Protein phosphatase 4 promotes Hedgehog signaling through dephosphorylation of Suppressor of fused

Hengqing Liao,Bo’Ang Han,Jing Cai,Xiaohong Pu,Tingting Yu,Longyan Shen,Steven Y Cheng,Chen Liu,Yixing Yao,Shen Yue

doi:10.1038/s41419-020-02843-w

Abstract

Reversible phosphorylation of Suppressor of fused (Sufu) is essential for Sonic Hedgehog (Shh) signal transduction. Sufu is stabilized under dual phosphorylation of protein kinase A (PKA) and glycogen synthase kinase 3β (GSK3β). Its phosphorylation is reduced with the activation of Shh signaling. However, the phosphatase in this reversible phosphorylation has not been found. Taking advantage of a proteomic approach, we identified Protein phosphatase 4 regulatory subunit 2 (Ppp4r2), an interacting protein of Sufu. Shh signaling promotes the interaction of these two proteins in the nucleus, and Ppp4 also promotes dephosphorylation of Sufu, leading to its degradation and enhancing the Gli1 transcriptional activity. Finally, Ppp4-mediated dephosphorylation of Sufu promotes proliferation of medulloblastoma tumor cells, and expression of Ppp4 is positively correlated with up-regulation of Shh pathway target genes in the Shh-subtype medulloblastoma, underscoring the important role of this regulation in Shh signaling.

Highlights

Introduction SonicHedgehog (Shh) is an essential morphogenic and mitogenic factor that plays a key role in embryonic development and postnatal physiological processes[1,2], regulating cell proliferation, differentiation, and patterning
We show Protein phosphatase 4 regulatory subunit 2 (Ppp4r2) contributes to the dephosphorylation and turnover of Suppressor of fused (Sufu) upon Sonic Hedgehog (Shh) signaling, and promotes the proliferation of SHH-subtype medulloblastoma (MB) cells through modulating Sufu repressor activity
Sufu is regulated in Shh signaling, we used liquid chromatography-tandem mass spectrometry to identify Sufu-interacting proteins in NIH3T3 cells, which are sensitive to the stimulation by Shh ligands

Summary

Introduction

Hedgehog (Shh) is an essential morphogenic and mitogenic factor that plays a key role in embryonic development and postnatal physiological processes[1,2], regulating cell proliferation, differentiation, and patterning. Aberrant activation of Shh signaling can lead to hyper-proliferation and the development of malignancies[3,4]. A comprehensive understanding of the regulatory mechanisms of Shh signaling is essential for us to understand development as well as disease process. In the absence of Shh signal, Gli[1] is not transcribed, and Gli2/3 proteins are proteolytically processed into C-terminally truncated repressors (GliR), shutting off target gene expression. Activation of Shh signaling abrogates Gli processing, allowing full-length activators (GliA) to turn on target gene expression in the nucleus. Gli[1] activator is transcribed as a Shh target gene, and autoregulates itself in a feed-forward loop. The output of Shh signal is determined by the ratio of GliA and GliR as the Gli code[14]

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Conclusion