Biomedical subjects

Dae-Sik Lim

Publications and source records attributed to Dae-Sik Lim.

12 recordsLinked to original sources

PubMed2006

Role of the tumor suppressor RASSF1A in Mst1-mediated apoptosis.

Mammalian sterile 20-like kinase 1 (Mst1) is activated by both caspase-mediated cleavage and phosphorylation in response to apoptotic stimuli, including Fas ligation. Here, we examined the possible role of the tumor suppressor RASSF1A in Mst1 activation and Mst1-mediated apoptosis induced by death receptor signaling. 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. Whereas purified recombinant RASSF1A inhibited the kinase activity of purified recombinant Mst1 in vitro, overexpression of RASSF1A increased the kinase activity of Mst1 in intact cells, suggesting that regulation of Mst1 by RASSF1A in vivo involves more than the simple association of the two proteins. Both the activation of Mst1 and the incidence of apoptosis induced by Fas ligation were markedly reduced in cells depleted of RASSF1A by RNA interference and were increased by restoration of RASSF1A expression in RASSF1A-deficient cells. Moreover, the stimulatory effect of RASSF1A overexpression on Fas-induced apoptosis was inhibited by depletion of Mst1. These findings indicate that RASSF1A facilitates Mst1 activation and thereby promotes apoptosis induced by death receptor signaling.

Apoptosis↗

PubMed2006

Dual role of Nbs1 in the ataxia telangiectasia mutated-dependent DNA damage response.

The Nbs1 protein associates with Mre11 and Rad50 proteins to form the Mre11-Rad50-Nbs1 complex, which plays an important role in the intracellular signaling pathway activated in response to DNA damage. Mutations in the genes for each of these three components of the Mre11-Rad50-Nbs1 complex result in human diseases characterized by genomic instability. Insight into the functions of Nbs1 in the DNA damage response mediated by the protein kinase, ataxia telangiectasia mutated, has been provided by recent studies. Nbs1 acts both as a downstream target of ataxia telangiectasia mutated in the S-phase checkpoint of the cell cycle as well as an upstream modulator or activator of ataxia telangiectasia mutated in the DNA damage response.

Ataxia Telangiectasia Mutated Proteins↗

PubMed2006

Mouse emi1 has an essential function in mitotic progression during early embryogenesis.

For successful mitotic entry and spindle assembly, mitosis-promoting factors are activated at the G(2)/M transition stage, followed by stimulation of the anaphase-promoting complex (APC), an E3 ubiquitin ligase, to direct the ordered destruction of several critical mitotic regulators. Given that inhibition of APC activity is important for preventing premature or improper ubiquitination and destruction of substrates, several modulators and their regulation mechanisms have been studied. Emi1, an early mitotic inhibitor, is one of these regulatory factors. Here we show, by analyzing Emi1-deficient embryos, that Emi1 is essential for precise mitotic progression during early embryogenesis. Emi1(-/-) embryos were found to be lethal due to a defect in preimplantation development. Cell proliferation appeared to be normal, but mitotic progression was severely defective during embryonic cleavage. Moreover, multipolar spindles and misaligned chromosomes were frequently observed in Emi1 mutant cells, possibly due to premature APC activation. Our results collectively suggest that the late prophase checkpoint function of Emi1 is essential for accurate mitotic progression and embryonic viability.

Anaphase-Promoting Complex-Cyclosome↗

PubMed2005

RASSF1A is not appropriate as an early detection marker or a prognostic marker for non-small cell lung cancer.

