NORE1A tumor suppressor candidate modulates p21CIP1 via p53

BRCA1 and NORE1A Form a Her2/Ras Regulated Tumor Suppressor Complex Modulating Senescence

BRCA1 is a tumor suppressor with a complex mode of action. Hereditary mutations in BRCA1 predispose carriers to breast cancer, and spontaneous breast cancers often exhibit defects in BRCA1 expression. However, haploinsufficiency or suppression of BRCA1 expression leads to defects in DNA repair, which can induce DNA damage responses, leading to senescence. Activating mutation or overexpression of the Her2 oncoprotein are also frequent drivers of breast cancer. Yet, over-activation of Her2, working through the RAS oncoprotein, can also induce senescence. It is thought that additional defects in the p53 and Rb tumor suppressor machinery must occur in such tumors to allow an escape from senescence, thus permitting tumor development. Although BRCA1 mutant breast cancers are usually Her2 negative, a significant percentage of Her2 positive tumors also lose their expression of BRCA1. Such Her2+/BRCA1- tumors might be expected to have a particularly high senescence barrier to overcome. An important RAS senescence effector is the protein NORE1A, which can modulate both p53 and Rb. It is an essential senescence effector of the RAS oncoprotein, and it is often downregulated in breast tumors by promotor methylation. Here we show that NORE1A forms a Her2/RAS regulated, endogenous complex with BRCA1 at sites of replication fork arrest. Suppression of NORE1A blocks senescence induction caused by BRCA1 inactivation and Her2 activation. Thus, NORE1A forms a tumor suppressor complex with BRCA1. Its frequent epigenetic inactivation may facilitate the transformation of Her2+/BRCA1- mediated breast cancer by suppressing senescence.

Nore1 inhibits age-associated myeloid lineage skewing and clonal hematopoiesis but facilitates termination of emergency (stress) granulopoiesis

Age-associated bone marrow changes include myeloid skewing and mutations that lead to clonal hematopoiesis. Molecular mechanisms for these events are ill defined, but decreased expression of Irf8/Icsbp (interferon regulatory factor 8/interferon consensus sequence binding protein) in aging hematopoietic stem cells may contribute. Irf8 functions as a leukemia suppressor for chronic myeloid leukemia, and young Irf8-/- mice have neutrophilia with progression to acute myeloid leukemia (AML) with aging. Irf8 is also required to terminate emergency granulopoiesis during the innate immune response, suggesting this may be the physiologic counterpart to leukemia suppression by this transcription factor. Identifying Irf8 effectors may define mediators of both events and thus contributors to age-related bone marrow disorders. In this study, we identified RASSF5 (encoding Nore1) as an Irf8 target gene and investigated the role of Nore1 in hematopoiesis. We found Irf8 activates RASSF5 transcription and increases Nore1a expression during emergency granulopoiesis. Similar to Irf8-/- mice, we found that young Rassf5-/- mice had increased neutrophils and progressed to AML with aging. We identified enhanced DNA damage, excess clonal hematopoiesis, and a distinct mutation profile in hematopoietic stem cells from aging Rassf5-/- mice compared with wildtype. We found sustained emergency granulopoiesis in Rassf5-/- mice, with repeated episodes accelerating AML, also similar to Irf8-/- mice. Identifying Nore1a downstream from Irf8 defines a pathway involved in leukemia suppression and the innate immune response and suggests a novel molecular mechanism contributing to age-related clonal myeloid disorders.

PLAGL2 induces nucleus pulposus cell apoptosis via regulating RASSF5 expression and thus accelerates intervertebral disc degeneration

Excessive apoptosis of nucleus pulposus (NP) cells is the main pathological change in intervertebral disc degeneration (IVDD) progression. Pleomorphic adenoma gene like-2 (PLAGL2) plays a key role in cell apoptosis, however, the effect of PLAGL2 on IVDD has not been clarified yet. In this study, we established mouse IVDD models via the annulus fibrosis needle puncture, TUNEL and safranin O staining were used to verify the successful establishment of IVDD models, and PLAGL2 expression was detected in disc tissues. Then, NP cells isolated from disc tissues were used to construct PLAGL2 knockdown cells. PLAGL2 expression in NP cells was analyzed with qRT-PCR and Western blot. The impact of PLAGL2 on the viability, apoptosis, and mitochondria function of NP cells was evaluated by MTT assay, TUNEL, JC1 staining, and flow cytometry assay. Additionally, the regulatory mechanism of PLAGL2 was further assessed. We found that PLAGL2 was upregulated in IVDD disc tissues and serum deprivation (SD)-stimulated NP cells. PLAGL2 knockdown inhibited apoptosis and mitochondria damage in NP cells. Moreover, knockdown of PLAGL2 downregulated the expression of downstream apoptosis-related factors RASSF5, Nip3, and p73. Mechanically, PLAGL2 transcriptionally activated RASSF5 via binding to its promoter. In general, our findings indicate that PLAGL2 induces apoptosis in NP cells and aggravates IVDD progression. This study provides a promising therapeutic target for IVDD treatment.

Serum Response Factor (SRF) Drives the Transcriptional Upregulation of the MDM4 Oncogene in HCC

Different molecular mechanisms support the overexpression of the mouse double minute homolog 4 (MDM4), a functional p53 inhibitor, in human hepatocellular carcinoma (HCC). However, the transcription factors (TFs) leading to its transcriptional upregulation remain unknown. Following promoter and gene expression analyses, putative TFs were investigated using gene-specific siRNAs, cDNAs, luciferase reporter assays, chromatin immunoprecipitation, and XI-011 drug treatment in vitro. Additionally, MDM4 expression was investigated in SRF-VP16iHep transgenic mice. We observed a copy-number-independent upregulation of MDM4 in human HCCs. Serum response factor (SRF), ELK1 and ELK4 were identified as TFs activating MDM4 transcription. While SRF was constitutively detected in TF complexes at the MDM4 promoter, presence of ELK1 and ELK4 was cell-type dependent. Furthermore, MDM4 was upregulated in SRF-VP16-driven murine liver tumors. The pharmacological inhibitor XI-011 exhibited anti-MDM4 activity by downregulating the TFs driving MDM4 transcription, which decreased HCC cell viability and increased apoptosis. In conclusion, SRF drives transcriptional MDM4 upregulation in HCC, acting in concert with either ELK1 or ELK4. The transcriptional regulation of MDM4 may be a promising target for precision oncology of human HCC, as XI-011 treatment exerts anti-MDM4 activity independent from the MDM4 copy number and the p53 status.

