Protein phosphatase PHLPP induces cell apoptosis and exerts anticancer activity by inhibiting Survivin phosphorylation and nuclear export in gallbladder cancer

Long Noncoding RNA NEAT1 Upregulates Survivin and Facilitates Gallbladder Cancer Progression by Sponging microRNA-335

Background

Gallbladder cancer (GBC) is the most common cancer of the biliary tract, but molecularly targeted therapies are not available for GBC. Loss of microRNA (miR)-335 expression may be a useful predictor of clinical outcomes and the reversal of its loss of expression may be a useful treatment strategy for GBC. In this study, we investigated whether a long noncoding RNA, nuclear paraspeckle assembly transcript 1 (NEAT1) sponges miR-335 in GBC cells.

Materials and Methods

Quantitative reverse transcription-polymerase chain reaction (qRT-PCR), Western blotting, and immunohistochemistry were used to determine the expression of miR-335; NEAT1; survivin; and Ki67 in GBC cell lines (GBC-SD and SGC-996) and tissue samples from patients (n = 25). Cell Counting Kit-8, colony-formation, and Transwell migration and invasion assays were performed to measure cell proliferation, migration, and invasion. Bioinformatic analysis and dual-luciferase reporter assays were utilized to analyze correlativity.

Results

miR-335 overexpression resulted in inhibition of GBC cell proliferation and invasion. In addition, knockdown of NEAT1 resulted in downregulation of survivin expression. As NEAT1 competitively “sponges” miR-335, NEAT1 knockdown resulted in inhibited GBC cell proliferation and invasion in vitro and GBC tumor growth in vivo. Furthermore, NEAT1 was found to be upregulated in GBC samples, and its expression was inversely correlated with miR-335 levels, but positively correlated with survivin levels.

Conclusion

These findings indicate that NEAT1 promotes survivin expression by functioning as a competitive endogenous RNA for miR-335 in GBC cells; thus, we have identified a potential biomarker and target for GBC diagnosis and therapy.

Survivin-Based Treatment Strategies for Squamous Cell Carcinoma

Survivin, an anti-apoptotic molecule abundantly expressed in most human neoplasms, has been reported to contribute to cancer initiation and drug resistance in a wide variety of human tumors. Efficient downregulation of survivin can sensitize tumor cells to various therapeutic interventions, generating considerable efforts in its validation as a new target in cancer therapy. This review thoroughly analyzes up-to-date information on the potential of survivin as a therapeutic target for new anticancer treatments. The literature dealing with the therapeutic targeting of survivin will be reviewed, discussing specifically squamous cell carcinomas (SCCs), and with emphasis on the last clinical trials. This review gives insight into the recent developments undertaken in validating various treatment strategies that target survivin in SCCs and analyze the translational possibility, identifying those strategies that seem to be the closest to being incorporated into clinical practice. The most recent developments, such as dominant-negative survivin mutants, RNA interference, anti-sense oligonucleotides, small-molecule inhibitors, and peptide-based immunotherapy, seem to be helpful for effectively downregulating survivin expression and reducing tumor growth potential, increasing the apoptotic rate, and sensitizing tumor cells to chemo- and radiotherapy. However, selective and efficient targeting of survivin in clinical trials still poses a major challenge.

MiR-495 inhibits esophageal squamous cell carcinoma progression by targeting Akt1

MicroRNAs are involved in tumor initiation and progression by regulating oncogenes and tumor suppressor genes. Here we found that miR-495 are lower in clinical ESCC tissues than in adjacent non-tumor tissues. Moreover, the lower miR-495 expression correlated with increased lymph node metastasis (LNM), invasion and TNM stage. miR-495 overexpression predicted a favorable outcome in ESCC patients. miR-495 targeted a site in the 3'-UTR of Akt1, and miR-495 levels correlated inversely with Akt1 protein levels in ESCC tissue samples. Overexpression of miR-495 suppressed cell proliferation, blocked G1/S phase transition, and decreased migration and invasion by two ESCC cell lines in vitro and in vivo. Restoration of Akt1 protein levels in miR-495-overexpressing ESCC cells attenuated the inhibitory effects of miR-495. In addition, miR-495 suppressed cell cycle transition and the EMT signaling pathway through targeting Akt1, thereby inhibiting ESCC cell proliferation, migration, and invasion. Our results suggest that miR-495 may act as a tumor suppressor by targeting Akt1 in ESCC.

