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1Fondation pour Recherches Médicales, Service of Nephrology, Geneva, Switzerland; 2Section of Integrative Physiology, Department of Surgical Sciences, Karolinska Institutet, Stockholm, Sweden; and 3Institut National de la Santé et de la Recherche Médicale U478, Faculté de Médecine Xavier Bichat, Paris, France
Submitted 14 May 2004 ; accepted in final form 8 October 2004
In the renal collecting duct (CD), water reabsorption depends on the presence of aquaporin-2 (AQP2) in the apical membrane of principal cells. AQP2 expression and subcellular repartition are under the control of AVP. Some pieces of experimental evidence indicate that additional hormonal factors, including insulin, may also control AQP2 expression and thereby CD water permeability. We have previously shown that AVP induces endogenous AQP2 expression in cultured mouse mpkCCDcl4 CD principal cells (23). In the present study, we investigated the effect of insulin on AQP2 expression in mpkCCDcl4 cells. Addition of insulin to the basal medium of cells grown on filters slightly increased AQP2 mRNA and protein expression, whereas insulin potentiated the effect of AVP. The potentiation of AVP-induced AQP2 expression by insulin was abolished by actinomycin D, a transcriptional inhibitor. Analysis of AQP2 protein expression under conditions of AVP washout and/or in the presence of chloroquine, a lysosomal degradation inhibitor, revealed that insulin did not significantly alter AQP2 protein degradation. Inhibition of ERK, p38 kinase, and phosphatidylinositol 3'-kinase (PI 3-kinase) activities prevented the insulin-induced stimulation of AQP2 expression, whereas inhibition of PKC has no effect. Taken together, our results indicate that insulin increased AQP2 protein expression mostly through increased AQP2 mRNA levels in cultured mpkCCDcl4 cells. This effect most likely relies on increased AQP2 gene transcription in response to MAPK and PI 3-kinase activation.
kidney; water transport; mitogen-activated protein kinases; phosphatidylinositol 3-kinase
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