WIP1 phosphatase modulates the Hedgehog signaling by enhancing GLI1 function

Abstract

The Hedgehog-GLI (HH-GLI) signaling plays a critical role in controlling growth and tissue patterning during embryogenesis and is implicated in a variety of human malignancies, including those of the skin. Phosphorylation events have been shown to regulate the activity of the GLI transcription factors, the final effectors of the HH-GLI signaling pathway. Here, we show that WIP1 (or PPM1D), an oncogenic phosphatase amplified/overexpressed in several types of human cancer, is a positive modulator of the HH signaling. Mechanistically, WIP1 enhances the function of GLI1 by increasing its transcriptional activity, nuclear localization and protein stability, but not of GLI2 nor GLI3. We also find that WIP1 and GLI1 are in a complex. Modulation of the transcriptional activity of GLI1 by WIP1 depends on the latter's phosphatase activity and, remarkably, does not require p53, a known WIP1 target. Functionally, we find that WIP1 is required for melanoma and breast cancer cell proliferation and self-renewal in vitro and melanoma xenograft growth induced by activation of the HH signaling. Pharmacological blockade of the HH pathway with the SMOOTHENED antagonist cyclopamine acts synergistically with inhibition of WIP1 in reducing growth of melanoma and breast cancer cells in vitro. Overall, our data uncover a role for WIP1 in modulating the activity of GLI1 and in sustaining cancer cell growth and cancer stem cell self-renewal induced by activation of the HH pathway. These findings open a novel therapeutic approach for human melanomas and, possibly, other cancer types expressing WIP1 and with activated HH pathway.

Forkhead Box M1 Is Essential for Nuclear Localization of Glioma-associated Oncogene Homolog 1 in Glioblastoma Multiforme Cells by Promoting Importin-7 Expression

“…Specific knockdown of IPO7 expression using siRNA resulted in reduced nuclear accumulation of GLI1, indicating the dependence of nuclear import of GLI1 on IPO7. Previous studies demonstrated that several molecules may affect nuclear localization of GLI1 (22)(23)(24)(25). For example, nuclear entry of GLI1 was regulated by its nuclear import factor Imp␤1 (importin ␤1) and SuFu (22); WIP1 (or PPM1D) enhanced the function of GLI1 by increasing its nuclear localization (23); Rab23 reduced the (24); and SHP (small heterodimer partner) inhibited GLI1 nuclear localization (25).…”

Akt confers cisplatin chemoresistance in human gynecological carcinoma cells by modulating PPM1D stability

“…PPM1D may also contribute to malignancy and metastasis. In this regard, it has recently been demonstrated that PPM1D promotes the stabilization of Gli1, a transcription factor known to promote the expression of proteins involved in stemness and epithelial to mesenchymal transition (EMT) [59]. While the staining intensity of PPM1D in chemonaive tumors in this study did not predict PFS, it should be noted that the baseline levels of PPM1D in chemosensitive and chemoresistant cell lines are not different, and it is the differential response to CDDP that appears to be important.…”

“…The experiment was conducted as previously described [59]. A2780cp cells were infected with adeno-DN-Akt (MOI ¼ 80; 24 h) or adeno-LacZ as a control, then incubated with leucine-deficient RPMI1640 media supplemented with dialyzed FBS (24 h).…”

Tug of War between Survival and Death: Exploring ATM Function in Cancer

“…The first hint comes from the identification of GLI-1 as a substrate of ITCH [109,110] and from the observation that ATM modulates ITCH [65]. A second hint comes from the observation that WIP1, a Ser/Thr phosphatase aberrantly upregulated in cancer that dephosphorylates and modulates, among other targets, also ATM activity [111], is involved in the modulation of the SHH signaling [112]. It has been proposed that during tumorigenesis WIP1 (wild-type p53-induced phosphatase 1) overexpression might contribute to increase proliferative and self-renewing activities of GLI-1, therefore enabling an expansion of cancer stem cells and derived progenitors that sustain tumor growth [112].…”