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Articles by P Liu
Total Records ( 11 ) for P Liu
  J. M Metzger , K Gagen , K. A Raustad , L Yang , A White , S. P Wang , S Craw , P Liu , T Lanza , L. S Lin , R. P Nargund , X. M Guan , A. M Strack and M. L. Reitman
 

Treatment of rodents with a bombesin receptor subtype-3 (BRS-3) agonist reduces food intake and increases fasting metabolic rate, causing weight loss with continued treatment. In small mammals, core body temperature (Tb) is regulated in part by nutritional status, with a reduced Tb during fasting. We report that fed Brs3 knockout mice have a lower Tb, which is discordant with their nutritional status. Treatment of wild-type mice with a BRS-3 agonist increased Tb, more so when the baseline Tb was reduced such as by fasting or during the inactive phase of the light cycle. With repeated BRS-3 agonist dosing, the Tb increase attenuated despite continued weight loss efficacy. The increase in Tb was not prevented by inhibitors of prostaglandin E (PGE) production but was partially reduced by a β-adrenergic blocker. These results demonstrate that BRS-3 has a role in body temperature regulation, presumably secondary to its effect on energy metabolism, including effects on sympathetic tone. By making use of this phenomenon, the reversal of the fasting Tb reduction was developed into a sensitive single-dose pharmacodynamic assay for BRS-3 agonism and other antiobesity compounds acting by various mechanisms, including sibutramine, cannabinoid-1, and melanin-concentrating hormone-1 receptor blockers, and melanocortin, β3-adrenergic, and cholecystokinin-1 receptor agonists. These drugs increased both the fasted Tb and the fasted, resting metabolic rates. The Tb assay is a robust, information-rich assay that is simpler and has a greater throughput than measuring metabolic rate and is a practical, effective tool for drug discovery.

  P Liu , A Khurana , R Rattan , X He , S Kalloger , S Dowdy , B Gilks and V. Shridhar
 

We recently identified HSulf-1 as a down-regulated gene in ovarian carcinomas. Our previous analysis indicated that HSulf-1 inactivation in ovarian cancers is partly mediated by loss of heterozygosity and epigenetic silencing. Here, we show that variant hepatic nuclear factor 1 (vHNF1), encoded by transcription factor 2 gene (TCF2, HNF1β), negatively regulates HSulf-1 expression in ovarian cancer. Immunoblot assay revealed that vHNF1 is highly expressed in HSulf-1–deficient OV207, SKOV3, and TOV-21G cell lines but not in HSulf-1–expressing OSE, OV167, and OV202 cells. By short hairpin RNA–mediated down-regulation of vHNF1 in TOV-21G cells and transient enhanced vHNF1 expression in OV202 cells, we showed that vHNF1 suppresses HSulf-1 expression in ovarian cancer cell lines. Reporter assay and chromatin immunoprecipitation experiments showed that vHNF1 is specifically recruited to HSulf-1 promoter at two different vHNF1-responsive elements in OV207 and TOV-21G cells. Additionally, down-regulation of vHNF1 expression in OV207 and TOV-21G cells increased cisplatin- or paclitaxel-mediated cytotoxicity as determined by both 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and clonogenic assays and this effect was reversed by down-regulation of HSulf-1. Moreover, nude mice bearing TOV-21G cell xenografts with stably down-regulated vHNF1 were more sensitive to cisplatin- or paclitaxel-induced cytotoxicity compared with xenografts of TOV-21G clonal lines with nontargeted control short hairpin RNA. Finally, immunohistochemical analysis of 501 ovarian tumors including 140 clear-cell tumors on tissue microarrays showed that vHNF1 inversely correlates to HSulf-1 expression. Collectively, these results indicate that vHNF1 acts as a repressor of HSulf-1 expression and might be a molecular target for ovarian cancer therapy. [Cancer Res 2009;69(11):4843–50]

  N Dong , S Chen , J Yang , L He , P Liu , D Zheng , L Li , Y Zhou , C Ruan , E Plow and Q. Wu
 

Background— Corin is a transmembrane protease that processes natriuretic peptides in the heart. Like many membrane proteins, corin is shed from the cell surface.

