arrest in the G0/G1 phase, promoted tumor cell apoptosis (p < 0.01), and inhibited tumorigenesis in xenograft animal models. Western blot analysis indicated that the protein levels of p-AKT and p-ERK were much lower in the SNCG siRNA group than in the control groups. The results of the present study suggest that SNCG siRNA plays a significant role in the proliferation, migration, and tumorigenesis of gastric cancer by downregulating the phosphorylation of AKT and ERK. RNA interference-mediated silencing of SNCG may provide an opportunity to develop a novel treatment strategy for gastric cancer.

Extracellular gamma-synuclein promotes tumor cell motility by activating β1 integrin-focal adhesion kinase signaling pathway and increasing matrix metalloproteinase-24, -2 protein secretion

Background

Increasing evidence reveals a significant correlation between gamma-synuclein (SNCG) level and tumor invasion and metastasis in various human cancers. Our previous investigation showed that SNCG could secrete into extracellular environment and promoted tumor cell motility, but the mechanism is unknown.

Methods

The membrane binding ability of SNCG was characterized by immunohistochemical staining, immunofluorescence staining and fractionation of colorectal cancer (CRC) cell membrane. Association between SNCG and β1 integrin was validated by coimmunoprecipitation and far Western blot. After inhibition of β1 integrin and focal adhesion kinase (FAK), effect of SNCG on cell motility was measured by transwell chamber assays and changes of protein levels were detected by Western blot. Association between SNCG and activated β1 integrin levels in human CRC tissues was determined by Spearman’s rank correlation analysis. Secreted proteins in conditioned medium (CM) were screened by antibody array.

Results

Extracellular SNCG bound β1 integrin on CRC cell membrane and increased levels of activated β1 integrin and FAK. Correspondingly, SNCG-enhanced cell motility was counteracted by knockdown or inhibition of β1 integrin or FAK. Further study revealed that high SNCG level indicated poor outcome and SNCG levels positively correlated with those of activated β1 integrin and phospho-FAK (Tyr³⁹⁷) in human CRC tissues. Additionally, extracellular SNCG promoted secretion of fibronectin (FN), vitronectin (VN), matrix metalloproteinase (MMP)-2, and MMP-24 from HCT116 cells. Protease activity of MMP-2 in the CM of HCT116 cells was increased by treatment with SNCG, which was abolished by inhibiting β1 integrin.

Conclusion

Our results highlight the potential role of SNCG in remodeling extracellular microenvironment and inducing β1 integrin-FAK signal pathway of CRC cells.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0783-6) contains supplementary material, which is available to authorized users.

Gamma synuclein is a novel Twist1 target that promotes TGF-β-induced cancer cell migration and invasion

Transforming growth factor β (TGF-β) is critical for embryonic development, adult tissue homeostasis, and tumor progression. TGF-β suppresses tumors at early stage, but promotes metastasis at later stage through oncogenes such as Twist1. Gamma-synuclein (SNCG) is overexpressed in a variety of invasive and metastatic cancer. Here, we show that TGF-β induces SNCG expression by Smad-Twist1 axis, thus promoting TGF-β- and Twist1-induced cancer cell migration and invasion. We identify multiple Twist1-binding sites (E-boxes) in SNCG promoter. Chromatin immunoprecipitation and luciferase assays confirm the binding of Twist1 to the E-boxes of SNCG promoter sequence (−129/−1026 bp). Importantly, the Twist1-binding site close to the transcription initiation site is critical for the upregulation of SNCG expression by TGF-β and Twist1. Mutations of Twist1 motif on the SNCG promoter constructs markedly reduces the promoter activity. We further show that TGF-β induces Twist1 expression through Smad thereby enhancing the binding of Twist1 to SNCG promoter, upregulating SNCG promoter activity and increasing SNCG expression. SNCG knockdown abrogates TGF-β- or Twist1-induced cancer cell migration and invasion. Finally, SNCG knockdown inhibits the promotion of cancer metastasis by Twist1. Together, our data demonstrate that SNCG is a novel target of TGF-β-Smad-Twist1 axis and a mediator of Twist1-induced cancer metastasis.

