CHANNELS EGF Is Connected Through PIP₂ to PKD2

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in either the pkd1 or pkd2 gene. Targeted deletion of the gene encoding the epidermal growth factor receptor (EGFR) in mice causes a similar phenotype as that of ADPKD. Thus, Ma et al. investigated whether there was a signaling pathway connecting EGFR to PKD2, which is a member of the transient receptor potential (TRP) family of channels. The authors studied the currents induced by application of EGF to a pig proximal tubule kidney cell line LLC-PK₁ and cells transfected with human PKD2 and various PKD2 mutants or tagged forms. Increased abundance of PKD2 enhanced currents stimulated by EGF, and these currents were abolished in cells in which PKD2 (native and transfected) was silenced with RNAi. A pathogenic variant of PKD2 (PKD2-D511V) also inhibited EGF-stimulated channel activity, consistent with this mutant acting as a dominant negative. Pharmacological manipulation indicated that the tyrosine kinase activity of EGFR and phospholipase C (PLC) activity were required for stimulation of channel activity by EGF. Although application of a diacylglycerol analog to the cells stimulated a current, this current was not enhanced in the cells overexpressing PKD2, which suggests that DAG is not responsible for the EGF-mediated increase in channel activity. When purified phosphatidylinositol-4,5-bisphosphate (PIP₂) was added to the recording electrode, EGF failed to stimulate an increase in whole-cell current. Inhibition of phosphatidylinositol 3-kinase (PI3K) inhibited both basal and EGF-stimulated whole-cell currents. These results suggest that PKD2 is inhibited by PIP₂ and that EGF, through the actions of PI3K and PLC, decreases PIP₂, thereby activating the PKD2 channel. This interpretation is supported by lack of EGF stimulation of current in cells transfected with PIP(5)K, which is a kinase that increases PIP₂. Coimmunoprecipitation experiments with transfected HEK-293 cells suggested an interaction between EGFR, PLC-2, and PKD2. In the LLC-PK1 cells, in which PLC-2 is present, PIP₂, EGFR, and PKD2 were colocalized in the cilium based on immunofluorescence. Thus, this complex may allow localized changes in PIP₂ abundance, which regulate the activity of the PKD2 channel. EGF, which is abundant in human urine, may decrease the threshold required for fluid shear stress to activate PKD2 in the kidney.

R. Ma, W-P. Li, D. Rundle, J. Kong, H. I. Akbarali, L. Tsiokas, PKD2 functions as an epidermal growth factor-activated plasma membrane channel. Mol. Cell. Biol. 25, 8285-8298 (2005). [Abstract] [Full Text]

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TRP Channels in Disease

Bernd Nilius, Thomas Voets, and John Peters (2 August 2005)
Sci. STKE 2005 (295), re8. [DOI: 10.1126/stke.2952005re8]
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