Calcium Restores a Normal Proliferation Phenotype in Human... : Journal of the American Society of Nephrology (original) (raw)

Pathophysiology of Renal Disease and Progression

Calcium Restores a Normal Proliferation Phenotype in Human Polycystic Kidney Disease Epithelial Cells

Yamaguchi, Tamio*, †; Hempson, Scott J.*, †; Reif, Gail A.*, †; Hedge, Anne-Marie*, †; Wallace, Darren P.*, †, ‡

*Kidney Institute, Departments of †Medicine and ‡Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas

Address correspondence to: Dr. Darren P. Wallace, Kidney Institute, Department of Medicine, University of Kansas Medical Center, 3901 Rainbow Boulevard, MSN 3018, Kansas City, KS 66160. Phone: 913-588-3889; Fax: 913-588-9251; E-mail: [email protected]

Accepted October 3, 2005

Received June 21, 2005

Abstract

Polycystic kidney disease (PKD) is a lethal disorder characterized by progressive expansion of renal cysts. Genetic mutations associated with PKD are thought to disrupt intracellular Ca2+ regulation, leading to abnormal proliferation of tubule epithelial cells. cAMP stimulates the B-Raf/MEK/extracellular signal-regulated kinase (B-Raf/MEK/ERK) pathway and accelerates the proliferation of cells that are cultured from PKD cysts. By contrast, cAMP inhibits the proliferation of cells from normal human kidneys (NHK) and M-1 mouse collecting duct cells. Previously, it was found that a sustained reduction of intracellular Ca2+ levels in NHK and M-1 cells that were treated with Ca2+ entry blockers allowed cAMP activation of the B-Raf/MEK/ERK pathway, switching the cells to a cAMP-growth stimulated phenotype. In this study, primary cultures of cyst epithelial cells from autosomal dominant (ADPKD) and recessive (ARPKD) PKD kidneys were used to determine whether controlled addition of Ca2+ could reverse the aberrant mitogenic response to cAMP. Steady-state intracellular Ca2+ levels were found to be 20 nM lower in cyst-derived ADPKD cells (57 ± 2 nM) compared with NHK cells (77 ± 2 nM). Treatment of ADPKD cells or ARPKD cells with either Bay K8644, a Ca2+ channel activator, or A23187, a Ca2+ ionophore, caused sustained increases in intracellular Ca2+ levels and completely reversed the mitogenic response to cAMP. Elevation of intracellular Ca2+ levels in ADPKD cells increased Akt activity and blocked cAMP-dependent B-Raf and ERK activation. Thus, increases in [Ca2+]i are able to restore the normal anti-mitogenic response to cAMP in cells that are derived from two genetically distinct forms of PKD.