Activation of the mTOR signaling pathway in renal clear cell carcinoma.
OBJECTIVE
We determined the frequency of mTOR/p70S6 kinase signaling pathway activation in clear cell renal cell carcinoma.


METHODS
Phospho-S6 (Ser235/236) and phospho-mTOR (Ser2448) staining was performed on renal tumor tissue microarrays containing 29 clear cell renal cell carcinomas. Mutational analysis of Rheb and RhebL1 was performed on DNA from phospho-mTOR/phospho-S6 positive clear cell renal cell carcinoma. The 3 clear cell renal cell carcinoma derived cell lines A498, 786-O and Caki1 were also assessed for mTOR activation and the effect of the mTOR inhibitor rapamycin (Biomol) on proliferation.


RESULTS
Moderate or strong phospho-S6 immunoreactivity was found in 17 of 29 clear cell carcinomas (59%), of which 14 were also moderately/strongly positive for phospho-mTOR (Ser2448). We hypothesized that this activation of the mTOR signaling pathway in clear cell renal cell carcinoma could reflect mutational activation of Rheb or RhebL1, which are Ras family members that directly activate mTOR. However, no mutations in exons 3 and 4 (homologous sites of Ras activating mutations) in Rheb or RhebL1 were identified. Two of 3 renal clear cell carcinoma derived cell lines also showed inappropriate S6 hyperphosphorylation. Treatment of all 3 cell lines with rapamycin significantly decreased S6 phosphorylation and proliferation.


CONCLUSIONS
The mTOR/p70S6 kinase signaling pathway is activated in most clear cell renal cell carcinomas. Moreover, the growth of renal clear cell carcinoma derived cell lines is inhibited by rapamycin. This is especially significant in light of new agents such as CCI-779, an ester of rapamycin and inhibitor of mTOR, which has shown promise in the treatment of renal carcinoma.
Robb
Victoria A
VA
Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Karbowniczek
Magdalena
M
Klein-Szanto
Andres J
AJ
Henske
Elizabeth P
EP
D002292:Carcinoma, Renal Cell / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D007150:Immunohistochemistry; D007680:Kidney Neoplasms / Q000737:chemistry* / Q000235:genetics; D011494:Protein Kinases / Q000032:analysis* / Q000235:genetics / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases; D014407:Tumor Cells, Cultured
D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases