Barrier to Autointegration Factor Interacts with the Cone-Rod Homeobox and Represses Its Transactivation Function

Abstract

Crx (cone-rod homeobox) is a homeodomain transcription factor implicated in regulating the expression of photoreceptor and pineal genes. To identify proteins that interact with Crx in the retina, we carried out a yeast two-hybrid screen of a retinal cDNA library. One of the identified clones encodes Baf (barrier to autointegration factor), which was previously shown to have a role in mitosis and retroviral integration. Additional biochemical assays provided supporting evidence for a Baf-Crx interaction. The Baf protein is detectable in all nuclear layers of the mouse retina, including the photoreceptors and the bipolar cells where Crx is expressed. Transient transfection assays with a rhodopsin-luciferase reporter in HEK293 cells demonstrate that overexpression of Baf represses Crx-mediated transactivation, suggesting that Baf acts as a negative regulator of Crx. Consistent with this role for Baf, an E80A mutation of CRX associated with cone-rod dystrophy has a higher than normal transactivation potency but a reduced interaction with Baf. Although our studies did not identify a causative Baf mutation in retinopathies, we suggest that Baf may contribute to the phenotype of a photoreceptor degenerative disease by modifying the activity of Crx. In view of the ubiquitous expression of Baf, we hypothesize that it may play a role in regulating tissueor cell type-specific gene expression by interacting with homeodomain transcription factors.Development and maintenance of photoreceptor function in mammalian retina requires the expression of photoreceptorspecific or photoreceptor-enriched genes. Under-or over-

Proteins that associate with lamins: Many faces, many functions

“…The binding of LEM-domain proteins with BAF could similarly influence gene regulation, as BAF has been found to repress gene expression in retinal cells via binding to the homeodomain transcription factor Crx [92]. Furthermore, pull-down studies identified an emerin-binding transcription factor, Lim domain only (Lmo7), which controls the expression of emerin and many muscle specific genes [66].…”

Direct Binding of Nuclear Membrane Protein MAN1 to Emerin in Vitro and Two Modes of Binding to Barrier-to-Autointegration Factor

“…We therefore hypothesized that BAF might recognize a novel motif conserved in other BAF-binding proteins that lack LEM domains, such as Crx (and related homeodomain transcription activators (23,24)), and certain histones including linker histone H1.1.…”

“…Crx is a homeodomain transcription activator; its SRV motif (residues 81-88) is located in the BAF-and DNAbinding region of Crx (residues 34 -107) (24). The E80A mutation in Crx, which alters a single residue flanking the SRV motif, disrupts Crx binding to BAF in vitro but does not disrupt Crx binding to DNA or Crx-activated gene expression (24). The SRV motif in histone H1.1 (residues 124 -131) is located within the minimal region required to bind BAF (residues 108 -215).…”

Systems analysis of the prostate tumor suppressor NKX3.1 supports roles in DNA repair and luminal cell differentiation

“…BANF1 was previously shown to bind two other proteins identified in the NKX3.1 interactome, emerin (EMD) and thymopoetin (TMPO) 49 . In addition, BANF1 interacts with several other homeodomain transcription factors and regulates the transcriptional activity of one of them, CRX 50 . It is thus likely that BANF1, in complex with emerin and thymopoetin, is involved in NKX3.1-mediated gene regulation.…”