Functional Analysis of Chromodomain Helicase DNA Binding Protein 2(CHD2) mediated Genomic Stability

Histone modifying enzymes and chromatin remodeling complexes play an important regulatory role in chromatin dynamics that dictate the interaction of regulatory factors involved in processes such as DNA replication, recombination, repair and transcription, with DNA template. The CHD (Chromodomain Helicase DNA Binding Protein) family of proteins is known to be involved in the regulation of gene expression, recombination and chromatin remodeling via their chromatin specific interactions and activities. Phenotypic analysis of the Chd2 mutant mouse model developed by our laboratory indicates that the Chd2 protein plays a critical role in tumor suppression as the heterozygous mutant mice develop spontaneous lymphomas. In this study we demonstrate that mutation of Chd2 renders cells susceptible to inefficient DNA repair and genomic instability. Homozygous and heterozygous Chd2 mutant mouse embryonic fibroblast accumulates higher levels of gamma-H2AX after DNA damage. Chd2 mutant cells show inefficiency in DNA repair of DNA lesions induced by X-rays and UV irradiation as assessed by single cell gel electrophoresis assays. These cells also exhibit increased chromosomal aberrations after treatment with low doses of X-ray irradiation (2 Gy) and show increased radiosensitivity in a clonogenic survival assay. At the molecular level, endogenous CHD2 protein level is induced after exposure to X-ray radiation. In addition, we have also demonstrated in this study that CHD2 is phosphorylated after DNA damage and is a potential substrate for phosphoinositide 3-kinase-related kinases (PIKK) - ATM/ATR. Additionally, mass spectrometric analysis showed possible association of CHD2 with the paraspeckle family of proteins known to be involved in an array of cellular processes specifically in RNA processing and DNA repair. An in vivo splicing assay demonstrated that CHD2 played a role in modulation of pre-mRNA splicing event. Collectively, our findings suggest that CHD2 is a multi-functional protein working with the paraspeckle protein complex to facilitate both the pre-mRNA splicing process and the initial DNA repair process. CHD2 may also be involved in the later stages of DNA damage response pathway by influencing p53’s transcriptional activity.