Cytoplasmic Cyclin D1 regulates glioblastoma dissemination

Abstract

Glioblastoma (GBM) is a highly invasive brain neoplasia with an elevated recurrence rate after surgical resection. The CyclinD1 (Ccnd1)/Cdk4-RB1 axis is frequently altered in GBM, leading to over-proliferation by RB1 deletion or by Ccnd1/Cdk4 over-activation. By not so well understood mechanisms, high levels of Ccnd1-Cdk4 also promote GBM cell invasion. The purpose of this work is to elucidate the in vivo role of cytoplasmic Ccnd1-Cdk4 activity in the dissemination of GBM. We show that Ccnd1 activates invasion of primary human GBM cells through cytoplasmic RB1-independent mechanisms. By using GBM mouse models, we observed that evaded GBM cells showed cytoplasmic Ccnd1 co-localizing with regulators of cell invasion such as RalA and Paxillin. Our genetic data strongly suggest that, in GBM cells, the Ccnd1/Cdk4 complex is acting upstream of those regulators. Accordingly, expression of Ccnd1 induces FAK, RalA and Rac1 activities. Finally, in vivo experiments demonstrated increased GBM dissemination after expression of membrane-targeted Ccnd1. We conclude that Ccnd1-Cdk4 activity promotes GBM dissemination through cytoplasmic and RB1-independent mechanisms. Therefore, inhibition of Ccnd1-Cdk4 activity may be useful to hinder dissemination of recurrent GBM.

We thank Sonia Rius, Marta Rafel, Laura Colas, Ana Velasco and Maria Ruiz (IRBLleida-Biobank) for technical assistance, and Maria Jesus Artiga and Patricia Gonzalez from Biobank and Histopathology Core Unit, CNIO for technical support. We especially thank Massimo Squatrito for providing the samples of the gliomagenesis model. This work was funded by the Spanish Ministry of Education and Science (BFU2013-42895-P; BFU2016-78826-P) and the Instituto de Salud Carlos III/FEDER (P13/01980), and supported by the Xarxa de Bancs de Tumors de Catalunya sponsored by Pla Director d'Oncologia de Catalunya (XBTC), IRBLleida Biobank (B.0000682) and PLATAFORMA BIOBANCOS PT17/0015/0027. T Cemeli (FPU13/06590) and I Felip (FPU14/02674) were supported by a predoctoral fellowship from Ministerio de Educacion, Cultura y Deportes and from Diputacio de Lleida. M Guasch and M Nager were supported by a predoctoral fellowship from UdL. AJ Schuhmacher was supported by a research contract from the Ramon y Cajal program (RYC-2015-17622) by the Spanish Ministry for the Economy, Industry and Competitiveness (MINECO).