The growth and tumor suppressors NORE1A and RASSF1A are targets for calpain-mediated proteolysis

Hypermethylation of RASSF1A gene in pediatric rhabdoid tumor of the kidney and clear cell sarcoma of the kidney

BACKGROUND

Among pediatric renal tumors, rhabdoid tumor of the kidney (RTK) and clear cell sarcoma of the kidney (CCSK) are rare and associated with an unfavorable prognosis, while congenital mesoblastic nephroma (CMN) is associated with a good prognosis. Methylation of the Ras association domain-containing protein 1 isoform A (RASSF1A) promoter has been reported to correlate with a poor prognosis in patients with Wilms tumors, while its methylation status is unclear in other types of pediatric renal tumors.

METHOD

DNA methylation of the RASSF1A promoter in several pediatric renal tumors was analyzed with pyrosequencing. In order to clarify the correlation between expression of RASSF1A and DNA methylation of its promoter, the RTK cell line was treated with 5-Aza-2'-deoxycytidine (5-Aza-dC). RASSF1A was overexpressed in the RTK cell line to evaluate its functional effects.

RESULTS

Quantitative methylation analysis demonstrated hypermethylation in the RASSF1A promoter region in RTK and CCSK, but not CMN. The 5-Aza-dC treatment induced demethylation of the RASSF1A promoter as well as increased RASSF1A mRNA expression. The transduction of RASSF1A has an effect on the suppression of viability and proliferation of RTK cells.

CONCLUSION

DNA methylation-mediated deficiency of RASSF1A might be involved in the development and aggressiveness of some pediatric renal tumors and correlated with a poor prognosis.

The Role and Function of Ras-association domain family in Cancer: A Review

Ras gene mutation has been observed in more than 30% of cancers, and 90% of pancreatic, lung and colon cancers. Ras proteins (K-Ras, H-Ras, N-Ras) act as molecular switches which are activated by binding to GTP. They play a role in the cascade of cell process control (proliferation and cell division). In the inactive state, transforming GTP to GDP leads to the activation of GTpase in Ras gene. However, the mutation in Ras leads to the loss of internal GTPase activity and permanent activation of the protein. The activated Ras can promote the cell death or stop cell growth, which are facilitated by Ras-association domain family. Various studies have been conducted to determine the importance of losing RASSF proteins in Ras-induced tumors. This paper examines the role of Ras and RASSF proteins. In general, RASSF proteins can be used as a suitable means for targeting a large group of Ras-induced tumors.

The role of the NORE1A tumor suppressor in Oncogene-Induced Senescence

The Ras genes are the most frequently mutated oncogenes in human cancer. However, Ras biology is quite complex. While Ras promotes tumorigenesis by regulating numerous growth promoting pathways, activated Ras can paradoxically also lead to cell cycle arrest, death, and Oncogene-Induced Senescence (OIS). OIS is thought to be a critical pathway that serves to protect cells against aberrant Ras signaling. Multiple reports have highlighted the importance of the p53 and Rb tumor suppressors in Ras mediated OIS. However, until recently, the molecular mechanisms connecting Ras to these proteins remained unknown. The RASSF family of tumor suppressors has recently been identified as direct effectors of Ras. One of these members, NORE1A (RASSF5), may be the missing link between Ras-induced senescence and the regulation of p53 and Rb. This occurs both quantitatively, by promoting protein stability, as well as qualitatively via promoting critical pro-senescent post-translational modifications. Here we review the mechanisms by which NORE1A can activate OIS as a barrier against Ras-mediated transformation, and how this could lead to improved therapeutic strategies against cancers having lost NORE1A expression.

Nonstructural protein 5B promotes degradation of the NORE1A tumor suppressor to facilitate hepatitis C virus replication

Hepatitis C virus (HCV) infection is a common risk factor for the development of liver cancer. The molecular mechanisms underlying this effect are only partially understood. Here, we show that the HCV protein, nonstructural protein (NS) 5B, directly binds to the tumor suppressor, NORE1A (RASSF5), and promotes its proteosomal degradation. In addition, we show that NORE1A colocalizes to sites of HCV viral replication and suppresses the replication process. Thus, NORE1A has antiviral activity, which is specifically antagonized by NS5B. Moreover, the suppression of NORE1A protein levels correlated almost perfectly with elevation of Ras activity in primary human samples. Therefore, NORE1A inactivation by NS5B may be essential for maximal HCV replication and may make a major contribution to HCV-induced liver cancer by shifting Ras signaling away from prosenescent/proapoptotic signaling pathways.

