Mutational analysis of salvador gene in human carcinomas

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.

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.

Activation of the tumor suppressive Hippo pathway by triptonide as a new strategy to potently inhibit aggressive melanoma cell metastasis

Metastatic melanoma has a very high mortality rate despite the availability of chemotherapy, radiotherapy, and immunotherapy; therefore, more effective therapeutics are needed. The Hippo pathway plays an inhibitory role in melanoma progression, but the tumor suppressors Salvador homolog-1 (SAV1) and large tumor suppressor 1 (LATS1) in this pathway are down-regulated in melanoma. As a result, the downstream oncogenic Yes-associated protein (YAP) is active, resulting in uncontrolled melanoma growth and metastasis. Therapeutics for remedying SAV1 and LATS1 deficiency in melanoma have not yet been reported in the literature. Here, we show that the small molecule triptonide (MW 358 Da) robustly suppressed melanoma cell tumorigenicity, migration, and invasion. Furthermore, triptonide markedly reduced tumor growth and melanoma lung metastasis in tumor-bearing mice with low toxicity. Molecular mechanistic studies revealed that triptonide promoted SAV1 and LATS1 expression, strongly activated the tumor-suppressive Hippo pathway, degraded oncogenic YAP via the lysosomal pathway, and reduced levels of tumorigenic microphthalmia-associated transcription factor (MITF) in melanoma cells. Triptonide also strongly inhibited activation of AKT, a SAV1-binding signaling protein. Collectively, our results conceptually demonstrate that induction of SAV1 and LATS1 expression and activation of the tumor-suppressive Hippo pathway by triptonide potently inhibits aggressive melanoma cell growth and metastasis. These findings suggest a new strategy for developing therapeutics to treat metastatic melanoma and highlight a novel drug candidate against aggressive melanoma.

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.

Filling out the Hippo pathway

How cell numbers are controlled during organ development is a problem that is still in need of answers. Recent studies in Drosophila melanogaster have delineated a novel signalling pathway, the Hippo pathway, which has an important role in restraining cell proliferation and promoting apoptosis in differentiating epithelial cells. Much like cancer cells, cells that contain mutations for components of the Hippo pathway proliferate inappropriately and have a competitive edge in genetically mosaic tissues. Although poorly characterized in mammals, several components of the Hippo pathway seem to be tumour suppressors in humans.