The tumor suppressor RASSF1A is a novel effector of small G protein Rap1A

RASSF effectors couple diverse RAS subfamily GTPases to the Hippo pathway

Small guanosine triphosphatases (GTPases) of the RAS superfamily signal by directly binding to multiple downstream effector proteins. Effectors are defined by a folded RAS-association (RA) domain that binds exclusively to GTP-loaded (activated) RAS, but the binding specificities of most RA domains toward more than 160 RAS superfamily GTPases have not been characterized. Ten RA domain family (RASSF) proteins comprise the largest group of related effectors and are proposed to couple RAS to the proapoptotic Hippo pathway. Here, we showed that RASSF1-6 formed complexes with the Hippo kinase ortholog MST1, whereas RASSF7-10 formed oligomers with the p53-regulating effectors ASPP1 and ASPP2. Moreover, only RASSF5 bound directly to activated HRAS and KRAS, and RASSFs did not augment apoptotic induction downstream of RAS oncoproteins. Structural modeling revealed that expansion of the RASSF effector family in vertebrates included amino acid substitutions to key residues that direct GTPase-binding specificity. We demonstrated that the tumor suppressor RASSF1A formed complexes with the RAS-related GTPases GEM, REM1, REM2, and the enigmatic RASL12. Furthermore, interactions between RASSFs and RAS GTPases blocked YAP1 nuclear localization. Thus, these simple scaffolds link the activation of diverse RAS family small G proteins to Hippo or p53 regulation.

Decreased expression of miR-410-3p correlates with poor prognosis and tumorigenesis in human glioma

Background

Gliomas are the most common type of primary tumors in the central nervous system. This study aimed to investigate the biological role of miR-410-3p in glioma and elucidate the potential molecular mechanisms involved.

Methods

The expression levels of miR-410-3p in clinical tissue samples and glioma cell lines were determined using qRT-PCR analysis. The clinical significance of miR-410-3p in glioma was evaluated using Kaplan-Meier survival analysis and Fisher’s exact test. The effects of miR-410-3p on glioma cell proliferation, apoptosis, migration and invasion were investigated using MTT assays, flow cytometry, transwell migration and invasion assays. Besides, corresponding mechanistic studies were carried out.

Results

miR-410-3p was significantly down-regulated in glioma tissues. Besides, Kaplan-Meier analysis demonstrated that patients with low miR-410-3p expression had a shorter overall survival. Decreased miR-410-3p expression was associated with larger tumor size, lower Karnofsky performance score (KPS), and higher World Health Organization (WHO) grade. Over-expression of miR-410-3p suppressed cell proliferation, migration, and invasion, and accelerated apoptosis; whereas depletion of miR-410-3p facilitated cell proliferation, migration, and invasion, and inhibited apoptosis. Mechanistic investigations demonstrated that Ras-related protein 1A (RAP1A) was a direct target of miR-410-3p, and that rescue of RAP1A expression reversed miR-410-3p over-expression-induced inhibitory effects on cell proliferation, migration, and invasion. Notably, miR-410-3p over-expression repressed tumor growth in mouse xenograft models.

Conclusion

Our findings indicate that miR-410-3p functions as a tumor suppressor in glioma by directly targeting RAP1A. Thus, this study may provide some new insights into gliomagenesis and progression.

RASSF1A, puppeteer of cellular homeostasis, fights tumorigenesis, and metastasis-an updated review

The Ras association domain family protein1 isoform A (RASSF1A) is a well-known tumor-suppressor protein frequently inactivated in various human cancers. Consistent with its function as a molecular scaffold protein, referred to in many studies, RASSF1A prevents initiation of tumorigenesis, growth, and dissemination through different biological functions, including cell cycle arrest, migration/metastasis inhibition, microtubular stabilization, and apoptosis promotion. As a regulator of key cancer pathways, namely Ras/Rho GTPases and Hippo signaling without ignoring strong interaction with microtubules, RASSF1A is indeed one of the guardians of cell homeostasis. To date, as we approach the two decade anniversary of RASSF1A's discovery, this review will summarize our current knowledge on the RASSF1A key interactions as a tumor suppressor and discuss their impact on cell fate during carcinogenesis. This could facilitate a deeper understanding of tumor development and provide us with new strategies in cancer treatment by targeting the RASSF1A pathway.