Histone demethylase Jmjd3 modulates osteoblast apoptosis induced by tumor necrosis factor-alpha through directly targeting RASSF5

Purpose: Regulation of gene expression is fine-tuned by a dynamic equilibrium between repressive modifications and transcriptional activation of histone tails. Jumonji domain-containing 3 (Jmjd3), also known as KDM6B, is a specific histone demethylase for trimethylation on histone H3 lysine 27 (H3K27me3) that specifically removes the methylation of H3K27me3 and promotes gene expression. Our previous study showed that Jmjd3 inhibits serum deprivation-induced osteoblast apoptosis. In this study, we clarified the role of Jmjd3 in tumor necrosis factor-alpha (TNF-α)-induced osteoblast apoptosis. Materials and Methods: Jmjd3 activity was inhibited by GSK-J4. Transfection of osteoblastic murine MC3T3-E1 cells with short hairpin RNA (shRNA) was used to establish stable Jmjd3 knockdown cells. Osteoblast apoptosis was detected using Annexin V-APC/PI staining, cysteinyl aspartate specific protease-3 (caspase-3) activity assays, and Western blot. Real-time polymerase chain reaction (PCR) and chromatin immunoprecipitation (ChIP) assays were performed to clarify the mechanism responsible for Jmjd3-regulated osteoblast apoptosis induced by TNF-α. Results: Based on Annexin V-APC/PI staining, caspase-3 activation, and poly ADP-ribose polymerase (PARP) cleavage, pretreatment with GSK-J4 and knockdown of Jmjd3 by shRNA transfection each inhibited osteoblast apoptosis. Furthermore, knockdown of Jmjd3 decreased the expression of Ras association domain family 5 (RASSF5), which is a pro-apoptotic gene of the Ras associated domain family. H3K27me3 levels in the promoter region of RASSF5 were up-regulated in the Jmjd3 knockdown cells. Conclusions: Jmjd3 regulated TNF-α-induced osteoblast apoptosis by targeting RASSF5.

In silico analysis predicting effects of deleterious SNPs of human RASSF5 gene on its structure and functions

Ras association domain-containing protein 5 (RASSF5), one of the prospective biomarkers for tumors, generally plays a crucial role as a tumor suppressor. As deleterious effects can result from functional differences through SNPs, we sought to analyze the most deleterious SNPs of RASSF5 as well as predict the structural changes associated with the mutants that hamper the normal protein-protein interactions. We adopted both sequence and structure based approaches to analyze the SNPs of RASSF5 protein. We also analyzed the putative post translational modification sites as well as the altered protein-protein interactions that encompass various cascades of signals. Out of all the SNPs obtained from the NCBI database, only 25 were considered as highly deleterious by six in silico SNP prediction tools. Among them, upon analyzing the effect of these nsSNPs on the stability of the protein, we found 17 SNPs that decrease the stability. Significant deviation in the energy minimization score was observed in P350R, F321L, and R277W. Besides this, docking analysis confirmed that P350R, A319V, F321L, and R277W reduce the binding affinity of the protein with H-Ras, where P350R shows the most remarkable deviation. Protein-protein interaction analysis revealed that RASSF5 acts as a hub connecting two clusters consisting of 18 proteins and alteration in the RASSF5 may lead to disassociation of several signal cascades. Thus, based on these analyses, our study suggests that the reported functional SNPs may serve as potential targets for different proteomic studies, diagnosis and therapeutic interventions.

NORE1A directs apoptotic switch of TNF signaling through reciprocal modulation of ITCH-mediated destruction of TNFRI and BAX

NORE1A (RASSF5) is a tumor suppressor of the Ras-association domain family (RASSF) that is commonly inactivated in multiple human cancers. However, the molecular mechanism underlying its growth inhibition function remains largely undefined. Here we report that NORE1A antagonizes tumor necrosis factor receptor I (TNFRI) through the assembly of ITCH-mediated destruction complex to suppress TNF-NF-κB signaling and tumorigenesis. Moreover, NORE1A is identified as a transcription target of NF-κB, which directs an apoptotic switch of TNF effect by blocking ITCH interaction with and ubiquitination of BAX. Mechanistically, NORE1A binds directly to TNFRI and ITCH via the C1 and PPXY domains, respectively to facilitate the formation of ITCH-mediated destruction complex followed by ubiquitination-mediated lysosomal degradation of TNFRI. Through this function, NORE1A suppresses TNF-induced NF-κB-mediated transcription of pro-inflammatory and tumor-promoting genes, epithelial-to-mesenchymal transition, invasion and migration of tumor cells, and also debilitates tumor cell activation of macrophage and fibroblast. While NORE1A suppresses TNF receptor-mediated apoptosis, it activates TNF-induced apoptosis through BAX activation by protecting BAX from ITCH binding and ubiquitination. Cytotoxic response to TNF is substantially attenuated in NORE1A-depleted cells and tumors, and NORE1A-induced tumor regression is highly impeded in BAX-depleted tumors. An inverse correlation is shown between NORE1A and TNFRI expression in both cancer cell lines and primary tumors, and NORE1A effect on survival of cancer patients is strongly associated with expression status of ITCH. Collectively, this study uncovers that NORE1A directs a substrate switch of ITCH favoring TNFRI over BAX to terminate TNF signaling and accelerate apoptosis, illuminating the mechanistic consequence of NORE1A inactivation in tumorigenesis.

Exosomal miR-532-5p from bone marrow mesenchymal stem cells reduce intervertebral disc degeneration by targeting RASSF5

The transplantation of bone marrow mesenchymal stem cells (BMSCs) has been found to be used as an effective therapy of intervertebral disc degeneration (IDD). However, the underlying mechanisms of BMSCs in the progress of IDD are not fully explained. In this study, we found that exosomes derived from BMSCs (BMSCs-Exos) inhibited the apoptotic rate, extracellular matrix (ECM) degradation, and fibrosis deposition in TNF-α-induced nucleus pulposus cells (NPCs). Importantly, the level of miR-532-5p was observed to be decreased in apoptotic NPCs, but abundant in BMSCs-Exos with TNF-α treatment. The results showed that BMSCs-Exos under TNF-α stimuli exerted better effects on NPCs than BMSCs-Exos, which might be mitigated by the inhibition of miR-532-5p in BMSCs-Exos. The gain-of-function results suggested that the direct overexpression of miR-532-5p in NPCs could inhibit TNF-α-induced increase of apoptotic process, activation of apoptotic proteins, imbalance of anabolism/catabolism levels, and accumulation of collagen I. In addition, RASSF5 was demonstrated to be a target of miR-532-5p. Knockdown of RASSF5 could decrease the apoptotic cells and reduce the activated apoptotic protein levels in TNF-α-induced NPCs. Overall, these data indicate that exosomes from BMSCs may suppress TNF-α-induced apoptosis, ECM degradation, and fibrosis deposition in NPCs through the delivery of miR-532-5p via targeting RASSF5. This work provides a promising therapeutic strategy for the progress of IDD.

The Role of the Cyclin Dependent Kinase Inhibitor p21cip1/waf1 in Targeting Cancer: Molecular Mechanisms and Novel Therapeutics

p21^cip1/waf1 mediates various biological activities by sensing and responding to multiple stimuli, via p53-dependent and independent pathways. p21 is known to act as a tumor suppressor mainly by inhibiting cell cycle progression and allowing DNA repair. Significant advances have been made in elucidating the potential role of p21 in promoting tumorigenesis. Here, we discuss the involvement of p21 in multiple signaling pathways, its dual role in cancer, and the importance of understanding its paradoxical functions for effectively designing therapeutic strategies that could selectively inhibit its oncogenic activities, override resistance to therapy and yet preserve its tumor suppressive functions.

