Neuroblastic tumors (NTs) include the neuroblastomas, ganglioneuroblastomas and ganglioneuromas. We have reported previously that the calcium-sensing receptor is expressed in differentiated, favorable NTs but almost undetectable in unfavorable neuroblastomas. We have now detected hypermethylation of a particular region within the CpG island encompassing the CaSR gene promoter 2 in neuroblastoma cell lines and 25% primary neuroblastomas. Hypermethylation of this region was associated with reduced CaSR messenger RNA expression and several predictors of poor outcome in neuroblastomas, including MYCN amplification. Treatment with 5'aza-2-deoxycitidine and/or trichostatin A restored CaSR expression in MYCN-amplified cell lines. Following 5'aza-2-deoxycitidine exposure, decreased percentages of methylated CpG sites were observed at the above-mentioned region. By interphase fluorescence in situ hybridization, variable percentages of nuclei with monosomy of chromosome 3, where the human CaSR gene resides, were observed in more than 90% of primary NTs of all subgroups. Nuclei harboring this alteration were heterogeneously distributed among tumor cells. Ectopic overexpression of the calcium-sensing receptor in two MYCN-amplified neuroblastoma cell lines in which this gene is silenced by promoter hypermethylation significantly reduced their in vitro proliferation rates and almost abolished their capacity to generate xenografts in immunocompromised mice. Finally, upon acute exposure to calcium, the primary activator of this receptor, calcium-sensing receptor-overexpressing neuroblastoma cells underwent apoptosis, a process dependent on sustained activation of ERK1/2. These data would support the hypothesis that epigenetic silencing of the CaSR gene is neither an in vitro artefact in neuroblastoma cell lines nor an irrelevant, secondary event in primary NTs, but a significant mechanism for neuroblastoma survival.
Background: Apoptotic nuclear morphology can occur independently of DFF40/CAD-mediated DNA fragmentation. Results: DFF40/CAD induces 3Ј-OH single-strand DNA nicks/breaks and nuclear collapse during caspase-dependent apoptosis. Conclusion: Caspase-dependent apoptotic nuclear collapse is prompted by DFF40/CAD-mediated single-strand DNA damage. Significance: The knowledge of how apoptotic nuclear collapse occurs should be relevant to understand the final steps of cell demise and its influence on the cellular environment.
Background: Apoptotic oligonucleosomal DNA degradation is mediated by DFF40/CAD endonuclease. Results: Poor DFF40/CAD expression in the cytosol coupled to the caspase-dependent cytosolic processing of ICAD L/S impair oligonucleosomal DNA degradation in SK-N-AS cells. Conclusion: Oligonucleosomal DNA fragmentation during apoptosis is directly correlated with adequate DFF40/CAD cytosolic levels. Significance: Learning how DFF40/CAD works is crucial for understanding the relevance of apoptosis ending in cancer development.
SummaryThe transforming growth factor beta (TGF-b) pathway plays key roles in development and cancer. TGF-b signaling converges on the Smad2 and Smad3 effectors, which can either cooperate or antagonize to regulate their transcriptional targets. Here we performed in vivo and in silico experiments to study how such cooperativity and antagonism might function during neurogenesis. In vivo electroporation experiments in the chick embryo neural tube show that Smad2 and Smad3 cooperate to promote neurogenesis, as well as the transcription of Smad3-specific targets. Knockdown of Smad2 enhances neurogenesis and the transcription of Smad3-specific targets. A mathematical model of the TGF-b pathway fits the experimental results and predicts that the proportions of the three different trimeric complexes formed dictates the transcriptional responses of the R-Smad proteins. As such, Smad2 targets are activated solely by the Smad2-Smad2-Smad4 complex, whereas Smad3 targets are activated both by Smad2-Smad3-Smad4 and Smad3-Smad3-Smad4 trimers. We have modeled the Smad responses onto arbitrary genes and propose that this mechanism might be extended to additional activities of TGF-b in development and disease.
Neuroblastoma is an embryonic tumor derived from cells of the neural crest. Taking advantage of a newly developed neural crest lineage tracer and based on the hypothesis that the molecular mechanisms that mediate neural crest delamination are also likely to be involved in the spread of neuroblastoma, we were able to identify genes that are active both in neural crest development and neuroblastoma tumor formation. A subsequent search of the neuroblastoma gene server for human orthologues of genes differentially expressed in the chick embryo neural crest screen retrieved the LIM domain only protein 4 (LMO4), which was expressed in both cell types analyzed. Functional experiments in these two model systems revealed that LMO4 activity is required for neuroblastoma cell invasion and neural crest delamination. Moreover, we identified LMO4 as an essential cofactor in Snail2-mediated cadherin repression and in the epithelial-tomesenchymal transition of both neural crest and neuroblastoma cells. Together, our results suggest that the association of high levels of LMO4 with aggressive neuroblastomas is dependent on LMO4 regulation of cadherin expression and hence, tumor invasiveness.
Background: DFF40/CAD mediates nuclear fragmentation and oligonucleosomal DNA degradation during apoptosis. Results: DFF40/CAD overexpression allows apoptotic-defective LN-18 cells to display internucleosomal DNA degradation but not chromatin disassembly upon cytotoxic insult. Conclusion: DFF40/CAD can induce DNA laddering in the absence of apoptotic chromatin disassembly. Significance: Dissecting DFF40/CAD regulation may shed light on some of the apparent non-desirable tumor responses in currently used anti-cancer therapies.
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