Aberrant methylation of several tumor suppressor genes often occurs during the pathogenesis of lung cancer. RASSF1A is one of the tumor suppressor genes, and it is frequently inactivated by hypermethylation of its promoter region in a variety of human cancers, including lung cancer. It has recently been suggested that RASSF1A methylation was frequently observed in poorly differentiated tumors, and that it was correlated with adverse survival in lung adenocarcinoma (Tomizawa Y, et al., Clin Cancer Res 2002;8:2362-8). In this study, we investigated the pathogenetic and clinicopathologic significance of RASSF1A methylation for the development and/or progression of non small cell lung cancer (NSCLC). We examined 116 cases of NSCLC for the methylation status of RASSF1A. Methylation-specific analysis demonstrated that 40.5% (47 of 116) of the cases were methylated at the CpG sites in the promoter. Methylation of RASSF1A was associated with cellular differentiation (p = 0.0244) and it was related to survival (p = 0.0276). However, there was no association between RASSF1A methylation and the individual clinicopathologic features: TNM stage (p > 0.1), recurrence (p > 0.1), lymphatic permeation (p > 0.1) and smoking duration time (p > 0.1). Furthermore, we analyzed RASSF1A's probability as a prognostic marker by using stepwise Cox proportional hazard regression testing. As a result, the stage proved to be the most important factor (p = 0.0089), more than any other factors such as age, gender, cell type, methylation status, differentiation, smoking duration time, tumor size and lymph node permeation. There was no other significant factor other than stage and age. These results show that epigenetic inactivation of RASSF1A cannot be a prognostic marker of NSCLC.

Adult↗

PubMed2004

The centrosomal protein RAS association domain family protein 1A (RASSF1A)-binding protein 1 regulates mitotic progression by recruiting RASSF1A to spindle poles.

The protein RAS association domain family protein 1A (RASSF1A), which is encoded by a gene that is frequently silenced in many types of sporadic tumor, functions in mitosis as a regulator of the anaphase-promoting complex (APC). With the use of a yeast two-hybrid screen, we identified a human protein, previously designated C19ORF5, that interacts with RASSF1A. This protein, here redesignated RASSF1A-binding protein 1 (RABP1), contains two microtubule-associated protein domains, and its association with RASSF1A was confirmed in mammalian cells by immunoprecipitation and immunofluorescence analyses. RABP1 was found to be localized to the centrosome throughout the cell cycle in a manner dependent on its microtubule-associated protein domains. Ectopic expression of RABP1 induced both stabilization of mitotic cyclins and mitotic arrest at prometaphase in a RASSF1A-dependent manner. It also increased the extent of association between RASSF1A and Cdc20. 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. These findings indicate that RABP1 is required for the recruitment of RASSF1A to the spindle poles and for its inhibition of APC-Cdc20 activity during mitosis.

Anaphase-Promoting Complex-Cyclosome↗

PubMed2004

Control of APC-Cdc20 by the tumor suppressor RASSF1A.

The tumor suppressor gene RASSF1A is frequently hypermethylated in various tumors. However, how RASSF1A functions in tumor suppression was unknown. Our study shows that RASSF1A regulates the stability of mitotic cyclins and the timing of mitotic progression by inhibiting APC-Cdc20. RASSF1A appears to work in early pro-metaphase, after Emi1 destruction and before activation of the Mad2-dependent spindle checkpoint. Loss of RASSF1A expression induces premature APC activation, thereby resulting in acceleration of mitotic cyclin degradation and mitotic progression as well as induction of mitotic abnormalities. Thus, RASSF1A plays a critical role in mitotic progression and tumor suppression by controlling APC-Cdc20 activity.

Anaphase-Promoting Complex-Cyclosome↗

PubMed2004

The tumour suppressor RASSF1A regulates mitosis by inhibiting the APC-Cdc20 complex.

The tumour suppressor gene RASSF1A is frequently silenced in lung cancer and other sporadic tumours as a result of hypermethylation of a CpG island in its promoter. However, the precise mechanism by which RASSF1A functions in cell cycle regulation and tumour suppression has remained unknown. Here we show that RASSF1A regulates the stability of mitotic cyclins and the timing of mitotic progression. RASSF1A localizes to microtubules during interphase and to centrosomes and the spindle during mitosis. The overexpression of RASSF1A induced stabilization of mitotic cyclins and mitotic arrest at prometaphase. RASSF1A interacts with Cdc20, an activator of the anaphase-promoting complex (APC), resulting in the inhibition of APC activity. Although RASSF1A does not contribute to either the Mad2-dependent spindle assembly checkpoint or the function of Emi1 (ref. 1), depletion of RASSF1A by RNA interference accelerated the mitotic cyclin degradation and mitotic progression as a result of premature APC activation. It also caused a cell division defect characterized by centrosome abnormalities and multipolar spindles. These findings implicate RASSF1A in the regulation of both APC-Cdc20 activity and mitotic progression.