CONCLUSION

HCV uses NS5B to specifically suppress NORE1A, facilitating viral replication and elevated Ras signaling. (Hepatology 2017;65:1462-1477).

Calpain3 is expressed in a proteolitically active form in papillomavirus-associated urothelial tumors of the urinary bladder in cattle

Background

Calpain 3 (Capn3), also named p94, is a skeletal muscle tissue-specific protein known to be responsible for limb-girdle muscular dystrophy type 2A (LGMD2A). Recent experimental studies have hypothesized a pro-apoptotic role of Capn3 in some melanoma cell lines. So far the link between calpain3 and tumors comes from in vitro studies. The objective of this study was to describe Capn3 activation in naturally occurring urothelial tumors of the urinary bladder in cattle.

Methods and Findings

Here we describe, for the first time in veterinary and comparative oncology, the activation of Capn3 in twelve urothelial tumor cells of the urinary bladder of cattle. Capn3 protein was initially identified with nanoscale liquid chromatography coupled with tandem mass spectrometry (nano LC-MS/MS) in a co-immunoprecipitation experiment on E2F3, known to be a transcription factor playing a crucial role in bladder carcinogenesis in humans. Capn3 expression was then confirmed by reverse transcription polymerase chain reaction (RT-PCR). Finally, the Ca²⁺-dependent proteolytic activity of Capn3 was assayed following ion exchange chromatography. Morphologically, Capn3 expression was documented by immunohistochemical methods. In fact numerous tumor cells showed an intracytoplasmic immunoreactivity, which was more rarely evident also at nuclear level. In urothelial tumors, bovine papillomavirus type 2 (BPV-2) DNA was amplified by PCR and the expression of E5 protein, the major oncogenic protein of BVP-2, was detected by western blotting, immunohistochemistry, and immunofluorescence. E2F3 overexpression and pRb protein downregulation were shown by western blotting.

Conclusion

The role of capn3 protein in urothelial cancer of the urinary bladder remains to be elucidated: further studies would be required to determine the precise function of this protease in tumor development and progression. However, we suggest that activated Capn3 may be involved in molecular pathways leading to the overexpression of E2F3, which in turn could be responsible for urothelial tumor cell proliferation also in cattle, though other mechanisms are likely to exist. If further studies corroborate the important role of Capn3 in urothelial tumors of the urinary bladder, cattle with urinary tumors may prove useful as animal model for bladder carcinogenesis.

RASSF2 associates with and stabilizes the proapoptotic kinase MST2

RASSF2 is a tumour suppressor that in common with the rest of the RASSF family contains Ras association and SARAH domains. We identified the proapoptotic kinases, MST1 and MST2, as the most significant binding partners of RASSF2, confirmed the interactions at endogenous levels and showed that RASSF2 immunoprecipitates active MST1/2. We then showed that RASSF2 can be phosphorylated by a co-immunoprecipitating kinase that is likely to be MST1/2. Furthermore, we showed that RASSF2 and MST2 do indeed colocalize, but whereas RASSF2 alone is nuclear, the presence of MST1 or MST2 results in colocalization in the cytoplasm. Expression of RASSF2 (stably in MCF7 or transiently in HEK-293) increases MST2 levels and knockdown of RASSF2 in HEK-293 cells reduces MST2 levels, in addition colorectal tumour cell lines and primary tumours with low RASSF2 levels show decreased MST2 protein levels. This is likely to be mediated by RASSF2-dependent protection of MST2 against proteolytic degradation. Our findings suggest that MST2 and RASSF2 form an active complex in vivo, in which RASSF2 is maintained in a phosphorylated state and protects MST2 from degradation and turnover. Thus, we propose that the frequent loss of RASSF2 in tumours results in the destablization of MST2 and thus decreased apoptotic potential.