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.

CDCA3 mediates p21-dependent proliferation by regulating E2F1 expression in colorectal cancer

Dysregulated cell cycle progression serves a crucial role in tumor development. Cell division cycle-associated 3 (CDCA3) is considered a trigger of mitotic entry; it is an important part of the S phase kinase-associated protein 1/Cullin/F-box ubiquitin ligase complex and mediates the destruction of mitosis-inhibitory kinase wee1. However, little is known about the role of CDCA3 in cancer, particularly colorectal cancer (CRC). The present study aimed to explore the biological and clinical significance of CDCA3 in CRC growth and progression. CDCA3 expression was significantly associated with tumor progression and poor survival. Overexpression of CDCA3 increased proliferation in LoVo CRC cells, whereas CDCA3 knockdown in SW480 CRC cells led to decreased proliferation, in vitro and in vivo. Further mechanistic investigations demonstrated that reduced CDCA3 expression resulted in G1/S phase transition arrest, which was attributed to a significant accumulation of p21 in SW480 cells; conversely, increased CDCA3 expression promoted G1/S phase transition through decreased p21 accumulation in LoVo cells. It was also demonstrated that CDCA3 was able to regulate the expression of transcription factor E2F1, thereby repressing p21 expression. Taken together, these results suggested that overexpression of CDCA3 may serve a crucial role in tumor malignant potential and that CDCA3 may be used as a prognostic factor and a potential therapeutic target in CRC.

RAS-mediated oncogenic signaling pathways in human malignancies

Abnormally activated RAS proteins are the main oncogenic driver that governs the functioning of major signaling pathways involved in the initiation and development of human malignancies. Mutations in RAS genes and or its regulators, most frequent in human cancers, are the main force for incessant RAS activation and associated pathological conditions including cancer. In general, RAS is the main upstream regulator of the highly conserved signaling mechanisms associated with a plethora of important cellular activities vital for normal homeostasis. Mutated or the oncogenic RAS aberrantly activates a web of interconnected signaling pathways including RAF-MEK (mitogen-activated protein kinase kinase)-ERK (extracellular signal-regulated kinase), phosphoinositide-3 kinase (PI3K)/AKT (protein kinase B), protein kinase C (PKC) and ral guanine nucleotide dissociation stimulator (RALGDS), etc., leading to uncontrolled transcriptional expression and reprogramming in the functioning of a range of nuclear and cytosolic effectors critically associated with the hallmarks of carcinogenesis. This review highlights the recent literature on how oncogenic RAS negatively use its signaling web in deregulating the expression and functioning of various effector molecules in the pathogenesis of human malignancies.

TET1 inhibits cell proliferation by inducing RASSF5 expression

Tet methylcytosine dioxygenases (TETs) catalyze the oxidative reactions of 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). However, TET1 roles in ovarian cancer cell growth are unknown. Here, we show that ectopic expression of TET1 increased 5hmC levels, and inhibited proliferation and colony formation in ovarian cancer cell lines. Furthermore, in vitro and in vivo functional studies demonstrated that TET1 overexpression is necessary for the suppression of ovarian cancer growth, whereas depletion of TET1 expression had the opposite effect. Furthermore, the results of RNA-seq and qRT-PCR analyses identified a tumor suppressor, Ras association domain family member 5 (RASSF5), as the key downstream target of TET1. TET1 promotes RASSF5 expression by demethylating a CpG site within RASSF5 promoter. Up-regulated RASSF5 expression leads to the suppression of ovarian cancer cells growth. Additionally, we demonstrated that inhibition of CUL4-DDB1 ubiquitin ligase complex decrease 5hmC levels in ovarian cancer cells. These results provide new insights into the understanding of how ovarian cancers develop and grow, and identify TET1 as a key player in this process.

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).

Ras signaling through RASSF proteins

There are six core RASSF family proteins that contain conserved Ras Association domains and may serve as Ras effectors. They lack intrinsic enzymatic activity and appear to function as scaffolding and localization molecules. While initially being associated with pro-apoptotic signaling pathways such as Bax and Hippo, it is now clear that they can also connect Ras to a surprisingly broad range of signaling pathways that control senescence, inflammation, autophagy, DNA repair, ubiquitination and protein acetylation. Moreover, they may be able to impact the activation status of pro-mitogenic Ras effector pathways, such as the Raf pathway. The frequent epigenetic inactivation of RASSF genes in human tumors disconnects Ras from pro-death signaling systems, enhancing Ras driven transformation and metastasis. The best characterized members are RASSF1A and RASSF5 (NORE1A).

NORE1A Regulates MDM2 Via β-TrCP

Mouse Double Minute 2 Homolog (MDM2) is a key negative regulator of the master tumor suppressor p53. MDM2 regulates p53 on multiple levels, including acting as an ubiquitin ligase for the protein, thereby promoting its degradation by the proteasome. MDM2 is oncogenic and is frequently found to be over-expressed in human tumors, suggesting its dysregulation plays an important role in human cancers. We have recently found that the Ras effector and RASSF (Ras Association Domain Family) family member RASSF5/NORE1A enhances the levels of nuclear p53. We have also found that NORE1A (Novel Ras Effector 1A) binds the substrate recognition component of the SCF-ubiquitin ligase complex β-TrCP. Here, we now show that NORE1A regulates MDM2 protein levels by targeting it for ubiquitination by SCF-β-TrCP. We also show the suppression of NORE1A protein levels enhances MDM2 protein expression. Finally, we show that MDM2 can suppress the potent senescence phenotype induced by NORE1A over-expression. Thus, we identify a mechanism by which Ras/NORE1A can modulate p53 protein levels. As MDM2 has several important targets in addition to p53, this finding has broad implications for cancer biology in tumor cells that have lost expression of NORE1A due to promoter methylation.

NORE1A induction by membrane-bound CD40L (mCD40L) contributes to CD40L-induced cell death and G1 growth arrest in p21-mediated mechanism

Membrane-bound CD40L (mCD40L) but not soluble CD40L (sCD40L) has been implicated in direct cell death induction and apoptosis in CD40-expressing carcinomas. In this study, we show that mCD40L but not sCD40L induces NORE1A/Rassf5 expression in an NFκB-dependant mechanism. NORE1A expression appeared to contribute to mCD40L-induced cell death and enhance cell transition from G1 to S phase of the cell cycle in a p21-dependent mechanism. The upregulation of p21 protein was attributed to NORE1A expression, since NORE1A inhibition resulted in p21 downregulation. p21 upregulation was concomitant with lower p53 expression in the cytoplasmic fraction with no detectable increase at the nuclear p53 level. Moreover, mCD40L-induced cell death mediated by NORE1A expression appeared to be independent of mCD40L-induced cell death mediated by sustained JNK activation since NORE1A inhibition did not affect JNK phosphorylation and vice versa. The presented data allow better understanding of the mechanism by which mCD40L induces cell death which could be exploited in the clinical development of CD40-targeted anti-cancer therapies.

