Disease relevance of RASSF1

• RASSF1A, one of the two major isoforms of the putative tumor suppressor gene RASSF1, located at 3p21.3, is inactivated in a variety of human cancers including lung, breast, bladder and renal cell carcinomas [1].
• RASSF1 and RARbeta2 represented 75.8% of methylation events occurring most frequently in salivary duct and acinic cell carcinomas [2].
• Methylation occurred in 9 of 23 (39.1%) benign tumors; 3 (25.0%) pleomorphic adenomas and 6 (66.7%) Warthin's tumors at the MGMT, DAPK, or RASSF1 genes [2].
• We examined RASSF1 in non-small lung cancer (NSCLC) to search for clinical implications [3].
• We investigated the expression and mutation of three isoforms of the Ras effector RASSF1 in 10 primary osteosarcomas and 6 osteosarcoma cell lines [4].
• This is the first report suggesting that reduced histone acetylation or H3K4me2 methylation and increased dimethyl-H3-K9 methylation play a critical role in the maintenance of promoter DNA methylation-associated RASSF1A gene silencing in prostate cancer [5].
• Aberrant mitotic spindles and chromosome aberrations are reported phenotypes in RASSF1A inactivated cells [6].

High impact information on RASSF1

• RASSF1A, the new guardian of mitosis [7].
• Loss of expression was correlated with methylation of the CpG-island promoter sequence of RASSF1A [8].
• These characteristics indicate a potential role for RASSF1A as a lung tumour suppressor gene [8].
• By controlling the stability of microtubules and the activity of the anaphase-promoting complex (APC), RASSF1A might provide a crucial link between mechanisms of tumor suppression and mitotic cell division [9].
• RASSF1A/MAP-1 binding relieved this inhibitory interaction, resulting in MAP-1 association with Bax [10].

Chemical compound and disease context of RASSF1

• The prevalence of methylation of the p16, DAPK and RASSF1A genes was investigated in lung adenocarcinoma from smokers, former uranium miners and never smokers [11].
• METHODS: The expression and methylation status of 6 RASSF family genes were examined using RT-PCR and bisulfite PCR in CRC cell lines and in primary CRCs and colorectal adenomas [12].
• Treatment of cell lines using 5-Aza-2'-deoxycytidine (5AZA) alone or in combination with trichostatin A (TSA) succeeded in re-establishing expression of RASSF1A in cell lines derived from a renal rhabdoid, an AT/RT and a medulloblastoma [13].
• In two neuroblastoma cell lines, methylation of RASSF1A correlated with loss of RASSF1A expression and RASSF1A expression was restored after treatment with the demethylating agent 5-azacytidine [14].
• Chronic oral exposure to inorganic arsenate interferes with methylation status of p16INK4a and RASSF1A and induces lung cancer in A/J mice [15].

Biological context of RASSF1

• We explored the hypothesis that RASSF1 encodes a tumor suppressor gene for lung and breast cancers [16].
• BACKGROUND: The recently identified RASSF1 locus is located within a 120-kilobase region of chromosome 3p21.3 that frequently undergoes allele loss in lung and breast cancers [16].
• The activities of RASSF2, which were distinct from those of RASSF1, included induction of morphologic changes and apoptosis; moreover, its ability to prevent cell transformation suggests that RASSF2 acts as a tumor suppressor in CRC [12].
• In this study, we investigated the expression and methylation status of the RASSF1 gene in thyroid carcinoma [17].
• Recently, two related novel Ras effectors, NORE1 and RASSF1, have been identified as mediators of apoptosis and cell cycle arrest [18].

Anatomical context of RASSF1

• Novel functional interaction between the plasma membrane Ca2+ pump 4b and the proapoptotic tumor suppressor Ras-associated factor 1 (RASSF1) [19].
• A two-hybrid screen of a human fetal heart cDNA library, using the region 652-840 of human PMCA4b (located in the catalytic, second intracellular loop) as bait, revealed a novel interaction between PMCA4b and the tumor suppressor RASSF1, a Ras effector protein involved in H-Ras-mediated apoptosis [19].
• EXPERIMENTAL DESIGN: We performed methylation-specific PCR and protein analyses of 29 normal salivary glands, 23 benign, and 79 malignant salivary gland neoplasms to determine the pattern and potential diagnostic and/or biological role of the RASSF1, RARbeta2, DAPK, and MGMT tumor suppressor gene methylation in these tumors [2].
• No somatic mutations were noted in RASSF1 in either the primary tumors or cell lines [4].
• Tumor cell-specific BRCA1 and RASSF1A hypermethylation in serum, plasma, and peritoneal fluid from ovarian cancer patients [20].

