RASSF6; the Putative Tumor Suppressor of the RASSF Family

Revealing the Roles of MOAP1 in Diseases: A Review

Modulator of apoptosis protein1 (MOAP1), also known as MAP1 and PNMA4, belongs to the PNMA gene family consisting of at least 15 genes located on different chromosomes. MOAP1 interacts with the BAX protein, one of the most important apoptosis regulators. Due to its critical role in a few of disease-associated pathways, MOAP1 is associated with many diseases such as cancers and neurological diseases. In this study, we introduced MOAP1 and its biological functions and reviewed the associations between MOAP1 and a few diseases including cancers, neurological diseases, and other diseases such as inflammation and heart diseases. We also explained possible biological mechanisms underlying the associations between MOAP1 and these diseases, and discussed a few future directions regarding MOAP1, especially its potential roles in neurodegenerative disorders. In summary, MOAP1 plays a critical role in the development and progression of cancers and neurological diseases by regulating a few genes related to cellular apoptosis such as BAX and RASSF1A and interacting with disease-associated miRNAs, including miR-25 and miR1228.

DNA damage triggers the nuclear accumulation of RASSF6 tumor suppressor protein via CDK9 and BAF53 to regulate p53-target gene transcription

RASSF6, a member of the tumor suppressor Ras-association domain family (RASSF) proteins, regulates cell cycle arrest and apoptosis via p53 and plays a tumor suppressor role. We previously reported that RASSF6 blocks MDM2-mediated p53 degradation and enhances p53 expression. In this study, we demonstrated that RASSF6 has nuclear-localization and nuclear-export signals and that DNA damage triggers the nuclear accumulation of RASSF6. We found that RASSF6 directly binds to BAF53, the component of SWI/SNF complex. DNA damage induces CDK9-mediated phosphorylation of BAF53, which enhances the interaction with RASSF6 and increases the amount of RASSF6 in the nucleus. Subsequently, RASSF6 augments the interaction between BAF53 and BAF60a, another component of SWI/SNF complex, and further promotes the interaction of BAF53 and BAF60a with p53. BAF53 silencing or BAF60a silencing attenuates RASSF6-mediated p53-target gene transcription and apoptosis. Thus, RASSF6 is involved in the regulation of DNA damage-induced complex formation including CDK9, BAF53, BAF60a, and p53.

Characterization of mouse embryonic fibroblasts derived from Rassf6 knockout mice shows the implication of Rassf6 in the regulation of NF-κB signaling

RASSF6 is a member of the tumor suppressor Ras association domain family (RASSF) proteins. We have reported using human cancer cell lines that RASSF6 induces apoptosis and cell cycle arrest via p53 and plays tumor suppressive roles. In this study, we generated Rassf6 knockout mice by CRISPR/Cas technology. Contrary to our expectation, Rassf6 knockout mice were apparently healthy. However, Rassf6-null mouse embryonic fibroblasts (MEF) were resistant against ultraviolet (UV)-induced apoptosis/cell cycle arrest and senescence. UV-induced p53-target gene expression was compromised, and DNA repair was delayed in Rassf6-null MEF. More importantly, KRAS active mutant promoted the colony formation of Rassf6-null MEF but not the wild-type MEF. RNA sequencing analysis showed that NF-κB signaling was enhanced in Rassf6-null MEF. Consistently, 7,12-dimethylbenz(a)anthracene (DMBA) induced skin inflammation in Rassf6 knockout mice more remarkably than in the wild-type mice. Hence, Rassf6 deficiency not only compromises p53 function but also enhances NF-κB signaling to lead to oncogenesis.

Down-regulation of circITCH promotes osteosarcoma development and resistance to doxorubicin via the miR-524/RASSF6 axis

BACKGROUND

Osteosarcoma (OS) is a malignant bone cancer, in which circular RNAs (circRNAs) act as important modulators. The present study aimed to explore the functional role of circRNA itchy E3 ubiquitin protein ligase (circITCH) in the development and doxorubicin (DXR) resistance of OS and the possible mechanistic pathway.

