Heat shock proteins and the cellular response to osmotic stress

In antidiuresis, the intrarenal distribution of HSP25/27, alpha beta -crystallin, HSP72, OSP94 and HSP110 corresponds to the osmotic gradient between cortex and papilla: low amounts in the cortex and high values in the inner medulla and papilla. In addition, medullary HSP72 levels change appropriately with the diuretic state. Studies on MUCK cells suggest that, in the renal medulla in vivo, stressors, such as NaCl and low pH, may act in concert to induce HSP72 expression. Urea, added to the medium at high concentrations (600 mM), causes the majority of MUCK cells to die. Prior exposure of these cells to hypertonic media (NaCl addition), a maneuver that induces HSP72, protects the cells against the deleterious effects of high urea concentrations. Inhibition of HSP72 expression by stable antisense transfection or SB203580 treatment abolishes the beneficial effects of prior hypertonic stress. Conversely, overexpression of HSP72 under isotonic conditions by a dexamethasone-driven vector confers substantial resistance against subsequent exposure to high urea concentrations. Taken together these results suggest that also in the renal inner medulla, NaCl-induced enhancement of HSP72 expression may help counteract the detrimental effects of high urea concentrations. Copyright (C) 2000 S. Karger AG Basel

The impact of founders´ personal characteristics on fundraising success in early-stage entrepreneurship

Launching a successful entrepreneurial project is one of biggest challenges entrepreneurs face. Therefore, research has already explored success factors of early-stage entrepreneurs and uncovered several biographical characteristics of founders, that positively impact a project's performance. As access to capital is one of the key drivers for early start-up success, this study specifically aims to expand existing knowledge by examining whether biographical characteristics have an impact on the founder's ability to raise funds when launching a crowdfunding campaign on the Kickstarter platform. By analyzing 247 design projects in Germany, we find that four characteristics influence the founder's ability to raise capital in a crowdfunding setting

Role of NFAT5 in Inflammatory Disorders Associated with Osmotic Stress

Nuclear factor of activated T cells 5 (NFAT5) is the most recently described member of the Rel family of transcription factors, including NF-κB and NFAT1-4, which play central roles in inducible gene expression during the immune response. NFAT5 was initially described to drive osmoprotective gene expression in renal medullary cells, which are routinely faced by high extracellular osmolalities. Recent data however indicate profound biological importance of the mammalian osmotic stress response in view of NFAT5 dependent gene regulation in non-renal tissues. In mononuclear cells and epithelial cells, NFAT5 stimulates the expression of various pro-inflammatory cytokines during elevated ambient tonicity. Accordingly, compared to plasma, the interstitial tonicity of lymphoid organs like spleen and thymus and that of liver is substantially hypertonic under physiological conditions. In addition, anisotonic disorders (hypernatremia, diabetes mellitus, dehydration) entail systemic hyperosmolality, and, in inflammatory disorders, the skin, intestine, and cornea are sites of local hyperosmolality. This article summarizes the current knowledge regarding systemic and local osmotic stress in anisotonic and inflammatory disorders in view of NFAT5 activation and regulation, and NFAT5 dependent cytokine production

NFAT5 Contributes to Osmolality-Induced MCP-1 Expression in Mesothelial Cells

Increased expression of the C-C chemokine monocyte chemoattractant protein-1 (MCP-1) in mesothelial cells in response to high glucose concentrations and/or high osmolality plays a crucial role in the development of peritoneal fibrosis during continuous ambulatory peritoneal dialysis (CAPD). Recent studies suggest that in kidney cells osmolality-induced MCP-1 upregulation is mediated by the osmosensitive transcription factor, nuclear factor of activated T cells 5 (NFAT5). The present study addressed the question of whether activation of NFAT5 by hyperosmolality, as present in PD fluids, contributes to MCP-1 expression in the mesothelial cell line Met5A. Hyperosmolality, induced by addition of glucose, NaCl, or mannitol to the growth medium, increased NFAT5 activity and stimulated MCP-1 expression in Met5A cells. siRNA-mediated knockdown of NFAT5 attenuated osmolality-induced MCP-1 upregulation substantially. Hyperosmolality also induced activation of nuclear factor-κB (NF-κB). Accordingly, pharmacological inhibition of NF-κB significantly decreased osmolality-induced MCP-1 expression. Taken together, these results indicate that high osmolalities activate the transcription factor NFAT5 in mesothelial cells. NFAT5 in turn upregulates MCP-1, likely in combination with NF-κB, and thus may participate in the development of peritoneal fibrosis during CAPD

