Rosiglitazone inhibits proliferation of renal proximal tubular cells via down-regulation of ERK and Akt

FGF/FGFR2 Protects against Tubular Cell Death and Acute Kidney Injury Involving Erk1/2 Signaling Activation

Background

Fibroblast growth factors (FGFs) are heparin-binding proteins involved in a variety of biological processes, and part of them may act through binding with cell membrane receptor FGFR2.

Objectives

To clarify the role and mechanisms of FGFR2 signaling in tubular cell survival and acute kidney injury (AKI).

Method

In this study, kidney ischemia/reperfusion (IR) or cisplatin injection was used to induce AKI in mice.

Results

In the kidneys after IR or cisplatin injection, the expression of FGFs and Erk1/2 phosphorylation were elevated. To investigate the role of FGFs in tubular cell survival and AKI, a mouse model with tubular cell specific FGFR2 gene disruption was generated. The knockouts were born normal. At 2 months of age, about one-third of the knockouts developed mild hydronephrosis. Ablation of FGFR2 in tubular cells aggravated acute kidney dysfunction as well as tubular cell apoptosis induced by IR or cisplatin. In addition, Erk1/2 phosphorylation was less in the knockout kidneys than in control littermates at day 1 after cisplatin injection. In cultured NRK-52E cells, recombinant FGF2 protein induced Erk1/2 phosphorylation and inhibited cisplatin-induced cell death. PD98059 abolished Erk1/2 phosphorylation and partly reversed the protective effect of FGF2 on cisplatin-induced cell death.

Conclusions

This study indicates that FGF/FGFR2 signaling plays an important role in protecting against tubular cell death and AKI, which is partly through stimulating Erk1/2 activation.

HCaRG/COMMD5 inhibits ErbB receptor-driven renal cell carcinoma

Hypertension-related, calcium-regulated gene (HCaRG/COMMD5) is highly expressed in renal proximal tubules, where it contributes to the control of cell proliferation and differentiation. HCaRG accelerates tubular repair by facilitating re-differentiation of injured proximal tubular epithelial cells, thus improving mouse survival after acute kidney injury. Sustained hyper-proliferation and de-differentiation are important hallmarks of tumor progression. Here, we demonstrate that cancer cells overexpressing HCaRG maintain a more differentiated phenotype, while several of them undergo autophagic cell death. Its overexpression in mouse renal cell carcinomas led to smaller tumor size with less tumor vascularization in a homograft tumor model. Mechanistically, HCaRG promotes de-phosphorylation of the proto-oncogene erythroblastosis oncogene B (ErbB)2/HER2 and epigenetic gene silencing of epidermal growth factor receptor and ErbB3 via promoter methylation. Extracellular signal-regulated kinase, AKT and mammalian target of rapamycin which mediate ErbB-dowstream signaling pathways are inactivated by HCaRG expression. In addition, HCaRG is underexpressed in human renal cell carcinomas and more expressed in normal tissue adjacent to renal cell carcinomas of patients with favorable prognosis. Taken together, our data suggest a role for HCaRG in the inhibition of tumor progression as a natural inhibitor of the ErbB signals in cancer and as a potential prognostic marker for renal cell carcinomas.

Hypertension-related, calcium-regulated gene (HCaRG/COMMD5) and kidney diseases: HCaRG accelerates tubular repair

Hypertension is a risk factor for renal impairment. While treatment of hypertension provides significant renal protection, there is still an unmet need requiring further exploration of additional pathogenetic mechanisms. We have found that the hypertension-related, calcium-regulated gene (HCaRG/COMMD5) is involved in renal repair. HCaRG is a small intracellular protein of 225 amino acids and its gene expression is negatively regulated by extracellular calcium concentrations. HCaRG is mostly expressed in the kidneys, with higher levels found in the spontaneously hypertensive rat than in normotensive rats. In an acute kidney injury model, HCaRG expression decreases immediately after injury but increases above baseline during the repair phase. In cell cultures, HCaRG has been shown to facilitate differentiation and to inhibit cell proliferation via p21 transactivation through the p53-independent signaling pathway. Induction of p21 independently of p53 is also observed in transgenic mice overexpressing HCaRG during the repair phase after ischemia/reperfusion injury, resulting in their improved renal function and survival with rapid re-differentiation of proximal tubular epithelial cells. In addition, transgenic mice recover rapidly from the inflammatory burst most likely as a result of maintenance of the tubular epithelial barrier. Recent studies indicate that facilitating re-differentiation and cell cycle regulation in injured renal proximal tubules might be important functions of HCaRG. We have proposed that HCaRG is a component of differential genetic susceptibility to renal impairment in response to hypertension.