👤 Jerry Kok Yen Chan

The RAS-RAF-MEK-extracellular signal-regulated kinase (ERK) pathway plays a pivotal role in various cellular responses, including cellular growth, differentiation, survival and motility. Constitutive activation of the ERK pathway has been linked to the development and progression of human cancers. Here, we reported that mitogen-activated protein kinase phosphatase (MKP)-3, a negative regulator of ERK1/2, lost its expression particularly in the protein level, was significantly correlated with high ERK1/2 activity in primary human ovarian cancer cells using quantitative reverse transcription-polymerase chain reaction and western blot analyses. Intriguingly, the loss of MKP3 protein was associated with ubiquitination/proteosome degradation mediated by high intracellular reactive oxygen species (ROS) accumulation such as hydrogen peroxide in ovarian cancer cells. Functionally, short hairpin RNA knock down of endogenous MKP3 resulted in increased ERK1/2 activity, cell proliferation rate, anchorage-independent growth ability and resistance to cisplatin in ovarian cancer cells. Conversely, enforced expression of MKP3 in MKP3-deficient ovarian cancer cells significantly reduced ERK1/2 activity and inhibited cell proliferation, anchorage-independent growth ability and tumor development in nude mice. Furthermore, the enforced expression of MKP3 succeeded to sensitize ovarian cancer cells to cisplatin-induced apoptosis in vitro and in vivo. These results suggest a molecular mechanism by which the accumulation of ROS during ovarian cancer progression may cause the degradation of MKP3, which in turn leads to aberrant ERK1/2 activation and contributes to tumorigenicity and chemoresistance of human ovarian cancer cells. Show less

Previous studies showed that expression of the novel candidate tumor suppressor gene, DEC1 (Deleted in Esophageal Cancer 1), is reduced in esophageal carcinoma and suppresses cancer cell growth in vitro and tumor growth in vivo in nude mice. This study shows that DEC1 gene expression was downregulated in 100% of 16 esophageal squamous cell carcinoma (ESCC) cell lines and 52 and 45%, respectively, of esophageal tumor specimens from Hong Kong and a high-risk ESCC region of Henan, China. Using epitope tagging, the DEC1 protein was localized to both the cytoplasm and nucleus of the cell. In 3D Matrigel culture, no significant difference in colony numbers formed was observed for DEC1 stable transfectants, as compared to vector-alone transfectant controls. However, significantly smaller colony sizes were observed for the DEC1 transfectants. In in vitro cell migration, invasion and soft agar assays of DEC1 transfectants, only the soft agar assay showed statistically significant differences in colony numbers with the vector-alone controls, indicating that DEC1 may be involved in anchorage-independent cell growth. In addition, the global gene expression affected by DEC1 in tumor-suppressive stable transfectants was investigated using cDNA oligonucleotide microarray hybridization. Three candidate genes, TFPI-2, GDF15 and DUSP6, were identified through this approach; they are downregulated in tumor segregants of DEC1 stable transfectants, ESCC cell lines and esophageal tumors and have a potential role in tumor growth and progression. These studies show that DEC1 is involved in esophageal cancer development and help elucidate its functional role in tumor development. Show less

The different clinical entities of osteochondromas, hereditary multiple exostoses (HME) and non-familial solitary exostosis, are known to express localized exostoses in their joint metaphyseal cartilage. In the current study biopsies of osteochondromas patients were screened with respect to a number of cellular and molecular parameters. Specifically, cartilaginous biopsy samples of nine HME patients, 10 solitary exostosis patients and 10 articular cartilages of control subjects were collected and cell cultures were established. Results obtained showed that one of the two HME samples that underwent DNA sequencing analysis (HME-1) had a novel mutation for an early stop codon, which led to an aberrant protein, migrating at a lower molecular weight position. The EXT-1 mRNA and protein levels in chondrocyte cultures derived from all nine HME patients were elevated, compared with solitary exostosis patients or control subjects. Furthermore, cell cultures of HME patients had significantly decreased pericellular heparan sulphate (HS) in comparison with cultures of solitary exostosis patients or control subjects. Immunohistochemical staining of tissue sections and Western blotting of cell cultures derived from HME patients revealed higher levels of heparanase compared with solitary exostosis patients and of control subjects. Further investigations are needed to determine whether the low pericellular HS levels in HME patients stem from decreased biosynthesis of HS, increased degradation or a combination of both. In conclusion, it appears that due to a mutated glycosyltransferase, the low content of pericellular HS in HME patients leads to the anatomical deformations with exostoses formation. Hence, elevation of HS content in the pericellular regions should be a potential molecular target for correction. Show less

