Identification of Novel Domains within Sox-2 and Sox-11 Involved in Autoinhibition of DNA Binding and Partnership Specificity

Tamara K. Nowling,Matthew S. Wiebe,Angie Rizzino

doi:10.1074/jbc.m212211200

Tamara K. Nowling, Matthew S. Wiebe + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m212211200

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Abstract

Sox transcription factors play key regulatory roles throughout development, binding DNA through a consensus (A/T)(A/T)CAA(A/T)G sequence. Although many different Sox proteins bind to this sequence, it has been observed that gene regulatory elements are commonly responsive to only a small subset of the entire family, implying that regulatory mechanisms exist to permit selective DNA binding and/or transactivation by Sox family members. To identify and explore the mechanisms modulating gene activation by Sox proteins further, we compared the function of Sox-2 and Sox-11. This led to the discovery that Sox proteins are regulated differentially at multiple levels, including transactivation, protein partnerships with Pit-Oct-Unc (POU) transcription factors, and DNA binding autoregulation. Specifically, we determined that Sox-11 activates transcription more strongly than Sox-2 and that the transactivation domain of Sox-11 is primarily responsible for this capability. Additionally, we demonstrate that the Sox-11 DNA binding domain is responsible for selective cooperation with the POU factor Brn-2. This requirement cannot be replaced by the DNA binding domain of Sox-2, indicating that the DNA binding domain of Sox proteins is critical for Sox-POU partnerships. Interestingly, we have also determined that a conserved domain of Sox-11 has the novel capability of autoinhibiting its ability to bind DNA in vitro and to activate gene expression in vivo. Our findings suggest that the autoinhibitory domain can repress promiscuous binding of Sox-11 to DNA and plays an important role in regulating the recruitment of Sox-11 to specific genes.

Highlights

The Sox family of transcription factors is comprised of a diverse group of proteins whose pattern of expression is regulated both spatially and temporally [1]
Many different Sox proteins bind to this sequence, it has been observed that gene regulatory elements are commonly responsive to only a small subset of the entire family, implying that regulatory mechanisms exist to permit selective DNA binding and/or transactivation by Sox family members
A review of the literature reveals that genes rely on a diverse array of mechanisms to regulate DNA binding among members of other transcription factor families, which may apply to Sox proteins

Summary

Introduction

The Sox family of transcription factors is comprised of a diverse group of proteins whose pattern of expression is regulated both spatially and temporally [1]. The observation that the HMG DNA binding domains of many members of the Sox family bind a consensus sequence has prompted the question of whether there are selective mechanisms in place to recruit a specific Sox protein to a gene regulated by an HMG binding site. Attempts to uncover the mechanisms through which Sox specificity is achieved have revealed that recruitment often requires proper interaction with other transcription factors at adjacent binding sites on the DNA. This is illustrated by one of the cis-regulatory elements that control expression of the fibroblast growth factor 4 (FGF-4) gene in embryonal carcinoma cells. CMV, cytomegalovirus; DC5, ␦-crystallin enhancer; ECF, enhanced chemifluorescence; EMSA, electrophoretic gel mobility shift analysis; FGF-4, fibroblast growth factor 4; POU, Pit-Oct-Unc; TAD, transactivation domain

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