多囊性腎臟病 (polycystic kidney disease, PKD)是常見的遺傳性疾病之一，疾病特色為腎臟會出現囊泡，囊泡不斷增生擴大影響到腎臟的正常組織功能，在疾病末期導致腎衰竭的發生。多囊性腎臟病可能是PKD1基因或者是PKD2基因發生突變所造成，大部分的患者屬於PKD1基因突變型，PKD1基因表現PC-1蛋白 (polycystin-1)，目前相關的研究已發現到PC-1蛋白會被γ-secretase進行剪切出一段細胞質端CTT (C-terminal cytoplasmic tail)，被切出來CTT片段會進一步入核並且參與活化調節許多的訊息路徑，且多囊性腎臟病患者腎臟會有CTT異常累積的情形，其中詳細的機制目前尚未清楚。有研究發現單獨過量表現CTT片段就足以導致斑馬魚胚胎有囊泡形成，不過若是抑制了PKD1的表達則會有發育生長異常的情形，此時若再給予CTT則可以挽救這些異常狀況，所以適量表現CTT蛋白能夠有效抑制多囊性腎臟病相關的生長死亡、發育型態等異常情況。關於多囊性腎臟病大家已熟知mTOR會失去控制過度活化，而有文獻指出mTOR會增加OGT (O-GlcNAc transferase)蛋白的穩定性，所以我們想要探討多囊性腎臟病之中OGT是否會扮演著什麼角色。在本研究中我們發現OGT會對CTT蛋白的穩定性及功能產生影響，過量表現的OGT可以讓CTT蛋白穩定性增加，且降低了CTT活化的訊息路徑表現，而將OGT進行抑制得到了反證結果。給予細胞藥物加強O-GlcNAc修飾作用之後，發現CTT蛋白表現位置從細胞核更進一步往細胞核仁集中。從動物實驗中發現Thiamet-G藥物可以減緩多囊性腎臟病小鼠的病症。本研究主要提出OGT會對CTT蛋白進行修飾，且造成CTT穩定性及功能發生改變，並且經由加強O-GlcNAc修飾作用的策略確實可以緩解多囊性腎臟病小鼠的病症。

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by presence of cysts in the kidney and other organs and eventual renal failure. Mutations of PKD1 (PC1) or PKD2 (PC2) are responsible for ADPKD. PC1 undergoes multiple cleavages that produce fragments. One of these cleavages is the C-terminal cytoplasmic tail (CTT) of PC1, which intervenes in several signaling pathways through nuclear translocation. Recent results show that CTT overexpression in the renal tissues of PKD patients is sufficient to rescue the dorsal body curvature phenotype in zebrafish embryos resulting from suppression of Pkd1 expression, suggesting that CTT is necessary for the physiological functions of kidney morphogenesis. However, the mechanisms of trafficking and protein stability are largely unknown. Here we show that O-linked N-acetylglucosamine (GlcNAc) transferase (OGT) is required for altering CTT protein stability and function. Overexpression of OGT up-regulated the protein stability of CTT through increasing O-GlcNAcylation of CTT, but down-regulated CTT-mediated signaling pathways. Meanwhile, OGT knockdown specifically up-regulated CTT-mediated transcriptional regulation. Treatment of cells with the OGA inhibitor PUGNAc increased OGT activity and altered CTT localization from the cytoplasm to the nucleolus, resulting in decreased CTT-mediated transcriptional regulation. Inhibition of OGA reversed disease progression in the ADPKD mouse model, suggesting that OGA inhibitors may be potential therapeutic agents for ADPKD. Taken together this study not only uncovers a functional posttranslational modification of CTT but also reveals a unique role of OGT in the development of ADPKD.

Arnould T, Kim E, Tsiokas L, Jochimsen F, Grüning W, Chang JD, Walz G. (1992) The polycystic kidney disease 1 gene product mediates protein kinase C alpha-dependent and c-Jun N-terminal kinase-dependent activation of the transcription factor AP-1. J Biol Chem. 273:6013-8.
