title: Phosphatidylinositol-4-phosphate 5-Kinase 1α Modulates Ribosomal RNA Gene Silencing through Its Interaction with Histone H3 Lysine 9 Trimethylation and Heterochromatin Protein HP1-α.
abstract: Phosphoinositide signaling has been implicated in the regulation of numerous cellular processes including cytoskeletal dynamics, cellular motility, vesicle trafficking, and gene transcription. Studies have also shown that nuclear phosphoinositide(s) regulates processes such as mRNA export, cell cycle progression, gene transcription, and DNA repair. We have shown previously that the nuclear form of phosphatidylinositol-4-phosphate 5-kinase 1α (PIP5K), the enzyme responsible for phosphatidylinositol 4,5-bisphosphate synthesis, is modified by small ubiquitin-like modifier (SUMO)-1. In this study, we have shown that due to the site-specific Lys to Ala mutations of PIP5K at Lys-244 and Lys-490, it is unable to localize in the nucleus and nucleolus, respectively. Furthermore, by using chromatin immunoprecipitation assays, we have observed that PIP5K associates with the chromatin silencing complex constituted of H3K9me3 and heterochromatin protein 1α at multiple ribosomal DNA (rDNA) loci. These interactions followed a definite cyclical pattern of occupancy (mostly G1) and release from the rDNA loci (G1/S) throughout the cell cycle. Moreover, the immunoprecipitation results clearly demonstrate that PIP5K SUMOylated at Lys-490 interacts with components of the chromatin silencing machinery, H3K9me3 and heterochromatin protein 1α. However, PIP5K does not interact with the gene activation signature protein H3K4me3. This study, for the first time, demonstrates that PIP5K, an enzyme actively associated with lipid modification pathway, has additional roles in rDNA silencing.
authors.affiliation: Department of Biochemistry, University of Calcutta, Kolkata 700019, India and.
authors.forename: Rajarshi
authors.initials: R
authors.lastname: Chakrabarti
authors.affiliation: Biophysics and Structural Genomics Division, Saha Institute of Nuclear Physics, Kolkata 700064, India.
authors.forename: Sulagna
authors.initials: S
authors.lastname: Sanyal
authors.affiliation: Department of Biochemistry, University of Calcutta, Kolkata 700019, India and.
authors.forename: Amit
authors.initials: A
authors.lastname: Ghosh
authors.affiliation: Department of Biochemistry, University of Calcutta, Kolkata 700019, India and.
authors.forename: Kaushik
authors.initials: K
authors.lastname: Bhar
authors.affiliation: Biophysics and Structural Genomics Division, Saha Institute of Nuclear Physics, Kolkata 700064, India. Electronic address: chandrima.das@saha.ac.in.
authors.forename: Chandrima
authors.initials: C
authors.lastname: Das
authors.affiliation: Department of Biochemistry, University of Calcutta, Kolkata 700019, India and. Electronic address: asiddhanto@yahoo.com.
authors.forename: Anirban
authors.initials: A
authors.lastname: Siddhanta
mesh_terms: D002453:Cell Cycle; D045744:Cell Line, Tumor; D002466:Cell Nucleolus / Q000235:genetics / Q000378:metabolism; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D004275:DNA, Ribosomal / Q000235:genetics / Q000378:metabolism*; D044127:Epigenesis, Genetic; D020868:Gene Silencing; D057809:HEK293 Cells; D006570:Heterochromatin / Q000737:chemistry / Q000378:metabolism; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008239:Lysine / Q000378:metabolism*; D061986:MCF-7 Cells; D008745:Methylation; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000096:biosynthesis; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D058207:Sumoylation
chemical_list: C000715594:CBX5 protein, human; D002868:Chromosomal Proteins, Non-Histone; D004275:DNA, Ribosomal; D006570:Heterochromatin; D006657:Histones; D019269:Phosphatidylinositol 4,5-Diphosphate; D000090266:Chromobox Protein Homolog 5; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D008239:Lysine
keywords: H3K9me3; HP1α; chromatin immunoprecipitation (ChIP); histone; nucleolus; phosphatidylinositol-4-phosphate 5-kinase 1α; rDNA; small ubiquitin-like modifier (SUMO); sumoylation