Biomedical subjects

Lin Geng

Publications and source records attributed to Lin Geng.

12 recordsLinked to original sources

PubMed2006

Polycystin-2 traffics to cilia independently of polycystin-1 by using an N-terminal RVxP motif.

Primary cilia play a key role in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). The affected proteins, polycystin-1 (PC1) and polycystin-2 (PC2), interact with each other and are expressed in cilia. We found that COOH-terminal truncated PC2 (PC2-L703X), lacking the PC1 interaction region, still traffics to cilia. We examined PC2 expression in several tissues and cells lacking PC1 and found that PC2 is expressed in cilia independently of PC1. We used N-terminal deletion constructs to narrow the domain necessary for cilia trafficking to the first 15 amino acids of PC2 and identified a conserved motif, R6VxP, that is required for cilial localization. The N-terminal 15 amino acids are also sufficient to localize heterologous proteins in cilia. PC2 has endogenous cilia trafficking information and is present in cilia of cells lining cysts that result from mutations in PKD1.

Amino Acid Motifs↗

PubMed2005

[Expression of melanoma antigen gene in urinary transitional cell carcinomas].

OBJECTIVE: To evaluate the significance of melanoma antigen (MAGE) gene expression in bladder transitional cell carcinoma (TCC). METHODS: MAGE-A1, A2, A3, A4 mRNA expression was detected by reverse transcription polymerase chain reaction (RT-PCR) in 3 clusters bladder TCC cells and 20 samples of bladder TCC patients (T(1) 7 samples, T(2) 5 samples, T(3) 6 samples, T(4) 2 samples, G(1) 1 samples, G(2) 11 samples, G(3) 8 samples). MAGE-A4 protein was detected by immunohistochemistry in 105 samples of bladder TCC patients (T(1) 35 samples, T(2) 12 samples, T(3) 26 samples, T(4) 13 samples, G(1) 13 samples, G(2) 44 samples, G(3) 48 samples). RESULTS: Three clusters bladder TCC cells had MAGE gene mRNA expression. In detection of MAGE mRNA of 20 samples of bladder TCC patients, 12 samples (60%) expressed MAGE-A1, 16 samples (80%) expressed MAGE-A2, 11 samples (55%) expressed MAGE-A3, 18 samples (90%) expressed MAGE-A4, 8 samples (40%) expressed all of MAGE-A1--A4. In 105 bladder TCC samples, 53 samples (50%) expressed MAGE-A4 protein. Strong expression (++ or +++) was significant higher in higher grade (13 samples/48 samples) or stage (14 samples/51 samples) than in lower grade (2 samples/57 samples) or stage (0 samples/35 samples). CONCLUSION: MAGE gene highly expresses in bladder TCC. Bladder TCC of high grade or high stage has higher MAGE-A4 protein strong expression.

Adult↗

PubMed2005

[Expression of SSX2 gene in human urologic neoplasms].

OBJECTIVE: To investigate the expression of SSX(2)gene in human renal cell carcinoma and urinary transitional cell carcinoma. METHODS: Reverse-transcription polymerase chain reaction (RT-PCR) was used for detecting SSX(2) gene in the specimens from renal cell carcinoma (n = 26), urinary transitional cell carcinoma (n = 27) and in 15 specimens taken from the tumor surrounding tissues. RESULTS: Positive expression of SSX(2) gene at mRNA was detected in 69% renal cell carcinomas (18/26), in 81% urinary transitional cell carcinomas (22/27). The mRNA of SSX(2) was not detected in the 15 specimens from tumor surrounding tissues. CONCLUSION: The SSX(2) gene is highly expressed in human renal cell carcinoma and urinary transitional cell carcinoma.

Adult↗

PubMed2004

Heparin regulates survival and differentiation of mesencephalic progenitors mediated via FGF2 in vitro.

