Biomedical subjects

Kwok Keung Chan

Publications and source records attributed to Kwok Keung Chan.

4 recordsLinked to original sources

PubMed2005

Hoxb3 vagal neural crest-specific enhancer element for controlling enteric nervous system development.

The neural and glial cells of the intrinsic ganglia of the enteric nervous system (ENS) are derived from the hindbrain neural crest at the vagal level. The Hoxb3 gene is expressed in the vagal neural crest and in the enteric ganglia of the developing gut during embryogenesis. We have identified a cis-acting enhancer element b3IIIa in the Hoxb3 gene locus. In this study, by transgenic mice analysis, we examined the tissue specificity of the b3IIIa enhancer element using the lacZ reporter gene, with emphasis on the vagal neural crest cells and their derivatives in the developing gut. We found that the b3IIIa-lacZ transgene marks only the vagal region and not the trunk or sacral region. Using cellular markers, we showed that the b3IIIa-lacZ transgene was expressed in a subset of enteric neuroblasts during early development of the gut, and the expression was maintained in differentiated neurons of the myenteric plexus at later stages. The specificity of the b3IIIa enhancer in directing gene expression in the developing ENS was further supported by genetic analysis using the Dom mutant, a spontaneous mouse model of Hirschsprung's disease characterized by the absence of enteric ganglia in the distal gut. The colonization of lacZ-expressing cells in the large intestine was incomplete in all the Dom/b3IIIa-lacZ hybrid mutants we examined. To our knowledge, this is the only vagal neural crest-specific genetic regulatory element identified to date. This element could be used for a variety of genetic manipulations and in establishing transgenic mouse models for studying the development of the ENS.

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PubMed2003

Analysis of SOX10 mutations identified in Waardenburg-Hirschsprung patients: Differential effects on target gene regulation.

SOX10 is a member of the SOX gene family related by homology to the high-mobility group (HMG) box region of the testis-determining gene SRY. Mutations of the transcription factor gene SOX10 lead to Waardenburg-Hirschsprung syndrome (Waardenburg-Shah syndrome, WS4) in humans. A number of SOX10 mutations have been identified in WS4 patients who suffer from different extents of intestinal aganglionosis, pigmentation, and hearing abnormalities. Some patients also exhibit signs of myelination deficiency in the central and peripheral nervous systems. Although the molecular bases for the wide range of symptoms displayed by the patients are still not clearly understood, a few target genes for SOX10 have been identified. We have analyzed the impact of six different SOX10 mutations on the activation of SOX10 target genes by yeast one-hybrid and mammalian cell transfection assays. To investigate the transactivation activities of the mutant proteins, three different SOX target binding sites were introduced into luciferase reporter gene constructs and examined in our series of transfection assays: consensus HMG domain protein binding sites; SOX10 binding sites identified in the RET promoter; and Sox10 binding sites identified in the P0 promoter. We found that the same mutation could have different transactivation activities when tested with different target binding sites and in different cell lines. The differential transactivation activities of the SOX10 mutants appeared to correlate with the intestinal and/or neurological symptoms presented in the patients. Among the six mutant SOX10 proteins tested, much reduced transactivation activities were observed when tested on the SOX10 binding sites from the RET promoter. Of the two similar mutations X467K and 1400del12, only the 1400del12 mutant protein exhibited an increase of transactivation through the P0 promoter. While the lack of normal SOX10 mediated activation of RET transcription may lead to intestinal aganglionosis, overexpression of genes coding for structural myelin proteins such as P0 due to mutant SOX10 may explain the dysmyelination phenotype observed in the patients with an additional neurological disorder.

Animals↗

PubMed2002

Comparison of perindopril versus captopril for treatment of acute myocardial infarction.

Angiotensin-converting enzyme (ACE) inhibitors reduce mortality in patients with acute myocardial infarction (AMI), but these benefits might be limited by acute hemodynamic changes and difficulties in titrating to recommended doses. The objective of this study was to compare the hemodynamic changes and tolerability of perindopril with captopril after AMI. We randomized 212 patients to receive either captopril (n = 102) or perindopril (n = 110) within 72 hours of AMI. Captopril was given as an initial dose of 6.25 mg, and then 50 mg/day on day 1 and 100 mg/day thereafter. The corresponding doses of perindopril were 2, 4, and 8 mg/day. Acute hemodynamic changes, the percentage of patients who reached target doses, and in-hospital and 6-month cardiovascular events were monitored. Baseline clinical characteristics of the 2 groups were identical, but patients randomized to perindopril were in a higher Killip class (1.4 +/- 0.6 vs 1.2 +/- 0.5, p = 0.05). During the first 6 hours, treatment with perindopril resulted in higher minimal systolic (97 +/- 15 vs 91 +/- 14 mm Hg, p <0.01) and diastolic blood pressure (BP) (57 +/- 11 vs 54 +/- 10 mm Hg, p <0.02), later occurrence of minimal BP (3.6 +/- 0.2 vs 2.7 +/- 0.1 hour, p <0.001), and a lower incidence of persistent hypotension with systolic BP < 90 mm Hg for > or =1 hour (5% vs 16%; p < 0.01) compared with captopril. At initial administration, target doses of perindopril and captopril were attained in 97% and 82% of the patients, respectively (p < 0.01). After 6 months, there were no differences between patients treated with perindopril and captopril in mortality rates (6% vs 13%, p = 0.16) and need for revascularization (20% vs 21%, p = 0.9). Thus, in patients during AMI, perindopril treatment showed better short-term tolerance than treatment with captopril, with significantly less acute hemodynamic changes and fewer withdrawals.

Aged↗

PubMed2002

Interaction of the heart-specific LIM domain protein, FHL2, with DNA-binding nuclear protein, hNP220.

Using a yeast two-hybrid library screen, we have identified that the heart specific FHL2 protein, four-and-a-half LIM protein 2, interacted with human DNA-binding nuclear protein, hNP220. Domain studies by the yeast two-hybrid interaction assay revealed that the second LIM domain together with the third and the fourth LIM domains of FHL2 were responsible to the binding with hNP220. Using green fluorescent protein (GFP)-FHL2 and blue fluorescent protein (BFP)-hNP220 fusion proteins co-expressed in the same cell, we demonstrated a direct interaction between FHL2 and hNP220 in individual nucleus by two-fusion Fluorescence Resonance Energy Transfer (FRET) assay. Besides, Western blot analysis using affinity-purified anti-FHL2 antipeptide antibodies confirmed a 32-kDa protein of FHL2 in heart only. Virtually no expression of FHL2 protein was detected in brain, liver, lung, kidney, testis, skeletal muscle, and spleen. Moreover, the expression of FHL2 protein was also detectable in the human diseased heart tissues. Our results imply that FHL2 protein can shuttle between cytoplasm and nucleus and may act as a molecular adapter to form a multicomplex with hNP220 in the nucleus, thus we speculate that FHL2 may be particularly important for heart muscle differentiation and the maintenance of the heart phenotype.

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