Expression of receptor-Ck and SREBP genes in mononuclear cells from acute leukemia patients

Importance of LXR-alpha transcriptome in the modulation of innate immunity

Liver-X-Receptor alpha (LXR-alpha) that belongs to nuclear receptor/transcriptional factor family has been recognized to play crucial role in the regulation of lipid metabolism and inflammation. Consequently, the present study was addressed to explore the functional genomics of LXR-alpha within human blood immunomodulatory cells. The results of such a study, which involved LXR-alpha gene silencing through siRNA approach, revealed that: (a) the mRNA expression of genes coding for IL-8, IL-4, CX3CR1, LDLR, hTERT and c-myc was significantly elevated in response to LXR-alpha gene silencing whereas mRNA expression of genes coding for PPARs(alpha, gamma), CD36 and Dicer could not be detected; (b) the expression of Receptor C( k ) protein remained unaffected; (c) the mRNA expression of IFN-gamma gene was down regulated in LXR-alpha knockdown cells. Based upon these results we propose that LXR-alpha gene plays a crucial role in the regulation of innate immunity at the genomic level.

Functional genomics of PPAR-γ in human immunomodulatory cells

Keeping in view the fact that peroxisome-proliferators activated receptors-PPARs (alpha,gamma) play a crucial role in atherogenic inflammation, the present study was addressed to explore as to how selective and specific PPAR-gamma gene silencing within human mononuclear cells affects genes involved in lipid metabolism and innate immune process. Such a study revealed that with respect to control cells, the PPAR-gamma knock-out cells exhibited significant reduction in the expression of genes coding for PPAR- alpha, CD-36, LDL-R as well as significant increase in the expression of genes coding for IL-4, IL-8, IFN-gamma, CX3CR1, hTERT. However, the expression of genes coding for LXR-alpha and Receptor-C( k ) could not be detected in PPAR-gamma knock-out cells. Based on these results, we propose that PPAR-gamma gene has the inherent capacity to influence the lipid mediated inflammation process in atherosclerotic lesions.

Effect of herbal polyphenols on atherogenic transcriptome

The ancient Indian system of medicine supports the antiatherogenic properties of some herbs. The crosstalk amongst the genes coding for LDLR, LXRalpha, PPARs (alpha,gamma), CD-36 and c-myc may be important in atherogenesis because these genes control lipid metabolism, cytokine production and cellular activity within the arterial wall. Hence, we attempted for the first time to explore whether or not the polyphenols extracted from medicinal herbs had any effect on the transcription of these genes. Normal human mononuclear cells were cultured in the presence of polyphenols (and their HPLC purified sub-fractions) extracted from Green tea (Camellia sinensis), Neem (Azadirachta indica) and Tulsi (Ocimum sanctum). Transcriptional expression of these genes was measured by using RT-PCR and SCION IMAGE analysis software. These polyphenolic extracts were found to have the inherent capacity to inhibit the transcriptional expression of genes having direct involvement in atherogenic process. On the basis of these results, we propose for the first time that HPLC purified polyphenolic fraction IV of Tulsi may have a profound antiatherogenic effect.

Quantitation of the sterol regulatory element-binding protein mRNA in mononuclear blood cells by competitive RT-PCR

BACKGROUND

The genes for the sterol regulatory element-binding protein-1a (SREBP-1a), -1c, and -2, the low-density lipoprotein (LDL) receptor, and the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase play a key role in the intracellular cholesterol and lipid metabolism.

METHODS

To enable the absolute and relative quantitation of the mRNA levels of these genes we developed a competitive reverse transcriptase-polymerase chain reaction (RT-PCR) assay. The inclusion of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene for reference and normalization enabled us to accurately discriminate between a twofold variance in the expression levels of these genes. We used this assay to study their expression in mononuclear peripheral blood cells (PBMNC).