Quantitative proteomics reveals molecular mechanism of gamabufotalin and its potential inhibition on Hsp90 in lung cancer

Gamabufotalin (CS-6) is a major bufadienolide of Chansu, which shows desirable metabolic stability and less adverse effect in cancer therapy. CS-6 treatment inhibited the proliferation of NSCLC in a nanomolar range. And CS-6 could induce G2/M cell cycle arrest and apoptosis in A549 cells. However, its molecular mechanism in antitumor activity remains poorly understood. We employed a quantitative proteomics approach to identify the potential cellular targets of CS-6, and found 38 possible target-related proteins. Among them, 31 proteins were closely related in the protein-protein interaction network. One of the regulatory nodes in key pathways was occupied by Hsp90. Molecular docking revealed that CS-6 interacted with the ATP-binding sites of Hsp90. In addition, CS-6 inhibited the chaperone function of Hsp90 and reduced expression of Hsp90-dependent client proteins. Moreover, CS-6 markedly down-regulated the protein level of Hsp90 in tumor tissues of the xenograft mice. Taken together, our results suggest that CS-6 might be a novel inhibitor of Hsp90, and the possible network associated with CS-6 target-related proteins was constructed, which provided experimental evidence for the preclinical value of using CS-6 as an effective antitumor agent in treatment of NSCLC.

Urine gamma-synuclein as a biomarker for the diagnosis of bladder cancer

Gamma-synuclein (SNCG) is secreted from tumor cells and elevated in the urine of bladder cancer (BCa) patients, however, the diagnostic and prognostic values of urine SNCG for BCa remain unknown. Here, we used enzyme immunoassay and western blotting to measure urine SNCG levels. Patients with BCa or other urological diseases and healthy controls were enrolled at four Chinese hospitals from April 2010 to November 2014. Diagnostic performance was evaluated by analyzing the area under receiver operating characteristic curves (AUROCs). The AUROC was 0.903 ± 0.019 (95% confidence interval [CI], 0.867 - 0.940) for the test and 0.929 ± 0.015 (95% CI, 0.901 - 0.958) for the validation cohort. The optimal cutoff value yielded sensitivities of 68.4%, 62.4% and specificities of 97.4%, 97.8% for the test and validation cohort, respectively. Urine SNCG levels were decreased after tumor resection, but were higher in BCa patients with recurrence than those without (P = 0.001). The urine SNCG levels in patients with urological benign diseases were significantly lower than BCa patients (all P < 0.05) but higher than healthy controls (all P < 0.05). Hematuria did not interfere with the SNCG detection by spiking urine specimens with whole blood. Compared with a nuclear-matrix-protein-22 assay in an additional cohort excluding hematuria, SNCG showed a similar sensitivity and higher specificity. In summary, our results demonstrated that urine SNCG can discriminate BCa from urinary diseases, and is a useful prognosticator of postsurgical recurrence.

Looking at the recent advances in understanding α-synuclein and its aggregation through the proteoform prism

Despite attracting the close attention of multiple researchers for the past 25 years, α-synuclein continues to be an enigma, hiding sacred truth related to its structure, function, and dysfunction, concealing mechanisms of its pathological spread within the affected brain during disease progression, and, above all, covering up the molecular mechanisms of its multipathogenicity, i.e. the ability to be associated with the pathogenesis of various diseases. The goal of this article is to present the most recent advances in understanding of this protein and its aggregation and to show that the remarkable structural, functional, and dysfunctional multifaceted nature of α-synuclein can be understood using the proteoform concept.

Synuclein-γ in uterine serous carcinoma impacts survival: An NRG Oncology/Gynecologic Oncology Group study

BACKGROUND

Synuclein-γ (SNCG) is highly expressed in advanced solid tumors, including uterine serous carcinoma (USC). The objective of the current study was to determine whether SNCG protein was associated with survival and clinical covariates using the largest existing collection of USCs from the Gynecologic Oncology Group (GOG-8023).

