Cytoplasmic sequestration of p27 via AKT phosphorylation in renal cell carcinoma.
OBJECTIVE
p27 localization and expression has prognostic and predictive value in cancer. Little is known regarding expression patterns of p27 in renal cell carcinoma (RCC) or how p27 participates in disease progression or response to therapy.


METHODS
RCC-derived cell lines, primary tumors, and normal renal epithelial cells were analyzed for p27 expression, phosphorylation (T157 of the NLS), and subcellular localization. RCC-derived cell lines were treated with phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitors and effects on p27 localization were assessed. The potential contribution of cytoplasmic p27 to resistance to apoptosis was also evaluated.


RESULTS
p27 was elevated in tumors compared with matched controls, and cytoplasmic mislocalization of p27 was associated with increasing tumor grade. Cytoplasmic localization of p27 correlated with phosphorylation at T157, an AKT phosphorylation site in the p27 NLS. In RCC cell lines, activated PI3K/AKT signaling was accompanied by mislocalization of p27. AKT activation and phosphorylation of p27 was associated with resistance to apoptosis, and small interfering RNA knockdown of p27 or relocalization to the nucleus increased apoptosis in RCC cells. Treatment with the PI3K inhibitors LY294002 or wortmannin resulted in nuclear relocalization of p27, whereas mTOR inhibition by rapamycin did not.


CONCLUSIONS
In RCC, p27 is phosphorylated at T157 of the NLS, with increasing tumor grade associated with cytoplasmic p27. PI3K inhibition (which reduces AKT activity) reduces T157 phosphorylation and induces nuclear relocalization of p27, whereas mTOR inhibition does not. Clinical testing of these findings may provide a rational approach for use of mTOR and PI3K/AKT pathway inhibitors in patients with RCC.
Kim
Jinhee
J
Department of Carcinogenesis, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, USA.
Jonasch
Eric
E
Alexander
Angela
A
Short
John D
JD
Cai
Shengli
S
Wen
Sijin
S
Tsavachidou
Dimitra
D
Tamboli
Pheroze
P
Czerniak
Bogdan A
BA
Do
Kim Anh
KA
Wu
Kevin J
KJ
Marlow
Laura A
LA
Wood
Christopher G
CG
Copland
John A
JA
Walker
Cheryl Lyn
CL
D002292:Carcinoma, Renal Cell / Q000378:metabolism*; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000378:metabolism*; D006801:Humans; D007680:Kidney Neoplasms / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
D000081082:Phosphoinositide-3 Kinase Inhibitors; D018809:Proliferating Cell Nuclear Antigen; D034741:RNA, Small Interfering; C413374:p27 antigen; D011494:Protein Kinases; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases