MED16 Negatively Regulates Erythropoiesis and Myelopoiesis through Modulation of Chromatin Accessibility

• Published in: Blood 2023-11, Vol.142 (Supplement 1), p.2673-2673
• Main Authors: Xie, Sera, Wu, Fan, Zhao, Xinying, Yue, Qiuyu, Zhu, Shicong, Yan, Ling-Hui, Zhou, Yuan, Xing, Tong, Hu, Qi, Li, Dong, Jia, Jin-Song, Kong, Yuan, Huang, Xiao-Jun, Gao, Xiaofei, Lee, Hsiang-Ying
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2023-189650

Tissue-specific transcription factors work in conjunction with numerous coregulators to modulate transcription networks during hematopoiesis; disruptions in this process may lead to hematopoietic disorders, including myelodysplastic syndromes (MDS). While the Mediator complex is known to regulate various aspects of hematopoiesis, the mechanisms underlying subunit-specific functions have not been fully understood. Here, we uncovered that MED16, a core component of Mediator tail module, serves as a crucial negative regulator of erythropoiesis and myelopoiesis by controlling chromatin accessibility at specific target genes. To investigate the function of MED16 in vivo, we transplanted control (shSCR) or MED16-deficient (shMED16) human cord blood CD34+ hematopoietic stem and progenitor cells (HSPCs) into immunodeficient mice. Mice receiving shMED16 HSPCs showed a higher proportion of human erythroid and myeloid cells in the bone marrow (BM), while B cell and T cell reconstitution remained unaffected. MED16 deficiency led to an increased number of myeloid colonies and a more pronounced increase in erythroid colonies in the colony-forming assay. During erythroid differentiation, MED16 deficiency resulted in an elevated ratio of CD235a+ cells and increased enucleation. Furthermore, hematopoietic-specific Med16 knockout ( Mx1-Cre × Med16 -/- Med16 KO)mice showed normal BM and spleen cellularity, with an increased frequency of common myeloid progenitors (CMPs). Med16 KO mice exhibited a higher frequency of CD11b+ myeloid cells and Ter119+ erythroid cells in the BM and spleen. A higher percentage of enucleated erythrocytes were observed in the BM of Med16 KO mice. Additionally, in the model of phenylhydrazine-induced hemolytic anemia, Med16 KO mice showed accelerated red blood cell recovery and pronounced splenomegaly, highlighting the crucial role of Med16 in stress erythropoiesis. Our findings demonstrate that MED16 plays a repressive role in hematopoietic development. To elucidate how MED16 regulates gene expression, we conducted single-cell RNA-seq and ATAC-seq of cultured CD34+ cells after MED16 knockdown in primary human CD34+ HSPCs. MED16 deficiency resulted in upregulation of erythroid and innate immunity genes in erythroid and myeloid cells, respectively. Interestingly, MED16 deficiency led to significantly increased chromatin accessibility around the transcription start sites of upregulated genes. Considering the Mediator complex often interacts with trans