Phosphorylated Mammalian Target of Rapamycin Is Upregulated in Both Cytoplasm and Nuclei along Cystic Epithelium of Adult Type Polycystic Kidney Disease
PL Zhang, RE Brown, SK Hicks, W Li. William Beaumont Hospital, Royal Oak, MI; University of Texas Health Science Center, Houston, TX
Background: Mammalian target of rapamycin pathway (mTOR) is a dominant growth pathway in development of polycystic kidney disease (PKD) in both animal models and human adults, since the mutated polycystin-1 gene activated this pathway (PNAS 2006; 103:5466-5471). It is known that phosphorylated form of mTOR complexes with either raptor (to form mTORC1 for activating its downstream signals p70S6K and elF4E to stimulate cell proliferation) or rictor (to form mTORC2, a rapamycin-insensitive complex, for mediating its downstream targets including PKCα). mTORC1 mainly stays in the cytoplasm and mTORC2 is chiefly located in nuclei. In this study, we stained p-mTOR and one of its main down stream signals p-p70S6K in adult type PKD (autosomal dominant) and compared the stain intensity with unremarkable renal tubules.
Design: 10 cases of human adult type of PKD and 10 cases of unremarkable renal parenchyma (from nephrectomy for tumors) were stained for p-mTOR (Ser 2448) and p-p70S6K (Thr 389) (from Cell Signaling Technology), using a Dako Autostainer. Chromogenic cytoplasmic and nuclear staining was assessed and categorized into four grades: 0 (background), 1+ (weak), 2+ (moderate), or 3+ (strong) based on intensity of staining.
Results: In our recent study, we found that all cystic lining stained positively for cytokeratin 7, confirming that the cystic lining of PKD was originated from the distal nephron tubules. In all cases (10/10) of the current study, p-mTOR showed strong (3+) staining in both nuclear and cytoplasmic cellular compartments of both residual distal nephron tubules and cystic lining compared to moderate (2+) cytoplasmic staining of p-mTOR in the normal distal nephron tubules without significant nuclear staining. However, the p-p70S6K showed moderate (2+) nuclear intensity in approximal 50% of cystic lining, similar to the distal nephron tubular epithelium.
Conclusions: In the cystic epithelium and residual distal nephron tubules of PKD, upregulated p-mTOR in both cytoplasm and nuclei may enhance formation of both mTORC1 and mTORC2 . Unchanged expression of p-p70S6K of mTORC1 branch in cystic epithelium implies that p-p70S6K may only partially contribute to cystic formation, whereas the other branch of mTORC1 via elF4E is still under investigation. In contrast, mTORC2 branch may play a major role in the cystic formation of PKD.
Category: Kidney (does not include tumors)
Wednesday, March 24, 2010 1:00 PM
Poster Session VI # 255, Wednesday Afternoon