Methods and Results— In this study, we obtained plasma samples from healthy controls and patients with heart failure (HF) and acute myocardial infarction. Soluble corin levels in plasma were measured by an ELISA method. In healthy adults (n=198), plasma corin levels were 690 pg/mL (SD, 260 pg/mL). The corin levels did not differ significantly among different age groups. In patients with HF (n=291), plasma corin levels were significantly lower compared with that of healthy controls (365 pg/mL [SD, 259]; P<0.001). The reduction in plasma corin levels seemed to correlate with the severity of HF. In patients of New York Heart Association classes II, III, and IV, plasma corin levels were 450 pg/mL (SD, 281 pg/mL; n=69), 377 pg/mL (SD, 270 pg/mL; n=132), and 282 pg/mL (SD, 194 pg/mL; n=90), respectively (P<0.001 class II vs class IV; P<0.05 class III vs class IV). In contrast, plasma corin levels in patients with acute myocardial infarction (n=73) were similar to that of healthy controls (678 pg/mL [SD, 285 pg/mL]; P>0.05).

Conclusions— Soluble corin was detected in human plasma. Plasma corin levels were reduced significantly in patients with HF but not in those with acute myocardial infarction. Our results indicate that corin deficiency may contribute to the pathogenesis of HF and that plasma corin may be used as a biomarker in the diagnosis of HF.

  B Bartkowiak , P Liu , H. P Phatnani , N. J Fuda , J. J Cooper , D. H Price , K Adelman , J. T Lis and A. L. Greenleaf
 

Drosophila contains one (dCDK12) and humans contain two (hCDK12 and hCDK13) proteins that are the closest evolutionary relatives of yeast Ctk1, the catalytic subunit of the major elongation-phase C-terminal repeat domain (CTD) kinase in Saccharomyces cerevisiae, CTDK-I. However, until now, neither CDK12 nor CDK13 has been demonstrated to be a bona fide CTD kinase. Using Drosophila, we demonstrate that dCDK12 (CG7597) is a transcription-associated CTD kinase, the ortholog of yCtk1. Fluorescence microscopy reveals that the distribution of dCDK12 on formaldehyde-fixed polytene chromosomes is virtually identical to that of hyperphosphorylated RNA polymerase II (RNAPII), but is distinct from that of P-TEFb (dCDK9 + dCyclin T). Chromatin immunoprecipitation (ChIP) experiments confirm that dCDK12 is present on the transcribed regions of active Drosophila genes. Compared with P-TEFb, dCDK12 amounts are lower at the 5' end and higher in the middle and at the 3' end of genes (both normalized to RNAPII). Appropriately, Drosophila dCDK12 purified from nuclear extracts manifests CTD kinase activity in vitro. Intriguingly, we find that cyclin K is associated with purified dCDK12, implicating it as the cyclin subunit of this CTD kinase. Most importantly, we demonstrate that RNAi knockdown of dCDK12 in S2 cells alters the phosphorylation state of the CTD, reducing its Ser2 phosphorylation levels. Similarly, in human HeLa cells, we show that hCDK13 purified from nuclear extracts displays CTD kinase activity in vitro, as anticipated. Also, we find that chimeric (yeast/human) versions of Ctk1 containing the kinase homology domains of hCDK12/13 (or hCDK9) are functional in yeast cells (and also in vitro); using this system, we show that a bur1ts mutant is rescued more efficiently by a hCDK9 chimera than by a hCDK13 chimera, suggesting the following orthology relationships: Bur1 CDK9 and Ctk1 CDK12/13. Finally, we show that siRNA knockdown of hCDK12 in HeLa cells results in alterations in the CTD phosphorylation state. Our findings demonstrate that metazoan CDK12 and CDK13 are CTD kinases, and that CDK12 is orthologous to yeast Ctk1.

  C. M.B Carvalho , F Zhang , P Liu , A Patel , T Sahoo , C. A Bacino , C Shaw , S Peacock , A Pursley , Y. J Tavyev , M. B Ramocki , M Nawara , E Obersztyn , A. M Vianna Morgante , P Stankiewicz , H. Y Zoghbi , S. W Cheung and J. R. Lupski
 

Duplication at the Xq28 band including the MECP2 gene is one of the most common genomic rearrangements identified in neurodevelopmentally delayed males. Such duplications are non-recurrent and can be generated by a non-homologous end joining (NHEJ) mechanism. We investigated the potential mechanisms for MECP2 duplication and examined whether genomic architectural features may play a role in their origin using a custom designed 4-Mb tiling-path oligonucleotide array CGH assay. Each of the 30 patients analyzed showed a unique duplication varying in size from ~250 kb to ~2.6 Mb. Interestingly, in 77% of these non-recurrent duplications, the distal breakpoints grouped within a 215 kb genomic interval, located 47 kb telomeric to the MECP2 gene. The genomic architecture of this region contains both direct and inverted low-copy repeat (LCR) sequences; this same region undergoes polymorphic structural variation in the general population. Array CGH revealed complex rearrangements in eight patients; in six patients the duplication contained an embedded triplicated segment, and in the other two, stretches of non-duplicated sequences occurred within the duplicated region. Breakpoint junction sequencing was achieved in four duplications and identified an inversion in one patient, demonstrating further complexity. We propose that the presence of LCRs in the vicinity of the MECP2 gene may generate an unstable DNA structure that can induce DNA strand lesions, such as a collapsed fork, and facilitate a Fork Stalling and Template Switching event producing the complex rearrangements involving MECP2.

