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1.  Carm1 Regulates Pax7 Transcriptional Activity Through MLL1/2 Recruitment During Asymmetric Satellite Stem Cell Divisions 
Cell stem cell  2012;11(3):333-345.
In skeletal muscle, asymmetrically dividing satellite stem cells give rise to committed satellite cells that transcribe the myogenic determination factor Myf5, a Pax7-target gene. We identified the arginine methyltransferase Carm1 as a Pax7 interacting protein and found that Carm1 specifically methylates multiple arginines in the N-terminus of Pax7. Methylated Pax7 directly binds the C-terminal cleavage forms of the trithorax proteins MLL1/2 resulting in the recruitment of the ASH2L:MLL1/2:WDR5:RBBP5 histone H3K4 methyltransferase complex to regulatory enhancers and the proximal promoter of Myf5. Finally, Carm1 is required for the induction of de novo Myf5 transcription following asymmetric satellite stem cell divisions. We defined the C-terminal MLL region as a novel reader domain for the recognition of arginine methylated proteins such as Pax7. Thus, arginine methylation of Pax7 by Carm1 functions as a molecular switch controlling the epigenetic induction of Myf5 during satellite stem cell asymmetric division and entry into the myogenic program.
PMCID: PMC3438319  PMID: 22863532
Satellite stem cells; Muscle regeneration; Pax7; Myf5; Carm1; Histone arginine methyltransferase; MLL; Histone H3K4 methyltransferase
3.  Transcriptional Dominance of Pax7 in Adult Myogenesis is Due to High-Affinity Recognition of Homeodomain Motifs 
Developmental Cell  2012;22(6):1208-1220.
Pax3 and Pax7 regulate stem cell function in skeletal myogenesis. However, molecular insight into their distinct roles has remained elusive. Using gene expression data combined with genome wide binding-site analysis we show that both Pax3 and Pax7 bind identical DNA motifs and jointly activate a large panel of genes involved in muscle stem cell function. Surprisingly, in adult myoblasts Pax3 binds a subset (6.4%) of Pax7 targets. Despite a significant overlap in their transcriptional network, Pax7 regulates distinct panels of genes involved in the promotion of proliferation and inhibition of myogenic differentiation. We show that Pax7 has a higher binding affinity to the homeodomain-binding motif relative to Pax3, suggesting that intrinsic differences in DNA binding contribute to the observed functional difference between Pax3 and Pax7 binding in myogenesis. Together, our data demonstrates distinct attributes of Pax7 function and provides mechanistic insight into the non-redundancy of Pax3 and Pax7 in muscle development.
PMCID: PMC3376216  PMID: 22609161
4.  The E3 Ubiquitin Ligase Activity of Trip12 Is Essential for Mouse Embryogenesis 
PLoS ONE  2011;6(10):e25871.
Protein ubiquitination is a post-translational protein modification that regulates many biological conditions [1], [2], [3], [4]. Trip12 is a HECT-type E3 ubiquitin ligase that ubiquitinates ARF and APP-BP1 [5], [6]. However, the significance of Trip12 in vivo is largely unknown. Here we show that the ubiquitin ligase activity of Trip12 is indispensable for mouse embryogenesis. A homozygous mutation in Trip12 (Trip12mt/mt) that disrupts the ubiquitin ligase activity resulted in embryonic lethality in the middle stage of development. Trip12mt/mt embryos exhibited growth arrest and increased expression of the negative cell cycle regulator p16 [7], [8], [9], [10]. In contrast, Trip12mt/mt ES cells were viable. They had decreased proliferation, but maintained both the undifferentiated state and the ability to differentiate. Trip12mt/mt ES cells had increased levels of the BAF57 protein (a component of the SWI/SNF chromatin remodeling complex) and altered gene expression patterns. These data suggest that Trip12 is involved in global gene expression and plays an important role in mouse development.
PMCID: PMC3196520  PMID: 22028794
5.  Functional interactions between BLM and XRCC3 in the cell 
The Journal of Cell Biology  2007;179(1):53-63.