METHODS

A quantitative real-time polymerase chain reaction or western blot assays were exploited to analyze the expression of circITCH, miR-524 and Ras association domain family member 6 (RASSF6). Cell viability and half-maximal inhibitory concentration (IC₅₀ ) value of DXR were monitored using a cell counting kit-8 assay. Cell migration, invasion and apoptosis were determined via a transwell assay and flow cytometry. The target interaction among circITCH, miR-524 and RASSF6 was validated by dual-luciferase reporter and RNA immunoprecipitation assays. A xenograft model of MG-63/DXR cells stably expressing circITCH in nude mice was established for assessing the role of circITCH in vivo.

RESULTS

Down-regulation of circITCH and RASSF6, as well as the up-regulation of miR-524, was revealed in OS by investigating 40 paired OS tissue and normal tissue samples. Overexpression of circITCH lowered the cell viability, IC₅₀ value of DXR, migration and invasion, whereas it facilitated apoptosis of OS cells. circITCH sponged miR-524 to up-regulate RASSF6, causing OS progression inhibition and DXR resistance reduction. Additionally, circITCH up-regulation reduced tumor growth in vivo.

CONCLUSIONS

Transduction with circITCH represses OS progression and promotes DXR sensitivity by the miR-524/RASSF6 axis, providing a new perspective for therapeutic intervention.

Methylation as a critical epigenetic process during tumor progressions among Iranian population: an overview

Cancer is one of the main health challenges and leading causes of deaths in the world. Various environmental and genetic risk factors are associated with tumorigenesis. Epigenetic deregulations are also important risk factors during tumor progression which are reversible transcriptional alterations without any genomic changes. Various mechanisms are involved in epigenetic regulations such as DNA methylation, chromatin modifications, and noncoding RNAs. Cancer incidence and mortality have a growing trend during last decades among Iranian population which are significantly related to the late diagnosis. Therefore, it is required to prepare efficient molecular diagnostic panels for the early detection of cancer in this population. Promoter hyper methylation is frequently observed as an inhibitory molecular mechanism in various genes associated with DNA repair, cell cycle regulation, and apoptosis during tumor progression. Since aberrant promoter methylations have critical roles in early stages of neoplastic transformations, in present review we have summarized all of the aberrant methylations which have been reported during tumor progression among Iranian cancer patients. Aberrant promoter methylations are targetable and prepare novel therapeutic options for the personalized medicine in cancer patients. This review paves the way to introduce a non-invasive methylation specific panel of diagnostic markers for the early detection of cancer among Iranians.

lncRNA TUSC7 inhibits osteosarcoma progression through the miR‑181a/RASSF6 axis

Osteosarcoma (OS) is one of the most aggressive malignancies, accompanied by an elevated incidence and a decreased rate of healing. Recently, several long non-coding RNAs (lncRNAs) have been reported to be involved in OS progression. Although tumor suppressor candidate 7 (TUSC7) was reported as a novel lncRNA, little is known about its biological functions in OS. The present study was designed to explore whether TUSC7 was involved in the pathological development of OS using various methods, including hematoxylin and eosin staining, Cell Counting Kit-8 assay, colony formation assay and Transwell assay. The present study revealed that TUSC7 expression was downregulated in OS tissues and cell lines compared with in normal tissues and cell lines. Functionally, the current results revealed that overexpression of TUSC7 inhibited OS cell proliferation, migration and invasion, while promoting apoptosis in vitro and in vivo. Next, the subcellular distribution of TUSC7 was examined by nuclear/cytoplasmic RNA fractionation and reverse transcription-quantitative PCR. Mechanistic studies revealed that TUSC7 exerted its role by sponging microRNA (miR)-181a in OS cell lines. Ras association domain family member 6 (RASSF6) was confirmed as a target gene of miR-181a, and the expression levels of RASSF6 were negatively regulated by miR-181a. Additionally, the results of rescue experiments suggested that overexpression of miR-181a neutralized the inhibitory effects of TUSC7 overexpression on OS cells. Overall, the present study demonstrated that the tumor suppressor role of TUSC7 in OS progression was mediated through the miR-181a/RASSF6 axis, which may represent a new therapeutic target for OS.