Associations of RASSF1 with chemical compounds

• RASSF1A expression was reactivated after treatment with 5-aza-2'-deoxycytidine [21].
• All tumors and cell lines were additionally analyzed for mutation and expression of BRAF, which encodes a Ras-regulated serine/threonine kinase with oncogenic properties, as well as for expression of RASSF1A, which encodes a Ras-binding protein with tumor suppressor properties [22].
• Conversely, loss of RASSF1 in RASSF1-/- mouse embryonic fibroblasts renders the cells more sensitive to nocodazole-induced depolymerization of microtubules [23].
• An association between a single nucleotide polymorphism (SNP) at codon 133 of the RASSF1 gene, encoding either alanine (GCT) or serine (TCT), and human cancer risk remains undefined [24].
• This inactivation was associated with deacetylation and lysine 9 trimethylation of histone H3 and an impaired binding of Sp1 at the RASSF1A promoter [25].

Physical interactions of RASSF1

• The scaffold protein CNK1 interacts with the tumor suppressor RASSF1A and augments RASSF1A-induced cell death [26].
• We now identify a novel pathway connecting RASSF1A to Bax via the Bax binding protein MOAP-1 [27].
• Conversely depletion of RABP1 by RNA interference prevented both the localization of RASSF1A to the spindle poles as well as its binding to Cdc20, resulting in premature destruction of mitotic cyclins and acceleration of mitotic progression [28].
• The putative tumor suppressor RASSF1A homodimerizes and heterodimerizes with the Ras-GTP binding protein Nore1 [29].
• These results provide evidence for the first time that arginine-rich signals are able to recognize different nuclear import receptors and transport the RASSF proteins into distinct sub-cellular compartments [30].
• We show that key steps in RASSF1A-induced apoptosis are the disruption of the inhibitory Raf1-MST2 complex by RASSF1A and the concomitant enhancement of MST2 interaction with its substrate, LATS1 [31].

Regulatory relationships of RASSF1

• Both hypermethylation of the tumor suppressor gene RASSF1A and activating mutations of the KRAS and/or BRAF gene have been reported in a variety of human cancers [32].
• The tumour suppressor RASSF1A regulates mitosis by inhibiting the APC-Cdc20 complex [33].
• Hypermethylation of the tumor suppressor gene RASSF1A and activating mutation of BRAF gene have been reported recently in thyroid cancers [34].
• Moreover, the stimulatory effect of RASSF1A overexpression on Fas-induced apoptosis was inhibited by depletion of Mst1 [35].
• RASSF1A can activate Bax via MOAP-1 [27].

Other interactions of RASSF1

• Colony formation assays and flow cytometry were used to assess the tumor suppressor activities of RASSF1 and RASSF2 [12].
• Thus, RASSF4 appears to be a new member of the RASSF family of potential Ras effector/tumor suppressors [36].
• NORE is homologous to the putative tumor suppressor RASSF1 and to the Caenorhabditis elegans polypeptide T24F1 [37].
• Overexpression of CNK1-(1-282), a fragment that binds RASSF1A but is not proapoptotic, blocks the apoptosis induced by CNK1 and by Ki-Ras(G12V) [26].
• Both tumour sample sets had previously been analysed for RASSF1A promoter methylation, and p16INK4a methylation results were also available for the Wilms' tumour samples [38].

Analytical, diagnostic and therapeutic context of RASSF1

• We have identified another member of the RASSF1 gene family by in silico sequence analysis using BLAST searches [39].
• In five of six cell lines, restoration of RASSF1A mRNA was confirmed by RT-PCR [40].
• There is no correlation between promoter methylation of RASSF1A and clinicopathological findings, including histological type or grade, tumor staging, p53 and K-ras mutational status, or patients' survival [3].
• We then screened a cDNA microarray containing more than 6000 probes to identify genes differentially regulated by RASSF1A [41].
• Immunoprecipitation and immunofluorescence analyses revealed that Mst1 was associated with RASSF1A in cultured mammalian cells, with both proteins colocalizing to microtubules throughout the cell cycle [35].

References