METHODS

High-density tissue microarrays (TMAs) of tumor tissues from 313 patients with USC were stained by immunohistochemistry for SNCG, p53, p16, FOLR1, pERK, pAKT, ER, PR, and HER2/neu. Associations of SNCG and other tumor markers with overall and progression-free survival were assessed using log-rank tests and Cox proportional-hazards models, which also were adjusted for age, race, and stage.

RESULTS

The overall survival at 5 years was 46% for women with high SNCG expression and 62% for those with low SNCG expression (log-rank P = .021; hazard ratio [HR], 1.31; 95% confidence interval [CI], 0.91-1.9 in adjusted Cox model). The progression-free survival rate at 5 years was worse for women who had high SNCG expression, at 40%, compared with 56% for those who had low SNCG expression (log-rank P = .0081; HR, 1.36; 95% CI, 0.96-1.92 in adjusted Cox model). High levels of both p53 and p16 were significantly associated with worse overall survival (p53: HR, 4.20 [95% CI, 1.54-11.45]; p16: HR, 1.95 [95% CI, 1.01-3.75]) and progression-free survival (p53: HR, 2.16 [95% CI, 1.09-4.27]; p16: HR, 1.53 [95% CI, 0.87-2.69]) compared with low levels.

CONCLUSIONS

This largest collection of USCs to date demonstrates that SNCG was associated with poor survival in univariate analyses. SNCG does not predict survival outcome independent of p53 and p16 in models that jointly consider multiple markers. Cancer 2017;123:1144-1155. © 2016 American Cancer Society.

Gamma-synuclein binds to AKT and promotes cancer cell survival and proliferation

Hyperactivation of AKT plays a critical role in the survival and proliferation of cancer cells. However, the molecular mechanisms underlying AKT activation remain elusive. Here, we tested the effect of γ-synuclein, a member of the synuclein family of proteins, on the activation of AKT. We show that the expression level of γ-synuclein is increased in non-small cell lung cancer (NSCLC) tissues. γ-Synuclein binds to the protein kinase domain of AKT and promotes its phosphorylation. Overexpression of γ-synuclein in H157 cells enhances cell proliferation and protects the cells from staurosporine-induced cytotoxicity. Knockdown of γ-synuclein attenuates AKT activation and cell proliferation induced by epidermal growth factor. The effect of γ-synuclein is abolished when AKT is depleted. Thus, γ-synuclein promotes cell survival and proliferation via activating AKT and may play a causal role in the pathogenesis of NSCLC.

Overexpression of synuclein-γ predicts lack of benefit from radiotherapy for breast cancer patients

Background

Although radiotherapy following mastectomy was demonstrated to reduce the recurring risk and improve the prognosis of patients with breast cancer, it is also notorious for comprehensive side effects, hence only a selected group of patients can benefit. Therefore, the screening of molecular markers capable of predicting the efficacy of radiotherapy is essential.

Methods

We have established a cohort of 454 breast cancer cases and selected 238 patients with indications for postoperative radiotherapy. Synuclein-γ (SNCG) protein levels were assessed by immunohistochemistry, and SNCG status was retrospectively correlated with clinical features and survival in patients treated or not treated with radiotherapy. Gene Set Enrichment Analysis (GSEA) and survival analysis for online datasets were also performed for further validation.

Results

Among patients that received radiotherapy (82/238), those demonstrating positive SNCG expression had a 55.0 month shorter median overall survival (OS) in comparison to those demonstrating negative SNCG expression (78.4 vs. 133.4 months, log rank χ² = 16.13; p < 0.001). Among the patients that received no radiotherapy (156/238), SNCG status was not correlated with OS (log rank χ² = 2.40; p = 0.121). A COX proportional hazard analysis confirmed SNCG as an independent predictor of OS, only for patients who have received radiotherapy. Similar results were also obtained for distant metastasis-free survival (DMFS). A GSEA analysis indicated that SNCG was strongly associated with genes related to a radiation stress response. A survival analysis was performed with online databases consisting of breast cancer, lung cancer, and glioblastoma and further confirmed SNCG’s significance in predicting the survival of patients that have received radiotherapy.