SNORA74B gene silencing inhibits gallbladder cancer cells by inducing PHLPP and suppressing Akt/mTOR signaling

Small nucleolar RNAs (snoRNAs) have been implicated in the development of many cancers. We therefore examined the differential expression of snoRNAs between gallbladder cancer (GBC) tissues and matched adjacent non-tumor tissues using expression microarray analysis with confirmation by quantitative real-time PCR (qRT-PCR). Western blot analysis showed that SNORA74B levels were higher in GBC than non-tumor tissues. SNORA74B expression was positively associated with local invasion, advanced TNM stage, CA19-9 level, and Ki67 expression in patients with GBC, while it was negatively associated with expression of PHLPP, an endogenous Akt inhibitor. Moreover, SNORA74B expression was prognostic for overall survival (OS) and disease-free survival (DFS). Functional studies revealed that silencing SNORA74B in GBC cells using sh-SNORA74B suppressed cell proliferation, induced G1 arrest, and promoted apoptosis. Preliminary molecular investigation revealed that SNORA74B silencing inhibited activation of the AKT/mTOR signaling pathway, while increasing PHLPP expression. PHLPP depletion using shRNA abrogated sh-SNORA74B suppression of GBC cell proliferation, indicating that the antitumor effects of SNORA74B silencing were mediated by PHLPP. These findings define the important role of SNORA74B in cell proliferation, cell cycle, and apoptosis of GBC, and suggest that it may serve as a novel target for GBC treatment.

Tumor suppressive protein phosphatases in human cancer: Emerging targets for therapeutic intervention and tumor stratification

Aberrant protein phosphorylation is one of the hallmarks of cancer cells, and in many cases a prerequisite to sustain tumor development and progression. Like protein kinases, protein phosphatases are key regulators of cell signaling. However, their contribution to aberrant signaling in cancer cells is overall less well appreciated, and therefore, their clinical potential remains largely unexploited. In this review, we provide an overview of tumor suppressive protein phosphatases in human cancer. Along their mechanisms of inactivation in defined cancer contexts, we give an overview of their functional roles in diverse signaling pathways that contribute to their tumor suppressive abilities. Finally, we discuss their emerging roles as predictive or prognostic markers, their potential as synthetic lethality targets, and the current feasibility of their reactivation with pharmacologic compounds as promising new cancer therapies. We conclude that their inclusion in clinical practice has obvious potential to significantly improve therapeutic outcome in various ways, and should now definitely be pushed forward.

DUSP1 inhibits cell proliferation, metastasis and invasion and angiogenesis in gallbladder cancer

DUSP1/MKP1 is a dual-specific phosphatase that regulates MAPK activity and is known to play a key role in tumor biology. Its function in gallbladder cancer (GBC) remains largely unknown, however. By exploring its activities in two GBC cell lines (SGC996 and GBC-SD), DUSP1 was found to inhibit GBC cell proliferation, migration and invasion. Moreover, DUSP1 inhibited GBC growth and metastasis in nude mice subcutaneously xenografted with SGC996 cells. The tumor suppression appeared to be mediated via the DUSP1-pERK/MAPK-MMP2 signal pathway. Angiogenesis was associated with the tumor metastasis in the mouse model and was impaired by DUSP1, which suppressed VEGF expression. These results suggest that DUSP1 suppresses GBC growth and metastasis by targeting the DUSP1-pERK-MMP2/VEGF axis. Identification of the DUSP1-pERK-MMP2/VEGF signals may provide new biomarkers and/or therapeutic targets to better suppress GBC metastasis in the future.

