Rictor-dependent AKT activation and inhibition of urothelial carcinoma by rapamycin.
OBJECTIVE
We previously reported a very high cumulative incidence of urothelial carcinoma in Taiwanese kidney transplant recipients. Rapamycin, the inhibitor of mTOR Complex 1, provides alternative immunosuppressive therapy after kidney transplantation with less neoplastic potential. We examined the in vivo and in vitro effects of rapamycin on urothelial carcinoma.


METHODS
The rat model of urothelial carcinoma was induced by 0.05% N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) in Fischer F344 rats. The anti-tumor effect of rapamycin was assessed grossly, microscopically, and by Western blot analysis. The mechanism of rapamycin's attenuation of urothelial carcinoma was also evaluated by T24 cells.


RESULTS
Rapamycin significantly reduced urinary bladder tumor growth in the rat model of 0.05% BBN-induced urothelial carcinoma (P < 0.001). The blood trough levels of rapamycin were correlated with the occurrence of urothelial carcinoma. In vitro, rapamycin also inhibited the cell proliferation, migration, and invasion, as well as the protein expression of vascular endothelial growth factor-A of T24 urothelial carcinoma cells, whereas rapamycin did not induce significant apoptosis in T24 cells. Rapamycin decreased the expression of phospho-mTOR, phospho-S6K, cyclin D1, and VEGF-A. Rapamycin also activated AKT in T24 cells in the rat model of urothelial carcinoma. The rapamycin-associated activation of AKT was inhibited by rictor siRNA, but not raptor siRNA.


CONCLUSIONS
This study provides in vitro and in vivo evidence that rapamycin may inhibit the development of urothelial carcinoma. The present findings also suggest rictor-dependent AKT activation as a consequence of mTORC1 inhibition.
Wu
Ming-Ju
MJ
Division of Nephrology, Taichung Veterans General Hospital, Taichung, Taiwan. wmj530@gmail.com
Chang
Chi-Hao
CH
Chiu
Yung-Tsung
YT
Wen
Mei-Chin
MC
Shu
Kuo-Hsiung
KH
Li
Jian-Ri
JR
Chiu
Kun-Yuan
KY
Chen
Yen-Ta
YT
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002295:Carcinoma, Transitional Cell / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D002352:Carrier Proteins / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D004195:Disease Models, Animal; D004789:Enzyme Activation; D007150:Immunohistochemistry; D008297:Male; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D051381:Rats; D011916:Rats, Inbred F344; D020123:Sirolimus / Q000494:pharmacology*; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology
D000903:Antibiotics, Antineoplastic; D002352:Carrier Proteins; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; C550254:rictor protein, rat; D051057:Proto-Oncogene Proteins c-akt; D020123:Sirolimus