Carbohydrate response element-binding protein (ChREBP) is a basic helix-loop-helix/leucine zipper transcription factor that binds to the carbohydrate response element in the promoter of certain lipogenic and glycolytic genes. High glucose can activate ChREBP by releasing an intramolecular inhibition within the glucose-sensing module (GSM) that occurs in low glucose. We report here that the glucose response of GSM is mediated by cooperation between five conserved submodules known as Mondo conserved regions (MCRs) I through V within GSM. Deletion of individual MCRs leads to complete (for MCR II, III, and IV) or partial (MCR I) loss of glucose response of ChREBP. MCR IV is necessary and sufficient for inhibiting the transcriptional activity of ChREBP under low glucose. The roles of MCR II and III in glucose response of ChREBP are independent of and distinct from their function in controlling subcellular localization. We further demonstrate that, instead of inhibiting ChREBP activity as would be predicted from its cytoplasmic retentive function, 14-3-3 binding with MCR III is essential for the glucose responsiveness of ChREBP. The interaction between 14-3-3 and ChREBP is constitutive, indicating a permissive role of 14-3-3 in the glucose response of ChREBP. We further uncovered an unconventional 14-3-3 binding motif (residues 116-135) lacking phosphor-serine/threonine within MCR III, a predicted alpha-helix highly conserved in all Mondo proteins. We conclude that individual subdomains in the GSM (MCR I through V) play diverse but crucial roles in cooperation with essential trans-acting cofactors such as 14-3-3 proteins to mediate the glucose response of ChREBP. Show less

Patients with diabetic nephropathy (DN) have increased plasma fasting triglyceride (TG) levels, and most prospective studies report that elevated TG precedes DN. TG-rich lipoprotein particles might promote progression of DN. To test the hypothesis that elevated TG levels contribute to the development of DN, one may examine whether a polymorphism strongly associated with TG levels affects DN risk. The apolipoprotein A5 (apoA5) -1131T-->C polymorphism has a large effect on the TG level, and all three genotypes are relatively common in East Asians. Therefore, we sought to examine the association of this polymorphism with DN. We genotyped the apoA5 -1131T-->C polymorphism in a case-control study involving 367 Chinese Type 2 diabetes patients with DN and 382 without DN, as well as 198 subjects without diabetes. Mean fasting TG levels were higher in CC than in TT carriers by 41%, 54%, and 62% in each of the three subject groups, respectively. However, the genotype distributions did not differ between patients with and without nephropathy (P=.69). Therefore, these results weigh against the hypothesis that high fasting TG per se causes DN. The strong association between TG level and DN may be due to a factor that is usually closely linked to TG level but that is not affected by the apoA5 polymorphism. Show less

Apolipoprotein A-V (apoA-V) plays a key role in the regulation of triglyceride (TG) metabolism. Given the very low concentration of apoA-V in plasma, we hypothesized that apoA-V may influence plasma TG levels by affecting the assembly and/or secretion of apoB-containing lipoproteins. When apoA-V was overexpressed in cultured Hep3B cells, neither the amount of apoB secreted nor the density distribution of apoB-containing lipoproteins was affected. Fluorescence microscopy and cell lysate immunoprecipitation studies revealed that apoA-V is not associated with apoB intracellularly, yet immunoprecipitation of apoA-V from the cell culture medium resulted in coprecipitation of apoB. These data suggest that the apoA-V association with apoB-containing lipoproteins is a postsecretory event. Confocal fluorescence microscopy revealed the presence of apoA-V in distinct cellular structures. Based on Nile Red staining, we identified these structures to be intracellular lipid droplets. These data suggest that apoA-V has a unique association with cellular lipids and, therefore, may be involved in the storage or mobilization of intracellular lipids. Show less

