PURPOSE: Heterochromatin protein 1gamma (HP1gamma) interacts with chromosomes by binding to lysine 9-methylated histone H3 or DNA/RNA. HP1gamma is involved in various biological processes. The purpose of this study is to gain an understanding of how HP1gamma functions in these processes by identifying HP1gamma-binding proteins using mass spectrometry. MATERIALS AND METHODS: We performed affinity purification of HP1gamma-binding proteins using G1/S phase or prometaphase HEK293T cell lysates that transiently express mock or FLAG-HP1gamma. Coomassie staining was performed for HP1gamma-binding complexes, using cell lysates prepared by affinity chromatography FLAG-agarose beads, and the bands were digested and then analyzed using a mass spectrometry. RESULTS: We identified 99 HP1gamma-binding proteins with diverse cellular functions, including spliceosome, regulation of the actin cytoskeleton, tight junction, pathogenic Escherichia coli infection, mammalian target of rapamycin signaling pathway, nucleotide excision repair, DNA replication, homologous recombination, and mismatch repair. CONCLUSION: Our results suggested that HP1gamma is functionally active in DNA damage response via protein-protein interaction.
Actin Cytoskeleton ; Biological Processes ; Chromatography, Affinity ; DNA Damage* ; DNA Mismatch Repair ; DNA Repair ; DNA Replication ; DNA* ; Escherichia coli Infections ; Heterochromatin* ; Histones ; Homologous Recombination ; Lysine ; Mass Spectrometry ; Prometaphase ; Sirolimus ; Spliceosomes ; Tight Junctions

The orbicularis oculi (OOc) is a sphincteric muscle of the eyelids, whereas contraction of the orbicularis oris (OOr), another sphincteric muscle, causes narrowing of the lips. Facial muscle fibers normally blend with adjacent muscles. However, muscle fibers connecting the various facial muscles that have different actions and that are located at distant sites, such as the OOc and the OOr have been rarely reported. Herein, we report a rare case of connecting fibers between the inferior margin of the OOc and the OOr. These connecting fibers were blended with the OOr between the inserting fibers of the levator labii superioris and levator anguli oris. Contraction of such variant muscles might affect typical facial expressions.

Mutations in the NF2 tumor suppressor gene cause neurofibromatosis type 2, an autosomal dominant inherited syndrome predisposed to the multiple tumors of the nervous system. Merlin, the NF2 gene product was reported to block Ras-mediated cell transformation and represses Ras-induced expression of cyclin D1. However, the potential mechanism underlying the anti-Ras function of merlin on the cyclin D1 is still unclear. In this study, we investigated whether merlin decreases Ha-ras-induced accumulation of cyclin D1 at the transcriptional level, and demonstrated that merlin suppressed Ras-induced cyclin D1 promoter activity mediated by the cyclic AMP-responsive element (CRE) in SK-N-BE (2) C neuroblastoma cells. Furthermore, we found that merlin attenuated active Ras and forskolin-induced CRE-driven promoter activity. These results suggest that the transcriptional repression of the cyclin D1 expression by merlin may contribute to the inhibition of Ras-induced cell proliferation
Cell Proliferation ; Cyclin D1* ; Cyclins* ; Genes, Tumor Suppressor ; Nervous System Neoplasms ; Neuroblastoma ; Neurofibromatosis 2 ; Neurofibromin 2* ; Repression, Psychology