Expression profile and prognostic value of SAV1 in patients with pancreatic ductal adenocarcinoma

Impaired Expression of the Salvador Homolog-1 Gene Is Associated with the Development and Progression of Colorectal Cancer

Salvador homolog-1 (SAV1) is a component of the Hippo pathway that regulates tissue growth and homeostasis by affecting diverse cell processes, including apoptosis, cell division, and differentiation. The aberrant expression of Hippo pathway components has been observed in various human cancers. This study aimed to examine the expression level of the SAV1 gene in colorectal cancer (CRC) and its prognostic value and associations with tumor progression. We obtained matched pairs of tumor tissue and non-cancerous mucosa of the large intestine from 94 CRC patients as well as 40 colon biopsies of healthy subjects collected during screening colonoscopy. The tissue samples and CRC cell lines were quantified for SAV1 mRNA levels using the quantitative polymerase chain reaction method, while SAV1 protein expression was estimated in the paired tissues of CRC patients using immunohistochemistry. The average level of SAV1 mRNA was decreased in 93.6% of the tumor tissues compared to the corresponding non-cancerous tissues and biopsies of healthy colon mucosa. A downregulated expression of SAV1 mRNA was also noted in the CRC cell lines. Although the average SAV1 immunoreactivity was increased in the CRC samples compared to the non-cancerous tissues, a decreased immunoreactivity of the SAV1 protein in the tumor specimens was associated with lymph node involvement and higher TNM disease stage and histological grade. The results of our study suggest that the impaired expression of SAV1 is involved in CRC progression.

Profiles of Expression of SAV1 in Normoxia or Hypoxia Microenviroment are Associated with Breast Cancer Prognosis

BACKGROUND

In breast cancer (BC), hypoxia is associated with poor prognosis. Protein Salvador homolog 1 (SAV1) acts as a tumor suppressor and is downregulated in the cancer cells. However, there is limited data on the expression profile of SAV1 and its importance in BC. It has not been studied to evaluate this phenomenon in a hypoxic microenvironment yet.

AIM

This study aimed to investigate SAV1 expression profiles under normoxia and hypoxia, and the potential of SAV1 in BC prognosis.

METHODS

Gene and protein expression analyses were performed using Real-Time quantitative PCR (RT-qPCR) and immunocytochemistry (ICC), respectively, and in silico analyses were performed using The Cancer Genome Atlas (TCGA). The survival curves were constructed using KMplotter.

RESULTS

SAV1 expression was lower in BC samples and tumor cell lines than in normal samples. The SAV1 mRNA levels were reduced in hypoxic estrogen receptor positive (ER⁺) tumors, which were associated with a lower survival probability as compared to normoxic ER⁺ tumors. Furthermore, lower levels of SAV1 were found in advanced cancer stage samples, which are associated with worse survival curves and can be a risk factor for BC.

CONCLUSIONS

These data suggest a potential prognostic role of SAV1 in BC, with lower expressions associated with worse prognosis.

Dysregulation of PI3K and Hippo signaling pathways synergistically induces chronic pancreatitis via CTGF upregulation

The role of PI3K and Hippo signaling in chronic pancreatitis (CP) pathogenesis is unclear. Therefore, we assessed the involvement of these pathways in CP by examining the PI3K and Hippo signaling components PTEN and SAV1, respectively. We observed significant decreases in pancreatic PTEN and SAV1 levels in 2 murine CP models: repeated cerulein injection and pancreatic ductal ligation. Additionally, pancreas-specific deletion of Pten and Sav1 (DKO) induced CP in mice. Pancreatic connective tissue growth factor (CTGF) was markedly upregulated in both CP models and DKO mice, and pancreatic CCAAT/enhancer-binding protein-α (CEBPA) expression was downregulated in the CP models. Interestingly, in pancreatic acinar cells (PACs), CEBPA knockdown reduced PTEN and SAV1 and increased CTGF levels in vitro. Furthermore, CEBPA knockdown in PACs induced acinar-to-ductal metaplasia and activation of cocultured macrophages and pancreatic stellate cells. These results were mitigated by CTGF inhibition. CP in DKO mice was also ameliorated by Ctgf gene deletion, and cerulein-induced CP was alleviated by antibody-mediated CTGF neutralization. Finally, we observed significantly decreased PTEN, SAV1, and CEBPA and increased CTGF levels in human CP tissues compared with nonpancreatitis tissues. Taken together, our results indicate that dysregulation of PI3K and Hippo signaling induces CP via CTGF upregulation.