RASSF10 regulates bone invasion of growth hormone-secreting adenomas via exosomes

BACKGROUND

Invasion of pituitary growth hormone-secreting adenoma into surrounding tissues poses a challenge for complete resection in surgery, which is the main reason for recurrence of this type of cancer. Studies have shown that abnormal methylation of RASSF10 can promote the expression of MDM2 and regulate the tumor microenvironment by affecting the secretion of exosomes. In the present study, we aim to uncover the specific underlying mechanism of this effect.

METHOD

Transwell co-culture assays was performed using GT1.1 cells or exosomes and RAW264.7 cells. RAW264.7 cells were collected for invasion, proliferation and apoptosis assays, RT-qPCR and western blotting. RNA-seq was performed and used to assess the potential molecular pathways of the effect of GT1.1 cell-exosomes on RAW264.7 cells.

RESULTS

GT1.1 cells with reduced RASSF10 expression could promote the proliferation and migration of RAW264.7 cells, and promote their expression of osteoclast markers TRAP and CK. The effect of GT1.1 cell exosomes on the RAW264.7-cell phenotype was shown to be achieved through the RASSF10-MDM2 pathway. RNA-seq allowed the identification of PI3K-AKT, MAPK, and calcium signaling as important in this regulation system of RASSF10-MDM2.

CONCLUSION

Our results indicate that GT1.1 cells activate PI3K-AKT, MAPK and calcium signaling via the RASSF10-MDM2 pathway, and promote the differentiation of RAW264.7 cells into osteoclasts through exosomes. This study may provide new ideas to aid in early diagnosis, prognostic assessment and treatment of aggressive pituitary adenomas.

MiR-496 promotes migration and epithelial-mesenchymal transition by targeting RASSF6 in colorectal cancer

Aberrant loss of tumor-suppressor genes plays a crucial role in tumorigenesis and development of colorectal cancer (CRC). Extensive studies have reported tha hypermethylation of Ras association domain family member 6 (RASSF6) is common in various solid tumors. Another important mode of epigenetic regulation, microRNA (miRNA) regulation of RASSF6, is far from clear. The aim of the present work was to screen out novel miRNA regulating RASSF6, and to explore its underlying mechanism in CRC. With the use of bioinformatics, clinical sample data, and luciferase binding assay, we determined that microRNA-496 (miR-496) could be a novel oncomiR that directly binds to RASSF6. Next, a series of miR-496 mimics or inhibitor, or RASSF6 small interfering RNA (siRNA) introduced into CRC cells were applied to examine the effect of miR-496 on CRC cell viability, migration, and epithelial-mesenchymal transition (EMT). The results demonstrated that miR-496/RASSF6 could promote cell migration and EMT via Wnt signaling activation, but had no effect on cell viability. Our results confirmed that the miR-496/RASSF6 axis is involved in Wnt pathway-mediated tumor metastasis, highlighting its potential as a therapeutic target for CRC.

The RASSF6 Tumor Suppressor Protein Regulates Apoptosis and Cell Cycle Progression via Retinoblastoma Protein

