Structural and Functional Insights into the Human Bor&jnodot;eson-Forssman-Lehmann Syndrome Associated Protein PHF6 [Gene Regulation]

February 19th, 2014 by Liu, Z., Li, F., Ruan, K., Zhang, J., Mei, Y., Wu, J., Shi, Y.

The plant homeodomain finger 6 (PHF6) was originally identified as the gene mutated in the X-linked mental retardation disorder, Borjeson-Forssman-Lehmann syndrome (BFLS). Mutations in the PHF6 gene have also been associated to T-cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML). Approximately half of the disease-associated mutations are distributed in the second conserved extended PHD (ePHD2) domain of PHF6, indicating the functional importance of the ePHD2 domain. Here, we report the high resolution crystal structure of the ePHD2 domain of PHF6, which contains an N-terminal pre-PHD (C2HC zinc finger), a long linker, and an atypical PHD finger. PHF6-ePHD2 appears to fold as a novel integrated structural module. Structural analysis of PHF6-ePHD2 reveals pathological implication of PHF6 gene mutations in BFLS, T-ALL and AML. The binding experiments show that PHF6-ePHD2 can bind dsDNA, but not histones. We also demonstrate PHF6 protein directly interacts with the NuRD complex component RBBP4. Via this interaction, PHF6 exerts its transcriptional repression activity. Taken together, these data support the hypothesis that PHF6 may function as a transcriptional repressor using its ePHD domains binding to the promoter region of its repressed gene and this process was regulated by the NuRD complex which was recruited to the genomic target site by NoLS region of PHF6.