Anaphase-Promoting Complex-Cyclosome↗

PubMed2004

Analysis of ataxia-telangiectasia mutated (ATM)- and Nijmegen breakage syndrome (NBS)-regulated gene expression patterns.

PURPOSE: Ataxia-telangiectasia (A-T) is a progressive, degenerative, complex autosomal recessive disease characterized by cerebellar degeneration, immunodeficiency, premature aging, radiosensitivity, and a predisposition to cancer. Mutations in the ataxia-telangiectasia mutated (atm) gene, which phosphorylates downstream effector proteins, are linked to A-T. One of the proteins phosphorylated by the ATM protein is Nijmegen Breakage Syndrome protein (NBS, p95/nibrin), which was recently shown to be encoded by a gene mutated in the Nijmegen breakage syndrome (nbs), an autosomal recessive disease with a phenotype virtually similar to that of A-T. The similarities in the clinical and cellular features of NBS and A-T have led us to hypothesize that the two corresponding gene products may function in similar ways in the cellular signaling pathway. Thus, we sought to identify genes whose expression is mediated by the atm and nbs gene products. MATERIAL AND METHODS: To identify genes, we performed an analysis of oligonucleotide microarrays using the appropriate cell lines, isogenic A-T (ATM-) and control cells (ATM+), and isogenic NBS (NBS-) and control cells (NBS+). RESULTS: We examined genes regulated by ATM and NBS, respectively. To determine the effect of ATM and NBS on gene expression in detail, we classified these genes into different functional categories, including those involved in apoptosis, cell cycle/DNA replication, growth/differentiation, signal transduction, cell-cell adhesion, and metabolism. In addition, we compared the genes regulated by the ATM and NBS to determine the relationship of their signaling pathways and to better understand their functional relationship. CONCLUSIONS: We found that, while ATM and NBS regulate several genes in common, both of these proteins also have distinct patterns of gene regulation, findings consistent with the functional overlap and distinctiveness of these two conditions. Due to the role of ATM and NBS in tumor suppression and the response to chemotherapy and radiotherapy, these findings may assist in the development of a more rational approach to cancer treatment, as well as a better understanding of tumorigenesis.

Ataxia Telangiectasia Mutated Proteins↗

PubMed2004

Chromatin association of rad17 is required for an ataxia telangiectasia and rad-related kinase-mediated S-phase checkpoint in response to low-dose ultraviolet radiation.

Activation of the S-phase checkpoint results in an inhibition of DNA synthesis in response to DNA damage. This is an active cellular response that may enhance cell survival and limit heritable genetic abnormalities. While much attention has been paid to elucidating signal transduction pathways regulating the ionizing radiation-induced S-phase checkpoint, less is known about whether UV radiation initiates the process and the mechanism controlling it. Here, we demonstrate that low-dose UV radiation activates an S-phase checkpoint that requires the ataxia telangiectasia and Rad-related kinase (ATR). ATR regulates the S-phase checkpoint through phosphorylation of the downstream target structural maintenance of chromosomal protein 1. Furthermore, the ATPase activity of Rad17 is crucial for its chromatin association and for the functional effects of ATR activation in response to low-dose UV radiation. These results suggest that low-dose UV radiation activates an S-phase checkpoint requiring ATR-mediated signal transduction pathway.

Adenosine Triphosphatases↗

PubMed2003

Association of hepatitis B virus polymerase with promyelocytic leukemia nuclear bodies mediated by the S100 family protein p11.

Hepatitis B virus (HBV) polymerase (Pol) interacts with cellular chaperone proteins and thereby performs multiple functions necessary for viral replication. Yeast two-hybrid analysis was applied to identify additional cellular targets required for HBV Pol function. HBV Pol interacted with S100A10 (p11), a Ca(2+)-modulated protein previously shown to bind to annexin II. The interaction between HBV Pol and p11 was confirmed by co-immunoprecipitation of the two proteins synthesized either in vitro or in transfected cells and by inhibition of the DNA polymerase activity of HBV Pol by p11. Immunofluorescence analysis of transfected human cell lines revealed that, although most HBV Pol and p11 was restricted to the cytoplasm, a small proportion of each protein colocalized as nuclear speckles; HBV Pol was not detected in the nucleus in the absence of p11. The HBV Pol-p11 nuclear speckles coincided with nuclear bodies containing the promyelocytic leukemia protein PML. Furthermore, the association of HBV Pol-p11 with PML was increased by exposure of cells to EGTA and inhibited by valinomycin. These results suggest a role for p11 in modulation of HBV Pol function and implicate PML nuclear bodies and intracellular Ca(2+) in viral replication.