Downregulation of CDC27 inhibits the proliferation of colorectal cancer cells via the accumulation of p21Cip1/Waf1

Dysregulated cell cycle progression has a critical role in tumorigenesis. Cell division cycle 27 (CDC27) is a core subunit of the anaphase-promoting complex/cyclosome, although the specific role of CDC27 in cancer remains unknown. In our study, we explored the biological and clinical significance of CDC27 in colorectal cancer (CRC) growth and progression and investigated the underlying molecular mechanisms. Results showed that CDC27 expression is significantly correlated with tumor progression and poor patient survival. Functional assays demonstrated that overexpression of CDC27 promoted proliferation in DLD1 cells, whereas knockdown of CDC27 in HCT116 cells inhibited proliferation both in vitro and in vivo. Further mechanistic investigation showed that CDC27 downregulation resulted in G1/S phase transition arrest via the significant accumulation of p21 in HCT116 cells, and the upregulation of CDC27 promoted G1/S phase transition via the attenuation of p21 in DLD1 cells. Furthermore, we also demonstrated that CDC27 regulated inhibitor of DNA binding 1 (ID1) protein expression in DLD1 and HCT116 cells, and rescue assays revealed that CDC27 regulated p21 expression through modulating ID1 expression. Taken together, our results indicate that CDC27 contributes to CRC cell proliferation via the modulation of ID1-mediated p21 regulation, which offers a novel approach to the inhibition of tumor growth. Indeed, these findings provide new perspectives for the future study of CDC27 as a target for CRC treatment.

Ras Regulates Rb via NORE1A

Mutations in the Ras oncogene are one of the most frequent events in human cancer. Although Ras regulates numerous growth-promoting pathways to drive transformation, it can paradoxically promote an irreversible cell cycle arrest known as oncogene-induced senescence. Although senescence has clearly been implicated as a major defense mechanism against tumorigenesis, the mechanisms by which Ras can promote such a senescent phenotype remain poorly defined. We have shown recently that the Ras death effector NORE1A plays a critical role in promoting Ras-induced senescence and connects Ras to the regulation of the p53 tumor suppressor. We now show that NORE1A also connects Ras to the regulation of a second major prosenescent tumor suppressor, the retinoblastoma (Rb) protein. We show that Ras induces the formation of a complex between NORE1A and the phosphatase PP1A, promoting the activation of the Rb tumor suppressor by dephosphorylation. Furthermore, suppression of Rb reduces NORE1A senescence activity. These results, together with our previous findings, suggest that NORE1A acts as a critical tumor suppressor node, linking Ras to both the p53 and the Rb pathways to drive senescence.

Selective multifaceted E3 ubiquitin ligases barricade extreme defense: Potential therapeutic targets for neurodegeneration and ageing

Efficient and regular performance of Ubiquitin Proteasome System and Autophagy continuously eliminate deleterious accumulation of nonnative protiens. In cellular quality control system, E3 ubiquitin ligases are significant employees for defense mechanism against abnormal toxic proteins. Few findings indicate that lack of functions of E3 ubiquitin ligases can be a causative factor of neurodevelopmental disorders, neurodegeneration, cancer and ageing. However, the detailed molecular pathomechanism implying E3 ubiquitin ligases in cellular functions in multifactorial disease conditions are not well understood. This article systematically represents the unique characteristics, molecular nature, and recent developments in the knowledge of neurobiological functions of few crucial E3 ubiquitin ligases. Here, we review recent literature on the roles of E6-AP, HRD1 and ITCH E3 ubiquitin ligases in the neuro-pathobiological mechanisms, with precise focus on the processes of neurodegeneration, and thereby propose new lines of potential targets for therapeutic interventions.

Nore1a drives Ras to flick the P53 senescence switch

RAS-induced senescence is a protective mechanism to avoid unrestricted cell growth due to aberrant mitogenic signals; however, the exact mechanism by which RAS induces senescence is not known. We recently identified a novel pathway linking RAS to p53 via NORE1A and HIPK2 that mechanistically explains how Ras induces senescence.

NORE1A is a Ras senescence effector that controls the apoptotic/senescent balance of p53 via HIPK2

NORE1A is a Ras senescence effector that modulates HIPK2-dependent posttranslational modifications of p53.

The Ras oncoprotein is a key driver of cancer. However, Ras also provokes senescence, which serves as a major barrier to Ras-driven transformation. Ras senescence pathways remain poorly characterized. NORE1A is a novel Ras effector that serves as a tumor suppressor. It is frequently inactivated in tumors. We show that NORE1A is a powerful Ras senescence effector and that down-regulation of NORE1A suppresses senescence induction by Ras and enhances Ras transformation. We show that Ras induces the formation of a complex between NORE1A and the kinase HIPK2, enhancing HIPK2 association with p53. HIPK2 is a tumor suppressor that can induce either proapoptotic or prosenescent posttranslational modifications of p53. NORE1A acts to suppress its proapoptotic phosphorylation of p53 but enhance its prosenescent acetylation of p53. Thus, we identify a major new Ras signaling pathway that links Ras to the control of specific protein acetylation and show how NORE1A allows Ras to qualitatively modify p53 function to promote senescence.

RASSF5A, a candidate tumor suppressor, is epigenetically inactivated in esophageal squamous cell carcinoma

As a result of alternative splicing and differential promoter usage, RASSF5 exists in at least three isoforms (RASSF5A-RASSF5C), which may play different roles in tumorigenesis. The present study was to detect the role of RASSF5A, B and C in esophageal squamous cell carcinoma (ESCC) and clarify the critical CpG sites of RASSF5A, in order to clarify more information on the role of RASSF5 with regard to the pathogenesis of ESCC. Frequent silencing of RASSF5A but not RASSF5B and RASSF5C were found in esophageal cancer cell lines and the silencing of RASSF5A may be reversed by 5-Aza-dC or TSA treatment. The aberrant CpG island 1 methylation of RASSF5A induces silencing of its expression in TE13 cell line. Decreased mRNA and protein expression of RASSF5A was observed in ESCC tumor tissues and was associated with RASSF5A CpG island 1 methylation status. Unlike RASSF5A, expression variation of RASSF5B and RASSF5C was not found in ESCC tissues. Aberrant promoter methylation of RASSF5C was also not found in ESCC. RASSF5A methylation and protein expression were independently associated with ESCC patients' survival. These data indicated that the inactivation of RASSF5A through CpG island 1 methylation may play an important role in ESCC carcinogenesis, RASSF5A may be a functional tumor suppressor and may serve as a prognostic biomarker for ESCC.

Molecular mechanisms of hepatic apoptosis regulated by nuclear factors

Apoptosis is a prominent characteristic in the pathogenesis of liver disease. The mechanism of hepatic apoptosis is not well understood. Hepatic apoptosis alters relative levels of nuclear factors such as Foxa2, NF-κB, C/EBPβ, and p53. Regulation of nuclear factors modulates the degree of hepatic apoptosis and the progression of liver disease. Nuclear factors have distinctive mechanisms to mediate hepatic apoptosis. The modification of nuclear factors is a novel therapeutic strategy for liver disease as demonstrated by pre-clinical models and clinical trials.

