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Bing Lim

Publications and source records attributed to Bing Lim.

26 records · Page 2Linked to original sources
PubMed2003

hZimp10 is an androgen receptor co-activator and forms a complex with SUMO-1 at replication foci.

The androgen receptor (AR) plays a central role in male sexual development and in normal and malignant prostate cell growth and survival. It has been shown that transcriptional activation of AR is regulated through interaction with various co-factors. Here we identify a novel PIAS-like protein, hZimp10, as an AR-interacting protein. The transactivation domain (TAD) of AR and the central region of hZimp10 were found to be responsible for the interaction. A strong intrinsic transactivation domain was identified in the C-terminal, proline-rich region of hZimp10. Endogenous AR and hZimp10 proteins were co-stained in the nuclei of prostate epithelial cells from human tissue samples. In human prostate cancer cells, hZimp10 augmented the transcriptional activity of AR. Moreover, hZimp10 co-localized with AR and SUMO-1 at replication foci throughout S phase, and it was capable of enhancing sumoylation of AR in vivo. Studies using sumoylation deficient AR mutants suggested that the augmentation of AR activity by hZimp10 is dependent on the sumoylation of the receptor. Taken together, these data demonstrate that hZimp10 is a novel AR co-regulator.

Amino Acid Sequence↗
PubMed2003

Long-term expansion of human functional epidermal precursor cells: promotion of extensive amplification by low TGF-beta1 concentrations.

We have previously introduced the concept of high proliferative potential-quiescent (HPP-Q) cells to refer to primitive human hematopoietic progenitors, on which transforming growth factor-beta1 (TGF-beta1) exerts a pleiotropic effect. TGF-beta1 confers to these slow-dividing cells a mitogenic receptor(low) phenotype and maintains immature properties by preventing differentiation and apoptosis. However, the effect of TGF-beta1 on long-term expansion has not yet been clearly demonstrated. Here, we describe the characterization of a human skin keratinocyte subpopulation, highly enriched for primitive epidermal precursors, on the basis of high adhesion capacity (Adh+++) and low expression of the epidermal growth factor receptor (Adh+++EGF-Rlow). In our standard culture condition without feeder cells, the mean estimated output for cells from an unfractionated population of primary foreskin keratinocytes was 10(7)-10(8), increasing to 10(12)-10(13) in cultures initiated with selected Adh+++EGF-Rlow precursors. Characterization of these cells revealed a hitherto unknown property of TGF-beta1: its addition at a very low concentration (10 pg/ml) in long-term cultures induces a very significant additional increase of expansion. In this optimized system, outputs obtained in cultures initiated with Adh+++EGF-Rlow cells repeatedly reached 10(16)-10(17) ( approximately 60 population doublings, approximately 4 x 10(18) keratinocytes produced per clonogenic cell present in the initial population). At the molecular level, this effect is associated with an increase in Smad1, Smad2 and Smad3 phosphorylation and an increase in alpha6 and beta1 integrin expression. No such effect could be observed on mature keratinocytes with low adhesion capacity (Adh-/+). We finally demonstrated that the progeny of Adh+++EGF-Rlow precursors after long-term expansion is still capable of generating a pluristratified epidermis in a model for skin reconstruction. In conclusion, after further characterizing the phenotype of primitive epidermal precursors, we demonstrated a new function of TGF-beta1, which is to promote undifferentiated keratinocyte amplification.

Cell Adhesion↗
PubMed2003

Autoimmunity as the consequence of a spontaneous mutation in Rasgrp1.

A mouse strain was identified with a recessive genetic lesion, which spontaneously developed a lymphoproliferative autoimmune syndrome exhibiting features of systemic lupus erythematosus. Positional mapping of the disease-associated locus revealed a lesion in Rasgrp1 that prevented the translation of the RasGRP1 protein. T cells from these mice failed to activate Ras or proliferate vigorously following antigen encounter and showed defects in positive selection. Peripheral RasGRP1lag T cells spontaneously adopted a memory phenotype and were able to transfer disease to lymphopenic recipient mice. CD4+ T cells accumulated in the lymphoid tissues of older RasGRP1lag mice and were resistant to activation-induced cell death. RasGRP1lag B cells were functionally normal, but activated B cells were detected in older mice, as were autoantibodies directed against self-antigens. Our findings indicate that Ras signaling pathways are required to maintain T cell tolerance and to prevent autoimmune disease.

Animals↗
PubMed2003

Insights into the role of DNA methylation in murine embryonic stem cells using a modified tetracycline-inducible gene expression system.

