Ubiquitin-dependent regulation of translesion polymerases

In response to DNA damage, TLS (translesion synthesis) allows replicative bypass of various DNA lesions, which stall normal replication. TLS is achieved by low-fidelity polymerases harbouring less stringent active sites. In humans, Y-family polymerases together with Polζ (polymerase ζ) are responsible for TLS across different types of damage. Protein-protein interaction contributes significantly to the regulation of TLS. REV1 plays a central role in TLS because it interacts with all other Y-family members and Polζ. Ubiquitin-dependent regulatory mechanisms also play important roles in TLS. Ubiquitin-binding domains have been found in TLS polymerases and they might be required for TLS activity. Mono-ubiquitination of PCNA (proliferating-cell nuclear antigen), the central scaffold of TLS polymerases, is thought to promote TLS. In addition, both non-proteolytic and proteolytic polyubiquitination of PCNA and TLS polymerases has been demonstrated. Owing to their low fidelity, the recruitment of TLS polymerases is strictly restricted to stalled replication forks. © The Authors Journal compilation.postprin

Regulation of ubiquitination and degradation of CRTC1 transcriptional coactivator by salt-inducible kinase SIK1

Poster presentation - Theme 1: Cell biologycAMP response element (CRE) binding protein (CREB) is a bZIP transcription factor centrally involved in the regulation of cellular proliferation, survival, energy metabolism and stress response. CREB-regulated transcriptional coactivator (CRTC) is an essential factor which potently activates the transcriptional activity of CREB by promoting the recruitment of TAFII130/135. Currently, several kinases and phosphatases are known to regulate the function of CRTCs. For example, salt-inducible kinases (SIKs) belonging to AMPK protein kinase family inhibit the activity of ...postprin

SiRNA and shRNA screens advance key understanding of host factors required for HIV-1 replication

A recent RNAi screen used a genome-wide shRNA library to search for cellular factors required for HIV-1 replication. This work complements three other siRNA-based screening studies and potentially opens the door to the discovery of factors that are important for HIV-1 replication in physiological host cells such as T lymphocytes. shRNA screens can be further improved, and they could promise to unravel new pathways and new facets of virus-cell interactions. © 2009 Kok et al; licensee BioMed Central Ltd.published_or_final_versio

Pancreatic tuberculosis with splenic tuberculosis mimicking advanced pancreatic cancer with splenic metastasizes: a case report

A 60-year-old woman presented with vague abdominal pain for one week was referred to pancreatic tail carcinoma accompanied with splenic metastasizes. She came to our hospital for further treatment. Ultrasonography and abdominal computed tomography (CT) revealed a pancreatic tail tumor with splenic metastasizes. There was no history of tuberculosis. Laparotomy was performed because pancreatic tail carcinoma with splenic metastasizes was highly suspected. Indurated mass in the pancreatic tail and sporadic metastasizes in the spleen had been found during the surgery. The pancreatic tail and the spleen were removed and proved to be tuberculosis on histological examination of a frozen section. The patient was given antituberculosis therapy and is now getting well. Tuberculosis should be considered in the differential diagnosis of pancreatic masses. The response to antituberculosis treatment is very favorable

Differential subcellular localization and activity of kelch repeat proteins KLHDC1 and KLHDC2.

We have previously identified and characterized human KLHDC2/HCLP-1, a kelch repeat protein that interacts with and inhibits transcription factor LZIP. In this study, we identified and characterized a paralog of KLHDC2 called KLHDC1. KLHDC1 and KLHDC2 share about 50% identity at the level of amino acid sequence and both gene loci localize to human chromosome 14q21.3. This cluster of KLHDC1 and KLHDC2 genes is highly conserved in vertebrates ranging from pufferfish to human. Both genes are expressed highly in skeletal muscle, but weakly in various other tissues. While KLHDC2 was predominantly found in the nucleus, KLHDC1 is a cytoplasmic protein. Neither KLHDC1 nor KLHDC2 binds to actin. In addition, KLHDC1 was unable to inhibit LZIP/CREB3-mediated transcriptional activation. Thus, KLHDC1 and KLHDC2 have differential localization and activity in cultured mammalian cells.postprin

Human TRBP and PACT directly interact with each other and associate with dicer to facilitate the production of small interfering RNA

Mammalian Dicer interacts with double-stranded RNA-binding protein TRBP or PACT to mediate RNA interference and micro-RNA processing. TRBP and PACT are structurally related but exert opposite regulatory activities on PKR. It is not understood whether TRBP and PACT are simultaneously required for Dicer. Here we show that TRBP directly interacts with PACT in vitro and in mammalian cells. TRBP and PACT form a triple complex with Dicer and facilitate the production of small interfering RNA (siRNA) by Dicer. Knockdown of both TRBP and PACT in cultured cells leads to significant inhibition of gene silencing mediated by short hairpin RNA but not by siRNA, suggesting that TRBP and PACT function primarily at the step of siRNA production. Taken together, these findings indicate that human TRBP and PACT directly interact with each other and associate with Dicer to stimulate the cleavage of double-stranded or short hairpin RNA to siRNA. Our work significantly alters the current model for the assembly and function of the Dicer-containing complex that generates siRNA and micro-RNA in human. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.postprin