Blocking COX-2 induces apoptosis and inhibits cell proliferation via the Akt/survivin- and Akt/ID3 pathway in low-grade-glioma

Approximately half of surgically-treated patients with low-grade-glioma (LGG) suffer recurrence or metastasis. Currently there is no effective drug treatment. While the selective COX-2 inhibitor celecoxib showed anti-neoplastic activity against several malignant tumors, its effects against LGG remain to be elucidated. Ours is the first report that the expression level of COX-2 in brain tissue samples from patients with LGG and in LGG cell lines is higher than in the non-neoplastic region and in normal brain cells. We found that celecoxib attenuated LGG cell proliferation in a dose-dependent manner. It inhibited the generation of prostaglandin E2 and induced apoptosis and cell-cycle arrest. We also show that celecoxib hampered the activation of the Akt/survivin- and the Akt/ID3 pathway in LGGs. These findings suggest that celecoxib may have a promising therapeutic potential and that the early treatment of LGG patients with the drug may be beneficial.

Expression, regulation and function of miR-495 in healthy and tumor tissues

MicroRNA-495 (miR-495) is a small non-coding RNA encoded by a gene located on chromosome 14 (14q32.31). Its expression is regulated by the transcription factors EF12 and EF47, in addition to promoter methylation status and the fusion oncoprotein mixed-lineage leukemia-AF9. Previous studies suggest that miR-495 is involved in various developmental, immunological and inflammatory processes in healthy tissue, and in the proliferation, invasion, metastasis and drug resistance of cancer cells. The role miR-495 serves in tumors is controversial. miR-495 primarily functions as a tumor suppressor; however, in a number of cases it acts as an oncogene. miR-495 has potential applications as a diagnostic and prognostic marker, and as a therapeutic target for genetic and pharmacological manipulation in the treatment of various diseases.

PHLPP negatively regulates cell motility through inhibition of Akt activity and integrin expression in pancreatic cancer cells

Pancreatic adenocarcinoma is currently the fourth leading cause for cancer-related mortality. Malignant progression of pancreatic cancer depends not only on rapid proliferation of tumor cells but also on increased cell motility. In this study, we showed that increased PHLPP expression significantly reduced the rate of migration in pancreatic ductal adenocarcinoma (PDAC) cells whereas knockdown of PHLPP had the opposite effect. In addition, cell motility at the individual cell level was negatively regulated by PHLPP as determined using time-lapse imaging. Interestingly, the expression of β1 and β4 integrin proteins were decreased in PHLPP overexpressing cells and increased in PHLPP knockdown cells whereas the mRNA levels of integrin were not altered by changes in PHLPP expression. In determining the molecular mechanism underlying PHLPP-mediated regulation of integrin expression, we found that inhibition of lysosome activity rescued integrin expression in PHLPP overexpressing cells, thus suggesting that PHLPP negatively controls cell motility by inhibiting Akt activity to promote lysosome-dependent degradation of integrins. Functionally, the increased cell migration observed in PHLPP knockdown cells was effectively blocked by the neutralizing antibodies against β1 or β4 integrin. Taken together, our study identified a tumor suppressor role of PHLPP in suppressing cell motility by negatively regulating integrin expression in pancreatic cancer cells.

MiR-495 functions as an adjuvant to radiation therapy by reducing the radiation-induced bystander effect

