MAIN METHODS: In silico approaches were utilized to characterize a set of 88 differentially expressed genes (DEGs) from intestinal cells of rat CMA model. Interaction networks were constructed for DEGs by GeneMANIA and hub genes as well as enriched clusters in the network were screened using GLay. Gene Ontology (GO) was used for enriching functions in each cluster.
KEY FINDINGS: Four gene hubs, i.e., trefoil factor 1, 5-hydroxytryptamine (serotonin) receptor 5a, solute carrier family 6 (neurotransmitter transporter), member 11, and glutamate receptor, ionotropic, n-methyl d-aspartate 2b, exhibiting the highest node degree were predicted. Six biologically related gene clusters were also predicted. Functional enrichment of GO terms predicted neurological processes such as neurological system process regulation and nerve impulse transmission which are related to negative and positive regulation of digestive system processes., intestinal motility and absorption and maintenance of gastrointestinal epithelium.
SIGNIFICANCE: The study predicted several important genomic pathways that potentially play significant roles in metabolic disruptions or compensatory adaptations of intestinal epithelium induced by CMA. The results provide a further insight into underlying molecular mechanisms associated with CMA.
METHODS: Potential MAR/SAR sites were predicted in the AF9 gene by using MAR/SAR prediction tools. Normal nasopharyngeal epithelial cells (NP69) and NPC cells (TWO4) were treated with BA at neutral and acidic pH. Inverse-PCR (IPCR) was used to identify chromosome breaks in SAR region (contains MAR/SAR) and non-SAR region (does not contain MAR/SAR). To map the chromosomal breakpoints within the AF9 SAR and non-SAR regions, DNA sequencing was performed.
RESULTS: In the AF9 SAR region, the gene cleavage frequencies of BA-treated NP69 and TWO4 cells were significantly higher than those of untreated control. As for the AF9 non-SAR region, no significant difference in cleavage frequency was detected between untreated and BA-treated cells. A few breakpoints detected in the SAR region were mapped within the AF9 region that was previously reported to translocate with the mixed lineage leukaemia (MLL) gene in an acute lymphoblastic leukaemia (ALL) patient.
CONCLUSIONS: Our findings suggest that MAR/SAR may be involved in defining the positions of chromosomal breakages induced by BA. Our report here, for the first time, unravelled the relation of these BA-induced chromosomal breakages to the AF9 chromatin structure.
RESULTS: By using MAR/SAR recognition signature (MRS), potential MAR/SAR sites were predicted in the AF9 gene. The predicted MAR/SAR sites precisely match to the experimentally determined MAR/SARs. Hydrogen peroxide (H2O2) was used to induce apoptosis in normal nasopharyngeal epithelial cells (NP69) and NPC cells (HK1). Nested inverse polymerase chain reaction was employed to identify the AF9 gene cleavages. In the SAR region, the gene cleavage frequency of H2O2-treated cells was significantly higher than that of the non-treated cells. A few chromosomal breakages were detected within the AF9 region which was previously found to be involved in the mixed lineage leukaemia (MLL)-AF9 translocation in an acute lymphoblastic leukaemia patient. As for the non-SAR region, no significant difference in the gene cleavage frequency was found between the untreated control and H2O2-treated cells. Furthermore, H2O2-induced cleavages within the SAR region were reduced by caspase-3 inhibitor, which indirectly inhibits CAD.
CONCLUSIONS: These results reaffirm our previous findings that oxidative stress-induced apoptosis could be one of the potential mechanisms underlying chromosome breakages in nasopharyngeal epithelial cells. MAR/SAR may play a vital role in defining the location of chromosomal breakages mediated by oxidative stress-induced apoptosis, where CAD is the major nuclease.