Project description:Skin pigmentation is paused following sun exposure, however the mechanism behind this pausing is unknown. Here we found that the UVB-induced DNA repair system, led by the ATM protein kinase, represses MITF transcriptional activity of pigmentation genes while placing MITF in DNA repair mode, thus directly inhibiting pigment production. Phosphoproteomics analysis revealed ATM to be the most significantly enriched pathway among all UVB-induced DNA repair systems. ATM inhibition in mouse or human skin, either genetically or chemically, induces pigmentation. Upon UVB, MITF transcriptional activation is blocked due to ATM dependent phosphorylation of MITF on S414, which modifies MITF activity and interactome towards DNA repair including binding to TRIM28 and RBBP4. Accordingly, MITF genome-occupancy is enriched in sites of high DNA damage that are likely repaired. This suggests that ATM harnesses the pigmentation key activator, for the necessary rapid, efficient DNA repair, thus optimizing the chances of the cell to survive.
Project description:Mediator complex is an integrative hub for transcriptional regulation. Here we show that Mediator regulates alternative mRNA processing via its Med23 subunit. Combining tandem affinity purification and mass spectrometry, we identified a number of mRNA processing factors that bind to a soluble recombinant Mediator subunit MED23 but not to several other Mediator components. One of these factors, hnRNP L, specifically interacts with MED23 in vitro and in vivo. Consistently, Mediator partially colocalizes with hnRNP L and the splicing machinery in the cell. Functionally Med23 regulates a subset of hnRNP L-targeted alternative splicing (AS) and alternative cleavage and polyadenylation (APA) events as shown by minigene reporters and exon array analysis. ChIP-seq analysis revealed that Med23 can regulate hnRNP L occupancy at their co-regulated genes. Taken together, these results demonstrate a crosstalk between Mediator and the splicing machinery, suggesting a novel mechanism for coupling mRNA processing to transcription. Examination of hnRNP L and H3K36me3 enrichment in sictrl and si23 Hela cells
Project description:Mediator complex is an integrative hub for transcriptional regulation. Here we show that Mediator regulates alternative mRNA processing via its Med23 subunit. Combining tandem affinity purification and mass spectrometry, we identified a number of mRNA processing factors that bind to a soluble recombinant Mediator subunit MED23 but not to several other Mediator components. One of these factors, hnRNP L, specifically interacts with MED23 in vitro and in vivo. Consistently, Mediator partially colocalizes with hnRNP L and the splicing machinery in the cell. Functionally Med23 regulates a subset of hnRNP L-targeted alternative splicing (AS) and alternative cleavage and polyadenylation (APA) events as shown by minigene reporters and exon array analysis. ChIP-seq analysis revealed that Med23 can regulate hnRNP L occupancy at their co-regulated genes. Taken together, these results demonstrate a crosstalk between Mediator and the splicing machinery, suggesting a novel mechanism for coupling mRNA processing to transcription. We performed an exon array experiment using HeLa cells expressing Med23, hnRNP L or control siRNAs which were established by a virus-mediated siRNA technology. Each sample was done in three biological replicates. Total RNA of these cell lines was processed and hybridized to the Affymetrix human exon array.
Project description:Mediator complex is an integrative hub for transcriptional regulation. Here we show that Mediator regulates alternative mRNA processing via its Med23 subunit. Combining tandem affinity purification and mass spectrometry, we identified a number of mRNA processing factors that bind to a soluble recombinant Mediator subunit MED23 but not to several other Mediator components. One of these factors, hnRNP L, specifically interacts with MED23 in vitro and in vivo. Consistently, Mediator partially colocalizes with hnRNP L and the splicing machinery in the cell. Functionally Med23 regulates a subset of hnRNP L-targeted alternative splicing (AS) and alternative cleavage and polyadenylation (APA) events as shown by minigene reporters and exon array analysis. ChIP-seq analysis revealed that Med23 can regulate hnRNP L occupancy at their co-regulated genes. Taken together, these results demonstrate a crosstalk between Mediator and the splicing machinery, suggesting a novel mechanism for coupling mRNA processing to transcription.
