The mechanism of cross talk between the Wnt signaling and cyclic AMP (cAMP)-dependent protein kinase (protein kinase A [PKA]) pathways was studied. Prostaglandin E 1 (PGE 1 ), isoproterenol, and dibutyryl cAMP (Bt 2 cAMP), all of which activate PKA, increased the cytoplasmic and nuclear ␤-catenin protein level, and these actions were suppressed by a PKA inhibitor and RNA interference for PKA. PGE 1 and Bt 2 cAMP also increased T-cell factor (Tcf)-dependent transcription through ␤-catenin. Bt 2 cAMP suppressed degradation of ␤-catenin at the protein level. Although PKA did not affect the formation of a complex between glycogen synthase kinase 3␤ (GSK-3␤), ␤-catenin, and Axin, phosphorylation of ␤-catenin by PKA inhibited ubiquitination of ␤-catenin in intact cells and in vitro. Ser675 was found to be a site for phosphorylation by PKA, and substitution of this serine residue with alanine in ␤-catenin attenuated inhibition of the ubiquitination of ␤-catenin by PKA, PKA-induced stabilization of ␤-catenin, and PKA-dependent activation of Tcf. These results indicate that PKA inhibits the ubiquitination of ␤-catenin by phosphorylating ␤-catenin, thereby causing ␤-catenin to accumulate and the Wnt signaling pathway to be activated.

ANG II induces secretion and activation of transforming growth factor-beta (TGF-beta) by glomerular mesangial cells. However, the mechanisms that operate this are unclear. Thrombospondin-1 (TSP-1), which is produced by mesangial cells in damaged glomeruli, is one of several molecules known to activate the latent TGF-beta1 complex. Therefore, we examined whether the ANG II-induced activation of latent TGF-beta1 in human mesangial cells (HMC) operates via TSP-1. The addition of ANG II (1-100 nM) to HMC significantly increased TSP-1 mRNA within 6 h, followed by an increase in TSP-1 protein production as shown by Western blot analysis of cells and immunoassay of the culture supernatant. Production of ANG II-induced TSP-1 mRNA and protein was completely inhibited by an ANG II type 1 (AT1)-receptor antagonist but was unaffected by an AT2-receptor antagonist. Use of a TSP-1-specific blocking peptide demonstrated that the ANG II-induced activation of latent TGF-beta1 operates via TSP-1. Next, we investigated the role of ERK1/2, p38 MAPK, and JNK in ANG II-induced TSP-1 production in HMC. The addition of the upstream ERK1/2 inhibitor PD-98059 did not affect ANG II-induced TSP-1 production, whereas addition of either the p38 MAPK inhibitor SB-203580 or the JNK inhibitor SP-600125 significantly reduced TSP-1 production. In conclusion, this study has demonstrated that ANG II-induced activation of latent TGF-beta1 in HMC operates via TSP-1. Furthermore, ANG II-induced TSP-1 production is dependent on p38 MAPK and JNK signaling.

Glycogen synthase kinase-3 (GSK-3) is regulated by various extracellular ligands and phosphorylates many substrates, thereby regulating cellular functions. Using yeast two-hybrid screening, we found that GSK-3␤ binds to AKAP220, which is known to act as an A-kinase anchoring protein. GSK-3␤ formed a complex with AKAP220 in intact cells at the endogenous level. Cyclic AMP-dependent protein kinase (PKA) and type 1 protein phosphatase (PP1) were also detected in this complex, suggesting that AKAP220, GSK-3␤, PKA, and PP1 form a quaternary complex. It has been reported that PKA phosphorylates GSK-3␤, thereby decreasing its activity. When COS cells were treated with dibutyryl cyclic AMP to activate PKA, the activity of GSK-3␤ bound to AKAP220 decreased more markedly than the total GSK-3␤ activity. Calyculin A, a protein phosphatase inhibitor, also inhibited the activity of GSK-3␤ bound to AKAP220 more strongly than the total GSK-3␤ activity. These results suggest that PKA and PP1 regulate the activity of GSK-3␤ efficiently by forming a complex with AKAP220.

Purpose It is unclear whether hypomagnesemia is an independent risk factor or innocent bystander for mortality in maintenance hemodialysis (MHD) patients. Thus, we studied associations between hypomagnesemia and all-cause as well as cardiovascular (CV) mortality in MHD patients. Methods Baseline clinical characteristics and coronary artery calcium score (CACS) of 353 Japanese MHD patients were reviewed. Three-year survival rate and mortality risk factors were assessed. Results Median (interquartile range) age, dialysis vintage, serum magnesium (Mg), serum albumin and CACS of the subjects were 68 (60–78) years, 75 (32–151) months, 2.4 (2.2–2.7) mg/dl, 3.6 (3.3–3.8) g/dl, and 1181 (278–3190), respectively. During the 3-year period, 91 patients died. Kaplan–Meier overall 3-year survival rates were 59.0% in in patients with Mg < 2.4 mg/dl ( n = 136) and 82.3% in patients with Mg ≥ 2.4 mg/dl ( n = 217), ( P < 0.0001). In Cox regression models not incorporating serum albumin, Mg < 2.4 mg/dl was significantly associated with 3-year all-cause death, independent of age, dialysis vintage, average ultrafiltration, Log (CACS + 1), warfarin use, serum potassium, high-sensitivity C-reactive protein (hsCRP), phosphate, uric acid, and intact parathyroid hormone [Hazard ratio (HR) 95% confidence interval (CI): 2.82 (1.31–6.29), P = 0.0078], and CV death, independent of age, dialysis vintage, Log (CACS + 1), warfarin use, serum hsCRP, and uric acid [HR (95% CI): 4.47 (1.45–16.76), P = 0.0086]. Nevertheless, associations of Mg < 2.4 mg/dl with all-cause and CV mortality were all absent in models that included serum albumin. Conclusions Hypomagnesemia is not an independent risk factor for mortality but is associated with malnutrition in MHD patients.

We evaluated the dose dependence of an oral adsorbent, AST-120, in 31 patients with early chronic renal failure (baseline serum creatinine: 1.2-3.0 mg/dl). Twenty-three patients were given AST-120 and eight patients were not. AST-120 was administered at three different maintenance doses, < 3.0 g, 3.0 g and 6.0 g/day, according to patients' ability to tolerate treatment. The treatment period was 12 months. The slope of the reciprocal of serum-creatinine concentration versus time was calculated to assess the progression of renal failure. This slope became significantly less steep after AST-120 treatment at 6.0 g/day, but did not change significantly at the other doses. These findings suggest that 6.0 g/day of AST-120 may delay the initiation of dialysis in patients with early chronic renal failure.