Introduction
Autosomal dominant polycystic kidney disease (ADPKD) is a common monogenetic disorder, affecting as many as 1 in 500 people in the general population. The disease is characterized by the formation of multiple fluid-filled renal cysts that expand over time and destroy the architecture of the kidney. Five percent of all cases of chronic renal failure are due to ADPKD, and approximately 50% of ADPKD patients will develop end-stage renal disease by the time they are 60 years of age [1].
In the early stages of ADPKD, numerous cysts begin to enlarge from many segments of the kidney. Later, the enlarged regions disassociate from the original nephron to form the actual cysts, which continue to enlarge due to proliferation of epithelial cells and fluid secretion into the cyst lumen. Progressive renal cyst formation and enlargement result in a loss of renal function and hypertension and culminate in renal failure. It is generally believed that cysts enlarge by means of abnormal cell growth, forming what is essentially a fluid-filled tumor that fills by transepithelial fluid secretion. Cyst enlargement may then lead to extracellular matrix remodeling, interstitial fibrosis, a general inflammatory response, and disruption of the normal renal parenchyma, which then interfere with glomerular filtration and vascular blood flow, giving rise to cell death by apoptosis and ultimately renal failure [2].
Many studies have indicated that most cases of ADPKD are accounted for by mutations in the PKD1 and PKD2 genes, encoding the transmembrane protein polycystin-1 (PC1) and polycystin-2 (PC2), respectively. Mice with targeted mutations in the PKD1 or PKD2 genes develop cystic kidneys during embryogenesis, and ADPKD in humans is associated with mutations in the PKD1 or PKD2 genes [3, 4]. In addition, the product of the PKD1 gene, PC1, has been implicated in a variety of pathways tied to proliferation, including G-protein signaling and the Wnt, activator protein 1 (AP-1), and Janus kinase-signal transducers and activators of transcription cascades [5, 6]. Moreover, depletion of PC1 has been shown to increase cell growth, whereas its overexpression slows cell growth, indicating that PC1 may negatively regulate cell proliferation [7, 8]. PC2, the protein product of PKD2, has also been implicated in cell cycle regulation via its calcium channel activity and stimulation of AP-1 [9, 10]; however, there has been little direct evidence tying PC2 to this process.
Here, we created a number of related cell lines that varied in their expression of PC2. We describe studies designed to identify target genes under the control of the PKD2 using Pkd2 knockout (KO) and PKD2 transgenic (TG) mouse embryo fibroblasts (MEFs). We used a mouse 30 K whole gene oligonucleotide microarray to identify messenger RNAs whose expression was altered by the overexpression of the PKD2 or KO of the Pkd2 in MEF cells.