Murine embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass of the mouse blastocyst. Their ability to differentiate into diverse cell types in vitro has served well as a model of early embryonic developmental processes. A powerful strategy for studying the role of key genes during this time is to be able to regulate their expression in a dose-dependent manner. Here, we outline our experience of applying the "tetracycline-inducible system" to study gene function during ES cell differentiation and describe a number of key modifications designed to overcome the central problem of transgene silencing. Finally, we demonstrate how this approach can yield insights into the role of DNA methylation during ES cell differentiation by studying the function of two genes: DNMT3A, involved in the de novo methylation of cytosine bases, and MBD2b, a methyl-dependent co-repressor and putative cytosine demethylase.

Animals↗
PubMed2003

RhoGTPases and their role in cancer.

The RhoGTPases constitute a large family of small GTP binding proteins that police many sensitive crossroads in diverse cellular functions. Therefore, it would not be surprising if aberrant RhoGTPase function led to perturbed growth and differentiation, including carcinogenesis and cancer progression. The evidence for a causative connection between RhoGTPases and primary human cancers is still weak but there are increasing findings to support this link. An appreciation of this connection is timely and important to alert readers to the possibilities of new disease mechanisms and new ways to diagnose and treat cancer.

Animals↗
PubMed2002

Linking beta-catenin to androgen-signaling pathway.

The androgen-signaling pathway is important for the growth and progression of prostate cancer cells. The growth-promoting effects of androgen on prostate cells are mediated mostly through the androgen receptor (AR). There is increasing evidence that transcription activation by AR is mediated through interaction with other cofactors. beta-Catenin plays a critical role in embryonic development and tumorigenesis through its effects on E-cadherin-mediated cell adhesion and Wnt-dependent signal transduction. Here, we demonstrate that a specific protein-protein interaction occurs between beta-catenin and AR. Unlike the steroid hormone receptor coactivator 1 (SRC1), beta-catenin showed a strong interaction with AR but not with other steroid hormone receptors such as estrogen receptor alpha, progesterone receptor beta, and glucocorticoid receptor. The ligand binding domain of AR and the NH(2) terminus combined with the first six armadillo repeats of beta-catenin were shown to be necessary for the interaction. Through this specific interaction, beta-catenin augments the ligand-dependent activity of AR in prostate cancer cells. Moreover, expression of E-cadherin in E-cadherin-negative prostate cancer cells results in redistribution of the cytoplasmic beta-catenin to the cell membrane and reduction of AR-mediated transcription. These data suggest that loss of E-cadherin can elevate the cellular levels of beta-catenin in prostate cancer cells, which may directly contribute to invasiveness and a more malignant tumor phenotype by augmenting AR activity during prostate cancer progression.

Androgens↗
PubMed2002

The hematopoiesis-specific GTP-binding protein RhoH is GTPase deficient and modulates activities of other Rho GTPases by an inhibitory function.

The Rho subfamily of small GTP-binding proteins mediates many fundamental cellular functions. The commonly studied members (Rho, Rac, and CDC42) regulate actin reorganization, affecting diverse cellular responses, including adhesion, cytokinesis, and motility. Another major function of the Rho GTPases is their role in regulating transcriptional factors and nuclear signaling. RhoH is encoded by a hematopoiesis-specific Rho-related gene recently identified in a fusion transcript with bcl6 in lymphoma cell lines. Significantly, translocations and a high frequency of RhoH mutation have been detected in primary lymphoma cells. We show here that RhoH functions differently from other Rho GTPases. RhoH exerts no significant effect on actin reorganization. However, RhoH is a potent inhibitor of the activation of NFkappaB and p38 by other Rho GTPases. This property, together with the differential expression of RhoH in the Th1 subset of T cells, suggests a role for RhoH in the functional differentiation of T cells. RhoH has different amino acids in two highly conserved residues critical for GTPase activity. Consequently, RhoH is GTPase deficient, remaining in a GTP-bound activated state without cycling. Reduction of RhoH levels in T cells augments the response to Rac activation. Furthermore, RhoH is dramatically down regulated after phorbol myristate acetate treatment and in Th1 cells after activation by anti-CD3. Hence, a mechanism for regulation of RhoH function is likely to exist at the transcriptional level. The inhibitory function of RhoH supports a model in which Rho GTPases with opposing functions may compete to modulate the final outcome of a particular GTPase-activated pathway.

Amino Acid Sequence↗