Hedgehog signaling drives medulloblastoma growth via CDK6
David R. Raleigh, … , Nicole Santos, Jeremy F. Reiter
David R. Raleigh, … , Nicole Santos, Jeremy F. Reiter
Published November 20, 2017
Citation Information: J Clin Invest. 2018;128(1):120-124. https://doi.org/10.1172/JCI92710.
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Hedgehog signaling drives medulloblastoma growth via CDK6

Abstract

Medulloblastoma, an aggressive cancer of the cerebellum, is among the most common pediatric brain tumors. Approximately one-third of medulloblastomas are associated with misactivation of the Hedgehog (Hh) pathway. GLI family zinc finger 2 (GLI2) coordinates the Hh transcriptional program; however, the GLI2 targets that promote cancer cell proliferation are unknown. Here, we incorporated a Gli2-EGFP allele into 2 different genetic mouse models of Hh-associated medulloblastoma. Hh signaling induced GLI2 binding to the Cdk6 promoter and activated Cdk6 expression, thereby promoting uncontrolled cell proliferation. Genetic or pharmacological inhibition of CDK6 in mice repressed the growth of Hh-associated medulloblastoma and prolonged survival through inhibition of cell proliferation. In human medulloblastoma, misactivation of Hh signaling was associated with high levels of CDK6, pointing to CDK6 as a direct transcriptional target of the Hh pathway. These results suggest that CDK6 antagonists may be a promising therapeutic approach for Hh-associated medulloblastoma in humans.

Authors

David R. Raleigh, Pervinder K. Choksi, Alexis Leigh Krup, Wasima Mayer, Nicole Santos, Jeremy F. Reiter

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Figure 2

GLI2 binds the Cdk6 promoter to activate gene expression.

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GLI2 binds the Cdk6 promoter to activate gene expression. (A) qRT-PCR of...
(A) qRT-PCR of NIH/3T3 cells treated vehicle (gray), SAG alone (green) or in combination with the translation inhibitor cycloheximide (black). *P < 0.02, t test. n = 3, representative of 3 experiments. (B) Schematic of Cdk6 promoter showing putative GLI-binding sites. (C) EGFP ChIP-qPCR from 3 Math1-Cre SmoM2c Gli2-EGFP tumors (blue) and 3 age- and sex-matched SmoM2c Gli2-EGFP littermate cerebella (gray). *P < 0.03, t test. Representative of 3 experiments. (D) Histone ChIP-qPCR from 3 Math1-Cre SmoM2c tumors (aqua) and 3 age- and sex-matched SmoM2c littermate control cerebella (gray). *P < 0.002, t test. Representative of 2 experiments. (E) EGFP ChIP-qPCR from NIH/3T3 cells stably expressing GLI2-EGFP treated with vehicle (gray), SAG alone (green), or SAG in combination with the SMO inhibitor vismodegib (black). *P < 0.008, t test. n = 3, representative of 3 experiments. (F) Activity of the Cdk6 promoter luciferase reporter in NIH/3T3 cells treated with vehicle (gray) or SAG (green). SAG activates the Cdk6 promoter extending from GLI2-binding site 1 to the transcriptional start site (1-Start) or from site 4 to the transcriptional start site (4-Start), but not from site 1 to site 3 (s1–3). *P < 0.01, t test. n = 3, representative of 3 experiments. (G) Activity of the Cdk6 promoter luciferase reporter in NIH/3T3 cells cotransfected with control vector (gray) or a constitutively active GLI2-CLEG plasmid (green). *P < 0.02, t test. n = 3, representative of 2 experiments. (H) Activity of the Cdk6 promotor luciferase reporter in NIH/3T3 cells cotransfected with control vector (gray) or GLI2-CLEG (green) shows GLI2-CLEG activates gene expression from 3 copies of the Cdk6 promoter site 4, but not from 3 tandem mutant copies. *P < 0.001, t test. n = 3, representative of 3 experiments.