Butkinaree C, Park K, Hart GW. (2010) O-linked beta-N-acetylglucosamine (O-GlcNAc): extensive crosstalk with phosphorylation to regulate signaling and transcription in response to nutrients and stress. Biochim Biophys Acta. 1800:96-106.
Carone FA, Nakamura S, Bacallao R, Nelson WJ, Khokha M, Kanwar YS. (1995) Impaired tubulogenesis of cyst-derived cells from autosomal dominant polycystic kidneys. Kidney Int. 47:861-8.
Chauvet V, Tian X, Husson H, Grimm DH, Wang T, Hiesberger T, Igarashi P, Bennett AM, Ibraghimov-Beskrovnaya O, Somlo S, Caplan MJ. (2004) Mechanical stimuli induce cleavage and nuclear translocation of the polycystin-1 C terminus. J Clin Invest. 114:1433-43.
Chapin HC, Caplan MJ. (2010) The cell biology of polycystic kidney disease. J Cell Biol. 191:701-10.
Chou TY, Hart GW, Dang CV. (1995) c-Myc is glycosylated at threonine 58 a known phosphorylation site and a mutational hot spot in lymphomas. J Biol Chem. 270:18961-65.
Comer FI, Hart GW. (1999) O-GlcNAc and the control of gene expression. Biochim Biophys Acta. 11473:161-71.
Consortium IPKD. (1995) Polycystic kidney disease: the complete structure of the PKD1 gene and its protein. Cell. 81:289-98.
Ekser B, Rigotti P. (2010) Images in clinical medicine.Autosomal dominant polycystic kidney disease. N Engl J Med. 363:71.
Grantham JJ. (1983) Polycystic kidney disease: a predominance of giant nephrons. Am J Physiol. 244:F3-10.
Gattone VH, Wang X, Harris PC, Torres VE. (2003) Inhibition of renal cystic disease development and progression by a vasopressin V2 receptor antagonist. Nat Med. 9:1323-6.
Hateboer N, v Dijk MA, Bogdanova N, Coto E, Saggar-Malik AK, San Millan JL, Torra R, Breuning M, Ravine D. (1999) Comparison of phenotypes of polycystic kidney disease types 1 and 2. European PKD1-PKD2 Study Group. Lancet. 353:103-7.
Hart GW, Housley MP, Slawson C. (2007) Cycling of O-linked beta-N-acetylglucosamine on nucleocytoplasmic proteins. Nature. 446:1017-22.
Hwang JY, Mangala LS, Fok JY, Lin YG, Merritt WM, Spannuth WA, Nick AM, Fiterman DJ, Vivas-Mejia PE, Deavers MT, Coleman RL, Lopez-Berestein G, Mehta K, Sood AK. (2008) Clinical and biological significance of tissue transglutaminase in ovarian carcinoma. Cancer Res. 68:5849-58.
Huber TB, Walz G, Kuehn EW. (2011) mTOR and rapamycin in the kidney: signaling and therapeutic implications beyond immunosuppression. Kidney Int. 79:502-11.
Ibraghimov-Beskrovnaya O, Natoli TA. (2011) mTOR signaling in polycystic kidney disease. Trends Mol Med. 17:625-33.
Ibraghimov-Beskrovnaya O, Dackowski WR, Foggensteiner L, Coleman N, Thiru S, Petry LR, Burn TC, Connors TD, Van Raay T, Bradley J, Qian F, Onuchic LF, Watnick TJ, Piontek K, Hakim RM, Landes GM, Germino GG, Sandford R, Klinger KW. (1997) Polycystin: in vitro synthesis, in vivo tissue expression, and subcellular localization identifies a large membrane-associated protein. Proc Natl Acad Sci USA. 94:6397-402.
Ibraghimov-Beskrovnaya O, Bukanov N. (2008) Polyctstic kidney diseases: from molecular discoveries to targeted therapeutic strategies. Cell Mol Life Sci. 65:605-19.
Igarashi P, Somlo S. (2002) Genetics and pathogenesis of polycystic kidney disease. J Am Soc Nephrol. 13:2384-98.
