The cAMP effectors Epac and protein kinase a (PKA) are involved in the hepatic cystogenesis of an animal model of autosomal recessive polycystic kidney disease (ARPKD)†
Open Access
- 28 December 2008
- journal article
- research article
- Published by Wolters Kluwer Health in Hepatology
- Vol. 49 (1) , 160-174
- https://doi.org/10.1002/hep.22636
Abstract
PCK rats, an animal model of autosomal recessive polycystic kidney disease (ARPKD), develop cholangiocyte-derived liver cysts associated with increased intracellular adenosine 3′,5′-cyclic adenosine monophosphate (cAMP), the inhibition of which suppresses cyst growth. We hypothesized that elevated cAMP stimulates cholangiocyte proliferation via two downstream effectors, exchange proteins activated by cAMP (Epac1 and Epac2 isoforms) and protein kinase A (PKA), and that intracellular calcium is also involved in this process. Assessment of Epac isoforms and PKA regulatory subunits at the messenger RNA and protein level showed that cultured normal rat cholangiocytes express Epac1, Epac2, and all regulatory PKA subunits. Epac isoforms and the PKA RIβ subunit were overexpressed in cultured PCK cholangiocytes. Proliferation analysis in response to Epac and PKA activation indicated that both normal and PCK cholangiocytes increase their growth upon Epac-specific stimulation, while PKA-specific stimulation results in differential effects, suppressing proliferation in normal cholangiocytes but accelerating this process in PCK cholangiocytes. On the other hand, both PKA and Epac activation of cystic structures generated by normal and PCK cholangiocytes when cultured under three-dimensional conditions resulted in increased cyst growth, particularly in PCK-cholangiocyte derived cysts. Pharmacological inhibitors and small interfering RNA–mediated gene silencing demonstrated the specificity of each effector activation, as well as the involvement of MEK-ERK1/2 signaling in all the observed effector-associated proliferation changes. Hyperproliferation of PCK cholangiocytes in response to PKA stimulation, but not to Epac stimulation, was found to be associated with decreased intracellular calcium, and restoration of calcium levels blocked the PKA-dependent proliferation via the PI3K/AKT pathway. Conclusion: Our data provide strong evidence that both cAMP effectors, Epac and PKA, and the levels of intracellular calcium are involved in the hepatic cystogenesis of ARPKD. (HEPATOLOGY 2009;49:160-174.)Keywords
This publication has 29 references indexed in Scilit:
- Hepatic Cystogenesis Is Associated with Abnormal Expression and Location of Ion Transporters and Water Channels in an Animal Model of Autosomal Recessive Polycystic Kidney DiseaseThe American Journal of Pathology, 2008
- Calcium Restriction Allows cAMP Activation of the B-Raf/ERK Pathway, Switching Cells to a cAMP-dependent Growth-stimulated PhenotypeJournal of Biological Chemistry, 2004
- Defects in cholangiocyte fibrocystin expression and ciliary structure in the PCK rat1 1The authors thank Dr. Torra for supplying ARPKD tissue.Gastroenterology, 2003
- Cellular and subcellular localization of the ARPKD protein; fibrocystin is expressed on primary ciliaHuman Molecular Genetics, 2003
- A novel Epac-specific cAMP analogue demonstrates independent regulation of Rap1 and ERKNature Cell Biology, 2002
- Identification and Characterization of Pkhd1, the Mouse Orthologue of the Human ARPKD GeneJournal of the American Society of Nephrology, 2002
- The gene mutated in autosomal recessive polycystic kidney disease encodes a large, receptor-like proteinNature Genetics, 2002
- Characterization of the Gene EPAC2: Structure, Chromosomal Localization, Tissue Expression, and Identification of the Liver-Specific IsoformGenomics, 2001
- Polycystic Kidney Rat Is a Novel Animal Model of Caroli’s Disease Associated with Congenital Hepatic FibrosisThe American Journal of Pathology, 2001
- cAMP stimulates the in vitro proliferation of renal cyst epithelial cells by activating the extracellular signal-regulated kinase pathwayKidney International, 2000