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Molecular Identification of Canine Podocalyxin-Like Protein 1 as a Renal Tubulogenic Regulator

Hsin-Yuan Cheng^*, Yu-Yu Lin^*, Chun-Ying Yu^*, Jen-Yau Chen^*, Kuo-Fang Shen^*, Wei-Ling Lin^*, Hsin-Kai Liao, Yu-Ju Chen, Chen-Hsuan Liu, Victor Fei Pang and Tzuu-Shuh Jou^*

^* Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine; Institute of Chemistry, Academia Sinica, Nankang; and Department of Veterinary Medicine, National Taiwan University, Taipei, Taiwan

Address correspondence to: Dr. Tzuu-Shuh Jou, Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, No. 7, Chung-Shan S. Road, Taipei, 100 Taiwan. Phone: 8862-23123456 x7625; Fax: 8862-23709820; E-mail: jouts{at}med.mc.ntu.edu.tw

Received for publication December 29, 2004. Accepted for publication March 1, 2005.

GP135 is an apical membrane protein expressed in polarized MDCK epithelial cells. When cultured in three-dimensional collagen gel, MDCK cells form branching tubules in response to hepatocyte growth factor stimulation in a manner that simulates the embryonic renal development. During this process, GP135 displays transient loss of membranous localization but reappears at the cell surface when nascent lumen emerges from the developing tubules. Despite being used for decades as the canonical hallmark of apical surface, the molecular identity and the significance of the dynamic expression of GP135 during the tubulogenic process remain elusive. For exploring the function of GP135, the full-length cDNA encoding GP135 was obtained. Sequence alignments and features analysis confirm GP135 as a canine homolog of podocalyxin, confirming the finding of an earlier independent study. Immunohistochemical assays on canine kidney sections identified both glomerular and tubular distribution of GP135 along the nephron. Mutant MDCK cells expressing siRNA targeted at two regions of GP135 show defects in hepatocyte growth factor–induced tubulogenesis. Re-expression of full-length and an O-linked glycosylation abbreviated construct of GP135 could recapitulate the tubulogenesis process lacking in siRNA knockdown cells; however, a deletion construct devoid of the cytoplasmic domain failed to rescue the phenotype. In summary, the data identify the MDCK apical domain marker GP135 as a tubular form of podocalyxin and provide evidence for its importance in renal tubulogenesis.

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Copyright © 2008 by the American Society of Nephrology. Online ISSN: 1533-3450 Print ISSN: 1046-6673