A WW Tandem-Mediated Dimerization Mode of SAV1 Essential for Hippo Signaling

The canonical mammalian Hippo pathway contains a core kinase signaling cascade requiring upstream MST to form a stable complex with SAV1 in order to phosphorylate the downstream LATS/MOB complex. Though SAV1 dimerization is essential for the trans-activation of MST, the molecular mechanism underlying SAV1 dimerization is unclear. Here, we discover that the SAV1 WW tandem containing a short Pro-rich extension immediately following the WW tandem (termed as "WW12ex") forms a highly stable homodimer. The crystal structure of SAV1 WW12ex reveals that the Pro-rich extension of one subunit binds to both WW domains from the other subunit. Thus, SAV1 WW12ex forms a domain-swapped dimer instead of a WW2 homodimerization-mediated dimer. The WW12ex-mediated dimerization of SAV1 is required for the MST/SAV1 complex assembly and MST kinase activation. Finally, we show that several cancer-related SAV1 variants disrupt SAV1 dimer formation, and thus, these mutations may impair the tumor-suppression activity of SAV1.

The tumor suppressor role of salvador family WW domain-containing protein 1 (SAV1): one of the key pieces of the tumor puzzle

PURPOSE

In the complex tumor scenario, understanding the function of proteins with protumor or antitumor roles is essential to support advances in the cancer clinical area. Among them, the salvador family WW domain-containing protein 1 (SAV1) is highlighted. This protein plays a fundamental role in the tumor suppressor face of the Hippo pathway, which are responsible for controlling cell proliferation, organ size, development and tissue homeostasis. However, the functional dysregulation of this pathway may contribute to tumorigenesis and tumor progression. As SAV1 is a tumor suppressor scaffold protein, we explored the functions performed by SAV1 with its partners, the regulation of its expression, and its antitumor role in various types of cancer.

METHODS

We selected and analyzed 80 original articles and reviews from Pubmed that focuses on the study of SAV1 in cancer.

RESULTS

SAV1 interacts with several proteins, has different functions and acts as tumor suppressor by other mechanisms besides Hippo pathway. SAV1 expression regulation seems to occur by microRNAs and rarely by mutation or promoter methylation. It is downregulated in different types of cancer, which leads to cancer promotion and progression and is associated with poor prognosis. In vivo models have shown that the loss of SAV1 contributes to tumorigenesis.

CONCLUSION

SAV1 plays a relevant role as tumor suppressor in several types of cancer, highlighting SAV1 and the Hippo pathway's importance to cancer. Thus, encouraging further studies to include the SAV1 as a molecular key piece in cancer biology and in clinical approaches to cancer.

Correction of the tumor suppressor Salvador homolog-1 deficiency in tumors by lycorine as a new strategy in lung cancer therapy

Salvador homolog-1 (SAV1) is a tumor suppressor required for activation of the tumor-suppressive Hippo pathway and inhibition of tumorigenesis. SAV1 is defective in several cancer types. SAV1 deficiency in cells promotes tumorigenesis and cancer metastasis, and is closely associated with poor prognosis for cancer patients. However, investigation of therapeutic strategies to target SAV1 deficiency in cancer is lacking. Here we found that the small molecule lycorine notably increased SAV1 levels in lung cancer cells by inhibiting SAV1 degradation via a ubiquitin-lysosome system, and inducing phosphorylation and activation of the SAV1-interacting protein mammalian Ste20-like 1 (MST1). MST1 activation then caused phosphorylation, ubiquitination, and degradation of the oncogenic Yes-associated protein (YAP), therefore inhibiting YAP-activated transcription of oncogenic genes and tumorigenic AKT and NF-κB signal pathways. Strikingly, treating tumor-bearing xenograft mice with lycorine increased SAV1 levels, and strongly inhibited tumor growth, vasculogenic mimicry, and metastasis. This work indicates that correcting SAV1 deficiency in lung cancer cells is a new strategy for cancer therapy. Our findings provide a new platform for developing novel cancer therapeutics.

SAV1, regulated by microRNA-21, suppresses tumor growth in colorectal cancer

This study investigated the role and action of the Salvador 1 protein (SAV1, also called WW45) in colorectal cancer (CRC). For this, CRC SW480 and HCT116 cells were infected with lentiviruses of SAV1 overexpression vector (lenti-SAV1) and SAV1 short hairpin RNA (sh-SAV1) to overexpress and silence SAV1 respectively, or transfected with microRNA-21 (miR-21) mimic to overexpress miR-21. Relative mRNA levels of SAV1 and relative miR-21 levels in CRC tissues or cells were detected. The effects of SAV1 and miR-21 on cell proliferation and apoptosis were evaluated using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and annexin V – fluorescein isothiocyanate (FITC) – propidium iodide (PI) flow cytometry, respectively. Our results revealed that SAV1 was downregulated in CRC tissues compared with the adjacent noncancerous tissues. Furthermore, SAV1 overexpression inhibited proliferation and promoted apoptosis in SW480 and HCT116 cells, whereas knockdown of SAV1 exerted the opposite effect. Additionally, the tumorigenesis of SW480 cells in xenografted mice was significantly inhibited by SAV1 overexpression but promoted by SAV1 knockdown. MiR-21 levels significantly and negatively correlated with SAV1 expression in CRC tissues. More importantly, miR-21 overexpression significantly abolished the SAV1-mediated inhibition of proliferation and stimulation of apoptosis of SW480. In conclusion, SAV1 suppresses tumor growth in CRC and is regulated by miR-21.