Dual effect of lithium on NFAT5 activity in kidney cells

Lithium salts are used widely for treatment of bipolar and other mental disorders. Lithium therapy is accompanied frequently by renal side effects, such as nephrogenic diabetes insipidus or chronic kidney disease (CKD),but the molecular mechanisms underlying these effects are still poorly understood. In the present study we examined the effect of lithium on the activity of the osmosensitive transcriptional activator nuclear factor of activated T cells 5 (NFAT5, also known as TonEBP),which plays a key role in renal cellular osmoprotection and urinary concentrating ability. Interestingly, we found different effects of lithium on NFAT5 activity, depending on medium osmolality and incubation time. When cells were exposed to lithium for a relative short period (24 h),NFAT5 activity was significantly increased, especially under isosmotic conditions, resulting in an enhanced expression of the NFAT5 target gene heat shock protein 70 (HSP70). Further analysis revealed that the increase of NFAT5 activity depended primarily on an enhanced activity of the c-terminal transactivation domain (TAD),while NFAT5 protein abundance was largely unaffected. Enhanced activity of the TAD is probably mediated by lithium-induced inhibitory phosphorylation of glycogen synthase kinase 3 beta (GSK-3 beta),which is in accordance with previous studies. When cells were exposed to lithium for a longer period (96 h),cellular NFAT5 activity and subsequently expression of HSP70 significantly decreased under hyperosmotic conditions, due to diminished NFAT5 protein abundance, also resulting from GSK-3 beta inhibition. Taken together, our results provide evidence that lithium has opposing effects on NFAT5 activity, depending on environmental osmolality and exposure duration. The potential impacts of these observations on the diverse effects of lithium on kidney function are discussed

NFAT5-mediated expression of S100A4 contributes to proliferation and migration of renal carcinoma cells

The osmosensitive transcription factor nuclear factor of activated T-cells (NEAT) 5, also known as tonicity enhancer binding protein (TonEBP),has been associated with the development of a variety of tumor entities, among them breast cancer, colon carcinoma, and melanoma. The aim of the present study was to determine whether NFAT5 is also involved in the development of renal cell carcinoma (RCC). The most common type of RCC, the clear cell RCC, originates from the proximal convoluted tubule. We tested our hypothesis in the clear cell RCC cell line CaKi-1 and the non-cancerous proximal tubule cell line HK-2, as control. Basal expression of NFAT5 and NFAT5 activity in CaKi-1 cells was several times higher than in HK-2 cells. Osmotic stress induced an increased NFAT5 activity in both CaKi-1 and HK-2 cells, again with significantly higher activities in CaKi-1 cells. Analysis of NFAT5-regulating signaling pathways in CaKi-1 cells revealed that inhibition of the MAP kinases p38, c-Jun-terminal kinase (JNK) and extracellular regulated kinase (ERK) and of the focal adhesion kinase (FAK) partially blunted NFAT5 activity. FAK and ERK were both constitutively active, even under isotonic conditions, which may contribute to the high basal expression and activity of NFAT5 in CaKi-1 cells. In contrast, the MAP kinases p38 and JNK were inactive under isotonic conditions and became activated under osmotic stress conditions, indicating that p38 and JNK mediate upregulation of NFAT5 activity under these conditions. siRNA-mediated knockdown of NFAT5 in CaKi-1 cells reduced the expression of S100A4, a member of the S100 family of proteins, which promotes metastasis. Knockdown of NFAT5 was accompanied by a significant decrease in proliferation and migration activity. Taken together, our results indicate that NFAT5 induces S100A4 expression in CaKi-1 cells, thereby playing an important role in RCC proliferation and migration