Sprouty2, PTEN, and PP2A interact to regulate prostate cancer progression
Rachana Patel, … , Owen J. Sansom, Hing Y. Leung
Rachana Patel, … , Owen J. Sansom, Hing Y. Leung
Published February 22, 2013
Citation Information: J Clin Invest. 2013;123(3):1157-1175. https://doi.org/10.1172/JCI63672.
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Research Article Oncology

Sprouty2, PTEN, and PP2A interact to regulate prostate cancer progression

Abstract

Concurrent activation of RAS/ERK and PI3K/AKT pathways is implicated in prostate cancer progression. The negative regulators of these pathways, including sprouty2 (SPRY2), protein phosphatase 2A (PP2A), and phosphatase and tensin homolog (PTEN), are commonly inactivated in prostate cancer. The molecular basis of cooperation between these genetic alterations is unknown. Here, we show that SPRY2 deficiency alone triggers activation of AKT and ERK, but this is insufficient to drive tumorigenesis. In addition to AKT and ERK activation, SPRY2 loss also activates a PP2A-dependent tumor suppressor checkpoint. Mechanistically, the PP2A-mediated growth arrest depends on GSK3β and is ultimately mediated by nuclear PTEN. In murine prostate cancer models, Pten haploinsufficiency synergized with Spry2 deficiency to drive tumorigenesis, including metastasis. Together, these results show that loss of Pten cooperates with Spry2 deficiency by bypassing a novel tumor suppressor checkpoint. Furthermore, loss of SPRY2 expression correlates strongly with loss of PTEN and/or PP2A subunits in human prostate cancer. This underlines the cooperation between SPRY2 deficiency and PTEN or PP2A inactivation in promoting tumorigenesis. Overall, we propose SPRY2, PTEN, and PP2A status as an important determinant of prostate cancer progression. Characterization of this trio may facilitate patient stratification for targeted therapies and chemopreventive interventions.

Authors

Rachana Patel, Meiling Gao, Imran Ahmad, Janis Fleming, Lukram B. Singh, Taranjit Singh Rai, Arthur B. McKie, Morag Seywright, Robert J. Barnetson, Joanne Edwards, Owen J. Sansom, Hing Y. Leung

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Figure 9

PP2A activation suppresses tumorigenesis by increasing nuclear localization of PTEN.

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PP2A activation suppresses tumorigenesis by increasing nuclear localizat...
(A) DU145 cells infected with control and PP2A-A–expressing viruses were treated with GSK3B siRNA for 24 hours and analyzed by Western blot and WST-1 assay for measuring cell proliferation (*P < 0.01; n = 3). (B) Representative immunofluorescence images of PP2A-A–expressing DU145 cells treated with GSK3B siRNA for 24 hours and stained for PTEN. Scale bars: 50 μm. (C) Western blot analysis of DU145 SPRY2 KD clones with stable expression of constitutively active GSK3B (S9A) treated with 5 nmol PP2A-A siRNA for 42 hours. (D) DU145 and MEF cells treated with 0.2 μM okadaic acid or 10 μM FTY720 for 12 hours were quantified for percentage of G1 cells (*P < 0.01; n = 3). (E) Representative images and PP2A activity measurement in s.c. xenografts of DU145 cells in nude mice treated with PP2A activator FTY720 (10 mg/kg/d i.p. injection) for 5 days. (*P < 0.01; n = 5). (F) Representative images and tumor burden of s.c. injected DU145 cells in nude mice treated as indicated. Red line indicates schedule of FTY720 treatment (10 mg/kg/d i.p. injection). (G) Representative IHC images and quantification of Ki67 (white), PTEN (gray), and p21 (blue) in DU145 s.c. xenografts treated as above. Scale bars: 50 μm. Box and whisker plots (E and G) show median (lines within boxes), interquartile range (bounds of boxes), and upper and lower range (whiskers). The values of Western blot represent relative immunoreactivity of each protein normalized to respective loading control. Data are presented as mean ± SEM and analyzed by Mann-Whitney test (A and D–F).