  P Liu , W Chen , H Zhu , B Liu , S Song , W Shen , F Wang , S Tucker , B Zhong and D. Wang
  Objective

The purpose of this study was to specifically investigate the clinicopathological role of expression of vascular endothelial growth factor-C (VEGF-C) as well as the correlation with clinical outcomes in esophageal squamous cell carcinomas (ESCCs).

Methods

Seventy-three patients with ESCC resected in our institute were included in this study. Formalin-fixed paraffin-embedded specimens were stained for VEGF-C and the correlation between the staining, its clinicopathological parameters and its prognostic power were analyzed statistically.

Results

Of the 73 ESCC patients studied, 39 cases (53.4%) were strongly positive for VEGF-C. Six cases (8.2%) were negative and 28 cases (38.4%) revealed unclear weak reactions. All 34 cases were included in the negative group (46.6%). VEGF-C expression correlated with histological grade (P = 0.005), depth of tumor invasion (pT) (P = 0.021), lymph node metastasis (pN) (P = 0.002) and lymphatic invasion (P = 0.008). The median overall survival of 39 patients who had positive staining for tumor cell VEGF-C and 34 patients who had negative staining were 10.4 months (95% CI, 6.9–13.9 months) and 28.5 months (95% CI, 12.6–44.4 months), respectively (P = 0.003). In univariate analysis by log-rank test, histological grade, pN, stage, lymphatic invasion and VEGF-C were significant prognostic factors (P = 0.047, 0.007, 0.018, 0.002 and 0.003, respectively.). In multivariate analysis, high VEGF-C expression (P = 0.0451) maintained its independent prognostic influence on overall survival, as well as pN status (P = 0.0029).

Conclusions

Expression of VEGF-C is related to histological grade, pT, pN and lymphatic invasion, and is a prognostic indicator for ESCC.

  M Dobkin Bekman , M Naidich , L Rahamim , F Przedecki , T Almog , S Lim , P Melamed , P Liu , T Wohland , Z Yao , R Seger and Z. Naor
 

Most receptor tyrosine kinases and G protein-coupled receptors (GPCRs) operate via a limited number of MAPK cascades but still exert diverse functions, and therefore signal specificity remains an enigma. Also, most GPCR ligands utilize families of receptors for mediation of diverse biological actions; however, the mammalian type I GnRH receptor (GnRHR) seems to be the sole receptor mediating GnRH-induced gonadotropin synthesis and release. Signaling complexes associated with GPCRs may thus provide the means for signal specificity. Here we describe a signaling complex associated with the GnRHR, which is a unique GPCR lacking a C-terminal tail. Unlike other GPCRs, this signaling complex is preformed, and exposure of LβT2 gonadotropes to GnRH induces its dynamic rearrangement. The signaling complex includes c-Src, protein kinase C, -, and -, Ras, MAPK kinase 1/2, ERK1/2, tubulin, focal adhesion kinase (FAK), paxillin, vinculin, caveolin-1, kinase suppressor of Ras-1, and the GnRHR. Exposure to GnRH (5 min) causes MAPK kinase 1/2, ERK1/2, tubulin, vinculin, and the GnRHR to detach from c-Src, but they reassociate within 30 min. On the other hand, FAK, paxillin, the protein kinase Cs, and caveolin-1 stay bound to c-Src, whereas kinase suppressor of Ras-1 appears in the complex only 30 min after GnRH stimulation. GnRH was found to activate ERK1/2 in the complex in a c-Src-dependent manner, and the activated ERK1/2 subsequently phosphorylates FAK and paxillin. In parallel, caveolin-1, FAK, vinculin, and paxillin are phosphorylated on Tyr residues apparently by GnRH-activated c-Src. Receptor tyrosine kinases and GPCRs translocate ERK1/2 to the nucleus to phosphorylate and activate transcription factors. We therefore propose that the role of the multiprotein signaling complex is to sequester a cytosolic pool of activated ERK1/2 to phosphorylate FAK and paxillin at focal adhesions.