Current staging methods are inadequate for predicting the outcome of treatment of non-small-cell lung cancer (NSCLC). We developed a five-gene signature that is closely associated with survival of patients with NSCLC. We used computer-generated random numbers to assign 185 frozen specimens for microarray analysis, real-time reverse-transcriptase polymerase chain reaction (RT-PCR) analysis, or both. We studied gene expression in frozen specimens of lung-cancer tissue from 125 randomly selected patients who had undergone surgical resection of NSCLC and evaluated the association between the level of expression and survival. We used risk scores and decision-tree analysis to develop a gene-expression model for the prediction of the outcome of treatment of NSCLC. For validation, we used randomly assigned specimens from 60 other patients. Sixteen genes that correlated with survival among patients with NSCLC were identified by analyzing microarray data and risk scores. We selected five genes (DUSP6, MMD, STAT1, ERBB3, and LCK) for RT-PCR and decision-tree analysis. The five-gene signature was an independent predictor of relapse-free and overall survival. We validated the model with data from an independent cohort of 60 patients with NSCLC and with a set of published microarray data from 86 patients with NSCLC. Our five-gene signature is closely associated with relapse-free and overall survival among patients with NSCLC. Show less

Neurons and glia share a mutual dependence in establishing a functional relationship, and none is more evident than the process by which axons control myelination. Here, we identify LRR and Ig domain-containing, Nogo receptor-interacting protein (LINGO-1) as a potent axonal inhibitor of oligodendrocyte differentiation and myelination that is regulated by nerve growth factor and its cognate receptor TrkA in a dose-dependent manner. Whereas LINGO-1 expressed by oligodendrocyte progenitor cells was previously identified as an inhibitor of differentiation, we demonstrate that axonal expression of LINGO-1 inhibits differentiation with equal potency. Disruption of LINGO-1 on either cell type is sufficient to overcome the inhibitory action and promote differentiation and myelination, independent of axon diameter. Furthermore, these results were recapitulated in transgenic mice overexpressing the full length LINGO-1 under the neuronal promoter synapsin. Myelination was greatly inhibited in the presence of enforced axonal LINGO-1. The implications of these results relate specifically to the development of potential therapeutics targeting extrinsic growth factors that may regulate the axonal expression of modulators of oligodendrocyte development. Show less

We investigated the associations between plasma very-low-density lipoprotein (VLDL)-apolipoprotein (apo)C-III and apoA-V concentrations and the kinetics of VLDL-apoB-100 and VLDL triglycerides in 15 men. We also explored the relationship between these parameters of VLDL metabolism and VLDL-apoC-III kinetics. ApoC-III, apoB, and triglyceride kinetics in VLDL were determined using stable isotopes and multicompartmental modeling to estimate production rate (PR) and fractional catabolic rate (FCR). Plasma VLDL-apoC-III concentration was significantly and inversely associated with the FCRs of VLDL triglycerides (r=-0.610) and VLDL-apoB (r=-0.791), and positively correlated with the PR of VLDL-apoC-III (r=0.842). However, apoA-V concentration was not significantly associated with any of the kinetic variables. There was a significant association (P<0.01) between the PRs of VLDL triglycerides and VLDL-apoB (r=0.641), and between the FCRs of VLDL triglycerides and VLDL-apoB (r=0.737). In multiple regression analysis, plasma VLDL-apoC-III concentration was a significant predictor of VLDL triglyceride FCR (beta-coefficient=-0.575) and VLDL-apoB FCR (beta-coefficient=-0.839). Our findings suggest that increased VLDL-apoC-III concentrations resulting from an overproduction of VLDL-apoC-III are strongly associated with the delayed catabolism of triglycerides and apoB in VLDL. We also demonstrated that the kinetics of VLDL triglycerides and apoB are closely coupled. Our data do not support a role for plasma apoA-V in regulating VLDL kinetics. Show less

