WIP1 phosphatase modulates the Hedgehog signaling by enhancing GLI1 function

Area of Science:

• Oncology
• Molecular Biology
• Cell Signaling

Background:

• The Hedgehog-GLI (HH-GLI) signaling pathway is crucial for embryonic development and implicated in human cancers.
• GLI transcription factors are key effectors of HH-GLI signaling, with their activity regulated by phosphorylation.
• WIP1 (PPM1D) is an oncogenic phosphatase found amplified or overexpressed in various human cancers.

Purpose of the Study:

• To investigate the role of WIP1 phosphatase in regulating the Hedgehog-GLI signaling pathway.
• To elucidate the mechanism by which WIP1 affects GLI transcription factors.
• To evaluate the therapeutic potential of targeting WIP1 in combination with HH pathway inhibitors for cancer treatment.

Main Methods:

• Assessed WIP1's effect on GLI1, GLI2, and GLI3 transcriptional activity, nuclear localization, and protein stability.
• Investigated the physical interaction between WIP1 and GLI1 using co-immunoprecipitation.
• Evaluated the functional role of WIP1 in cancer cell proliferation, self-renewal, and tumor growth in vitro and in vivo.
• Tested the synergistic effect of WIP1 inhibition and cyclopamine (SMO antagonist) on cancer cell growth.

Main Results:

• WIP1 positively modulates HH signaling by enhancing GLI1 activity, stability, and nuclear localization, but not GLI2 or GLI3.
• WIP1 and GLI1 form a complex, and WIP1's modulation of GLI1 activity requires its phosphatase function, independent of p53.
• WIP1 is essential for melanoma and breast cancer cell proliferation and self-renewal, and for melanoma xenograft growth.
• Pharmacological blockade of the HH pathway synergizes with WIP1 inhibition to reduce cancer cell growth.

Conclusions:

• WIP1 acts as a positive regulator of GLI1, promoting cancer cell proliferation and self-renewal in HH-activated cancers.
• Targeting WIP1 in combination with HH pathway inhibitors presents a promising therapeutic strategy for melanomas and other relevant cancers.