the Role of the Atrophin Domain in the Function of AFF1-SEC as a Transcription Inhibitor

Mari Brady, Sarah Lloyd, Dr. Xiaomin Bao, Department of Molecular Biosciences, Northwestern University, 2200 Campus Dr, Evanston, IL 60208

The identity of a cell is determined by which genes are expressed and in what quantities they are expressed. Thus, it is crucial for a cell to carefully regulate its gene expression. In human epidermis, progenitor cells both self-renew and differentiate to form stratified epidermal tissue; this process requires strict, dynamic regulation of gene expression. The Super Elongation Complex (SEC) regulates gene expression at the level of transcription elongation by releasing RNA Polymerase II from its paused state and is therefore known as a transcription activator. The SEC contains two mutually exclusive scaffolding subunits, AFF1 and AFF4. Therefore, the SEC can exist in two variants, depending on which protein is used as the scaffold, but it is unknown by how much these variants differ in function. Dysregulation of the SEC has been identified in leukemia and fragile X syndrome, but the role of the SEC in regulating gene expression during healthy tissue differentiation is unknown. Here we show that in addition to functioning as a transcription activator, the SEC is capable of inhibiting the transcription of epidermal differentiation markers by using AFF1 as its scaffolding protein. We hypothesize that the Atrophin domain located on the AFF1 protein is necessary for AFF1-SEC to function as an inhibitor. To test this hypothesis, we first overexpressed AFF1 in human keratinocytes. Overexpression of AFF1 downregulated transcription of differentiation genes, implying that alternating complex composition is a mechanism through which the SEC selectively utilizes AFF1 to suppress expression of differentiation genes in order to maintain cells in the progenitor state. Then, we overexpressed a variant of the AFF1 protein with the Atrophin domain deleted. This had no observable effect on the transcription of differentiation genes, suggesting that the domain is necessary for AFF1-SEC to function as a transcription inhibitor. 

Additional Abstract Information

Presenter: Mari Brady

Institution: Northwestern University

Type: Poster

Subject: Biology

Status: Approved

Time and Location

Session: Poster 2
Date/Time: Mon 3:00pm-4:00pm
Session Number: 2566