Jiang ST, Chiou YY, Wang E, Lin HK, Lin YT, Chi YC, Wang CK, Tang MJ, Li H. (2006) Defining a link with autosomal-dominant polycystic kidney disease in mice with congenitally low expression of Pkd1. Am J Pathol. 168:205-20.
Kim E, Arnould T, Sellin LK, Benzing T, Fan MJ, Grüning W, Sokol SY, Drummond I, Walz G. (1999) The polycystic kidney disease 1 gene product modulates Wnt signaling. J Biol Chem. 274:4947-53.
Korgaonkar C, Hagen J, Tompkins V, Frazier AA, Allamargot C, Quelle FW, Quelle DE. (2005) Nucleophosmin (B23) targets ARF to nucleoli and inhibits its function. Mol Cell Biol. 25:1258-71.
Keith E. Mostov. (2006) mTOR is out of control in polycystic kidney disease. Proc Natl Acad Sci USA. 103:5247-48.
Le NH, van der Wal A, van der Bent P, Lantinga-van Leeuwen IS, Breuning MH, van Dam H, de Heer E, Peters DJ. (2005) Increased activity of activator protein-1 transcription factor components ATF2, c-Jun, and c-Fos in human and mouse autosomal dominant polycystic kidney disease. J Am Soc Nephrol. 16:2724-31.
Love DC, Hanover JA. (2005) The hexosamine signaling pathway: deciphering the“O-GlcNAc code”. Sci STKE. 2005:re13.
Low SH, Vasanth S, Larson CH, Mukherjee S, Sharma N, Kinter MT, Kane ME, Obara T, Weimbs T. (2006) Polycystin-1, STAT6, and P100 function in a pathway that transduces ciliary mechanosensation and is activated in polycystic kidney disease. Dev Cell. 10:57-69.
Merrick D, Chapin H, Baggs JE, Yu Z, Somlo S, Sun Z, Hogenesch JB, Caplan MJ. (2012) The γ-secretase cleavage product of polycystin-1 regulates TCF and CHOP-mediated transcriptional activation through a p300-dependent mechanism. Dev Cell. 22:197-210.
Mochizuki T, Wu G, Hayashi T, Xenophontos SL, Veldhuisen B, Saris JJ, Reynolds DM, Cai Y, Gabow PA, Pierides A, Kimberling WJ, Breuning MH, Deltas CC, Peters DJ, Somlo S. (1996) PKD2, a gene for polycystic kidney disease that encodes an integral membrane protein. Science. 272:1339-42.
Ong AC, Harris PC. (2005) Molecular pathogenesis of ADPKD: the polycystin complex gets complex. Kidney Int. 67:1234-47.
Paweł Jóźwiak, Ewa Forma, Magdalena Bryś, and Anna Krześlak. (2014) O-GlcNAcylation and Metabolic Reprograming in Cancer. Front Endocrinol (Lausanne). 5:145.
Park S, Pak J, Jang I, Cho JW. (2014) Inhibition of mTOR affects protein stability of OGT. Biochem Biophys Res Commun. 453:208-12.
Parnell SC, Magenheimer BS, Maser RL, Zien CA, Frischauf AM, Calvet JP. (2002) Polycystin-1 activation of c-Jun N-terminal kinase and AP-1 is mediated by heterotrimeric G proteins. J Biol Chem. 277:19566-72.
Qin S, Taglienti M, Cai L, Zhou J, Kreidberg JA. (2012) c-Met and NF-κB-dependent overexpression of Wnt7a and -7b and Pax2 promotes cystogenesis in polycystic kidney disease. J Am Soc Nephrol. 23:1309-18.
Rebecca Kelsey. (2013) Tolvaptan in ADPKD—TEMPO3:4 trial results. Nat Rev Nephrol. 9:1.
Ruhee Dere, Patricia D. Wilson, Richard N. Sandford, Cheryl Lyn Walker. (2010) Carboxy Terminal Tail of Polycystin-1 Regulates Localization of TSC2 to Repress mTOR. PLoS One. 5:e9239.