The radiation-induced bystander effect (RIBE) is an important factor in tumor radiation therapy because it may increase the probability of normal cellular injury and the likelihood of secondary cancers after radiotherapy. Here, we identified the role of miR-495 in alleviating RIBEs during radiotherapy. Luciferase reporter assay results confirmed that miR-495 regulated endothelial nitric oxide synthase (eNOS) by targeting the Sp1 3'-untranslated region. Consequently, after radiation, tumor cells expressed less eNOS and Sp1 than controls. In vitro cell irradiation data based on flow-cytometric analysis and enzymed linked immunosorbent assay confirmed that nitric oxide (NO) and its downstream product transforming growth factor β1 (TGF-β1) were critical signaling factors contributing to RIBEs. Fewer normal LO₂ liver cells were injured and fewer micronuclei were observed when treated with the medium of the miR-495 overexpressing HepG2 and ZR75-1 tumor cells. Accordingly, treatment with the miR-495 antagomir led to higher NO and TGF-β1 levels and more injured LO₂ cells. In vivo experiments indicated that local irradiation of tumors overexpressing miR-495 produced fewer necrotic foci in non-irradiated liver tissue compared with controls. miR-495 was upregulated in clinical cancer tissues compared with adjacent non-cancerous tissues, and radiation significantly reduced the expression level of miR-495 in carcinoma cell lines. In summary, miR-495 may have promise as an adjuvant for tumor radiation therapy to decrease RIBEs involving the Sp1/eNOS pathway.

High PHLPP expression is associated with better prognosis in patients with resected lung adenocarcinoma

Background

PH domain Leucine-rich-repeats protein phosphatase (PHLPP) is a novel family of Ser/Thr protein dephosphatases that play a critical role in maintaining the balance in cell signaling. PHLPP negatively regulates PI3K/Akt and RAF/RAS/′ signaling activation, which is crucial in development, growth, and proliferation of lung cancer. The aim of this study was to investigate the association of PHLPP expression with biological behavior and prognosis of lung adenocarcinoma.

Methods

One hundred and fifty eight patients with pathologically documented stage I, II or IIIA lung adenocarcinoma were recruited in this study. Expression of PHLPP, p-AKT and p-ERK were evaluated by immunohistochemistry (IHC) in paraffin-embedded resected specimens. The correlation of their expression, which was dichotomized to low expression (a score of 0, 1) versus high expression (a score of 2, 3), with the clinicopathological parameters and prognosis of the patients also analyzed.

Results

High PHLPP expression rate in lung adenocarcinoma was 23.4 %. PHLPP expression level was significantly associated with tumor differentiation (p = 0.025) and tumor stage (p = 0.024). Patients with high expression of PHLPP showed significantly longer average survival time and higher 3 years survival rate than those with low expression of PHLPP (45 months versus 38 months, 85.8 % versus 73.5 % respectively) (Log rank test x² = 7.086, p =0.008). A significant inverse correlation was observed between PHLPP expression and p-AKT (r = −0.523, p = 0.000) or p-ERK (r = −0.530, p = 0.000).

Conclusion

Our results suggest that high levels of PHLPP might reflect a less aggressive lung adenocarcinoma phenotype and predict better survival in patients with lung adenocarcinoma. PHLPP can be a potential prognostic marker to screen patients for favorable prognoses.

Survivin in survival of hepatocellular carcinoma

Survivin is an anti-apoptotic protein belonging to the inhibitor of apoptosis protein (IAP) family. It is involved in the regulation of important physiological and pathological processes in cells and functions to inhibit cell apoptosis and promote cell proliferation. Normally and terminally differentiated tissues are nearly negative for survivin. In contrast, survivin is highly expressed in most human tumor tissues, including hepatocellular carcinoma (HCC). The abnormal overexpression of survivin is closely related to the malignant biological behaviors of tumors. During the development and progression of HCC, the high level of survivin expression promotes cancer cell proliferation, inhibits cancer cell apoptosis, induces tumor stromal angiogenesis, reduces the sensitivity of cancer cells to radiotherapy and chemotherapy, and ultimately affects the prognosis of patients with HCC. Survivin expression is regulated by a large number of factors. The latest discovery indicated that the transcription factor octamer-binding transcription factor 4 (OCT4) enhances the expression of survivin though cyclin D1 (CCND1), which, in part, accounts for tumor cell proliferation, recurrence and metastasis. Survivin plays key roles in HCC, which renders it an ideal target for the treatment of HCC. The present article reviews the research progress on the relationship between survivin and HCC and on the HCC treatment strategies targeting survivin.