STAT1 Interacts with RXRα to Upregulate ApoCII Gene Expression in Macrophages

Abstract

Apolipoprotein CII (apoCII) is a specific activator of lipoprotein lipase and plays an important role in triglyceride metabolism. The aim of our work was to elucidate the regulatory mechanisms involved in apoCII gene modulation in macrophages. Using Chromosome Conformation Capture we demonstrated that multienhancer 2 (ME.2) physically interacts with the apoCII promoter and this interaction facilitates the transcriptional enhancement of the apoCII promoter by the transcription factors bound on ME.2. We revealed that the transcription factor STAT1, previously shown to bind to its specific site on ME.2, is functional for apoCII gene upregulation. We found that siRNA-mediated inhibition of STAT1 gene expression significantly decreased the apoCII levels, while STAT1 overexpression in RAW 264.7 macrophages increased apoCII gene expression. Using transient transfections, DNA pull down and chromatin immunoprecipitation assays, we revealed a novel STAT1 binding site in the −500/−493 region of the apoCII promoter, which mediates apoCII promoter upregulation by STAT1. Interestingly, STAT1 could not exert its upregulatory effect when the RXRα/T3Rβ binding site located on the apoCII promoter was mutated, suggesting physical and functional interactions between these factors. Using GST pull-down and co-immunoprecipitation assays, we demonstrated that STAT1 physically interacts with RXRα. Taken together, these data revealed that STAT1 bound on ME.2 cooperates with RXRα located on apoCII promoter and upregulates apoCII expression only in macrophages, due to the specificity of the long-range interactions between the proximal and distal regulatory elements. Moreover, we showed for the first time that STAT1 and RXRα physically interact to exert their regulatory function.

Regulation of HDL Genes: Transcriptional, Posttranscriptional, and Posttranslational

“…In addition, STAT1 can interact and cooperate with other transcription factors bound on the ME.2 or on the apoE promoter, for the modulation of apoE gene expression. Recently, we have revealed that STAT1 can interact with RXR and modulate gene expression of the apoC-II gene (Trusca et al 2012). Since RXRα binds to the ME.2, we can speculate that apoE expression in macrophages may be modulated by the STAT1-RXRα interactions, similarly with apoC-II.…”

Apolipoprotein C-II: New findings related to genetics, biochemistry, and role in triglyceride metabolism

“…Trusca et al . 76 found two STAT1 binding sites involved in APOC2 gene regulation: one in the proximal promoter (nt −500–−493) and the second in ME.2, 20 kb upstream of the APOC2 promoter (Fig. 3A).…”

“…Interestingly, differentiation of monocytes into macrophages markedly increases STAT1 protein synthesis 76 . Trusca et al .…”

The oncoprotein HBXIP upregulates Lin28Bviaactivating TF II D to promote proliferation of breast cancer cells

“…The cDNA of HBXIP was cloned into pGEX‐4T1 expression vector (pGEX‐HBXIP), while the cDNA of TBP was cloned into pET‐28a expression vector (pET‐TBP), and the construct vectors (pGEX‐HBXIP, pGEX‐4T1 and pET‐TBP) were transformed into E.coli strains BL21 (DE3), respectively. The detailed procedure was performed according to published protocols . Glutathione beads were recovered by a brief centrifugation and washed eight times with lysis buffer and the last wash used PBS before resolved by SDS‐PAGE and detected by western blotting using the rabbit anti‐TBP antibody (Cell Signaling Technology, Beverly, MA).…”

“…The detailed procedure was performed according to published protocols. 37,38 Glutathione beads were recovered by a brief centrifugation and washed eight times with lysis buffer and the last wash used PBS before resolved by SDS-PAGE and detected by western blotting using the rabbit anti-TBP antibody (Cell Signaling Technology, Beverly, MA).…”