ABSTRACT
Epigenomic abnormalities caused by genetic mutation in epigenetic regulators can result in neurodevelopmental disorders, deficiency in neural plasticity and mental retardation. As a histone demethylase, plant homeodomain finger protein 8 (Phf8) is a candidate gene for syndromal and non-specific forms of X-chromosome-linked intellectual disability (XLID). Here we report that Phf8 knockout mice displayed impaired learning and memory, and impaired hippocampal long-term potentiation (LTP) without gross morphological defects. We also show that mTOR signaling pathway is hyperactive in hippocampus in Phf8 knockout mouse. Mechanistically, we show that demethylation of H4K20me1 by Phf8 results in transcriptional suppression of RSK1 and homeostasis of mTOR signaling. Pharmacological suppression of mTOR signaling with rapamycin in Phf8 knockout mice recovers the weakened LTP and cognitive deficits. Together, our results indicate that loss of Phf8 in animals causes deficient learning and memory by epigenetic disruption of mTOR signaling, and provides a potential therapeutic drug target to treat XLID.
Subject(s)
Cognitive Dysfunction/genetics , Histone Demethylases/genetics , Signal Transduction , TOR Serine-Threonine Kinases/genetics , Transcription Factors/genetics , Animals , Cognitive Dysfunction/metabolism , Cognitive Dysfunction/physiopathology , Female , Gene Expression Profiling , Hippocampus/metabolism , Hippocampus/physiopathology , Histone Demethylases/deficiency , Long-Term Potentiation/genetics , Maze Learning/physiology , Mice, Inbred C57BL , Mice, Knockout , Mice, Transgenic , Motor Activity/genetics , Motor Activity/physiology , TOR Serine-Threonine Kinases/metabolism , Transcription Factors/deficiencyABSTRACT
Parathyroid hormone-related peptide (PTHrP) and the parathyroid hormone-PTHrP receptor increase chondrocyte proliferation and delay chondrocyte maturation in endochondral bone development at least partly through cyclic AMP (cAMP)-dependent signaling pathways. Because data suggest that the ability of cAMP to stimulate cell proliferation involves the mitogen-activated protein kinase kinase kinase B-Raf, we hypothesized that B-Raf might mediate the proliferative action of PTHrP in chondrocytes. Though B-Raf is expressed in proliferative chondrocytes, its conditional removal from cartilage did not affect chondrocyte proliferation and maturation or PTHrP-induced chondrocyte proliferation and PTHrP-delayed maturation. Similar results were obtained by conditionally removing B-Raf from osteoblasts. Because A-raf and B-raf are expressed similarly in cartilage, we speculated that they may fulfill redundant functions in this tissue. Surprisingly, mice with chondrocytes deficient in both A-Raf and B-Raf exhibited normal endochondral bone development. Activated extracellular signal-regulated kinase (ERK) was detected primarily in hypertrophic chondrocytes, where C-raf is expressed, and the suppression of ERK activation in these cells by PTHrP or a MEK inhibitor coincided with a delay in chondrocyte maturation. Taken together, these results demonstrate that B-Raf and A-Raf are dispensable for endochondral bone development and they indicate that the main role of ERK in cartilage is to stimulate not cell proliferation, but rather chondrocyte maturation.
Subject(s)
Bone and Bones/metabolism , Chondrocytes/metabolism , Extracellular Signal-Regulated MAP Kinases/metabolism , Hypertrophy/metabolism , Parathyroid Hormone-Related Protein/metabolism , Proto-Oncogene Proteins A-raf/metabolism , Proto-Oncogene Proteins B-raf/metabolism , Animals , Cartilage/metabolism , Cell Differentiation , Cell Proliferation , Cells, Cultured , Chondrocytes/cytology , Enzyme Activation , Gene Expression Regulation, Developmental , Mice , Mice, Inbred C57BL , Mice, Knockout , Osteogenesis , Parathyroid Hormone-Related Protein/genetics , Proto-Oncogene Proteins A-raf/deficiency , Proto-Oncogene Proteins A-raf/genetics , Proto-Oncogene Proteins B-raf/deficiency , Proto-Oncogene Proteins B-raf/genetics , Signal TransductionABSTRACT
Histone methylation is a dynamic process that participates in a diverse array of cellular processes and has been found to associate with cancer. Recently, several histone demethylases have been identified that catalyze the removal of methylation from histone H3 lysine residues. Through bioinformatic and biochemical analysis, we identified JARID1B as a H3K4 demethylase. Overexpression of JARID1B resulted in loss of tri-, di-, and monomethyl H3K4 but did not affect other histone lysine methylations. In vitro biochemical experiments demonstrated that JARID1B directly catalyzes the demethylation. The enzymatic activity requires the JmjC domain and uses Fe(II) and alpha-ketoglutarate as cofactors. Furthermore, we found that JARID1B is up-regulated in prostate cancer tissues, compared with benign prostate samples. We also demonstrated that JARID1B associates with androgen receptor and regulates its transcriptional activity. Thus, we identified JARID1B as a demethylase capable of removing three methyl groups from histone H3 lysine 4 and up-regulated in prostate cancer.