Regulation of gene expression

A fundamental tenet of biology is that the phenotype of an organism is ultimately determined by its complement of genes. In multicellular organisms, it is the regulated pattern of expression of genes which determines the proliferation and differentiation of individual cell lineages and hence establishes the adult phenotype. It is therefore no surprise that both neoplasia and many developmental pathologies involve lesions in the regulation of specific genes. For this reason, an understanding of how genes are regulated has become an area of intense interest in both medicine and biology.     

Regulation of the rat glutathione S-transferase A2 gene by glucocorticoids: crosstalk through C/EBPs

Regulation of the rat glutathione S-transferase A2 (GSTA2) gene by glucocorticoids is biphasic in its concentration dependence to glucocorticoids, with concentrations of 10-100 nM repressing gene activity (GR-dependent), and concentrations above 1 microM increasing transactivation (PXR-dependent) in adult rat hepatocytes or transient transfection assays. Over-expression of either C/EBP alpha or beta negatively regulates basal and inducible expression of a 1.65 Kb GSTA2 luciferase reporter, and synergizes the response to glucocorticoids (GC). C/EBP responsive elements have been identified in the GSTA2 5'-flanking sequence, associated with the palindrominic Glucocorticoid Responsive Element (GRE), the Ah receptor response elements, and the antioxidant response element. In reporters lacking the palindromic GRE, negative regulation by GC is observed only when C/EBP alpha is co-expressed. Co-transfection of C/EBP alpha/beta induced gene expression of the GSTA2 XRE reporter, but negatively regulated the GSTA2 ARE-reporter. In contrast, the ARE from the rat NAD(P)H quinone oxidoreductase gene was induced by co-transfection of C/EBPs, but was still negatively regulated by GC. PXR-induction of the GSTA2 reporter was partially ablated by co-transfection of C/EBP alpha and enhanced by co-transfection of C/EBPbeta. We conclude that C/EBP alpha and beta are involved in GC-dependent repression of GSTA2 gene expression and ARE sequences that bind C/EBPs appears to be critical for these responses.     

Regulation of apoptosis through bcl-2/bax proteins expression and DNA damage by Zanthoxylum alatum

Context: Many of the major chemotherapeutic agents are secondary metabolites found in nature. Zanthoxylum alatum Roxb. (Rutaceae) is traditionally used in the treatment of various diseases.

Objective: The present study evaluates the apoptotic activity of methanol extract of Z. alatum (MEZA) on Ehrlich ascites tumor (EAT) in Swiss albino mice.

Materials and methods: The presence of flavonoids in MEZA was standardized by HPLC. The in vitro cytotoxicity of MEZA was measured by the MTT assay. The in vivo antitumor activity of MEZA (100 and 200?mg/kg b.w., i.p. for 9 days) was also evaluated. On the 10th day, EAT tumor volume, cell viability, and hematological parameters were assayed. Apoptotic morphology was determined by acredine orange/ethedium bromide using fluorescence microscopy. Apoptosis percentage was measured by flow cytometric analysis using annexine-V-FITC. Also, DNA damage and bcl-2/bax were estimated by UV-method and western blot, respectively.

Results and discussion: HPLC analysis revealed presence of three flavonoids, rutin, myricetin, and quercetin. MEZA showed satisfactory cytotoxicity in MTT assay (IC₅₀?=?111.50?µg/ml). The extract significantly (p?<?0.01) changed the tumor volume, viable, non-viable cell count, and hematological parameters towards the normal. Apoptotic activity of MEZA was confirmed by acridine orange/ethidium bromide staining, annexin-V-FITC staining, DNA fragmentation, and Bcl-2/Bax ratio.

Conclusion: The study showed that MEZA has antitumor activity which may be due to the presence of flavonoids in the extract.     

Regulation of gene expression in atherosclerosis: insights from microarray studies in monocytes/macrophages

Atherosclerosis is a pathological phenomenon in which the walls of large arteries thicken and lose elasticity as a result of the growth of atheromatous lesions. It is a complex, multifactorial disease that involves several cell types and various pathobiological processes. Its genetic basis has not yet been deciphered, but it is related to complex multigene patterns influenced by environmental interactions. In this review, we focus specifically on the application of microarrays to atherosclerosis research using monocytes and monocyte-derived macrophages, as these are key cells in all phases of atherosclerosis, from the formation of foam cells to the destabilization and rupture of the atherosclerotic plaque. These studies have provided relevant information on genes involved in atherosclerosis development, contributing to our understanding of the molecular mechanisms that underlie this complex disease.     

Clock gene mutation modulates the cellular sensitivity to genotoxic stress through altering the expression of N-methylpurine DNA glycosylase gene

Although Clock gene product, a component of the circadian pacemaker, has been suggested to participate in the regulation of cellular sensitivity to genotoxic stress, the underlying mechanism remains to be fully understood. In this study, we showed that Clock gene mutation modulates the sensitivity of hepatocytes to alkylating agent-induced genotoxic stress through altering the expression of N-methylpurine DNA glycosylase (MPG), the first enzyme in the base excision repair pathway. Neither wild-type nor Clock mutant (Clock/Clock) mice showed a significant 24-h variation in the hepatic expression of MPG. However, the mRNA and protein levels of MPG in the liver of Clock/Clock mice were significantly lower than those in wild-type liver. The cytotoxic effect of methyl methanesulfonate (MMS), a methylating agent, on primary cultured hepatocytes prepared from Clock/Clock mice was more potent than on wild-type hepatocytes, while overexpression of MPG in Clock/Clock hepatocytes restored their MMS sensitivity to the wild-type level. These findings suggest that the product of the Clock gene controls the sensitivity of cells to genotoxic stress through regulating the expression of the MPG gene. Our present findings would provide a molecular link between the circadian clock and DNA repair pathway.     

Regulation of LDL receptor expression by the effect of curcumin on sterol regulatory element pathway

To investigate the molecular mechanisms of the effect of curcumin on up-regulation of LDL receptor expression, a sterol regulatory report system was established in Xenopus laevis oocytes by microinjection of a plasmid pLXRN-4SRE-fPA, in which green fluorescence protein (GFP) gene was constructed downstream from the sterol regulatory element-1 (SRE-1), in the nucleus of the oocytes. The oocytes were treated with different kinds of natural medicines: curcumin, tea polyphenols, tanshinone, ligustrazine, ginkgolide, astragalosides. The expression of GFP was induced only by curcumin. In addition, it was also proved that the curcumin can increase the expression of functional LDL receptors in human liver hepatoma cell line HepG2. In conclusion, curcumin may up-regulate the expression of LDL receptor by its effect on SRE pathway.