RASSF6 is a member of the tumor suppressor Ras association domain family (RASSF) proteins. RASSF6 is frequently suppressed in human cancers, and its low expression level is associated with poor prognosis. RASSF6 regulates cell cycle arrest and apoptosis and plays a tumor suppressor role. Mechanistically, RASSF6 blocks MDM2-mediated p53 degradation and enhances p53 expression. However, RASSF6 also induces cell cycle arrest and apoptosis in a p53-negative background, which implies that the tumor suppressor function of RASSF6 does not depend solely on p53. In this study, we revealed that RASSF6 mediates cell cycle arrest and apoptosis via pRb. RASSF6 enhances the interaction between pRb and protein phosphatase. RASSF6 also enhances P16INK4A and P14ARF expression by suppressing BMI1. In this way, RASSF6 increases unphosphorylated pRb and augments the interaction between pRb and E2F1. Moreover, RASSF6 induces TP73 target genes via pRb and E2F1 in a p53-negative background. Finally, we confirmed that RASSF6 depletion induces polyploid cells in p53-negative HCT116 cells. In conclusion, RASSF6 behaves as a tumor suppressor in cancers with loss of function of p53, and pRb is implicated in this function of RASSF6.

UNC119 is a binding partner of tumor suppressor Ras-association domain family 6 and induces apoptosis and cell cycle arrest by MDM2 and p53

Ras-association domain family 6 (RASSF6) is a tumor suppressor that interacts with MDM2 and stabilizes p53. Caenorhabditis elegans unc-119 encodes a protein that is required for normal development of the nervous system. Humans have 2 unc-119 homologues, UNC119 and UNC119B. We have identified UNC119 as a RASSF6-interacting protein. UNC119 promotes the interaction between RASSF6 and MDM2 and stabilizes p53. Thus, UNC119 induces apoptosis by RASSF6 and p53. UNC119 depletion impairs DNA repair after DNA damage and results in polyploid cell generation. These findings support that UNC119 is a regulator of the RASSF6-MDM2-p53 axis and functions as a tumor suppressor.

Tumor suppressor C-RASSF proteins

Human genome has ten genes that are collectedly called Ras association domain family (RASSF). RASSF is composed of two subclasses, C-RASSF and N-RASSF. Both N-RASSF and C-RASSF encode Ras association domain-containing proteins and are frequently suppressed by DNA hypermethylation in human cancers. However, C-RASSF and N-RASSF are quite different. Six C-RASSF proteins (RASSF1-6) are characterized by a C-terminal coiled-coil motif named Salvador/RASSF/Hippo domain, while four N-RASSF proteins (RASSF7-10) lack it. C-RASSF proteins interact with mammalian Ste20-like kinases-the core kinases of the tumor suppressor Hippo pathway-and cross-talk with this pathway. Some of them share the same interacting molecules such as MDM2 and exert the tumor suppressor role in similar manners. Nevertheless, each C-RASSF protein has distinct characters. In this review, we summarize our current knowledge of how C-RASSF proteins play tumor suppressor roles and discuss the similarities and differences among C-RASSF proteins.

BCL-XL binds and antagonizes RASSF6 tumor suppressor to suppress p53 expression

RASSF6, a member of the tumor suppressor Ras-association domain family proteins, induces apoptosis in the caspase-dependent and caspase-independent manners. RASSF6 interacts with MDM2 and stabilizes p53. BCL-XL is a prosurvival member of BCL-2 family proteins. BCL-XL directly inhibits proapoptotic BAX and BAK. BCL-XL also traps tBID, a proapoptotic activator BH3-only protein, and sequesters p53. In addition, BCL-XL regulates the mitochondrial membrane permeability via voltage-dependent anion channel. In these manners, BCL-XL plays an antiapoptotic role. We report the interaction of BCL-XL with RASSF6. BCL-XL inhibits the interaction between RASSF6 and MDM2 and suppresses p53 expression. Consequently, BCL-XL antagonizes RASSF6-mediated apoptosis. Thus, the inhibition of RASSF6-mediated apoptosis also underlies the prosurvival role of BCL-XL.

DNA hypermethylation of tumor suppressor genes RASSF6 and RASSF10 as independent prognostic factors in adult acute lymphoblastic leukemia

BACKGROUND

The Hypermethylation of Ras association domain family (RASSF) often plays a key role in malignant progression of solid tumors; however, their impact on the prognosis and survival of adult ALL patients remain elusive.

METHODS

The frequency of the promoter methylation pattern of RASSF6 and RASSF10 were analyzed in the peripheral blood (PB) samples taken at the time of diagnosis of 45 ALL patients. The methylation-specific PCR (MSP) assay was used to detect the DNA methylation patterns.

RESULTS

RASSF6 was frequently hypermethylated in patients diagnosed with pre-B-ALL (90.9%) and B-ALL (87.5%), followed by T-ALL (66.7%); whereas, RASSF10 methylation was more confined to T-ALL (80%) as compared to B-ALL (25%) and pre-B ALL (9.1%) patients. Moreover, hypermethylation of RASSF6 was significantly associated with a poor prognosis and shorter overall survival (OS) in patients with pre-B-ALL (log-rank test; P=0.041).

CONCLUSION

RASSF6 and RASSF10 were frequently hypermethylated in the samples at the time of diagnosis of adult ALL patients. Our study represents the first report of methylation of RASSF6 at a high frequency in patients with pre-B ALL. Furthermore, hypermethylation of RASSF6 was significantly associated with inferior overall survival in pre-B ALL patients. It may suggest that the frequent epigenetic inactivation of RASSF6 plays an important role in the pathogenesis and progression of pre-B-ALL.

Diagnostic value of selected markers and apoptotic pathways for pancreatic cancer

Pancreatic cancer occupies the fourth place as a cause of death from cancer, and the mortality rate is similar to the number of newly detected cases. Due to the late diagnosis, only 5-6% of patients with pancreatic cancer survive for five years. Given that early diagnosis is critical for improving patients' survival rates, there is an urgent need for the discovery and validation of new biomarkers with sufficient sensitivity and specificity to help diagnose pancreatic cancer early. Detection of serum tumor markers (CA19-9, CEA, CA125 and CA242) is conducive to the early diagnosis of pancreatic cancer. The combination of miR-16, miR-196a and CA19-9 plasma level was more effective, especially in early tumor screening. Furthermore, recent studies reported that mainly miR-21, miR-155 and miR-196 were dysregulated in IPMN (intraductal papillary mucinous neoplasms) and PanIN (pancreatic intraepithelial neoplasia) lesions, suggesting their usefulness as early biomarkers of these diseases. The reduced rate of apoptosis plays a crucial role in carcinogenesis, and it is one of the most important characteristics acquired by pancreatic cancer cells, which protects them from attack by the immune system and reduces the effectiveness of pharmacological treatment. This review summarizes the data concerning the clinical utility of selected biomarkers in pancreatic cancer patients. The review mainly focuses on the genetic aspects of signaling pathway disorders associated with apoptosis in the pathogenesis and diagnosis of pancreatic cancer.

HPV16 integration probably contributes to cervical oncogenesis through interrupting tumor suppressor genes and inducing chromosome instability

Background

The integration of human papilloma virus (HPV) into host genome is one of the critical steps that lead to the progression of precancerous lesion into cancer. However, the mechanisms and consequences of such integration events are poorly understood. This study aims to explore those questions by studying high risk HPV16 integration in women with cervical intraepithelial neoplasia (CIN) and cervical squamous cell carcinoma (SCC).

Methods

Specifically, HPV integration status of 13 HPV16-infected patients were investigated by ligation-mediated PCR (DIPS-PCR) followed by DNA sequencing.

Results

In total, 8 HPV16 integration sites were identified inside or around genes associated with cancer development. In particular, the well-studied tumor suppressor genes SCAI was found to be integrated by HPV16, which would likely disrupt its expression and therefore facilitate the migration of tumor. On top of that, we observed several cases of chromosome translocation events coincide with HPV integration, which suggests the existence of chromosome instability. Additionally, short overlapping sequences were observed between viral derived and host derived fragments in viral-cellular junctions, indicating that integration was mediated by micro homology-mediated DNA repair pathway.

Conclusions

Overall, our study suggests a model in which HPV16 might contribute to oncogenesis not only by disrupting tumor suppressor genes, but also by inducing chromosome instability.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0454-4) contains supplementary material, which is available to authorized users.