  C Bourdon , S Hojna , M Jordan , J Berube , V Kren , M Pravenec , P Liu , S Arab and Z. Pausova
 

Obesity is a leading cause of diabetes mellitus and hypertension. Molecular signals produced by adipose tissue may contribute to the pathogenesis of these two disorders. We showed previously that a specific segment of rat chromosome 20 (RNO20) contains a gene(s) regulating the degree of obesity, glucose intolerance, and hypertension in response to a chronic high-fat diet (HFD). Here we examined microarray gene expression profiles and cellular morphology of adipose tissues and whole body energy expenditure in this model. Adult male spontaneously hypertensive rats (SHR) and a congenic strain (SHR.1N) that differs from SHR by the above-mentioned segment of RNO20 were fed for 12 wk with HFD or a normal diet. At the end of this period, whole body energy expenditure was measured with indirect calorimetry. In response to HFD, body weight, fat pad weights, adipocyte size, and serum leptin levels increased significantly more in SHR.1N than SHR. Microarray gene expression profiles [Affymetrix, 15,923 genes and expressed sequence tags (ESTs)] showed that multiple genes of molecular pathways involved in lipogenesis were downregulated to a similar level in both strains, whereas genes involved in fatty acid oxidation and energy dissipation were upregulated less in SHR.1N than SHR. This was associated with lower whole body energy expenditure in SHR.1N than SHR at the end of the 12-wk HFD. Our results suggest that a gene(s) within the RNO20 segment regulate(s) HFD-induced increases in adiposity, and that this effect may be mediated, at least in part, by the impact of that gene(s) on fat burning and energy expenditure.

  S Bunda , Y Wang , T. F Mitts , P Liu , S Arab , M Arabkhari and A. Hinek
 

We previously demonstrated that aldosterone, which stimulates collagen production through the mineralocorticoid receptor (MR)-dependent pathway, also induces elastogenesis via a parallel MR-independent mechanism involving insulin-like growth factor-I receptor (IGF-IR) signaling. The present study provides a more detailed explanation of this signaling pathway. Our data demonstrate that small interfering RNA-driven elimination of MR in cardiac fibroblasts does not inhibit aldosterone-induced IGF-IR phosphorylation and subsequent increase in elastin production. These results exclude the involvement of the MR in aldosterone-induced increases in elastin production. Results of further experiments aimed at identifying the upstream signaling component(s) that might be activated by aldosterone also eliminate the putative involvement of pertussis toxin-sensitive Gi proteins, which have previously been shown to be responsible for some MR-independent effects of aldosterone. Instead, we found that small interfering RNA-dependent elimination of another heterotrimeric G protein, G13, eliminates aldosterone-induced elastogenesis. We further demonstrate that aldosterone first engages G13 and then promotes its transient interaction with c-Src, which constitutes a prerequisite step for aldosterone-dependent activation of the IGF-IR and propagation of consecutive downstream elastogenic signaling involving phosphatidylinositol 3-kinase/Akt. In summary, the data we present reveal new details of an MR-independent cellular signaling pathway through which aldosterone stimulates elastogenesis in human cardiac fibroblasts.

  S Zhang , M Rozell , R. K Verma , D. I Albu , D Califano , J VanValkenburgh , A Merchant , J Rangel Moreno , T. D Randall , N. A Jenkins , N. G Copeland , P Liu and D. Avram
 

CD8+ T lymphocytes mediate the immune response to viruses, intracellular bacteria, protozoan parasites, and tumors. We provide evidence that the transcription factor Bcl11b/Ctip2 controls hallmark features of CD8+ T cell immunity, specifically antigen (Ag)-dependent clonal expansion and cytolytic activity. The reduced clonal expansion in the absence of Bcl11b was caused by altered proliferation during the expansion phase, with survival remaining unaffected. Two genes with critical roles in TCR signaling were deregulated in Bcl11b-deficient CD8+ T cells, CD8 coreceptor and Plc1, both of which may contribute to the impaired responsiveness. Bcl11b was found to bind the E8I, E8IV, and E8V, but not E8II or E8III, enhancers. Thus, Bcl11b is one of the transcription factors implicated in the maintenance of optimal CD8 coreceptor expression in peripheral CD8+ T cells through association with specific enhancers. Short-lived Klrg1hiCD127lo effector CD8+ T cells were formed during the course of infection in the absence of Bcl11b, albeit in smaller numbers, and their Ag-specific cytolytic activity on a per-cell basis was altered, which was associated with reduced granzyme B and perforin.

 
 
 
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