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Tissue-specific regulation of low density lipoprotein receptor gene expression
1Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235-8887.
Abstract:
LDL receptor mRNA levels are increased by mitogenic stimulation of PBMC and are less effectively regulated by exogenous LDL in the activated cells. Enhanced LDL receptor mRNA levels reflect increased rates of gene transcription and not stabilization of mRNA. The alteration of LDL-mediated regulation of LDL receptor gene expression in mitogen-activated PBMC is not the result of cellular proliferation alone and occurs without apparent changes in measurable regulatory pools of cholesterol. These results indicate that signals transduced during mitogenic stimulation, as well as ambient LDL concentration, play a major role in regulating LDL receptor gene transcription. Fibroblasts apparently differ from PBMC in the effect of modulatory proteins on LDL receptor mRNA levels. In fibroblasts, LDL receptor gene transcription appears to be down-regulated by a short-lived protein whereas the dominant regulatory influence in PBMC appears to be a short-lived protein with a positive effect on transcription. Differences in the expression of specific transcription factors may contribute to cell-specific alterations in the regulation of LDL receptor gene expression by lipids.
Insights
Mitogenic stimulation of peripheral blood mononuclear cells (PBMC) increases LDL receptor mRNA by enhancing gene transcription, overriding typical LDL regulation. This suggests cell-specific transcription factors influence lipid gene expression.
Area of Science:
- Molecular Biology
- Immunology
- Lipid Metabolism
Background:
- Low-density lipoprotein (LDL) receptor expression is crucial for cholesterol homeostasis.
- Regulation of LDL receptor gene expression is complex and can vary between cell types.
Purpose of the Study:
- To investigate how mitogenic stimulation affects LDL receptor mRNA levels and regulation in peripheral blood mononuclear cells (PBMC).
- To compare the regulatory mechanisms of LDL receptor gene expression in PBMC with those in fibroblasts.
Main Methods:
- Analysis of LDL receptor mRNA levels in mitogen-activated PBMC.
- Assessment of gene transcription rates and mRNA stability.
- Comparison of regulatory protein effects on LDL receptor gene expression in PBMC and fibroblasts.
Main Results:
- Mitogenic stimulation significantly increases LDL receptor mRNA in PBMC through enhanced gene transcription, not mRNA stabilization.
- Activated PBMC show reduced regulation by exogenous LDL, independent of cell proliferation or cholesterol pool changes.
- Fibroblasts and PBMC exhibit opposing regulatory mechanisms involving short-lived proteins, with fibroblasts down-regulating and PBMC up-regulating LDL receptor gene transcription.
Conclusions:
- Signals from mitogenic stimulation, alongside LDL concentration, are key regulators of LDL receptor gene transcription in PBMC.
- Cell-specific differences in transcription factor expression likely underlie the distinct regulation of LDL receptor gene expression in PBMC versus fibroblasts.