Heparin plays an important role in the survival and differentiation of mesencephalic progenitors mediated by FGF-2 in vitro. If the heparin concentration is gradually increased, cell survival mediated by FGF-2 can be greatly enhanced, to a maximum concentration of 20 ng/ml FGF-2 from 5 microg/ml heparin. However, differentiation of FGF-2 responsive mesencephalic progenitors is inhibited by heparin. When cortical, mesencephalic and hippocampal astrocytes were primed with FGF-2 and heparin, the latter two astrocytes promoted the differentiation of TH-positive neurons from mesencephalic progenitors. RT-PCR analysis showed that FGFR1, FGFR2 and FGFR3 were expressed in the cortical astrocytes, but only FGFR1 and FGFR3 were expressed in the mesencephalic and hippocampal astrocytes.

Animals↗

PubMed2004

Calcium dependence of polycystin-2 channel activity is modulated by phosphorylation at Ser812.

Polycystin-2 (PC-2) is a non-selective cation channel that, when mutated, results in autosomal dominant polycystic kidney disease. In an effort to understand the regulation of this channel, we investigated the role of protein phosphorylation in PC-2 function. We demonstrated the direct incorporation of phosphate into PC-2 in cells and tissues and found that this constitutive phosphorylation occurs at Ser(812), a putative casein kinase II (CK2) substrate domain. Ser(812) can be phosphorylated by CK2 in vitro and substitution S812A results in failure to incorporate phosphate in cultured epithelial cells. Non-phosphorylated forms of PC-2 traffic normally in the endoplasmic reticulum and cilial compartments and retain homo- and hetero-multimerization interactions with PC-2 and polycystin-1, respectively. Single-channel studies of PC-2, S812A, and a substitution mutant, T721A, not related to phosphorylation show that PC-2 and S812A function as divalent cation channels with similar current amplitudes across a range of holding potentials; the T721A channel is not functional. Channel open probabilities for PC-2 and S812A show a bell-shaped dependence on cytoplasmic Ca(2+) but there is a shift in this Ca(2+) dependence such that S812A is 10-fold less sensitive to Ca(2+) activation/inactivation than the wild type PC-2 channel. In vivo analysis of PC-2-dependent enhanced intracellular Ca(2+) transients found that S812A resulted in enhanced transient duration and relative amplitude intermediate between control cells and those overexpressing wild type PC-2. Phosphorylation at Ser(812) modulates PC-2 channel activity and factors regulating this phosphorylation are likely to play a role in the pathogenesis of polycystic kidney disease.

Animals↗

PubMed2004

[Expression of MAGE genes and MAGE gene products in human renal and urinary bladder tumor].

OBJECTIVE: To observe the expression of MAGE-1 MAGE-3 genes and MAGE-3 gene product in renal and urinary bladder tumor, and to explore the possibility of MAGE-1 and MAGE-3 genes encoding proteins or MAGE-3 gene product used as a target for immunotherapy in renal and urinary bladder tumor patients. METHODS: Reverse transcriptase polymerase chain reaction for MAGE-1 and MAGE-3 genes was performed using 39 renal and urinary bladder tumor specimens. Immunohistochemical technique for MAGE-3 antigen was performed using formal infixed paraffin embedded section of 121 renal and urinary bladder tumor specimens. RESULTS: MAGE-1 and MAGE-3 mRNAs were detected in 23(59.0%) and 22(56.4%) of 39 patients with renal and urinary bladder tumor without expression in 10 tumor surrounding tissues.MAGE-3 antigen was detected in 56(46.3%) of 121 patients with renal and urinary bladder tumor without expression in 10 tumor surrounding tissues. The expression rates of MAGE-1 and MAGE-3 mRNA and MAGE-3 gene product were significantly higher in renal and urinary bladder tumors tissues than in tumor surrounding tissues. The frequency of MAGE-3 gene product expression was examined according to clinical stage and differentiation of histopathology. The results revealed no significant differences in MAGE gene product expression among the clinical stage and the grade of differentiation of histopathology according to Logistic Regression test(P>0.05). CONCLUSION: The tumor-specific antigens might be used as molecular markers and targets for human renal and urinary bladder tumor.

Adult↗

PubMed2003

Polycystin-1 distribution is modulated by polycystin-2 expression in mammalian cells.

