MED8, a subunit of the Mediator complex, is crucial for transcription as it links transcription factors to the RNA polymerase II transcriptional machinery [2,4,6]. It is involved in various biological processes across different organisms, highlighting its overall biological importance [1-5, 8-10]. Genetic models, such as gene-edited mutants in plants and knockdown models in cell lines, are valuable for studying MED8.

In Arabidopsis, loss-of-function of MED8 leads to a late-flowering phenotype due to increased expression of FLOWERING LOCUS C (FLC), as MED8 promotes floral transition by recruiting FPA to the FLC locus to repress its expression [1]. In tomato, overexpression of SlMED8 renders transgenic plants more tolerant to Botrytis cinerea, while antisense plants show compromised resistance, indicating its role in JA-dependent defense response [2]. In the diatom Phaeodactylum tricornutum, gene-editing mutants of MED8 exhibit decreased fucoxanthin content and reduced expression of key fucoxanthin-synthesis genes [3]. In hepatocellular carcinoma (HCC) cell lines, knockdown of MED8 weakens cell proliferation, colony-forming, and migration abilities [5]. High MED8 expression predicts poor disease-specific survival in HCC patients, and functional analysis shows enrichment in cell-cycle-related processes associated with MED8 expression [7].

In conclusion, MED8 is essential for multiple biological processes including floral transition, plant defense response, fucoxanthin synthesis, and is associated with HCC prognosis. Studies using gene-edited mutants and knockdown models have revealed its role in these processes, contributing to our understanding of plant development, stress response, and cancer-related mechanisms.

References:

1. Yuan, Chen, Hu, Yikai, Liu, Qinggang, Shen, Lisha, Qin, Cheng. 2023. MED8 regulates floral transition in Arabidopsis by interacting with FPA. In The Plant journal : for cell and molecular biology, 116, 1234-1247. doi:10.1111/tpj.16419. https://pubmed.ncbi.nlm.nih.gov/37565662/

2. Zhang, Lili, Song, Yunpeng, Liu, Kaige, Gong, Fanrong. 2021. The tomato Mediator subunit MED8 positively regulates plant response to Botrytis cinerea. In Journal of plant physiology, 266, 153533. doi:10.1016/j.jplph.2021.153533. https://pubmed.ncbi.nlm.nih.gov/34601339/

3. Zhao, Hejing, Liu, Yan, Zhu, Zhengjiang, Yan, Xiaojun, Li, Xiaohui. 2023. Mediator subunit MED8 interacts with heat shock transcription factor HSF3 to promote fucoxanthin synthesis in the diatom Phaeodactylum tricornutum. In The New phytologist, 241, 1574-1591. doi:10.1111/nph.19467. https://pubmed.ncbi.nlm.nih.gov/38062856/

4. Mehta, Surbhi, Miklos, Ida, Sipiczki, Matthias, Sengupta, Sagar, Sharma, Nimisha. 2009. The Med8 mediator subunit interacts with the Rpb4 subunit of RNA polymerase II and Ace2 transcriptional activator in Schizosaccharomyces pombe. In FEBS letters, 583, 3115-20. doi:10.1016/j.febslet.2009.08.036. https://pubmed.ncbi.nlm.nih.gov/19720063/

5. Jin, Xiaojun, Song, Yongfei, An, Zhanglu, Lu, Hongsheng, Lian, Jiangfang. 2022. A Predictive Model for Prognosis and Therapeutic Response in Hepatocellular Carcinoma Based on a Panel of Three MED8-Related Immunomodulators. In Frontiers in oncology, 12, 868411. doi:10.3389/fonc.2022.868411. https://pubmed.ncbi.nlm.nih.gov/35558516/

6. Chaves, R S, Herrero, P, Moreno, F. . Med8, a subunit of the mediator CTD complex of RNA polymerase II, directly binds to regulatory elements of SUC2 and HXK2 genes. In Biochemical and biophysical research communications, 254, 345-50. doi:. https://pubmed.ncbi.nlm.nih.gov/9918841/

7. Wu, Shuang, Li, Qiao, Cao, Yuan, Wang, Zengguo, Zhang, Taoyuan. 2022. Mediator complex subunit 8 is a prognostic biomarker in hepatocellular carcinoma. In American journal of translational research, 14, 1765-1777. doi:. https://pubmed.ncbi.nlm.nih.gov/35422940/