Conclusion

A positive SNCG may serve as a potential marker to identify breast cancer patients who are less likely to benefit from radiotherapy and may also be extended to other types of cancer. However, the role of SNCG in radiotherapy response still needs to be further validated in randomized controlled trials prior to being exploited in clinical practice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2750-y) contains supplementary material, which is available to authorized users.

Role and Characterization of Synuclein-γ Unconventional Protein Secretion in Cancer Cells

Synuclein-γ (SNCG), the third member of synuclein family, is implicated in both neurodegenerative diseases and cancer. Overexpression of SNCG in cancer cells is linked to tumor progression and chemoresistance. Without any known signal sequence required for conventional protein secretion, SNCG is elevated in the serum of cancer patients and the medium of cultured cancer cells. SNCG actively secretes from cancer cells and extracellular SNCG promotes malignant phenotypes of cancer cells. Here, we describe methods for the characterization of SNCG as an unconventional secretion protein from cancer cells and investigation of the effect of extracellular SNCG on the phenotypes of cancer cells.

Structural transition of ETS1 from an auto-inhibited to functional state upon association with the p16INK4anative and mutated promoter region

Detailed elucidation of structural changes invoked on transcriptional factors and their target genes upon their association is pivotal for understanding the genetic level regulations imposed in several diseases including ovarian cancer.

γ-Synuclein Expression Is a Malignant Index in Oral Squamous Cell Carcinoma

Dysregulation of γ-synuclein (SNCG) has been reported in many cancers; however, its role in cancer development is still controversial. Here, we examined the potential involvement of DNA methylation in regulating SNCG and its role in oral squamous cell carcinoma (OSCC). We used 8 OSCC cell lines to investigate SNCG methylation and expression. SNCG methylation was examination by methylation-specific polymerase chain reaction and bisulfate sequencing. Cells showing a high degree of SNCG methylation were treated with 5-aza (methylation inhibitor), and changes in their methylation and expression profiles were analyzed. Functional effects of SNCG in OSCC were examined by its overexpression and knockdown. Additionally, methylation and expression of SNCG in OSCC tissues were investigated and correlated with clinicopathologic features. All OSCC cells showed detectable SNCG expression at the mRNA and protein levels. Methylation-specific polymerase chain reaction and bisulfate sequencing revealed high SNCG expression in SCC25 cells with the unmethylated allele, and their 15 CpG islands were unmethylated. The methylated allele was detected only in OEC-M1 cells exhibiting low SNCG expression, and their CpG islands were partially methylated. 5-aza treatment in OEC-M1 cells attenuated methylation and restored SNCG expression. SNCG overexpression increased colony forming, migration, and invasion abilities in OEC-M1 cells. Silencing SNCG in SCC25 cells suppressed these behaviors. All 25 tumor-adjacent normal tissues were negative for SNCG immunostaining. SNCG upregulation was frequently observed in dysplastic and OSCC tissues. Positive SNCG expression was found in 45% (37 of 82) OSCC tissues. Positive SNCG expression in OSCC significantly correlated with cancer staging and lymph node metastasis. However, SNCG methylation did not correlate with its expression and clinicopathologic variables in OSCC tissues. DNA methylation may participate in regulating SNCG expression in some OSCC cells. SNCG upregulation could be involved in OSCC progression.

Structural insights into tumor-specific chaperoning activity of gamma synuclein in protecting estrogen receptor alpha 36 and its role in tamoxifen resistance in breast cancer

This study investigates structural aspects underlying the chaperoning activity of an intrinsically disordered protein, gamma synuclein, in promoting estrogen mediated breast cancer.