Identification and characterization of EBP, a novel EEN binding protein that inhibits Ras signaling and is recruited into the nucleus by the MLL-EEN fusion protein

The chimeric MLL-EEN fusion protein is created as a result of chromosomal translocation t(11;19)(q23;p13). EEN, an Src homology 3 (SH3) domain-containing protein in the endophilin family, has been implicated in endocytosis, although little is known about its role in leukemogenesis mediated by the MLL-EEN fusion protein. In this study, we have identified and characterized EBP, a novel EEN binding protein that interacts with the SH3 domain of EEN through a proline-rich motif PPERP. EBP is a ubiquitous protein that is normally expressed in the cytoplasm but is recruited to the nucleus by MLL-EEN with a punctate localization pattern characteristic of the MLL chimeric proteins. EBP interacts simultaneously with EEN and Sos, a guanine-nucleotide exchange factor for Ras. Coexpressoin of EBP with EEN leads to suppression of Ras-induced cellular transformation and Ras-mediated activation of Elk-1. Taken together, our findings suggest a new mechanism for MLL-EEN-mediated leukemogenesis in which MLL-EEN interferes with the Ras-suppressing activities of EBP through direct interaction. © 2004 by The American Society of Hematology.postprin

Differential expression, localization and activity of two alternatively spliced isoforms of human APC regulator CDH1

The timely destruction of key regulators through ubiquitin-mediated proteolysis ensures the orderly progression of the cell cycle. The APC (anaphase-promoting complex) is a major component of this degradation machinery and its activation is required for the execution of critical events. Recent studies have just begun to reveal the complex control of the APC through a regulatory network involving WD40 repeat proteins CDC20 and CDH1. In the present paper, we report on the identification and characterization of human CDH1β, a novel alternatively spliced isoform of CDH1. Both CDH1α and CDH1β can bind to the APC and stimulate the degradation of cyclin B1, but they are differentially expressed in human tissues and cells. CDH1α contains a nuclear localization signal which is absent in CDH1β. Intracellularly, CDH1α appears in the nucleus whereas CDH1β is a predominantly cytoplasmic protein. The forced overexpression of CDH1α in cultured cells correlates with the reduction of nuclear cyclin A, but the steady-state amount of cyclin A does not change noticeably in CDH1β-overexpressed cells. In Xenopus embryos, ectopic overexpression of human CDH1α, but not of CDH1β, induces cell-cycle arrest during the first G1 phase at the midblastula transition. Taken together, our findings document the differential expression, subcellular localization and cell-cycle-regulatory activity of human CDH1 isoforms.postprin

Severe acute respiratory syndrome coronavirus nucleocapsid protein does not modulate transcription of the human FGL2 gene

Among the structural and nonstructural proteins of severe acute respiratory syndrome coronavirus (SARS-CoV), the nucleocapsid (N) protein plays pivotal roles in the biology and pathogenesis of viral infection. N protein is thought to dysregulate cell signalling and the transcription of cellular genes, including FGL2, which encodes a prothrombinase implicated in vascular thrombosis, fibrin deposition and pneumocyte necrosis. Here, we showed that N protein expressed in cultured human cells was predominantly found in the cytoplasm and was competent in repressing the transcriptional activity driven by interferon-stimulated response elements. However, the expression of N protein did not influence the transcription from the FGL2 promoter. More importantly, N protein did not modulate the expression of FGL2 mRNA or protein in transfected or SARS-CoV-infected cells. Taken together, our findings did not support the model in which SARS-CoV N protein specifically modulates transcription of the FGL2 gene to cause fibrosis and vascular thrombosis. © 2009 SGM.published_or_final_versio

CRTC1 transcriptional coactivator is required for hepatitis B virus gene expression and replication

This journal suppl. entitled: Metabolism, Diet and Disease 2014: Cancer and metabolismConference Theme: Cancer and metabolismPoster Presentation: P31BACKGROUND: Chronic hepatitis B virus (HBV) infection occurs in over 400 million people worldwide, 15-40% of whom will terminally develop severe liver diseases including hepatocellular carcinoma. Although development of HCC is a multi-step process, high HBV DNA level is a major risk factor for disease progression. Transcription of HBV from the cccDNA template is essential for its replication and requires CREB transcription factor, a master regulator of cell metabolism. However, transcriptional coactivators that facilitate CREB-dependent activation of HBV transcription remain to be identified and characterized …published_or_final_versio