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. In DN patients, triglyceride (TG) level is elevated and lipoprotein lipase (LPL) activity, which hydrolyzes TG, is decreased. The LPL S447X and apolipoprotein E (APOE) exon 4 polymorphisms affect TG levels, and the APOC3 -455T>C polymorphism affects LPL activity. Our aim was to examine the association of these polymorphisms with nephropathy in type 2 diabetes. We examined these polymorphisms in a case-control study of type 2 diabetic patients including 374 with DN and 392 without DN. LPL 447X-containing genotypes (447X+) were significantly decreased in DN patients [18.6 vs 25.6%, odds ratio (OR) = 0.66, p = 0.02], as were APOE epsilon3/epsilon3 genotypes (64.8 vs 73.1%, OR = 0.68, p = 0.01). In addition, combinations of genotypes [APOE epsilon3/epsilon3 and LPL 447X+ (OR = 0.56), APOC3 CC and LPL 447X+ (OR = 0.31), APOE epsilon3/epsilon3 and APOC3 CC (OR = 0.61] were protective for DN compared with the most common combination of the respective polymorphisms. Our findings suggest the importance of interactions among lipid genes in modulating the risk of DN. Show less

Male infertility is now a major reproductive health problem because of an increasing number of environmental pollutants and chemicals, which eventually result in gene mutations. Genetic alterations caused by environmental factors account for a significant percentage of male infertility. Microarray technology is a powerful tool capable of measuring simultaneously the expression of thousands of genes expressed in a single sample. Eventually, advances in genetic technology will allow for the diagnosis of patients with male infertility due to congenital reasons or environmental factors. Since its introduction in 1994, microarray technology has made significant advances in the identification and characterization of novel or known genes possibly correlated with male infertility in mice, as well as in humans. This provides a rational basis for the application of microarray to establishing molecular signatures for the diagnosis and gene therapy targets of male infertility. In this review, the differential gene expression patterns characterized by microarray in germ and somatic cells at different steps of development or in response to stimuli, as well as a number of novel or known genes identified to be associated with male infertility in mice and humans, are addressed. Moreover, issues pertaining to measurement reproducibility are highlighted for the application of microarray data to male infertility. Show less

In spite of recent evidence showing the importance of DBY (DEAD-box RNA helicase Y) in spermatogenesis in human, the biologic role of its homolog Dby (also known as Ddx3y) in the mouse is less clear. The present study aims at characterizing the molecular structure of Dby and comparing its expression with its X- and autosome-linked homologs in embryonic gonads and developing germ cells in mice. Molecular cloning by rapid amplification of 3'-cDNA ends showed that the Dby gene in the mouse gives rise to 2 transcripts that differ only in the length of the 3'-untranslated region as a consequence of the use of alternative polyadenylation signals. Measurement by quantitative real-time polymerase chain reaction showed that both transcripts were ubiquitously expressed and were present in male germ cells and Sertoli cells. They were more abundant in type A spermatogonia compared with pachytene spermatocytes and round spermatids. Expression of Dby in the embryonic gonad increased from day 10.5 and reached a peak at day 17.5. The expression level of Dby decreased after birth and remained low in adult male gonads. Although the level of expression of Dby was much lower than its X chromosome homolog, Ddx3 (also known as Ddx3x) in all samples examined, the pattern of expression of the 2 genes was comparable. In contrast, their autosomal homolog, D1Pas1(also known as PL10), was predominantly expressed in pachytene spermatocytes and round spermatids. This result is in accord with meiotic sex chromosome inactivation in that Dby and Ddx are replaced in pachytene spermatocytes by their autosomal retroposon. These observations indicate that unlike DBY in humans, the role of Dby in spermatogenesis is less obvious in the mouse and its biologic activity may be replaced by that of Ddx3 and D1Pas1. Show less

Gene expression profiling was performed using the National Institute on Aging 15,000-cDNA microarray to reveal the differential expression pattern of 160 genes between meiotic pachytene spermatocytes and postmeiotic round spermatids of the mouse. Our results indicate that more genes are expressed in spermatids than in spermatocytes. Genes participating in cell cycle regulation and chromatin structure and dynamics are preferentially expressed in spermatocytes, while genes for protein turnover, signal transduction, energy metabolism, and intracellular transport are prevalent in spermatids. This suggests that a switch of functional requirement occurs when meiotic germ cells differentiate into haploid spermatids. Concordant expression patterns were obtained when quantitative real-time polymerase chain reaction was performed to verify the microarray data. Interestingly, the majority of the differentially expressed genes were underrepresented in mitotic type A spermatogonia, and they were preferentially expressed in the testis. Our results suggest that an even higher proportion of the mouse genome is devoted to male gamete development from meiosis than was previously estimated. We also provide evidence that underscores the advantage of using purified germ cells over whole testes in profiling spermatogenic gene expression to identify transcripts that demonstrate stage-specific expression patterns. Show less

