Chromatin Protein PC4 Orchestrates B Cell Differentiation by Collaborating with IKAROS and IRF4 (Agilent microarrays)
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ABSTRACT: B cell development is orchestrated by various transcription factors collaborating with chromatin remodelers that determine the genomic architecture. However, chromatin regulation in mature B cells is still poorly understood. Here, we show the critical function of positive coactivator 4 (PC4), a bona fide non-histone chromatin protein encoded by Sub1. B-cell specific Sub1-deficient mice showed the decreased number and response against antigen stimulation of mature B cells. By combining PC4 chromatin immunoprecipitation-sequencing and complex purification, we identified transcription factor IKAROS as a partner of PC4 in gene regulation. PC4 and IKAROS cooperated to promote heterochromatin formation of their target gene loci and thereby established B cell identity. Importantly, PC4 stabilized IKAROS protein in mature B cells and inhibited IKAROS degradation by the anti-cancer drug lenalidomide in human B-cell lymphoma cells. These findings establish PC4 as not only a chromatin regulator of B cells but also a new therapeutic target in B-cell malignancies.
Project description:B cell development is orchestrated by various transcription factors collaborating with chromatin remodelers that determine the genomic architecture. However, chromatin regulation in mature B cells is still poorly understood. Here, we show the critical function of positive coactivator 4 (PC4), a bona fide non-histone chromatin protein encoded by Sub1. B-cell specific Sub1-deficient mice showed the decreased number and response against antigen stimulation of mature B cells. By combining PC4 chromatin immunoprecipitation-sequencing and complex purification, we identified transcription factor IKAROS as a partner of PC4 in gene regulation. PC4 and IKAROS cooperated to promote heterochromatin formation of their target gene loci and thereby established B cell identity. Importantly, PC4 stabilized IKAROS protein in mature B cells and inhibited IKAROS degradation by the anti-cancer drug lenalidomide in human B-cell lymphoma cells. These findings establish PC4 as not only a chromatin regulator of B cells but also a new therapeutic target in B-cell malignancies.
Project description:Chromatin protein positive coactivator 4 (PC4) has multiple functions, including chromatin compaction. However, its role in immune cells is largely unknown. We show that PC4 orchestrates chromatin structure and gene expression in mature B cells. B-cell specific PC4-deficient mice showed impaired production of antibody upon antigen stimulation. The PC4 complex purified from B cells contained transcription factors IKAROS and IRF4. IKAROS protein was reduced in PC4-deficient mature B cells, resulting in de-repression of their target genes in part by diminished interactions with gene silencing components. Upon activation, IRF4 protein amount was not increased in PC4-deficient B cells, resulting in reduction of plasma cells. Importantly, IRF4 reciprocally induced PC4 expression via a super-enhancer. PC4 knockdown in human B-cell lymphoma cells reduced IKAROS protein as an anticancer drug lenalidomide. Our findings establish PC4 as a chromatin regulator of B cells and a possible therapeutic target adjoining IKAROS in B-cell malignancies.
Project description:To assess the mechanisms by which PC4 mediates chromatin compaction in cells and regulation of genome organization by its phosphorylation state, we measured the chromatin accessibility landscape using ATAC-seq of vector control 293 cells (Control/shNS), PC4 knockdown (KD/PC4 KD) and upon ectopic expression of Flag tagged PC4 (FP/PC4), Phosphomimic-PC4 (PM/PM-PC4) and phospho-mutant (MTP/MTP5) in PC4 knockdown cells.
Project description:Radiotherapy is one of the mainstays for the treatment of hepatocellular carcinoma (HCC); however, a substantial fraction of HCC patients develops radioresistance and eventually suffer from tumour progression or relapse, a major impediment to the use of radiotherapy. One of the main goals in HCC management is to elucidate the mechanisms underlying radioresistance and identify novel therapeutic targets to improve the patients' prognosis. In this study, we report a DNA repair enhancer, human positive cofactor 4 (PC4), that promotes NHEJ-based DNA repair and renders HCC cells resistant to radiation. Mechanistically, PC4 interacts with PARP1 and directs Ku complex PARylation, resulting in successful recruitment of the Ku complex to damaged chromatin and increasing the efficiency of NHEJ repair. Clinically, PC4 is highly expressed in tumour tissues, which is correlated with poor prognosis in HCC patients. Taken together, our data suggest that PC4 is a DNA repair driver that can be targeted to radiosensitize HCC.
Project description:To investigate the downstream targets of PC4 in controlling cell cycle, we knockdowned PC4 with two different siRNAs in Huh7 cells. We performed RNA-seq in Huh7 cells transfected with NC, siPC4-1 or siPC4-2.
Project description:To investigate the mRNA targets of PC4 that worked as an RNA binding protein to control cell cycle progression. RIP-seq was displayed to profile PC4-binding RNA targets in Huh7 cells.