Abstract 5046: Protein tyrosine phosphatase epsilon (PTPE), a candidate tumor-suppressor in Wilms tumors of childhood, can regulate PI3K/AKT/mTOR pathway.
Authors: Shukla Abhay A. , Khokhar Shama , Amatruda James F. , Rakheja Dinesh 
Published: August 2014

Wilms Tumor is the most common pediatric cancer of the genitourinary tract. It is a primitive multilineage malignant neoplasm of embryonic renal precursor cells and is often associated with persistent foci of embryonic renal tissue known as Nephrogenic Rests. However, early molecular events that orchestrate the progression of Nephrogenic Rests to Wilms Tumor are unknown. Protein tyrosine phosphorylation, a critical regulator of signaling pathways, is a reversible process controlled by the opposing activities of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). The possible role of PTPs in Wilms Tumor has not been explored. Through immunohistochemical (IHC) analysis of tissue microarrays containing Wilms Tumors, Nephrogenic Rests, and normal kidney, we have identified downregulation of protein tyrosine phosphatase epsilon (PTPE) as a potential early event in Wilms tumorigenesis. IHC results showed strong staining for PTPE in 6 of 6 (100%) Nephrogenic Rests. In contrast, of the 51 Wilms Tumors studied, PTPE staining was absent in 2 (4%), weak in 26 (51%), moderate in 16 (31%), and strong in 7 (14%) compared to normal renal cortex. In addition, quantitative reverse-transcription PCR showed decreased PTPE expression in Wilms Tumor tissues compared to normal renal cortex. To identify potential targets of PTPE, we performed phosphokinase arrays and demonstrated that overexpression of PTPE in HEK293 cells results in dephosphorylation of Focal adhesion kinase (FAK), Lymphocyte-specific protein tyrosine kinase (LCK), and Gardner-Rasheed feline sarcoma viral (v-fgr) oncogene homolog (FGR). To validate the relevance of PTPE in Wilms Tumors, we established primary tumor cultures from nephrectomy specimens of children undergoing treatment for Wilms Tumor. Consistent with our IHC data, these primary cultures exhibit varying levels of PTPE expression. We have extended our results in these primary Wilms Tumor cells and found that overexpression of PTPE leads to dephosphorylation of FAK and LCK. We also probed downstream effector pathways and found that PTPE overexpression leads to dephosphorylation and inactivation of AKT (T308 and S375) and mTOR (S2448). Collectively, these PTPE targets have been established to control essential functions like cell proliferation, adhesion, and migration. In light of our results, we suggest that PTPE is a putative tumor suppressor in Wilms Tumor, acting to control signaling through FAK, LCK, and other SRC family proteins, as well as the PI3K/AKT/mTOR pathway. These results establish the utility of primary Wilms Tumor culture models, and provide the rationale for exploring SRC family kinase and AKT/mTOR pathway inhibitors as novel targeted agents for the treatment of Wilms Tumor.

Citation Format: Abhay A. Shukla, Shama Khokhar, James F. Amatruda, Dinesh Rakheja. Protein tyrosine phosphatase epsilon (PTPE), a candidate tumor-suppressor in Wilms tumors of childhood, can regulate PI3K/AKT/mTOR pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5046. doi:10.1158/1538-7445.AM2013-5046