Decreased expression and aberrant methylation of RASSF5A correlates with malignant progression of gastric cardia adenocarcinoma

Due to alternative splicing and differential promoter usage, RASSF5 exists in at least three isoforms, RASSF5A, RASSF5B, and RASSF5C. Expression and epigenetic inactivation of different transcripts of RASSF5 in gastric cardia adenocarcinoma (GCA) progression have not been evaluated. Quantitative real-time RT-PCR and immunohistochemistry (IHC) methods were used respectively to detect the role of RASSF5A, RASSF5B, and RASSF5C in 132 GCA cases and BS-MSP method was used to clarify the critical CpG sites of RASSF5A. Expression of RASSF5A and RASSF5C transcripts were easily detectable in all normal gastric cardia epithelial tissues; however, expression of RASSF5B was rare detected in normal gastric cardia epithelial tissues and tumor tissues. Both RASSF5A and RASSF5C expression were frequently downregulated in GCA tumor tissues and RASSF5A was more commonly down-regulated compared to RASSF5C. Abnormal reduction of RASSF5A was more commonly observed in advanced stage and poor differentiated tumors. The methylation frequency of CpG island 1 region of RASSF5A in GCA tumor tissues was significantly higher than that in corresponding normal tissues and was inversely correlated with RASSF5A expression. Aberrant promoter methylation of RASSF5C was not found in GCA. RASSF5A methylation and protein expression were independently associated with GCA patients' survival. These results indicate that down-regulation of RASSF5A and RASSF5C expression is a tumor-specific phenomenon and RASSF5A may be a more common target for inactivation in GCA. Inactivation of RASSF5A through CpG island 1 methylation may play an important role in GCA carcinogenesis and may serve as a prognostic biomarker for GCA.

EEF1A2 inactivates p53 by way of PI3K/AKT/mTOR-dependent stabilization of MDM4 in hepatocellular carcinoma

Mouse Double Minute homolog 4 (MDM4) gene up-regulation often occurs in human hepatocellular carcinoma (HCC), but the molecular mechanisms responsible for its induction remain poorly understood. Here we investigated the role of the phosphoinositide-3-kinase/v-akt murine thymoma viral oncogene homolog/mammalian target of rapamycin (PI3K/AKT/mTOR) axis in the regulation of MDM4 levels in HCC. The activity of MDM4 and the PI3K/AKT/mTOR pathway was modulated in human HCC cell lines by way of silencing and overexpression experiments. Expression of main pathway components was analyzed in an AKT mouse model and human HCCs. MDM4 inhibition resulted in growth restraint of HCC cell lines both in vitro and in vivo. Inhibition of the PI3K-AKT and/or mTOR pathways lowered MDM4 protein levels in HCC cells and reactivated p53-dependent transcription. Deubiquitination by ubiquitin-specific protease 2a and AKT-mediated phosphorylation protected MDM4 from proteasomal degradation and increased its protein stability. The eukaryotic elongation factor 1A2 (EEF1A2) was identified as an upstream inducer of PI3K supporting MDM4 stabilization. Also, we detected MDM4 protein up-regulation in an AKT mouse model and a strong correlation between the expression of EEF1A2, activated/phosphorylated AKT, and MDM4 in human HCC (each rho > 0.8, P < 0.001). Noticeably, a strong activation of this cascade was associated with shorter patient survival.

CONCLUSION

The EEF1A2/PI3K/AKT/mTOR axis promotes the protumorigenic stabilization of the MDM4 protooncogene in human HCC by way of a posttranscriptional mechanism. The activation level of the EEF1A2/PI3K/AKT/mTOR/MDM4 axis significantly influences the survival probability of HCC patients in vivo and may thus represent a promising molecular target.

Genetic and epigenetic mutations of tumor suppressive genes in sporadic pituitary adenoma

Human pituitary adenomas are the most common intracranial neoplasms. Approximately 5% of them are familial adenomas. Patients with familial tumors carry germline mutations in predisposition genes, including AIP, MEN1 and PRKAR1A. These mutations are extremely rare in sporadic pituitary adenomas, which therefore are caused by different mechanisms. Multiple tumor suppressive genes linked to sporadic tumors have been identified. Their inactivation is caused by epigenetic mechanisms, mainly promoter hypermethylation, and can be placed into two groups based on their functional interaction with tumor suppressors RB or p53. The RB group includes CDKN2A, CDKN2B, CDKN2C, RB1, BMP4, CDH1, CDH13, GADD45B and GADD45G; AIP and MEN1 genes also belong to this group. The p53 group includes MEG3, MGMT, PLAGL1, RASSF1, RASSF3 and SOCS1. We propose that the tumor suppression function of these genes is mainly mediated by the RB and p53 pathways. We also discuss possible tumor suppression mechanisms for individual genes.

Ribonucleotide reductase M2B inhibits cell migration and spreading by early growth response protein 1-mediated phosphatase and tensin homolog/Akt1 pathway in hepatocellular carcinoma

Ribonucleotide reductase (RR)M2B is an enzyme belonging to the ribonucleotide reductase enzyme family, which is essential for DNA synthesis and repair. RRM2B plays an important role in tumor progression and metastasis; however, little is known about the expression and underlying molecular mechanisms of RRM2B in hepatocellular carcinoma (HCC). In the present study, we report that down-regulation of RRM2B in HCC is negatively associated with intrahepatic metastasis, regardless of p53 status. Moreover, the ectopic overexpression of RRM2B decreased HCC cell migration and invasion in vitro, whereas silencing RRM2B expression resulted in increased migration and invasion in vitro and intrahepatic and lung metastasis in vivo. Additionally, knockdown of RRM2B by short hairpin RNA (shRNA) in HCC cells was associated with epithelial-mesenchymal transition (EMT), including the down-regulation of E-cadherin, and the concomitant up-regulation of N-cadherin and slug. A further experiment showed that RRM2B inhibited cell migration and spreading through regulation of the early growth response protein 1 (Egr-1)/phosphatase and tensin homolog (PTEN)/Akt1 pathway. Consistently, we also detected a significant correlation between RRM2B and E-cadherin protein expression in HCC tissues. Furthermore, Egr-1 also directly bound to the RRM2B promoter and repressed RRM2B transcription, thereby establishing a negative regulatory feedback loop.

CONCLUSION

These findings indicate that RRM2B suppresses cell migration and spreading by way of modulation of the Egr-1/PTEN/Akt1 pathway.

RASSF6 promotes p21(Cip1/Waf1)-dependent cell cycle arrest and apoptosis through activation of the JNK/SAPK pathway in clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is a highly aggressive and common pathological subtype of renal cancer. This cancer is characterized by biallelic inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene, which leads to the accumulation of hypoxia-inducible factors (HIFs). Although therapies targeted at HIFs can significantly improve survival, nearly all patients with advanced ccRCC eventually succumb to the disease. Thus, additional oncogenic events are thought to be involved in the development of ccRCC tumors. In this study, we investigated the role of RASSF6 in ccRCC. Downregulation of RASSF6 was commonly observed in primary tumors relative to matched adjacent normal tissues. Moreover, functional studies established that ectopic re-expression of RASSF6 in ccRCC cells inhibited cell proliferation, clonogenicity, and tumor growth in mice, whereas silencing of RASSF6 dramatically enhanced cell proliferation in vitro and in vivo. Mechanistic investigation suggested that RASSF6 triggers p21(Cip1/Waf1) accumulation to induce G 1 cell cycle arrest and promote apoptosis upon exposure to pro-apoptotic agents, and both of these mechanisms appear to be mediated by activated JNK signaling. Together, these findings suggest that RASSF6 may play a tumor suppressor role in the progression of ccRCC.

