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Pontin Functions as A Transcriptional Co-activator for Retinoic Acid-induced HOX Gene Expression.

ABSTRACT: Pontin is a AAA+ ATPase protein that has functions in various biological contexts including gene transcription regulation, chromatin remodeling, DNA damage sensing and repair, as well as assembly of protein and ribonucleoprotein complexes. Pontin is known to regulate the transcription of several important signaling pathways, including Wnt signaling. However, its role in early embryonic signaling regulation remains unclear. Retinoic acid (RA) signaling plays a central role in vertebrate development. Using an in vivo biotin tagging technology, we mapped the genome-wide binding pattern of Pontin before and after RA-induced differentiation in the pluripotent embryo carcinoma cell line NTERA-2. Biotin ChIP-seq revealed significant changes in genome-wide Pontin binding sites upon RA stimulation. We also identified a substantial amount of overlapping binding peaks between Pontin and RARα, especially on all of the HOX gene loci (A-D clusters). Pontin knockdown experiments showed that its chromatin binding at the HOX gene clusters is required for RA-induced HOX gene expression. Furthermore, we performed Global Run-On sequencing (GRO-seq) to map de novo transcripts genome-wide and found that Pontin knockdown significantly diminished nascent HOX gene transcripts, indicating that Pontin regulates HOX gene expression at the transcriptional level. Finally, proteomic analysis demonstrated that Pontin associates with chromatin organization/remodeling complexes and various other functional complexes. Altogether, we have demonstrated that Pontin is a critical transcriptional co-activator for RA-induced HOX gene activation.

SUBMITTER: Tang D

PROVIDER: S-EPMC8184613 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The mechanism of action of retinoic acid (RA) is of broad relevance to cell and developmental biology, nutrition, and cancer chemotherapy. RA is known to induce expression of the Burkitt's lymphoma receptor 1 (BLR1) gene which propels RA-induced cell cycle arrest and differentiation of HL-60 human myeloblastic leukemia cells, motivating the present analysis of transcriptional regulation of blr1 expression by RA. The RA-treated HL-60 cells used here expressed all RA receptor (RAR) and retinoid X receptor (RXR) subtypes (as detected by Northern analysis) except RXRgamma. Treatment with RAR- and RXR-selective ligands showed that RARalpha synergized with RXRalpha to transcriptionally activate blr1 expression. A 5'-flanking region capable of supporting RA-induced blr1 activation in HL-60 cells was found to contain a 205-bp sequence in the distal portion that was necessary for transcriptional activation by RA. Within this sequence DNase I footprinting revealed that RA induced binding of a nuclear protein complex to an element containing two GT boxes. Electromobility shift assays (EMSAs) and supershift assays showed that this element bound recombinant RARalpha and RXRalpha. Without RA there was neither complex binding nor transcriptional activation. Both GT boxes were needed for binding the complex, and mutation of either GT box caused the loss of transcriptional activation by RA. The ability of this cis-acting RAR-RXR binding element to activate transcription in response to RA also depended on downstream sequences where an octamer transcription factor 1 (Oct1) site and a nuclear factor of activated T cells (NFATc) site between this element and the transcriptional start, as well as a cyclic AMP response element binding factor (CREB) site between the transcriptional start and first exon of the blr1 gene, were necessary. Each of these sites bound its corresponding transcription factor. A transcription factor-transcription factor binding array analysis of nuclear lysate from RA-treated cells indicated several prominent RARalpha binding partners; among these, Oct1, NFATc3, and CREB2 were identified by competition EMSA and supershift and chromatin immunoprecipitation assays as components of the complex. RA upregulated expression of these three factors. In sum the results of the present study indicate that RA-induced expression of blr1 expression depends on a novel RA response element. This cis-acting element approximately 1 kb upstream of the transcriptional start consists of two GT boxes that bind RAR and RXR in a nuclear protein complex that also contains Oct1, NFATc3, and CREB2 bound to their cognate downstream consensus binding sites.

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Pontin Functions as A Transcriptional Co-activator for Retinoic Acid-induced HOX Gene Expression.

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