We report here a novel mechanism for glucose-mediated activation of carbohydrate response element binding protein (ChREBP), a basic helix-loop-helix/leucine zipper (bHLH/ZIP) transcription factor of Mondo family that binds to carbohydrate response element in the promoter of some glucose-regulated genes and activates their expression upon glucose stimulation. Structure-function analysis of ChREBP in a highly glucose-sensitive system using GAL4-ChREBP fusion constructs revealed a glucose-sensing module (GSM) that mediates glucose responsiveness of ChREBP. GSM is conserved among Mondo family members; MondoA, a mammalian paralog of unknown function, and the GSM region of a Drosophila homolog were also found to be glucose responsive. GSM is composed of a low-glucose inhibitory domain (LID) and a glucose-response activation conserved element (GRACE). We have identified a new mechanism accounting for glucose responsiveness of ChREBP that involves specific inhibition of the transactivation activity of GRACE by LID under low glucose concentration and reversal of this inhibition by glucose in an orientation-sensitive manner. The intramolecular inhibition and its release by glucose is a regulatory mechanism that is independent of changes of subcellular localization or DNA binding activity, events that also appear to be involved in glucose responsiveness. This evolutionally conserved mechanism may play an essential role in glucose-responsive gene regulation. Show less

Triglyceride-rich lipoprotein particles may promote the progression of diabetic nephropathy. Patients with diabetic nephropathy have increased plasma triglycerides and reduced activity of hepatic lipase (HL), which hydrolyzes triglycerides. We hypothesized that the HL -514C-->T polymorphism, which reduces HL expression, and its interactions with polymorphisms in apolipoprotein (apo) E and apoC3 increase the risk of diabetic nephropathy. In a case-control study involving 374 Chinese type 2 diabetic patients with and 392 without diabetic nephropathy, we genotyped the HL -514C-->T, apoE exon 4, and apoC3 -482C-->T polymorphisms. HL -514T-containing genotypes (T+) were associated with diabetic nephropathy (OR = 1.7, P = 0.0009). Adjustment by multiple logistic regression for hypertension, triglycerides, sex, non-HDL cholesterol, BMI, smoking, and alcohol intake did not diminish the association (OR = 1.8, P = 0.003). The association between HL T+ genotypes and diabetic nephropathy appeared stronger in diabetic patients with apoC3 -482 non-TT genotypes (OR = 1.9, P = 0.003) or apoE epsilon2 or epsilon4 alleles (OR = 2.2, P = 0.005). Subjects with HL TT exhibited trends toward increased triglyceride and non-HDL cholesterol levels compared with CC carriers. HL T+ genotypes might increase the risk of developing diabetic nephropathy by slowing clearance of triglyceride-rich remnant lipoproteins. In concert with other risk factors (e.g., hyperglycemia), lipid abnormalities may damage the kidneys and endothelium, where reduced binding sites for lipases may precipitate a vicious cycle of dyslipidemia, proteinuria, and nephropathy. Show less

The transcriptomes of mouse type A spermatogonia (Spga), pachytene spermatocytes (Spcy), and round spermatids (Sptd) were determined by sequencing the respective SAGE (Serial Analysis of Gene Expression) libraries. A total of 444,015 tags derived from one Spga, two Spcy, and one Sptd library were analyzed, and 34,619 different species of transcripts were identified, 5279 of which were novel. Results indicated the germ-cell transcriptome comprises of more than 30,000 transcripts. Virtual subtraction showed that cell-specific transcripts constitute 12-19.5% of the transcriptome. Components of the protein biosynthetic machinery are highly expressed in Spga. In Spcy transcription factors are abundantly expressed while transcripts encoding proteins involved in chromosome remodeling and testis-specific transcripts are prominent in Sptd. The databases generated by this work provide very useful resources for cellular localization of genes in silico. They are also extremely useful as sources for identification of splice variants of genes in germ cells. Show less

