Mediator complex proximal Tail subunit MED30 is critical for Mediator core stability and cardiomyocyte transcriptional network

Abstract

Dysregulation of cardiac transcription programs has been identified in patients and families with heart failure, as well as those with morphological and functional forms of congenital heart defects. Mediator is a multi-subunit complex that plays a central role in transcription initiation by integrating regulatory signals from gene-specific transcriptional activators to RNA polymerase II (Pol II). Recently, Mediator subunit 30 (MED30), a metazoan specific Mediator subunit, has been associated with Langer-Giedion syndrome (LGS) Type II and Cornelia de Lange syndrome-4 (CDLS4), characterized by several abnormalities including congenital heart defects. A point mutation in MED30 has been identified in mouse and is associated with mitochondrial cardiomyopathy. Very recent structural analyses of Mediator revealed that MED30 localizes to the proximal Tail, anchoring Head and Tail modules, thus potentially influencing stability of the Mediator core. However, in vivo cellular and physiological roles of MED30 in maintaining Mediator core integrity remain to be tested. Here, we report that deletion of MED30 in embryonic or adult cardiomyocytes caused rapid development of cardiac defects and lethality. Importantly, cardiomyocyte specific ablation of MED30 destabilized Mediator core subunits, while the kinase module was preserved, demonstrating an essential role of MED30 in stability of the overall Mediator complex. RNAseq analyses of constitutive cardiomyocyte specific Med30 knockout (cKO) embryonic hearts and inducible cardiomyocyte specific Med30 knockout (icKO) adult cardiomyocytes further revealed critical transcription networks in cardiomyocytes controlled by Mediator. Taken together, our results demonstrated that MED30 is essential for Mediator stability and transcriptional networks in both developing and adult cardiomyocytes. Our results affirm the key role of proximal Tail modular subunits in maintaining core Mediator stability in vivo.

Comparative analysis of retroviral Gag-host cell interactions: focus on the nuclear interactome

“…Interestingly, Med26 and Med30 are both metazoan-specific Mediator proteins, implying that Gag may display selectivity for metazoan-specific Mediator complexes over those with protozoan orthologs. Med26 and Med30 both also have critical roles in transcription, with Med26 responsible for the recruitment of important elongation factors to sites of transcription, and Med30 providing stabilization of the intact Mediator core (78, 79).…”

Gene Amplification of Mediator Subunit 30 Redirects the MYC Transcriptional Program and Oncogenesis

“…While the human samples clustered together by treatment, the Drosophila samples evenly distributed in all samples (Figure S4D). With > 95% of the MED30 mRNA lost by shRNA knockdown, the major portion of the Mediator complex was presumably lost [35]. This MED30 knockdown resulted in a down-regulation of 13% (n = 2695) and up-regulation of 3.2% (n = 647) of expressed genes (Fig.…”

Genetically Engineered Mice Unveil In Vivo Roles of the Mediator Complex

“…The deficiencies of various Mediator subunits in mouse cardiomyocytes have similar phenotypic manifestations: animals develop cardiomyopathy, myocardial fibrosis, and decreased heart contractility, leading to early mortality. Different authors have described similar mechanisms behind this phenotype, based on disturbances in gene expression patterns, although the specific genes that are regulated by Mediator KOs could differ [77][78][79][80].…”

“…At transcriptional level, Med12 deletion led to changes in the gene expression profiles (suppression of Atp2a2, Gja1, Gja5, Kcnn1, Pln, Ryr2, and Tnnt1; activation of Cacna1d, Casq1, Gja3, and Slc8a2), the products of which are involved in calcium metabolism in the heart, which in turn led to a change in the contractility of cardiomyocytes [81]. Med30 was required for the maintenance of a regulatory network specific for cardiomyocyte genes (Mycn, Hey2, Tnni2, Mhy7, Gja1, Gaj5, and Pln) [79]. In addition, RNA-seq showed that Ccnc cardiomyocyte-specific KO mice had a suppressed expression of genes involved in PPAR signaling pathways (Pck1, Plin1, Plin5, Acadm, DBI, and Slc27a1), FoxO signaling pathways (Rag1), and AMPK signaling pathways (Adipoq and Scd1).…”

“…Many of the described mutations and deletions of the mediator complex disrupted in one way or another the normal mitochondrial homeostasis. For example, Med30 deletion in adult cardiomyocytes led to a decrease in the expression level of a number of mitochondrial genes [79]. The I44F substitution in MED30 also led to a decrease in the ability of mitochondria to carry out oxidative phosphorylation.…”