RESULTS

We found that the relative expression of SREBP-1a is tenfold higher than that of SREBP-1c, but only half of that of SREBP-2. The level of SREBP-1a transcripts correlated with that of the SREBP-1c, LDL receptor, HMG-CoA reductase, and SREBP-2 genes, whereas the amount of SREBP-1c mRNA did not show a relationship with that of the latter three genes. The most abundant transcript in PBMNC is that of SREBP-2, followed by that of SREBP-1a, whereas SREBP-1c mRNA is only found in smaller amounts.

CONCLUSIONS

This competitive RT-PCR method is very well suited for the accurate quantitation of the respective mRNAs.

Effect of green tea polyphenols on the genes with atherosclerotic potential

The genomics of atherosclerosis can arise as a result of cross-talk between the genes coding for the LDL-receptor (LDL-R), LXR-alpha, PPARs (alpha, gamma), CD36 and C-myc because these genes control lipid metabolism, cytokine production and cellular activity within the arterial wall. The effect of green tea polyphenols (GTPs) upon such genomics revealed their ability to down-regulate genes coding for PPAR-gamma, CD36, LXR-alpha, C-myc coupled with up-regulation of genes coding for LDL-R and PPAR-alpha at the transcriptional level. Based upon these results, it is proposed that GTPs have the inherent capacity to inhibit the development of atherosclerotic lesions.

NF-kappa B-binding activity in an animal diet-induced overweightness model and the impact of subsequent energy restriction

An impaired immune function linked to obesity has been shown in both human and animal studies. The purpose of this work was to analyse the hypothesis that PPAR gamma 1 participates in the inhibition of the immune response by affecting the DNA-binding ability of the NF-kappa B complex and whether the SREBP-1 expression can regulate PPAR gamma 1 expression in spleen. Diet-induced overweight rats showed higher PPAR gamma 1 (p<0.05) and lower SREBP-1 (p<0.01) mRNA expression levels with an inhibition of the DNA-binding ability of NF-kappa B compared to control rats as determined by gel-shift analysis. On the other hand, energy restriction decreased SREBP-1 (p<0.01) mRNA expression with no differences in PPAR gamma 1 mRNA expression compared to non-restricted rats, which was accompanied by a restoration in the DNA-binding ability of NF-kappa B as shown by gel-shift analysis. These results suggest that PPAR gamma 1 may be involved in the altered immune response through changes in the activity of NF-kappa B.

Regulation of PPAR-gamma gene in human promyelocytic HL-60 cell line

The present study employed human promyelocytic cell line, HL-60, as an archetype model to understand the role of cholesterol receptors (Receptor-C(k) and oxysterol-specific receptor-transcription factor LxR-alpha) in the regulation of PPAR-gamma gene recognized to control cellular differentiation and apoptosis. Such a study revealed that Receptor "C(k)"-dependent signalling pathway not only regulates PPAR-gamma gene transcription but also provides ligands for the activation of this nuclear receptor superfamily of transcription factors that control hematopoiesis. Based upon these and our earlier results, we propose a molecular cross-talk pathway between cholesterol-specific cell surface Receptor-C(k) and nuclear receptors (LxR-alpha and PPAR-gamma), which may add a new dimension in the understanding and control of leukemogenesis.

Receptor-Ck regulates membrane-bound 125 kDa protein having affinity for genomic sterol regulatory sequence

The study addressed, to resolve the role of Receptor-Ck activation in the proteolytic maturation of 125 kDa (membrane bound) sterol regulatory element binding protein (SREBP), revealed that Receptor-Ck dependent signalling is not only responsible for the proteoloytic cleavage of this 125 kDa SREBP resulting in the generation of an active 47 kDa factor but also Receptor-Ck protein has high binding affinity for both 125 kDa SREBP as well as its cleaved 47 kDa product. Based upon these coupled with our earlier findings, we propose that Receptor-Ck may be regulating genes, have sterol regulatory element (SRE) in their promoter region, through the proteolytic maturation of 125 kDa SREBP into an active 47 kDa transcription factor.