Multiple Developmental Defects Derived from Impaired Recruitment of ASC-2 to Nuclear Receptors in Mice: Implication for Posterior Lenticonus with Cataract

Abstract

ASC-2, a recently isolated transcriptional coactivator molecule, stimulates transactivation by multiple transcription factors, including nuclear receptors. We generated a potent dominant negative fragment of ASC-2, encompassing the N-terminal LXXLL motif that binds a broad range of nuclear receptors. This fragment, termed DN1, specifically inhibited endogenous ASC-2 from binding these receptors in vivo, whereas DN1/m, in which the LXXLL motif was mutated to LXXAA to abolish the receptor interactions, was inert. Interestingly, DN1 transgenic mice but not DN1/m transgenic mice exhibited severe microphthalmia and posterior lenticonus with cataract as well as a variety of pathophysiological phenotypes in many other organs. Our results provide a novel insight into the molecular and histopathological mechanism of posterior lenticonus with cataract and attest to the importance of ASC-2 as a pivotal transcriptional coactivator of nuclear receptors in vivo.The nuclear receptor superfamily is a group of proteins that regulate, in a ligand-dependent manner, transcriptional initiation of target genes by binding to specific DNA sequences named hormone response elements (for a review, see reference 15). Genetic studies indicated that transcription coactivators without specific DNA-binding activity are essential for transcriptional activation, which led to the identification of many proteins interacting with the C-terminal ligand-dependent transactivation domain of nuclear receptors (for reviews, see references 1 and 19). These coactivators, including the p160 family, CBP/p300, p/CAF, TRAP/DRIP, and many others, bridge transcription factors and the basal transcription apparatus and/or remodel the chromatin structures.ASC-2, also named AIB3, TRBP, RAP250, NRC, and PRIP, is a recently isolated transcriptional coactivator molecule which is gene amplified and overexpressed in human cancers and stimulates transactivation by nuclear receptors, AP-1, NF-B, SRF, and numerous other transcription factors (1, 10-12, 14, 24). In particular, the single-cell microinjection results with ASC-2 antibody demonstrated that endogenous ASC-2 is required for transactivation by nuclear receptors and AP-1 (11, 12). More recently, ASC-2 was found to exist in a steady-state complex of approximately 2 MDa that contains histone H3-lysine 4-specific methyltransferase enzymes, and chromatin immunoprecipitation experiments demonstrated that this complex specifically binds to the retinoid-responsive ␤-retinoic acid response element and p21 WAF1 promoter regions in a liganddependent manner (Goo et al., unpublished data).Interestingly, ASC-2 contains two nuclear receptor interaction domains (12), both of which are dependent on the integrity of their core LXXLL sequences (16,19). The C-terminal LXXLL motif specifically interacts with the liver X receptors (LXR␣ and LXR␤), whereas the N-terminal motif binds a broad range of nuclear receptors (12).In this report, we show that inhibition of ASC-2 recruitment to nuclear receptors by using a dominant negative fragm...

A tumor suppressive coactivator complex of p53 containing ASC-2 and histone H3-lysine-4 methyltransferase MLL3 or its paralogue MLL4

“…Transfection and luciferase assays were performed in triplicate as described in ref. 41, and the results were normalized to the LacZ expression. Similar results were obtained in 2 independent experiments.…”

Regulation of gene expression by Pax6 in ocular cells: a case of tissue-preferred expression of crystallins in lens

“…ASC-2, also termed AIB3, TRBP, RAP250, NRC and PRIP ( Fig. 2A), is a co-activator interacting with histone H3-lysine 4-specific methyltransferase and its function is also required in vivo for αA-, γD-and γF-crystallins (Kim et al, 2002). Some of the DNAbinding factors, e.g.…”

“…Interestingly, ASC-2 null lenses exhibit reduced expression of the αA-but not αB-crystallin (see Table 1). ASC-2 is a transcriptional coactivator of nuclear receptors, AP-1 and other transcription factors that function in the lens (Kim et al, 2002). Additional studies of the mouse αA-crystallin locus including its promoter are required to fully understand regulatory mechanisms that account for its temporal and spatial regulation and links to the fiber-cell differentiation signals.…”

Genetic and epigenetic mechanisms of gene regulation during lens development

“…This enzyme is a component of a large multisubunit complex ASCOM, a coactivator complex of nuclear receptors. The complex includes activating signal cointegrator 2 (ASC-2) with a pair of LXXLL motifs (Plevin et al, 2005) (see Table 1) that was earlier shown to participate in regulation of mouse lens development and crystallin gene expression (Kim et al, 2002).…”