Shafi R, Lyer SP, Ellies LG, O’Donnell N, Marek KW, Chui D. (2000) The O-GlcNAc transferase gene resides on the X chromosome and is essential for embryonic stem cell viability and mouse ontogeny. Proc Natl Acad Sci USA. 97:5735-9.
Shillingford JM, Murcia NS, Larson CH, Low SH, Hedgepeth R, Brown N, Flask CA, Novick AC, Goldfarb DA, Kramer-Zucker A, Walz G, Piontek KB, Germino GG, Weimbs T. (2006) The mTOR pathway is regulated by polycystin-1, and its inhibition reverses renal cystogenesis in polycystic kidney disease. Proc Natl Acad Sci USA. 103:5466-71.
Torres VE, Chapman AB, Devuyst O, Gansevoort RT, Grantham JJ, Higashihara E, Perrone RD, Krasa HB, Ouyang J, Czerwiec FS; TEMPO 3:4 Trial Investigators. (2012) Tolvaptan in patients with autosomal dominant polycystic kidney disease. N Engl J Med. 367: 2407-18.
Trudel M, D'Agati V, Costantini F. (1991) C-myc as an inducer of polycystic kidney disease in transgenic mice. Kidney Int. 39:665-71.
Tapia MA, Gonzalez-Navarrete I, Dalmases A, Bosch M, Rodriguez-Fanjul V, Rolfe M, Ross JS, Mezquita J, Mezquita C, Bachs O, Gascón P, Rojo F, Perona R, Rovira A, Albanell J. (2007) Inhibition of the canonical IKK/NF-κB pathway sensitizes human cancer cells to doxorubicin. Cell Cycle. 6:2284-92.
Torres VE, Harris PC, Pirson Y. (2007) Autosomal dominant polycystic kidney disease. Lancet. 369: 1287-301.
Talbot JJ, Shillingford JM, Vasanth S, Doerr N, Mukherjee S, Kinter MT, Watnick T, Weimbs T. (2011) Polycystin-1 regulates STAT activity by a dual mechanism. Proc Natl Acad Sci U S A. 108:7985-90.
Thomas Weimbs, Erin E.Olsan, and Jeffrey J. Talbot. (2013) Regulation of STATs by polycystin-1 and their role in polycystic kidney disease. JAKSTAT. 2:e23650.
Torres CR, Hart GW. (1984) Topography and polypeptide distribution of terminal N-acetylglucosamine residues on the surfaces of intact lymphocytes, Evidence for O linked GlcNAc. J Biol Chem. 259:3308-17.
Van Keimpema L, Nevens F, Vanslembrouck R, van Oijen MG, Hoffmann AL, Dekker HM, de Man RA, Drenth JP. (2009) Lanreotide reduces the volume of polycystic liver: a randomized, doubleblind, placebo-controlled trial. Gastroenterology. 137:1661-8.
Wang X, Wu Y, Ward CJ, Harris PC, Torres VE. (2008) Vasopressin directly regulates cyst growth in polycystic kidney disease. J Am Soc Nephrol. 19:102-8.
Warner JR. (1990) The nucleolus and ribosome formation. Curr Opin Cell Bio. 2:521-27.
Wilson PD. (2004) Polycystic kidney disease. N Engl J Med. 350:151-64.
Wilson PD, Goilav B. (2007) Cystic disease of the kidney. Annu Rev Pathol. 2:341-68.
Wang X, Wu Y, Ward CJ, Harris PC, Torres VE. (2008) Vasopressin directly regulates cyst growth in polycystic kidney disease. J Am Soc Nephrol. 19:102-8.
Zachara NE. (2012) The roles of O-linked β-N-acetylglucosamine in cardiovascular physiology and disease. Am J Physiol Heart Circ Physiol. 302:H1905-18.
Zachara NE, O’Donnell N, Cheung WD, Mercer JJ, Marth JD, Hart GW. (2004) Dynamic O-GlcNAc modification of nucleocytoplasmic proteins in response to stress. A survival response of mammalian cells. J Biol Chem. 279:30133-42.