Hippo pathway affects survival of cancer patients: extensive analysis of TCGA data and review of literature

The disruption of the Hippo pathway occurs in many cancer types and is associated with cancer progression. Herein, we investigated the impact of 32 Hippo genes on overall survival (OS) of cancer patients, by both analysing data from The Cancer Genome Atlas (TCGA) and reviewing the related literature. mRNA and protein expression data of all solid tumors except pure sarcomas were downloaded from TCGA database. Thirty-two Hippo genes were considered; for each gene, patients were dichotomized based on median expression value. Survival analyses were performed to identify independent predictors, taking into account the main clinical-pathological features affecting OS. Finally, independent predictors were correlated with YAP1 oncoprotein expression. At least one of the Hippo genes is an independent prognostic factor in 12 out of 13 considered tumor datasets. mRNA levels of the independent predictors coherently correlate with YAP1 in glioma, kidney renal clear cell, head and neck, and bladder cancer. Moreover, literature data revealed the association between YAP1 levels and OS in gastric, colorectal, hepatocellular, pancreatic, and lung cancer. Herein, we identified cancers in which Hippo pathway affects OS; these cancers should be candidates for YAP1 inhibitors development and testing.

Deubiquitinating Enzyme USP9X Suppresses Tumor Growth via LATS Kinase and Core Components of the Hippo Pathway

The core LATS kinases of the Hippo tumor suppressor pathway phosphorylate and inhibit the downstream transcriptional co-activators YAP and TAZ, which are implicated in various cancers. Recent studies have identified various E3 ubiquitin ligases that negatively regulate the Hippo pathway via ubiquitination, yet few deubiquitinating enzymes (DUB) have been implicated. In this study, we report the DUB USP9X is an important regulator of the core kinases of this pathway. USP9X interacted strongly with LATS kinase and to a lesser extent with WW45, KIBRA, and Angiomotin, and LATS co-migrated exclusively with USP9X during gel filtration chromatography analysis. Knockdown of USP9X significantly downregulated and destabilized LATS and resulted in enhanced nuclear translocation of YAP and TAZ, accompanied with activation of their target genes. In the absence of USP9X, cells exhibited an epithelial-to-mesenchymal transition phenotype, acquired anchorage-independent growth in soft agar, and led to enlarged, disorganized, three-dimensional acini. YAP/TAZ target gene activation in response to USP9X knockdown was suppressed by knockdown of YAP, TAZ, and TEAD2. Deletion of USP9X in mouse embryonic fibroblasts resulted in significant downregulation of LATS. Furthermore, USP9X protein expression correlated positively with LATS but negatively with YAP/TAZ in pancreatic cancer tissues as well as pancreatic and breast cancer cell lines. Overall, these results strongly indicate that USP9X potentiates LATS kinase to suppress tumor growth. Cancer Res; 77(18); 4921-33. ©2017 AACR.

SAV1 represses the development of human colorectal cancer by regulating the Akt-mTOR pathway in a YAP-dependent manner

OBJECTIVES

SAV1 is a human homologue of Salvador that contains two protein-protein interaction modules known as WW domains and acts as a scaffolding protein. SAV1 participates in the development of diverse types of cancer. We aimed to investigate the role of SAV1 in human colorectal cancer.

MATERIALS AND METHODS

Human colorectal cancer samples were used to study the expression of SAV1 and YAP. Loss-of-function and gain-of-function strategies were used to study the effects of SAV1 on colorectal cancer cell growth. Rapamycin was used to treat cells and mice to investigate the effect of mTOR signalling.

RESULTS

SAV1 represses the development of colorectal cancer by inhibiting the Akt-mTOR signalling in a YAP-dependent manner. The mRNA and protein levels of SAV1 are down-regulated in human colorectal cancer tissues compared with adjacent non-cancer tissues. SAV1 knockdown promotes the growth of colorectal cancer cells in vitro and in vivo, whereas SAV1 overexpression leads to opposing results. SAV1 represses the activation of the Akt-mTOR signalling, and rapamycin treatment blunts the effects of SAV1 on in vitro and in vivo growth of colorectal cancer cells. Finally, we show that SAV1 promotes the phosphorylation and inactivation of YAP, which contributes to the effect of SAV1 on Akt-mTOR signalling pathway.

CONCLUSIONS

SAV1 is a repressor during the development of human colorectal cancer by inhibiting the YAP-Akt-mTOR signalling pathway.