Annexin A2↗

PubMed2003

Distinct functions of Nijmegen breakage syndrome in ataxia telangiectasia mutated-dependent responses to DNA damage.

Phosphorylation of NBS1, the product of the gene mutated in Nijmegen breakage syndrome (NBS), by ataxia telangiectasia mutated (ATM), the product of the gene mutated in ataxia telangiectasia, is required for activation of the S phase checkpoint in response to ionizing radiation (IR). However, NBS1 is also thought to play additional roles in the cellular response to DNA damage. To clarify these additional functions of NBS1, we generated NBS cell lines stably expressing various NBS1 mutants from retroviral vectors. The ATM-dependent activation of CHK2 by IR was defective in NBS cells but was restored by ectopic expression of wild-type NBS1. The defects in ATM-dependent activation of CHK2, S phase checkpoint control, IR-induced nuclear focus formation, and radiation sensitivity apparent in NBS cells were not corrected by expression of NBS1 mutants that lack an intact MRE11 binding domain, suggesting that formation of the NBS1-MRE11-RAD50 complex is required for the corresponding normal phenotypes. Expression of NBS1 proteins with mutated ATM-targeted phosphorylation sites (serines 278 or 343) did not restore S phase checkpoint control but did restore the ability of IR to activate CHK2 and to induce nuclear focus formation and normalized the radiation sensitivity of NBS cells. Expression of NBS1 containing mutations in the forkhead-associated or BRCA1 COOH terminus domains did not correct the defects in radiation sensitivity or nuclear focus formation but did restore S phase checkpoint control in NBS cells. Together, these data demonstrate that multiple functional domains of NBS1 are required for ATM-dependent activation of CHK2, nuclear focus formation, S phase checkpoint control, and cell survival after exposure to IR.

Acid Anhydride Hydrolases↗

PubMed2002

Two molecularly distinct G(2)/M checkpoints are induced by ionizing irradiation.

Cell cycle checkpoints are among the multiple mechanisms that eukaryotic cells possess to maintain genomic integrity and minimize tumorigenesis. Ionizing irradiation (IR) induces measurable arrests in the G(1), S, and G(2) phases of the mammalian cell cycle, and the ATM (ataxia telangiectasia mutated) protein plays a role in initiating checkpoint pathways in all three of these cell cycle phases. However, cells lacking ATM function exhibit both a defective G(2) checkpoint and a prolonged G(2) arrest after IR, suggesting the existence of different types of G(2) arrest. Two molecularly distinct G(2)/M checkpoints were identified, and the critical importance of the choice of G(2)/M checkpoint assay was demonstrated. The first of these G(2)/M checkpoints occurs early after IR, is very transient, is ATM dependent and dose independent (between 1 and 10 Gy), and represents the failure of cells which had been in G(2) at the time of irradiation to progress into mitosis. Cell cycle assays that can distinguish mitotic cells from G(2) cells must be used to assess this arrest. In contrast, G(2)/M accumulation, typically assessed by propidium iodide staining, begins to be measurable only several hours after IR, is ATM independent, is dose dependent, and represents the accumulation of cells that had been in earlier phases of the cell cycle at the time of exposure to radiation. G(2)/M accumulation after IR is not affected by the early G(2)/M checkpoint and is enhanced in cells lacking the IR-induced S-phase checkpoint, such as those lacking Nbs1 or Brca1 function, because of a prolonged G(2) arrest of cells that had been in S phase at the time of irradiation. Finally, neither the S-phase checkpoint nor the G(2) checkpoints appear to affect survival following irradiation. Thus, two different G(2) arrest mechanisms are present in mammalian cells, and the type of cell cycle checkpoint assay to be used in experimental investigation must be thoughtfully selected.

Ataxia Telangiectasia↗