Mutations in PKD1 and PKD2, the genes that encode polycystin-1 and polycystin-2 respectively, account for almost all cases of autosomal dominant polycystic kidney disease. Although the polycystins are believed to interact in vivo, the two proteins often display dissimilar patterns and gradients of expression during development. In an effort to understand this apparent discrepancy, we investigated how changes in polycystin-2 expression can affect the subcellular localization of polycystin-1. We show that, when polycystin-1 is expressed alone in a PKD2 null cell line, it localizes to the cell surface, as well as to the endoplasmic reticulum. When co-expressed with polycystin-2, however, polycystin-1 is not seen at the cell surface and co-localizes completely with polycystin-2 in the endoplasmic reticulum. The localization of a polycystin-1 fusion protein was similarly affected by changes in its level of expression relative to that of polycystin-2. This phenomenon was observed in populations as well as in individual COS-7 cells. Our data suggest that the localization of polycystin-1 can be regulated via the relative expression level of polycystin-2 in mammalian cells. This mechanism may help to explain the divergent patterns and levels of expression observed for the polycystins, and may provide clues as to how the function of these two proteins are regulated during development.

Animals↗

PubMed2003

Frequency modulation of synchronized Ca2+ spikes in cultured hippocampal networks through G-protein-coupled receptors.

Synchronized spontaneous Ca2+ spikes in networked neurons represent periodic burst firing of action potentials, which are believed to play a major role in the development and plasticity of neuronal circuitry. How these network activities are shaped and modulated by extrinsic factors during development, however, remains to be studied. Here we report that synchronized Ca2+ spikes among cultured hippocampal neurons can be modulated by two small factors that act on G-protein-coupled receptors (GPCRs): the neuropeptide PACAP (pituitary adenylate cyclase-activating polypeptide) and the chemokine SDF-1 (stromal cell-derived factor-1). PACAP effectively increases the frequency of the synchronized Ca2+ spikes when applied acutely; the PACAP potentiation of Ca2+ spikes requires the activation of the PACAP-specific PAC1 GPCRs and is mediated by the activation of cAMP signaling pathway. SDF-1, on the other hand, significantly reduces the frequency of these Ca2+ spikes through the activation of its specific GPCR CXCR4; the inhibitory action of SDF-1 is mediated by the inhibition of cAMP pathway through the Gi component of GPCRs. Taken together, these results demonstrate that synchronized neuronal network activity can be effectively modulated by physiologically and developmentally relevant small factors that act on GPCRs to target the cAMP pathway. Such modulation of neuronal activity through GPCRs may represent a significant mechanism that underlies the neuronal plasticity during neural development and functioning.

Action Potentials↗

PubMed2003

Towards understanding the polycystins.

Autosomal dominant polycystic kidney disease (ADPKD) is a very common inherited disease caused by mutations in PKD1 or PKD2 genes characterized by progressive enlargement of fluid-filled cysts and loss of renal function [1]. Previous studies proposed a role for human polycystin-1 in renal morphogenesis acting as a matrix receptor in focal adhesions and for polycystin-2 as a putative calcium channel [2, 3]. The genome of Caenorhabditis elegans contains 2 new members of the polycystin family: lov-1, the homolog for PKD1; and pkd-2, the homolog for PKD2 [4; this paper]. Mutation analysis in C. elegans showed similarly compromised male mating behaviors in all single and double lov-1 and pkd-2 mutants, indicating their participation in a single genetic pathway. Expression analysis localized LOV-1 and PKD-2 to the ends of sensory neurons in male tails and to the tips of CEM neurons in the head, consistent with functions as chemo- or mechanosensors. Human and C. elegans PKD1 and PKD2 homologs, transfected into mammalian renal epithelial cells, co-localized with paxillin in focal adhesions suggesting function in a single biological pathway. Based on the role of polycystins in C. elegans sensory neuron function and the conservation of PKD pathways we suggest that polycystins act as sensors of the extracellular environment, initiating, via focal adhesion assembly, intracellular transduction events in neuronal or morphogenetic processes.

