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

Abstract

The osmosensitive transcription factor nuclear factor of activated T-cells (NFAT) 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.

How do kinases contribute to tonicity-dependent regulation of the transcription factor NFAT5?

“…FAK is constitutively active in a renal cell carcinoma cell line Caki-1 under an isotonic condition. This is probably due to a high Src kinase activity in the cells [55] . The high activities of Src and FAK in Caki-1 cells are in part responsible for the high basal activity of NFAT5 in the cells as compared with that in the noncancerous proximal tubule cell line HK-2 [55] .…”

“…The chemical inhibitors of MEK-ERK1/2 PD98059 and U-0126 inhibit high NaCl-induced activation of NFAT5 in nucleus pulposus cells [62] , renal carcinoma cells [55] and possibly in mIMCD3 cells [76] . ERK2 siRNA reduces high NaCl-dependent NFAT5 transcriptional activity in nucleus pulposus [62] and in HEK293 cells [29] .…”

“…The effect of JNK on tonicity-dependent activation of NFAT5 is elusive and also least studied. Both lack of effect [64] and a positive effect of JNK1/2 [55] on NFAT5 have been reported. Like the effect on p38, hypotonicity also increases phosphorylation of ERK1/2 in human keratinocytes [73] , mIMCD3 cells [77] , renal epithelial A6 cells [72] , although inhibition of ERK by hypotonic stress in A6 cells was also reported [78] .…”

“…SB203580, its analogs, p38α dominant negative mutant or siRNAs uniformly inhibits hypertonicity-induced NFAT5 transcriptional activity [53][54][55][56][57][58][59][60][61][62][63] . Because p38α is also called p38, it has been often concluded that p38 signals hypertonicityinduced activation of NFAT5.…”

Health effects of desalinated water: Role of electrolyte disturbance in cancer development

“…NFAT5 was discovered originally in the renal medulla, where it drives the expression of osmoregulatory genes such asbetaine-GABA-transporter-1(BGT-1), aldose reductase (AR), sodium-myo-inositol transporter (Smit), taurine transporter (TauT), or heat shock protein (HSP) 70, as well as genes that are part of the urinary concentrating mechanism including aquaporin-2 (AQP-2) and urea transporter-A (UT-A) (Kuper et al, 2014). A number of reports have implicated NFAT5 in the pathogenesis of various carcinomas including lung cancer, melanoma, breast cancer, colon carcinoma and renal cancer (Zhong et al, 2004;Mijatovic et al, 2006;Levy et al, 2010;Chen et al, 2011;Germann et al, 2012;Kuper et al, 2014). In breast, colon, and renal cancer cells, NFAT5 has been shown to drive the expression of the pro-metastatic factor S100A4, also known as metastasin-1 (Mts1) (Garrett et al, 2006;Chen et al, 2009;2011).…”