Bloom's syndrome (BS), which is caused by mutations in the BLM gene, is characterized by a predisposition to a wide variety of cancers. BS cells exhibit elevated frequencies of sister chromatid exchanges (SCEs), interchanges between homologous chromosomes (mitotic chiasmata), and sensitivity to several DNA-damaging agents. To address the mechanism that confers these phenotypes in BS cells, we characterize a series of double and triple mutants with mutations in BLM and in other genes involved in repair pathways. We found that XRCC3 activity generates substrates that cause the elevated SCE in blm cells and that BLM with DNA topoisomerase IIIα suppresses the formation of SCE. In addition, XRCC3 activity also generates the ultraviolet (UV)- and methyl methanesulfonate (MMS)–induced mitotic chiasmata. Moreover, disruption of XRCC3 suppresses MMS and UV sensitivity and the MMS- and UV-induced chromosomal aberrations of blm cells, indicating that BLM acts downstream of XRCC3.
PMCID: PMC2064734  PMID: 17923529
6.  Turning Off Estrogen Receptor β-Mediated Transcription Requires Estrogen-Dependent Receptor Proteolysis▿  
Molecular and Cellular Biology  2006;26(21):7966-7976.
Recent studies have shed light on the ligand-dependent transactivation mechanisms of nuclear receptors (NRs). When the ligand dose is reduced, the transcriptional activity of NRs should be downregulated. Here we show that a ubiquitin-proteasome pathway plays a key role in turning off transcription mediated by estrogen receptor β (ERβ). ERβ shows estrogen-dependent proteolysis, and its degradation is regulated by two regions in the receptor. The N-terminal 37-amino acid-region is necessary for the recruitment of the ubiquitin ligase, i.e., the carboxyl terminus of HSC70-interacting protein (CHIP), to degrade ERβ. In contrast, the C-terminal F domain protects ligand-unbound ERβ from proteolysis to abrogate proteasome association. Suppression of CHIP by interfering RNA inhibited this switching off of receptor-mediated transcription when the ligand dose was reduced. Our results suggest that after ligand withdrawal, the active form of the NR is selectively eliminated via ligand-dependent proteolysis to downregulate receptor-mediated transcription.
PMCID: PMC1636734  PMID: 16940184
7.  Functional Relation among RecQ Family Helicases RecQL1, RecQL5, and BLM in Cell Growth and Sister Chromatid Exchange Formation 
Molecular and Cellular Biology  2003;23(10):3527-3535.
Human RECQL1 and RECQL5 belong to the RecQ family that includes Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome causative genes. Cells derived from individuals suffering from these syndromes show significant levels of genomic instability. However, neither RECQL1 nor RECQL5 has been related to a disease, and nothing is known about the functions of RecQL1 and RecQL5. We generated here RECQL1−/−, RECQL5−/−, RECQL1−/−/RECQL5−/−, RECQL1−/−/BLM−/−, and RECQL5−/−/BLM−/− cells from chicken B-lymphocyte line DT40 cells. Although BLM−/− DT40 cells showed a slow-growth phenotype, a higher sensitivity to methyl methanesulfonate than the wild type, and an ∼10-fold increase in the frequency of sister chromatid exchange (SCE) compared to wild-type cells, RECQL1−/−, RECQL5−/−, and RECQL1−/−/RECQL5−/− cells showed no significant difference from the wild-type cells in growth, sensitivity to DNA-damaging agents, and the frequency of SCE. However, both RECQL1−/−/BLM−/− and RECQL5−/−/BLM−/− cells grew more slowly than BLM−/− cells because of the increase in the population of dead cells, indicating that RecQL1 and RecQL5 are somehow involved in cell viability under the BLM function-impaired condition. Surprisingly, RECQL5−/−/BLM−/− cells showed a higher frequency of SCE than BLM−/− cells, indicating that RecQL5 suppresses SCE under the BLM function-impaired condition.
PMCID: PMC164753  PMID: 12724411

Results 1-7 (7)