Project description:Mediator complex is an integrative hub for transcriptional regulation. Here we show that Mediator regulates alternative mRNA processing via its Med23 subunit. Combining tandem affinity purification and mass spectrometry, we identified a number of mRNA processing factors that bind to a soluble recombinant Mediator subunit MED23 but not to several other Mediator components. One of these factors, hnRNP L, specifically interacts with MED23 in vitro and in vivo. Consistently, Mediator partially colocalizes with hnRNP L and the splicing machinery in the cell. Functionally Med23 regulates a subset of hnRNP L-targeted alternative splicing (AS) and alternative cleavage and polyadenylation (APA) events as shown by minigene reporters and exon array analysis. ChIP-seq analysis revealed that Med23 can regulate hnRNP L occupancy at their co-regulated genes. Taken together, these results demonstrate a crosstalk between Mediator and the splicing machinery, suggesting a novel mechanism for coupling mRNA processing to transcription.
Project description:MED23, a subunit of the Mediator coactivator complex, is important for the expression of a subset of MAPK/ERK pathway-dependent target genes; however, the genes in this subset varies between cell types. MAPK/ERK pathway-dependent processes are essential for T-cell development and function, but whether MED23 has a role in this context is unknown. We generated Med23 conditional knockout mice and induced Med23 deletion in early T cell development using the lineage specific Lck-Cre transgene. While the total cell number and distribution of cell populations in the thymuses of Med23flox/flox;Lck-Cre mice were essentially normal, MED23 null T-cells failed to efficiently populate the peripheral lymphoid organs. MED23 null thymocytes displayed decreased expression of the MAPK/ERK-responsive genes Egr1, Egr2, as well as of the membrane glycoprotein Cd52 (CAMPATH-1). MED23 null CD4 single-positive thymocytes also showed decreased expression of KLF2 (LKLF), a T cell master regulatory transcription factor. Indeed, similarities between the phenotypes of mice lacking MED23 or KLF2 in T-cells suggest that KLF2 deficiency in MED23 null T-cells is one of their key defects. Mechanistic experiments using MED23 null MEFs further suggest that MED23 is required for full activity of the MAPK-responsive transcription factor MEF2, which has previously been shown to mediate Klf2 expression. In summary, our data indicate that MED23 has critical roles in enabling T-cells to populate the peripheral lymphoid organs, possibly by potentiating MEF2-dependent expression of the T-cell transcription factor KLF2. 12 samples, 2 of each genotype (Lck-Cre, Med23flox/flox and Med23flox/flox;Lck-Cre) both with mock and anti-CD3 treatment
Project description:Hepatocellular carcinoma (HCC) is frequently linked to compensatory proliferating hepatocytes in damaged livers, yet the underlying molecular mechanisms remain elusive. The Mediator complex precisely coordinates multiple transcription factors and cofactors to regulate diverse physiological and pathological processes. Here we discovered that Mediator subunit MED23 is involved in the progression of HCC. Both constitutive and inducible liver-specific ablation of Med23 effectively inhibited HCC development in diethylnitrosamine (DEN)-induced HCC mouse models. Mechanistically, MED23 deficiency significantly compromised hepatocyte cell viability by reducing the stability of the NQO1 protein, thereby leading to an increase in reactive oxygen species (ROS) production. Furthermore, MED23 collaborates with the transcription factor RFX5 to regulate a novel enhancer function for IGF2 expression, which thus influences hepatocyte viability and HCC development. Consistently, overexpression of IGF2 in MED23-deficient HCC cells stabilizes NQO1 and partially restored cell growth and reduced apoptosis. Collectively, our findings underscore the significance of the MED23-IGF2-NQO1 axis in HCC progression and propose a novel therapeutic strategy for the treatment of HCC.
Project description:Hepatocellular carcinoma (HCC) is frequently linked to compensatory proliferating hepatocytes in damaged livers, yet the underlying molecular mechanisms remain elusive. The Mediator complex precisely coordinates multiple transcription factors and cofactors to regulate diverse physiological and pathological processes. Here we discovered that Mediator subunit MED23 is involved in the progression of HCC. Both constitutive and inducible liver-specific ablation of Med23 effectively inhibited HCC development in diethylnitrosamine (DEN)-induced HCC mouse models. Mechanistically, MED23 deficiency significantly compromised hepatocyte cell viability by reducing the stability of the NQO1 protein, thereby leading to an increase in reactive oxygen species (ROS) production. Furthermore, MED23 collaborates with the transcription factor RFX5 to regulate a novel enhancer function for IGF2 expression, which thus influences hepatocyte viability and HCC development. Consistently, overexpression of IGF2 in MED23-deficient HCC cells stabilizes NQO1 and partially restored cell growth and reduced apoptosis. Collectively, our findings underscore the significance of the MED23-IGF2-NQO1 axis in HCC progression and propose a novel therapeutic strategy for the treatment of HCC.