The RASSF6 tumor suppressor protein regulates apoptosis and the cell cycle via MDM2 protein and p53 protein

Ras association domain family (RASSF) 6 is a member of the C-terminal RASSF proteins such as RASSF1A and RASSF3. RASSF6 is involved in apoptosis in various cells under miscellaneous conditions, but it remains to be clarified how RASSF6 exerts tumor-suppressive roles. We reported previously that RASSF3 facilitates the degradation of MDM2, a major E3 ligase of p53, and stabilizes p53 to function as a tumor suppressor. In this study, we demonstrate that RASSF6 overexpression induces G1/S arrest in p53-positive cells. Its depletion prevents UV- and VP-16-induced apoptosis and G1/S arrest in HCT116 and U2OS cells. RASSF6-induced apoptosis partially depends on p53. RASSF6 binds MDM2 and facilitates its ubiquitination. RASSF6 depletion blocks the increase of p53 in response to UV exposure and up-regulation of p53 target genes. RASSF6 depletion delays DNA repair in UV- and VP-16-treated cells and increases polyploid cells after VP-16 treatment. These findings indicate that RASSF6 stabilizes p53, regulates apoptosis and the cell cycle, and functions as a tumor suppressor. Together with the previous reports regarding RASSF1A and RASSF3, the stabilization of p53 may be the common function of the C-terminal RASSF proteins.

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.

Silencing of RASSF3 by DNA hypermethylation is associated with tumorigenesis in somatotroph adenomas

The pathogenic mechanisms underlying pituitary somatotroph adenoma formation, progression are poorly understood. To identify candidate tumor suppressor genes involved in pituitary somatotroph adenoma tumorigenesis, we used HG18 CpG plus Promoter Microarray in 27 human somatotroph adenomas and 4 normal human adenohypophyses. RASSF3 was found with frequent methylation of CpG island in its promoter region in somatotroph adenomas but rarely in adenohypophyses. This result was confirmed by pyrosequencing analysis. We also found that RASSF3 mRNA level correlated negatively to its gene promoter methylation level. RASSF3 hypermethylation and downregulation was also observed in rat GH3 and mouse GT1.1 somatotroph adenoma cell lines. 5-Aza-2′ deoxycytidine and trichostatin-A treatment induced RASSF3 promoter demethylation, and restored its expression in GH3 and GT1.1 cell lines. RASSF3 overexpression in GH3 and GT1.1 cells inhibited proliferation, induced apoptosis accompanied by increased Bax, p53, and caspase-3 protein and decreased Bcl-2 protein expression. We also found that the antitumor effect of RASSF3 was p53 dependent, and p53 knockdown blocked RASSF3-induced apoptosis and growth inhibition. Taken together, our results suggest that hypermethylation-induced RASSF3 silencing plays an important role in the tumorigenesis of pituitary somatotroph adenomas.

The E3 ubiquitin ligase Itch regulates tumor suppressor protein RASSF5/NORE1 stability in an acetylation-dependent manner

Ras association (RalGDS/AF-6) domain family member RASSF5 is a non-enzymatic RAS effector super family protein, known to be involved in cell growth regulation. Expression of RASSF5 is found to be extinguished by promoter hypermethylation in different human cancers, and its ectopic expression suppresses cell proliferation and tumorigenicity. Interestingly, this role in tumorigenesis has been confounded by the fact that regulation at molecular level remains unclear and many transformed cells actually display elevated RASSF5 expression. Here, we demonstrate that E3 ubiquitin ligase Itch is a unique binding partner of RASSF5. Itch can interact with PPxY motif in RASSF5 both in vivo and in vitro through its WW domains. Importantly, the overexpression of Itch induces RASSF5 degradation by poly-ubiquitination via 26S proteasome pathway. In addition, our results indicate that the elevated levels of RASSF5 found in tumor cells due to acetylation, which restricts its binding to Itch and results in a more stable inert protein. Inhibition of RASSF5 acetylation permits its interaction with Itch and provokes proteasomal degradation. These data suggest that apart from promoter methylation, hyperacetylation could also be downregulating RASSF5 function in different human cancer. Finally, results from functional assays suggest that the overexpression of wild type, not the ligase activity defective Itch negatively regulate RASSF5-mediated G1 phase transition of cell cycle as well as apoptosis, suggesting that Itch alone is sufficient to alter RASSF5 function. Collectively, the present investigation identifies a HECT class E3 ubiquitin ligase Itch as a unique negative regulator of RASSF5, and suggests the possibility that acetylation as a potential therapeutic target for human cancer.

Colorectal cancer and RASSF family--a special emphasis on RASSF1A

The RAS-association domain family, commonly referred to as RASSF, is a family of 10 members (RASSF1-10) implicated in a variety of key biological processes, including cell cycle regulation, apoptosis and microtubule stability. Furthermore, RASSFs have been implicated in tumorigenesis and several family members are now thought to be tumor suppressors. As opposed to the KRAS oncogene, for which mutational activation is frequent in colorectal cancer (CRC), RASSFs are found to be silenced mainly by aberrant promoter methylation. In particular, RASSF1A, RASSF2 and RASSF5 methylation has been associated with CRC development, though the mechanisms of action remain poorly understood. This review focus on the current knowledge of RASSF inactivation in CRC, particularly RASSF1A, and on the implications RASSFs may have as potential biomarkers and for the development of new targeted therapies for CRC.

The RASSF gene family members RASSF5, RASSF6 and RASSF7 show frequent DNA methylation in neuroblastoma

Background

Hypermethylation of promotor CpG islands is a common mechanism that inactivates tumor suppressor genes in cancer. Genes belonging to the RASSF gene family have frequently been reported as epigenetically silenced by promotor methylation in human cancers. Two members of this gene family, RASSF1A and RASSF5A have been reported as methylated in neuroblastoma. Data from our previously performed genome-wide DNA methylation array analysis indicated that other members of the RASSF gene family are targeted by DNA methylation in neuroblastoma.

Results

In the current study, we found that several of the RASSF family genes (RASSF2, RASSF4, RASSF5, RASSF6, RASSF7, and RASSF10) to various degrees were methylated in neuroblastoma cell lines and primary tumors. In addition, several of the RASSF family genes showed low or absent mRNA expression in neuroblastoma cell lines. RASSF5 and RASSF6 were to various degrees methylated in a large portion of neuroblastoma tumors and RASSF7 was heavily methylated in most tumors. Further, CpG methylation sites in the CpG islands of some RASSF family members could be used to significantly discriminate between biological subgroups of neuroblastoma tumors. For example, RASSF5 methylation highly correlated to MYCN amplification and INRG stage M. Furthermore, high methylation of RASSF6 was correlated to unfavorable outcome, 1p deletion and MYCN amplification in our tumor material.

In conclusion

This study shows that several genes belonging to the RASSF gene family are methylated in neuroblastoma. The genes RASSF5, RASSF6 and RASSF7 stand out as the most promising candidate genes for further investigations in neuroblastoma.

The RASSF3 candidate tumor suppressor induces apoptosis and G1-S cell-cycle arrest via p53

RASSF3 is the smallest member of the RASSF family of proteins that function as tumor suppressors. Unlike other members of this important family, the mechanisms through which RASSF3 suppresses tumor formation remain unknown. Here, we show that RASSF3 expression induces p53-dependent apoptosis and its depletion attenuates DNA damage-induced apoptosis. We found that RASSF3-induced apoptosis depended upon p53 expression. Exogenous expression of RASSF3 induced G(1)-S arrest, which was also p53 dependent. In contrast, loss of RASSF3 promoted cell-cycle progression, abrogated UVB- and VP-16-induced G(1)-S arrest, decreased p53 protein and target gene expression, and prevented DNA repair. RASSF3 was shown to directly interact with and facilitate the ubiquitination of MDM2, the E3 ligase that targets p53 for degradation, thereby increasing p53 stabilization. Together, our findings show the tumor suppressor activity of RASSF3, which occurs through p53 stabilization and regulation of apoptosis and the cell cycle.

Pathogenetic and Prognostic Significance of Inactivation of RASSF Proteins in Human Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent solid tumors worldwide, with limited treatment options and a dismal prognosis. Thus, there is a strong need to expand the basic and translational research on this deadly disease in order to improve the prognosis of HCC patients. Although the etiologic factors responsible for HCC development have been identified, the molecular pathogenesis of liver cancer remains poorly understood. Recent evidence has shown the frequent downregulation of Ras association domain family (RASSF) proteins both in the early and late stages of hepatocarcinogenesis. Here, we summarize the data available on the pathogenetic role of inactivation of RASSF proteins in liver cancer, the molecular mechanisms responsible for suppression of RASSF proteins in HCC, and the possible clinical implications arising from these discoveries. Altogether, the data indicate that inactivation of the RASSF1A tumor suppressor is ubiquitous in human liver cancer, while downregulation of RASSF2 and RASSF5 proteins is limited to specific HCC subsets. Also, the present findings speak in favour of therapeutic strategies aimed at reexpressing RASSF1A, RASSF2, and RASSF5 genes and/or inactivating the RASSF cellular inhibitors for the treatment of human liver cancer.

Combined RASSF1A and RASSF2A Promoter Methylation Analysis as Diagnostic Biomarker for Bladder Cancer

Promoter hypermethylation, a widely studied epigenetic event known to influence gene expression levels, has been proposed as a potential biomarker in multiple types of cancer. Clinical diagnostic biomarkers are needed for reliable prediction of bladder cancer recurrence. In this paper, DNA promoter methylation of five C-terminal Ras-association family members (RASSF1A, RASSF2A, RASSF4, RASSF5, and RASSF6) was studied in 64 formalin-fixed paraffin-embedded (FFPE) bladder cancer and normal adjacent tissues using methylation-specific high-resolution melting (MS-HRM) analysis. Results showed that 73% (30/41) of transitional cell carcinoma, 100% (3/3) of squamous cell carcinoma, and 100% (4/4) of small cell carcinoma demonstrated promoter methylation of the RASSF1A or RASSF2A gene, but only 6% (1/16) of normal tissues had promoter methylation of RASSF genes. Testing positive for hypermethylation of RASSF1A or RASSF2A promoter provided 77% sensitivity and 94% specificity for identification of cancer tissues with an area under the curve of 0.854, suggesting that promoter methylation analysis of RASSF1A and RASSF2A genes has potential for use as a recurrence biomarker for bladder cancer patients.

Activation of v-Myb avian myeloblastosis viral oncogene homolog-like2 (MYBL2)-LIN9 complex contributes to human hepatocarcinogenesis and identifies a subset of hepatocellular carcinoma with mutant p53

Up-regulation of the v-Myb avian myeloblastosis viral oncogene homolog-like2 B-Myb (MYBL2) gene occurs in human hepatocellular carcinoma (HCC) and is associated with faster progression of rodent hepatocarcinogenesis. We evaluated, in distinct human HCC prognostic subtypes (as defined by patient survival length), activation of MYBL2 and MYBL2-related genes, and relationships of p53 status with MYBL2 activity. Highest total and phosphorylated protein levels of MYBL2, E2F1-DP1, inactivated retinoblastoma protein (pRB), and cyclin B1 occurred in HCC with poorer outcome (HCCP), compared to HCC with better outcome (HCCB). In HCCP, highest LIN9-MYBL2 complex (LINC) and lowest inactive LIN9-p130 complex levels occurred. MYBL2 positively correlated with HCC genomic instability, proliferation, and microvessel density, and negatively with apoptosis. Higher MYBL2/LINC activation in HCC with mutated p53 was in contrast with LINC inactivation in HCC harboring wildtype p53. Small interfering RNA (siRNA)-mediated MYBL2/LINC silencing reduced proliferation, induced apoptosis, and DNA damage at similar levels in HCC cell lines, irrespective of p53 status. However, association of MYBL2/LINC silencing with doxorubicin-induced DNA damage caused stronger growth restraint in p53(-/-) Huh7 and Hep3B cells than in p53(+/+) Huh6 and HepG2 cells. Doxorubicin triggered LIN9 dissociation from MYBL2 in p53(+/+) cell lines and increased MYBL2-LIN9 complexes in p53(-/-) cells. Doxorubicin-induced MYBL2 dissociation from LIN9 led to p21(WAF1) up-regulation in p53(+/+) but not in p53(-/-) cell lines. Suppression of p53 or p21(WAF1) genes abolished DNA damage response, enhanced apoptosis, and inhibited growth in doxorubicin-treated cells harboring p53(+/+) .

CONCLUSION

We show that MYBL2 activation is crucial for human HCC progression. In particular, our data indicate that MYBL2-LIN9 complex integrity contributes to survival of DNA damaged p53(-/-) cells. Thus, MYBL2 inhibition could represent a valuable adjuvant for treatments against human HCC with mutated p53.

