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Montagnani V, Stecca B. Role of Protein Kinases in Hedgehog Pathway Control and Implications for Cancer Therapy. Cancers (Basel) 2019; 11:cancers11040449. [PMID: 30934935 PMCID: PMC6520855 DOI: 10.3390/cancers11040449] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 03/20/2019] [Accepted: 03/26/2019] [Indexed: 02/08/2023] Open
Abstract
Hedgehog (HH) signaling is an evolutionarily conserved pathway that is crucial for growth and tissue patterning during embryonic development. It is mostly quiescent in the adult, where it regulates tissue homeostasis and stem cell behavior. Aberrant reactivation of HH signaling has been associated to several types of cancer, including those in the skin, brain, prostate, breast and hematological malignancies. Activation of the canonical HH signaling is triggered by binding of HH ligand to the twelve-transmembrane protein PATCHED. The binding releases the inhibition of the seven-transmembrane protein SMOOTHENED (SMO), leading to its phosphorylation and activation. Hence, SMO activates the transcriptional effectors of the HH signaling, that belong to the GLI family of transcription factors, acting through a not completely elucidated intracellular signaling cascade. Work from the last few years has shown that protein kinases phosphorylate several core components of the HH signaling, including SMO and the three GLI proteins, acting as powerful regulatory mechanisms to fine tune HH signaling activities. In this review, we will focus on the mechanistic influence of protein kinases on HH signaling transduction. We will also discuss the functional consequences of this regulation and the possible implications for cancer therapy.
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Affiliation(s)
- Valentina Montagnani
- Core Research Laboratory⁻Institute for Cancer Research, Prevention and Clinical Network (ISPRO), 50139 Florence, Italy.
| | - Barbara Stecca
- Core Research Laboratory⁻Institute for Cancer Research, Prevention and Clinical Network (ISPRO), 50139 Florence, Italy.
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Praktiknjo SD, Saad F, Maier D, Ip P, Hipfner DR. Activation of Smoothened in the Hedgehog pathway unexpectedly increases Gα s-dependent cAMP levels in Drosophila. J Biol Chem 2018; 293:13496-13508. [PMID: 30018136 DOI: 10.1074/jbc.ra118.001953] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 07/13/2018] [Indexed: 12/28/2022] Open
Abstract
Hedgehog (Hh) signaling plays a key role in the development and maintenance of animal tissues. This signaling is mediated by the atypical G protein-coupled receptor (GPCR) Smoothened (Smo). Smo activation leads to signaling through several well-characterized effectors to activate Hh target gene expression. Recent studies have implicated activation of the heterotrimeric G protein subunit Gαi and the subsequent decrease in cellular cAMP levels in promoting the Hh response in flies and mammals. Although Hh stimulation decreases cAMP levels in some insect cell lines, here using a bioluminescence resonance energy transfer (BRET)-based assay we found that this stimulation had no detectable effect in Drosophila S2-R+ cells. However, we observed an unexpected and significant Gαs-dependent increase in cAMP levels in response to strong Smo activation in Smo-transfected cells. This effect was mediated by Smo's broadly conserved core, and was specifically activated in response to phosphorylation of the Smo C-terminus by GPCR kinase 2 (Gprk2). Genetic analysis of heterotrimeric G protein function in the developing Drosophila wing revealed a positive role for cAMP in the endogenous Hh response. Specifically, we found that mutation or depletion of Gαs diminished low-threshold Hh responses in Drosophila, whereas depletion of Gαi potentiated them (in contrast to previous findings). Our analysis suggested that regulated cAMP production is important for controlling the sensitivity of cellular responses to Hh in Drosophila.
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Affiliation(s)
- Samantha D Praktiknjo
- From the Institut de recherches cliniques de Montréal, Montreal, Quebec H2W 1R7.,the Departments of Anatomy and Cell Biology and
| | - Farah Saad
- From the Institut de recherches cliniques de Montréal, Montreal, Quebec H2W 1R7.,Biology, McGill University, Montreal, Quebec H3A 0C7, and
| | - Dominic Maier
- From the Institut de recherches cliniques de Montréal, Montreal, Quebec H2W 1R7.,the Departments of Anatomy and Cell Biology and
| | - Pamela Ip
- From the Institut de recherches cliniques de Montréal, Montreal, Quebec H2W 1R7.,the Departments of Anatomy and Cell Biology and
| | - David R Hipfner
- From the Institut de recherches cliniques de Montréal, Montreal, Quebec H2W 1R7, .,the Departments of Anatomy and Cell Biology and.,Biology, McGill University, Montreal, Quebec H3A 0C7, and.,the Département de médecine, Université de Montréal, Montreal, Quebec H3C 3J7, Canada
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Sanial M, Bécam I, Hofmann L, Behague J, Argüelles C, Gourhand V, Bruzzone L, Holmgren RA, Plessis A. Dose-dependent transduction of Hedgehog relies on phosphorylation-based feedback between the G-protein-coupled receptor Smoothened and the kinase Fused. Development 2017; 144:1841-1850. [PMID: 28360132 DOI: 10.1242/dev.144782] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Accepted: 03/20/2017] [Indexed: 12/28/2022]
Abstract
Smoothened (SMO) is a G-protein-coupled receptor-related protein required for the transduction of Hedgehog (HH). The HH gradient leads to graded phosphorylation of SMO, mainly by the PKA and CKI kinases. How thresholds in HH morphogen regulate SMO to promote switch-like transcriptional responses is a central unsolved issue. Using the wing imaginal disc model in Drosophila, we identified new SMO phosphosites that enhance the effects of the PKA/CKI kinases on SMO accumulation, its localization at the plasma membrane and its activity. Surprisingly, phosphorylation at these sites is induced by the kinase Fused (FU), a known downstream effector of SMO. In turn, activation of SMO induces FU to act on its downstream targets. Overall, our data provide evidence for a SMO/FU positive regulatory loop nested within a multikinase phosphorylation cascade. We propose that this complex interplay amplifies signaling above a threshold that allows high HH signaling.
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Affiliation(s)
- Matthieu Sanial
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris F-75205, France
| | - Isabelle Bécam
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris F-75205, France
| | - Line Hofmann
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris F-75205, France
| | - Julien Behague
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris F-75205, France
| | - Camilla Argüelles
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris F-75205, France
| | - Vanessa Gourhand
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris F-75205, France
| | - Lucia Bruzzone
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris F-75205, France
| | - Robert A Holmgren
- Department of Molecular Bioscience, Northwestern University, Evanston, IL 60208-3500, USA
| | - Anne Plessis
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris F-75205, France
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