Modulator of apoptosis 1 (MOAP-1) is a tumor suppressor protein linked to the RASSF1A protein

Modulator of apoptosis 1 (MOAP-1) is a BH3-like protein that plays key roles in cell death or apoptosis. It is an integral partner to the tumor suppressor protein, Ras association domain family 1A (RASSF1A), and functions to activate the Bcl-2 family pro-apoptotic protein Bax. Although RASSF1A is now considered a bona fide tumor suppressor protein, the role of MOAP-1 as a tumor suppressor protein has yet to be determined. In this study, we present several lines of evidence from cancer databases, immunoblotting of cancer cells, proliferation, and xenograft assays as well as DNA microarray analysis to demonstrate the role of MOAP-1 as a tumor suppressor protein. Frequent loss of MOAP-1 expression, in at least some cancers, appears to be attributed to mRNA down-regulation and the rapid proteasomal degradation of MOAP-1 that could be reversed utilizing the proteasome inhibitor MG132. Overexpression of MOAP-1 in several cancer cell lines resulted in reduced tumorigenesis and up-regulation of genes involved in cancer regulatory pathways that include apoptosis (p53, Fas, and MST1), DNA damage control (poly(ADP)-ribose polymerase and ataxia telangiectasia mutated), those within the cell metabolism (IR-α, IR-β, and AMP-activated protein kinase), and a stabilizing effect on microtubules. The loss of RASSF1A (an upstream regulator of MOAP-1) is one of the earliest detectable epigenetically silenced tumor suppressor proteins in cancer, and we speculate that the additional loss of function of MOAP-1 may be a second hit to functionally compromise the RASSF1A/MOAP-1 death receptor-dependent pathway and drive tumorigenesis.

PLCɛ and the RASSF family in tumour suppression and other functions

Not all proteins implicated in direct binding to Ras appear to have a positive role in the generation and progression of tumours; examples include Phospholipase C epsilon (PLCɛ) and some members of the Ras-association domain family (RASSF). The RASSF family comprises of ten members, known as RASSF1 to RASSF10. PLCɛ and RASSF members carry a common Ras-association domain (RA) that can potentially bind Ras oncoproteins and mediate Ras-regulated functions. RASSF1 to RASSF6 also share a common SARAH domain that facilitates protein-protein interactions with other SARAH domain proteins. The majority of the family are frequently downregulated by epigenetic silencing in cancers. They are implicated in various important biological processes including apoptosis, microtubule stabilisation and cell cycle regulation. Recent studies have reinforced the tumour suppressive properties of the RASSF family, with new evidence of emerging pathways and novel functions that suggest a wider role for these proteins. This review will first describe an emerging role of PLCɛ in tumour suppression and then focus on and summarise the new findings on the RASSF family in the last five years to consolidate their well-established functions, and highlight the new regulatory roles of specific RASSF members.

Galectin-1 is up-regulated by RASSF1A gene in human gastric carcinoma cell line SGC7901

We have previously shown that overexpression of RASSF1A inhibits the growth of human gastric cancer SGC7901 cells, but the underlying mechanism remains unknown. In this study, the differential protein expression by RASSF1A gene in human gastric cancer cell line SGC7901 was determined by 2-D gel electrophoresis combined with matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and bioinformatics. Differential expression analysis of the protein profiles by RASSF1A gene identified a total of 35 protein spots, of which 10 were up-regulated and 25 were down-regulated. Eight proteins were identified by MALDI-TOF MS: Galectin-1, TRP-14, ACBP, PSMB5, PSMB4, TIM, vimentin, CD79α. RASSF1A up-regulated the mRNA expression of Galectin-1, TRP-14, ABCP in SGC7901. RASSF1A also led to an increased expression of Galectin-1 protein in SGC7901 confirmed by western blotting and immunocytochemistry analysis. RASSF1A inhibited the activity of NF-κB in SGC7901 cells. These data indicated that Galectin-1 may be playing a role in RASSF1A signaling in SGC7901.