The role of the casein kinase 1 (CK1) family in different signaling pathways linked to cancer development

The members of the casein kinase 1 (CK1) family are highly conserved and are expressed in many eukaryotes ranging from yeast to humans. Mammalian CK1 isoforms (alpha, beta, gamma, delta, epsilon) and their splice variants are involved in diverse cellular processes including membrane trafficking, circadian rhythm, cell cycle progression, chromosome segregation, apoptosis and cellular differentiation. Mutations and deregulation of CK1 expression and activity has been linked to various diseases including neurodegenerative disorders such as Alzheimer's and Parkinson's disease, sleeping disorders and proliferative diseases such as cancer. In this review, we summarize the functions of CK1 and outline the participation of CK1 in signal transduction pathways linked to cancer development

Activation of hepatocytes by extracellular heat shock protein 72

Heat shock protein (HSP) 72 is released by cells during stress and injury. HSP-72 also stimulates the release of cytokines in macrophages by binding to Toll-like receptors (TLR) 2 and 4. Circulating levels of HSP-72 increase during hepatic ischemia-reperfusion injury. The role of extracellular HSP-72 (eHSP-72) in the injury response to ischemia-reperfusion is unknown. Therefore, the objective of the present study was to determine whether eHSP-72 has any direct effects on hepatocytes. Primary mouse hepatocytes were treated with purified human recombinant HSP-72. Conditioned media were evaluated by ELISA for the cytokines, TNF-α, IL-6, and macrophage inflammatory protein 2 (MIP-2). Stimulation of hepatocytes with eHSP-72 did not induce production of TNFα or IL-6 but resulted in dose-dependent increases in MIP-2 production. To evaluate the pathway responsible for this response, expression of TLR2 and TLR4 was confirmed on hepatocytes by immunohistochemistry. Hepatocyte production of MIP-2 was significantly decreased in hepatocytes obtained from TLR2 or TLR4 knockout mice. MIP-2 production was found to be partially dependent on NF-κB because inhibition of NF-κB with Bay 11-7085 significantly decreased eHSP-72-induced MIP-2 production. Inhibitors of p38 mitogen-activated protein kinase or c-Jun NH2-terminal kinase had no effect on production of MIP-2 induced by eHSP-72. The data suggest that eHSP-72 binds to TLR2 and TLR4 on hepatocytes and signals through NF-κB to increase MIP-2 production. The fact that eHSP-72 did not increase TNF-α or IL-6 production may be indicative of a highly regulated signaling pathway downstream from TLR

Peroxiredoxin-6 protects against mitochondrial dysfunction and liver injury during ischemia-reperfusion in mice

Hepatic ischemia-reperfusion (I/R) injury is an important complication of liver surgery and transplantation. Mitochondrial function is central to this injury. To examine alterations in mitochondrial function during I/R, we assessed the mitochondrial proteome in C57Bl/6 mice. Proteomic analysis of liver mitochondria revealed 234 proteins with significantly altered expression after I/R. From these, 13 proteins with the greatest expression differences were identified. One of these proteins, peroxiredoxin-6 (Prdx6), has never before been described in mitochondria. In hepatocytes from sham-operated mice, Prdx6 expression was found exclusively in the cytoplasm. After ischemia or I/R, Prdx6 expression disappeared from the cytoplasm and appeared in the mitochondria, suggesting mitochondrial trafficking. To explore the functional role of Prdx6 in hepatic I/R injury, wild-type and Prdx6-knockout mice were subjected to I/R injury. Prdx6-knockout mice had significantly more hepatocellular injury compared with wild-type mice. Interestingly, the increased injury in Prdx6-knockout mice occurred despite reduced inflammation and was associated with increased mitochondrial generation of H2O2 and dysfunction. The mitochondrial dysfunction appeared to be related to complex I of the electron transport chain. These data suggest that hepatocyte Prdx6 traffics to the mitochondria during I/R to limit mitochondrial dysfunction as a protective mechanism against hepatocellular injury

Matrix-Dependent Regulation of AKT in Hepsin-Overexpressing PC3 Prostate Cancer Cells12

The serine-protease hepsin is one of the most prominently overexpressed genes in human prostate carcinoma. Forced expression of the enzyme in mice prostates is associated with matrix degradation, invasive growth, and prostate cancer progression. Conversely, hepsin overexpression in metastatic prostate cancer cell lines was reported to induce cell cycle arrest and reduction of invasive growth in vitro. We used a system for doxycycline (dox)-inducible target gene expression in metastasis-derived PC3 cells to analyze the effects of hepsin in a quantitative manner. Loss of viability and adhesion correlated with hepsin expression levels during anchorage-dependent but not anchorage-independent growth. Full expression of hepsin led to cell death and detachment and was specifically associated with reduced phosphorylation of AKT at Ser473, which was restored by growth on matrix derived from RWPE1 normal prostatic epithelial cells. In the chorioallantoic membrane xenograft model, hepsin overexpression in PC3 cells reduced the viability of tumors but did not suppress invasive growth. The data presented here provide evidence that elevated levels of hepsin interfere with cell adhesion and viability in the background of prostate cancer as well as other tissue types, the details of which depend on the microenvironment provided. Our findings suggest that overexpression of the enzyme in prostate carcinogenesis must be spatially and temporally restricted for the efficient development of tumors and metastases