Pleckstrin homology domain of G protein-coupled receptor kinase-2 binds to PKC and affects the activity of PKC kinase

The connection between GRKs and various signaling pathways involved in diabetic nephropathy

Diabetic nephropathy (DN) is a known microvascular complication in patients with diabetes mellitus. DN has become one of the main causes of death in diabetic patients. The occurrence and development of DN results from the comprehensive action of multi-factors, though the exact mechanism is not very clear. Recently, a study found that numerous pathways are activated during the course of the disease, including the PGE2-EP-G protein system, the renin-angiotensin system, protein kinase C, MAPK and oxidative stress, and transforming growth factor-β. G protein-coupled receptor kinases (GRKs), specifically recognize and phosphorylate agonist-activated G protein-coupled receptors, which play a major role in the above-mentioned pathways. The purpose of this paper is to review current information concerning the connection between GRKs and various signaling pathways involved in DN.

A kinetic model for calcium dynamics in RAW 264.7 cells: 1. Mechanisms, parameters, and subpopulational variability

Calcium (Ca(2+)) is an important second messenger and has been the subject of numerous experimental measurements and mechanistic studies in intracellular signaling. Calcium profile can also serve as a useful cellular phenotype. Kinetic models of calcium dynamics provide quantitative insights into the calcium signaling networks. We report here the development of a complex kinetic model for calcium dynamics in RAW 264.7 cells stimulated by the C5a ligand. The model is developed using the vast number of measurements of in vivo calcium dynamics carried out in the Alliance for Cellular Signaling (AfCS) Laboratories. Ligand binding, phospholipase C-beta (PLC-beta) activation, inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R) dynamics, and calcium exchange with mitochondria and extracellular matrix have all been incorporated into the model. The experimental data include data from both native and knockdown cell lines. Subpopulational variability in measurements is addressed by allowing nonkinetic parameters to vary across datasets. The model predicts temporal response of Ca(2+) concentration for various doses of C5a under different initial conditions. The optimized parameters for IP(3)R dynamics are in agreement with the legacy data. Further, the half-maximal effect concentration of C5a and the predicted dose response are comparable to those seen in AfCS measurements. Sensitivity analysis shows that the model is robust to parametric perturbations.

Identification of interaction sites of protein kinase Cα on phospholipase D1

Phospholipase D (PLD) is regulated by many factors, including protein kinase C (PKC) and small G-proteins of the Rho and ADP-ribosylation factor families. Previous studies revealed that the activation of PLD1 by phorbol ester is associated with the binding of PKCalpha to a site in the N-terminus of PLD1. The purpose of the present study was to determine this site more precisely. Immunoprecipitation with a series of four PLD1 deletion mutants confirmed that PKCalpha strongly interacted with the amino acid sequence 1-318 at the N-terminus of PLD1 and weakly with the sequence 841-1036 at the C-terminus. Further immunoprecipitation studies with deletion mutants of the 1-318 and 1-215 PLD1 fragments revealed that there were binding sites in the 1-49 N-terminal sequence and also in the 216-318 sequence containing the PH domain. Studies of N-terminal deletion mutants of full-length PLD1 confirmed the presence of a binding site in the 1-49 sequence and a further site in the 1-318 sequence. Both deletion mutants showed impaired activation by PKCalpha in vivo, but unchanged activation by active V(14)RhoA. These findings identify the 1-49 sequence is a major binding/activation site for PKCalpha on PLD1, but also indicate involvement of the PH domain.

PldB, a putative phospholipase D homologue in Dictyostelium discoideum mediates quorum sensing during development

Quorum sensing, also known as cell-density sensing in the unicellular eukaryote Dictyostelium discoideum, is required for efficient entry into the differentiation and development segment of its life cycle. Quorum sensing is accomplished by simultaneously secreting and sensing the glycoprotein Conditioned Medium Factor, or CMF. When the density of starving cells is high, CMF levels are high, which leads to aggregation followed by development. Here, we describe the role of pldB, a gene coding for a putative phospholipase D (PLD) homologue, in quorum sensing. We find that in submerged culture, adding butanol, an inhibitor of PLD-catalyzed phosphatidic acid production, allows cells to bypass the requirement for CMF mediated quorum sensing and aggregate at low cell density. Deletion of pldB mimics the presence of butanol, allowing cells to aggregate at low cell density. pldB- cells also initiate and finish aggregation rapidly. Analysis of early developmental gene expression in pldB- cells reveals that the cyclic AMP receptor cAR1 is expressed at higher levels earlier than in wild-type cells, which could explain the rapid aggregation phenotype. As would be predicted, cells overexpressing pldB are unable to aggregate even at high cell density. Adding CMF to these pldB- overexpressing cells does not rescue aggregation. Both of these phenotypes are cell autonomous, as mixing a small number of pldB- cells with wild-type cells does not cause the wild-type cells to behave like pldB- cells.

Expression of PCNA and CD44mRNA in colorectal cancer with venous invasion and its relationship to liver metastasis

AIM: To investigate the expression of proliferating cell nuclear antigen (PCNA) and CD44mRNA in colorectal cancer with venous invasion and its relationship with liver metastasis.

METHODS: Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect the expression of PCNA and CD44mRNA in 31 cases of colorectal cancer with venous invasion.

RESULTS: Positive expression rates of PCNA and CD44mRNA in colorectal cancer were higher than those without liver metastasis (P < 0.05 and P < 0.01). In case of colorectal cancer with liver metastasis, strongly positive rates of PCNA and CD44mRNA were 94.1% and 70.6%, respectively, significantly higher than those without liver metastasis. There was a positive relationship between the expressions of PCNA and CD44mRNA (r = 0.67, P < 0.05).

CONCLUSION: Detection of PCNA and CD44mRNA expression in colorectal cancer may be useful for evaluating liver metastasis of cancer cells.