Cycling Quiescence in Temozolomide Resistant Glioblastoma Cells Is Partly Explained by microRNA-93 and -193-Mediated Decrease of Cyclin D.

Jessian L Munoz,Nykia D Walker,Steven J Greco,Sri Harika Pamarthi,Pranela Rameshwar,Garima Sinha,Satvik Mareedu

doi:10.3389/fphar.2019.00134

Abstract

Glioblastoma multiforme (GBM) is a fatal malignancy of the central nervous system, commonly associated with chemoresistance. The alkylating agent Temozolomide (TMZ) is the front-line chemotherapeutic agent and has undergone intense studies on resistance. These studies reported on mismatch repair gene upregulation, ABC-targeted drug efflux, and cell cycle alterations. The mechanism by which TMZ induces cell cycle arrest has not been well-established. TMZ-resistant GBM cells have been linked to microRNA (miRNA) and exosomes. A cell cycle miRNA array identified distinct miRNAs only in exosomes from TMZ-resistant GBM cell lines and primary spheres. We narrowed the miRs to miR-93 and -193 and showed in computational analyses that they could target Cyclin D1. Since Cyclin D1 is a major regulator of cell cycle progression, we performed cause-effect studies and showed a blunting effects of miR-93 and -193 in Cyclin D1 expression. These two miRs also decreased cell cycling quiescence and induced resistance to TMZ. Taken together, our data provide a mechanism by which GBM cells can exhibit TMZ-induced resistance through miRNA targeting of Cyclin D1. The data provide a number of therapeutic approaches to reverse chemoresistance at the miRNA, exosomal and cell cycle points.

Highlights

Glioblastoma multiforme (GBM) is the most common adult primary brain tumor
We demonstrated that the regulation of Cyclin D1 by these two miRNAs led to TMZ resistance in GBM cells
Prior to testing the role for exosome-containing miRNA in TMZ-resistance, we studied the exosomes by phenotype and size to ensure no contamination with other microvesicles such as apoptotic bodies

Summary

Introduction

Glioblastoma multiforme (GBM) is the most common adult primary brain tumor. GBM is the most lethal brain cancer with a 5-year survival rate of ∼8% (Naydenov et al, 2011). GBMs uniformly acquire resistance to the front-line alkylating chemotherapeutic agent, Temozolomide (TMZ) (Jiang et al, 2011). Cell cycle progression requires the concerted activity of a number of factors both positive and negative (Louis, 2006). The expression and degradation of Cyclin D1 is highly regulated to coordinate the temporal role of Cyclin D1 (Freemantle et al, 2007). Since microRNAs (miRs) have been linked to miRNA in Cyclin D Decrease in GBM chemoresistance, we studied if miRNAs, through the regulation of Cyclin D1, affected the response of GBM cells to TMZ

Methods

Results

Conclusion