Complementary DNA microarray and quantitative polymerase chain reaction were used as tools for discovering genes that are differentially expressed in the mouse under normal physiological conditions at distinctive stages of male germ cell development, that is, type A spermatogonia, pachytene spermatocytes, and round spermatids. By using this strategy, we identified a set of genes exhibiting differential expression patterns in spermatogenesis, suggesting that specific functions of the encoded products occurred during the developmental process. Among them were several genes previously not known to be active in testis, which signified undiscovered functional roles of these genes during spermatogenesis. Many of the genes identified were not previously characterized. This study highlights new targets for manipulation to unravel the molecular mechanism of spermatogenesis. Show less

The effect of adjuvant arthritis (AA) on the pattern of rat serum proteins includes the upregulation of haptoglobin, orosomucoid, alpha2-macroglobulin, serine protease inhibitor-3, thiostatin, alpha1-antitrypsin, C-reactive protein, and the downregulation of kallikrein-binding protein, alpha1-inhibitor III, apolipoprotein A-I, alpha2-HS-glycoprotein, albumin, apolipoprotein A-IV, transthyretin and transferrin. Minor changes (+/- 20%) are observed for Gc-globulin, ceruloplasmin, and alpha1-macroglobulin. AA thus grossly resembles the acute inflammatory response elicited by the injection of turpentine, although the changes in the levels of negative acute-phase proteins (APP) are smaller in acute inflammation. Indomethacine and ibuprofen inhibit the effects of arthritis on the synthesis of rat serum proteins in different ways: The former is, on average, three times as effective as the latter. Each drug interferes differently with different proteins. In animals without AA, both nonsteroidal anti-inflammatory drugs (NSAID) mimic the inflammatory pattern to a certain extent, with more effect on the negative than on the positive APPs. Overall, the shifts in serum protein levels parallel changes in inflammatory parameters such as joint swelling and serum interleukin-6 (IL-6) activity. Protein quantitation after two-dimensional electrophoresis (2-DE) reveals some effects of the drugs per se which escape detection by other routine tests. Show less

In order to establish the rat testis as a model system for studying the human pregnancy-specific beta1-glycoprotein (PSG), expression and cellular distribution of PSG in rat testis were examined. Three partial PSG cDNAs, namely, rnCGM6, rnGCM7, and rnCGM8 were obtained when rat testis cDNA libraries were screened with a human placental PSG cDNA probe. Unlike the human PSGs, the rat PSGs show less nucleotide and amino acid sequence homology among family members. The rat PSGs also have multiple truncated leader sequences followed by immunoglobulin variable-like N domains while human PSGs have a single N domain. Examination of the testis, intestine, kidney, liver, lung, and muscle of male rats by reverse transcription-polymerase chain reaction (RT-PCR) with nested gene-specific primers showed that rnCGM6 was present only in the testis, while rnCGM8 was present in the testis, intestine and lung. On the other hand rnCMG7 was found in all tissues examined. Furthermore, rnCGM7 transcript was present in all somatic cells examined whereas rnCGM6 was predominantly in myoid cells and rnCMG8 in Leydig cells. These results suggest that there is cell-specificity in the expression of PSGs in the rat testis and that the rat testis is a good model for studying the biological activities of the PSGs. Show less

Human pregnancy-specific beta 1-glycoprotein (PSG) is found in high concentrations in the serum of pregnant women, but also has been found in the serum of males and nonpregnant females. Northern slot-blot analysis has demonstrated the presence of PSG mRNA in a variety of tissues in the rat, with the highest levels being found in the testis. Therefore, we have investigated further the expression of PSG in the rat male reproductive tract using in situ hybridization. In testes from immature and adult rats, PSG mRNA was localized in Leydig and peritubular cells, and in the walls of the interstitial blood vessels. PSG transcripts were noted also in the tunica albuginea and in the stromal tissue of the caput and cauda epididymis, prostate, and seminal vesicle from adult rats. The function of PSG is unknown, but it has been speculated that PSG may have immunosuppressive properties or that it may serve as a paracrine regulator of growth and differentiation. It is possible, then, that PSG could contribute to the immunological privilege of the testis or that it plays a role in the cellular interactions which increasingly are being shown to be important in the regulation of male reproductive tract tissues. Show less