Suppression of hydroxyurea-induced centrosome amplification by NORE1A and down-regulation of NORE1A mRNA expression in non-small cell lung carcinoma

The candidate tumor suppressor NORE1A is a nucleocytoplasmic shuttling protein, and although a fraction of the NORE1A in cells is localized to their centrosomes, the role of centrosomal NORE1A has not been elucidated. In this study we investigated the role of NORE1A in the numerical integrity of centrosomes and chromosome stability in lung cancer cells. Exposure of p53-deficient H1299 lung cancer cell line to hydroxyurea (HU) resulted in abnormal centrosome amplification (to 3 or more centrosomes per cell) as determined by immunofluorescence analysis with anti-γ-tubulin antibody, and forced expression of wild-type NORE1A partially suppressed the centrosome amplification. The nuclear export signal (NES) mutant (L377A/L384A) of NORE1A did not localize to centrosomes and did not suppress the centrosome amplification induced by HU. Fluorescence in situ hybridization analyses with probes specific for chromosomes 2 and 16 showed that wild-type NORE1A, but not NES-mutant NORE1A, suppressed chromosome instability in HU-exposed H1299 cells that was likely to have resulted from centrosome amplification. We next examined the status of NORE1A mRNA expression in non-small cell lung carcinoma (NSCLC) and detected down-regulation of NORE1A mRNA expression in 25 (49%) of 51 primary NSCLCs by quantitative real-time-polymerase chain reaction analysis. These results suggest that NORE1A has activity that suppresses the centrosome amplification induced by HU and that NORE1A mRNA down-regulation is one of the common gene abnormalities in NSCLCs, both of which imply a key preventive role of NORE1A against the carcinogenesis of NSCLC.

Tumor suppressor RASSF1A promoter: p53 binding and methylation

Oncogenes and tumor suppressors work in concert to regulate cell growth or death, which is a pair of antagonist factors for regulation of tumorigenesis. Here we show promoter characteristic of tumor suppressor RASSF1A, which revealed a p53 binding site in the distal and a GC-rich region in the proximal promoter region of RASSF1A, in despite of TATA box-less. The GC-rich region, which is ∼300 bp upstream from the RASSF1A ATG, showed the strongest promoter activity in an assay of RASSF1A-driving GFP expression. Methylation analysis of the CpG island showed that 78.57% of the GC sties were methylated in testis tumor samples compared with methylation-less in normal testis. Hypermethylation of the GC-rich region is associated with RASSF1A silencing in human testis tumors. In addition, electrophoretic mobility shift assay indicated that p53 protein bound to the RASSF1A promoter. Further chromatin immunoprecipitation confirmed p53 binding to the RASSF1A. Moreover, p53 binding to the promoter down-regulated RASSF1A expression. These results suggest that p53 protein specifically binds to the RASSF1A promoter and inhibits its expression. Our results provide new insight into the mechanism of action of tumor suppressors and may be a starting point for development of new approaches to cancer treatment.

Epigenetic inactivation of the NORE1 gene correlates with malignant progression of colorectal tumors

Background

NORE1 (RASSF5) is a newly described member of the RASSF family with Ras effector function. NORE1 expression is frequently inactivated by aberrant promoter hypermethylation in many human cancers, suggesting that NORE1 might be a putative tumor suppressor. However, expression and mutation status of NORE1 and its implication in colorectal tumorigenesis has not been evaluated.

Methods

Expression, mutation, and methylation status of NORE1A and NORE1B in 10 cancer cell lines and 80 primary tumors were characterized by quantitative PCR, SSCP, and bisulfite DNA sequencing analyses. Effect of NORE1A and NORE1B expression on tumor cell growth was evaluated using cell number counting, flow cytometry, and colony formation assays.

Results

Expression of NORE1A and NORE1B transcript was easily detectable in all normal colonic epithelial tissues, but substantially decreased in 7 (70%) and 4 (40%) of 10 cancer cell lines and 31 (38.8%) and 25 (31.3%) of 80 primary carcinoma tissues, respectively. Moreover, 46 (57.6%) and 38 (47.5%) of 80 matched tissue sets exhibited tumor-specific reduction of NORE1A and NORE1B, respectively. Abnormal reduction of NORE1 was more commonly observed in advanced stage and high grade tumors compared to early and low grade tumors. While somatic mutations of the gene were not identified, its expression was re-activated in all low expressor cells after treatment with the demethylating agent 5-aza-dC. Bisulfite DNA sequencing analysis of 31 CpG sites within the promoter region demonstrated that abnormal reduction of NORE1A is tightly associated with promoter CpG sites hypermethylation. Moreover, transient expression and siRNA-mediated knockdown assays revealed that both NORE1A and NORE1B decrease cellular growth and colony forming ability of tumor cells and enhance tumor cell response to apoptotic stress.

Conclusion

Our data indicate that epigenetic inactivation of NORE1 due to aberrant promoter hypermethylation is a frequent event in colorectal tumorigenesis and might be implicated in the malignant progression of colorectal tumors.

Intracellular signaling and hepatocellular carcinoma

Liver cancer is the fifth most common cancer and the third most common cause of cancer related death in the world. The recent development of new techniques for the investigations of global change in the gene expression, signaling pathways and wide genome binding has provided novel information for the mechanisms underlying liver cancer progression. Although these studies identified gene expression signatures in hepatocellular carcinoma, the early steps of the development of hepatocellular carcinomas (HCC) are not well understood. The development of HCC is a multistep process which includes the progressive alterations of gene expression leading to the increased proliferation and to liver cancer. This review summarizes recent progress in the identification of the key steps of the development of HCC with the focus on early events of carcinogenesis and on the role of translational and epigenetic alterations in the development of HCC. Quiescent stage of the liver is supported by several tumor suppressor proteins including p53, Rb and C/EBPα. Studies with chemical models of liver carcinogenesis and with human HCC have shown that the elevation of gankyrin is responsible for the elimination of these three proteins at early steps of carcinogenesis. Later stages of progression of the liver cancer are associated with alterations in many signaling pathways including translation which leads to epigenetic silencing/activation of many genes. Particularly, recent reports suggest a critical role of histone deacetylase 1, HDAC1, in the development of HCC through the interactions with transcription factors such as C/EBP family proteins.

Examination of the expanding pathways for the regulation of p21 expression and activity

p21(Waf1/Cip1/Sdi1) was originally identified as an inhibitor of cyclin-dependent kinases, a mediator of p53 in growth suppression and a marker of cellular senescence. p21 is required for proper cell cycle progression and plays a role in cell death, DNA repair, senescence and aging, and induced pluripotent stem cell reprogramming. Although transcriptional regulation is considered to be the initial control point for p21 expression, there is growing evidence that post-transcriptional and post-translational regulations play a critical role in p21 expression and activity. This review will briefly discuss the activity of p21 and focus on current knowledge of the determinants that control p21 transcription, mRNA stability and translation, and protein stability and activity.

The N-terminal RASSF family: a new group of Ras-association-domain-containing proteins, with emerging links to cancer formation

The RASSF (Ras-association domain family) has recently gained several new members and now contains ten proteins (RASSF1-10), several of which are potential tumour suppressors. The family can be split into two groups, the classical RASSF proteins (RASSF1-6) and the four recently added N-terminal RASSF proteins (RASSF7-10). The N-terminal RASSF proteins have a number of differences from the classical RASSF members and represent a newly defined set of potential Ras effectors. They have been linked to key biological processes, including cell death, proliferation, microtubule stability, promoter methylation, vesicle trafficking and response to hypoxia. Two members of the N-terminal RASSF family have also been highlighted as potential tumour suppressors. The present review will summarize what is known about the N-terminal RASSF proteins, addressing their function and possible links to cancer formation. It will also compare the N-terminal RASSF proteins with the classical RASSF proteins and ask whether the N-terminal RASSF proteins should be considered as genuine members or imposters in the RASSF family.