Amino Acid Sequence↗

PubMed2002

Trans-heterozygous Pkd1 and Pkd2 mutations modify expression of polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) occurs by germline mutation in PKD1 or PKD2. Evidence of homozygous inactivation of either gene in human cyst lining cells as well as in mouse knockout models strongly supports a two-hit mechanism for cyst formation. Discovery of trans-heterozygous mutations in PKD1 and PKD2 in a minority of human renal cysts has led to the proposal that such mutations also can play a role in cyst formation. In the current study, we investigated the role of trans-heterozygous mutations in mouse models of polycystic kidney disease. In Pkd1(+/-), Pkd2 (+/-) and Pkd1(+/-) : Pkd2 (+/-) mice, the renal cystic lesion was mild and variable with no adverse effect on survival at 1 year. In keeping with the two-hit mechanism of cyst formation, approximately 70% of kidney cysts in Pkd2 (+/-) mice exhibited uniform loss of polycystin-2 expression. Cystic disease in trans-heterozygous Pkd1(+/-) : Pkd2 (+/-) mice, however, was notable for severity in excess of that predicted by a simple additive effect based on cyst formation in singly heterozygous mice. The data suggest a modifier role for the 'trans' polycystin gene in cystic kidney disease, and support a contribution from threshold effects to cyst formation and growth.

Animals↗

PubMed2002

Polycystin-2 is an intracellular calcium release channel.

Polycystin-2, the product of the gene mutated in type 2 autosomal dominant polycystic kidney disease (ADPKD), is the prototypical member of a subfamily of the transient receptor potential (TRP) channel superfamily, which is expressed abundantly in the endoplasmic reticulum (ER) membrane. Here, we show by single channel studies that polycystin-2 behaves as a calcium-activated, high conductance ER channel that is permeable to divalent cations. Epithelial cells overexpressing polycystin-2 show markedly augmented intracellular calcium release signals that are lost after carboxy-terminal truncation or by the introduction of a disease-causing missense mutation. These data suggest that polycystin-2 functions as a calcium-activated intracellular calcium release channel in vivo and that polycystic kidney disease results from the loss of a regulated intracellular calcium release signalling mechanism.

Animals↗

PubMed2001

Vascular expression of polycystin-2.

The expression of polycystin-1 in the vascular smooth muscle cells (VSMC) of elastic and large distributive arteries suggests that some vascular manifestations of autosomal-dominant polycystic kidney disease (ADPKD) result directly from the genetic defect. Intracranial aneurysms have been reported in PKD2, as well as in PKD1 families. To determine whether the vascular expression of polycystin-2 is similar to that of polycystin-1, the expression of PKD2 mRNA and protein in cultured pig aortic VSMC was studied and immunofluorescence and immunohistochemistry were used to study the localization of polycystin-2 in cultured pig aortic VSMC, pig ascending thoracic aorta, and normal elastic and intracranial arteries and intracranial aneurysms obtained at autopsy from patients without or with ADPKD. Tissues derived from Pkd2 wild-type and Pkd2 null mice were used to confirm the specificity of the immunostaining for polycystin-2. Northern blots of VSMC revealed the expected 5.3-kb band. Western blotting detected a 110-kb band in a 100,000 x g fraction of VSMC homogenates. Cultured VSMC as well as VSMC between the elastic lamellae of pig thoracic aorta were positive for polycystin-2 by immunofluorescence. The staining pattern was cytoplasmic. Treatment of the cells before fixation with Taxol, colchicine, or cytochalasin-D altered the pattern of staining in a way suggesting alignment with the cytoskeleton. The immunohistochemical staining for polycystin-2 was abolished by extraction with 0.5% Triton X-100, indicating that polycystin-2 is not associated with the cytoskeleton. Weak immunoreactivity for polycystin-2, which was markedly enhanced by protease digestion, was detected in formaldehyde-fixed normal human elastic and intracranial arteries. Immunostaining of variable intensity for polycystin-2, which was not consistently enhanced by protease digestion, was seen in the spindle-shaped cells of the wall of the intracranial aneurysms. The similar expression of polycystin-1 and polycystin-2 in the vascular smooth muscle is consistent with the proposed interaction of these proteins in a single pathway. These observations suggest a direct pathogenic role for PKD1 and PKD2 mutations in the vascular complications of ADPKD.

Animals↗