Hyperkalemic solutions are widely used to preserve organs for transplantation and for cardiac surgery. The present study was designed to test the hypothesis that hyperkalemia may alter endothelial function through a non-nitric oxide (NO) pathway, since preliminary studies have shown that the NO pathway may not be affected. Porcine coronary artery rings were studied in organ chambers. After incubation with 20 or 50 mM K+ for 1 h, the indomethacin- and NG-nitro-L-arginine+ (L-NNA)-resistant relaxation induced by A23187 or bradykinin, which could be further inhibited by tetraethylammonium but not glibenclamide, was significantly reduced. Incubation with hyperkalemia also significantly increased the concentration eliciting 50% of the maximal response to A23187 and bradykinin. A23187-induced hyperpolarization of the membrane potential was significantly reduced by hyperkalemic incubation. However, 1-h incubation with hyperkalemia does not affect the endothelial Ca2+ concentration. We conclude that exposure to hyperkalemia reduces the indomethacin- and L-NNA-resistant endothelium-dependent relaxation and endothelium-dependent hyperpolarization. This reduction in the relaxation and hyperpolarization is related to the endothelium-derived hyperpolarizing factor by affecting its effect on the smooth muscle cell, probably through partially depolarizing the membrane, and the Ca2(+)- activated K+ channels rather than by affecting its biosynthesis and/or release in the endothelial cell. Our study may suggest a new mechanism for coronary dysfunction after exposure to hyperkalemic cardioplegia and organ preservation solutions.

The Wnt/β-catenin pathway is constitutively active and promotes multiple tumor processes, including breast cancer metastasis. However, the underlying mechanism by which the Wnt/β-catenin pathway is constitutively activated in breast cancer metastasis remains unclear. Inhibition of Wnt antagonists is important for Wnt/β-catenin signaling activation, and post-transcriptional regulation of these antagonists by microRNAs (miRNAs) might be a possible mechanism underlying signaling activation. Regulation of nuclear pre-mRNA domain-containing 1A (RPRD1A) is a known inhibitor of cell growth and Wnt/β-catenin signaling activity, but the function and regulatory mechanism of RPRD1A in breast cancer have not been clarified. The aim of this study was to understand how regulators of the Wnt/β-catenin pathway may play a role in the metastasis of this cancer. Methods: RPRD1A expression and its association with multiple clinicopathological characteristics was analyzed immunohistochemically in human breast cancer specimens. miR-454-3p expression was analyzed using real-time PCR. RPRD1A or miR-454-3p knockdown and overexpression were used to determine the underlying mechanism of their functions in breast cancer cells. Xenografted tumor model, 3D invasive culture, cell migration and invasion assays and sphere formation assay were used to determine the biofunction of RPRD1A and miR-454-3p in breast cancer. Electrophoretic mobility shift assay (EMSA), luciferase reporter assay, and RNA immunoprecipitation (RIP) were performed to study the regulation and underlying mechanisms of RPRD1A and miR-454-3p expression and their correlation with the Wnt/β-catenin pathway in breast cancer. Results: The Wnt/β-catenin signaling antagonist RPRD1A was downregulated and its upstream regulator miR-454-3p was amplified and overexpressed in metastatic breast cancer, and both were correlated with overall and relapse-free survival in breast cancer patients. The suppression by miR-454-3p on RPRD1A was found to activate Wnt/β-catenin signaling, thereby promoting metastasis. Simultaneously, three other negative regulators of the Wnt/β-catenin pathway, namely, AXIN2, dickkopf WNT signaling pathway inhibitor (DKK) 3 and secreted frizzled related protein (SFRP) 1, were also found to be targets of miR-454-3p and were involved in the signaling activation. miR-454-3p was found to be involved in early metastatic processes and to promote the stemness of breast cancer cells and early relapse under both in vitro and in vivo conditions. Conclusions: The findings indicate that miR-454-3p-mediated suppression of Wnt/β-catenin antagonist RPRD1A, as well as AXIN2, DKK3 and SFRP1, sustains the constitutive activation of Wnt/β-catenin signaling; thus, miR-454-3p and RPRD1A might be potential diagnostic and therapeutic targets for breast cancer metastasis.

Depolarizing arrest reduces endothelium-derived hyperpolarizing factor-mediated membrane hyperpolarization and relaxation by affecting mainly the Ca(2+)-activated K channels and by depolarizing the membrane for a prolonged period. We suggest that this is one of the mechanisms for coronary dysfunction after exposure to depolarizing (hyperkalemic) cardioplegic and organ-preservation solutions and that, therefore, "perfect" protection of the heart or other organs should restore the endothelium-derived hyperpolarizing factor-related endothelial function.

Nuclear factor-κB (NF-κB) is a core regulator in multiple tumorigenic pathways. Its activation is mediated by IκB kinase β (IKKβ). Protein phosphatase PPM1B is reported to dephosphorylate IKKβ, thereby terminating IKKβ-mediated NF-κB activation. However, the role of PPM1B in bladder cancer is unclear. The aim of this study was to determine the expression patterns and molecular mechanisms of PPM1B in bladder cancer. Comparative analyses were conducted in six bladder cancer cell lines, a normal urinary epithelial cell line, and adjacent non-tumorous bladder epithelia. Searches were conducted through publicly available algorithms and The Cancer Genome Atlas. HT-1376 and RT4 cells were transduced to stably overexpress PPM1B and its predicted regulator miR-186. Subsequent in vitro studies included 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), colony formation, anchorage-independent growth ability, luciferase reporter assays, and flow cytometric cell cycle analyses. A xenograft model was established in nude mice to evaluate the effect of PPM1B in bladder tumors in vivo. The results revealed that PPM1B was frequently downregulated in bladder cancer cells at both protein and messenger RNA (mRNA) levels, whereas miR-186 was upregulated. Further analyses showed that miR-186 promoted G1-S transition by targeting PPM1B at its 3'-untranslated region (3'UTR). Conversely, ectopic expression of PPM1B significantly suppressed proliferation and tumorigenicity in bladder cancer cells in vitro and in vivo, thereby neutralizing the oncogenic effect of miR-186. This study has identified PPM1B and miR-186 as potential diagnostic markers in bladder cancer. Promotion of PPM1B and suppression of miR-186 may offer effective therapeutic strategies in the treatment of bladder cancer.