Glioblastoma (GBM) is the most common and aggressive malignant brain tumor with a dismal survival rate that averages 15 months. Few therapeutic options are available, and virtually all patients experience disease progression within less than a year of initial treatment, primarily resulting from glioma cell invasion. Therapies attempting to target invasion have been ineffective because of the complex heterogeneous nature of GBM and migratory signaling; however, these pathways converge on the nonmuscle myosin II (NMMII) molecular motor proteins, making these molecular motors essential and non-redundant. The lab of my sponsor, Dr. Steven Rosenfeld, has established that NMMII motors are fundamental to glioma migration because of their ability to generate force on the actin cytoskeleton. The NMMII heavy chain has three different isoforms (IIA, IIB, and IIC), and each likely has different roles in glioma invasion based on its distinct biomechanical properties. However, the exact physiologic role of each isoform has never been defined at the mechanistic level but could prove critical to understanding glioma cell invasion. This proposal focuses on the role of NMMIIA, as this isoform is upregulated in GBM and high expression predicts worse prognosis. Interestingly a specific regulator of NMMIIA dynamics, S100A4, mirrors the expression and survival correlation of NMMIIA. I hypothesize that both NMMIIA and S100A4 are integral in the dispersion of glioma cells through the brain and targeting NMMIIA-mediated migration will increase efficacy of current local therapies or in combination with other targeted therapies. Indeed, preliminary data indicates that cre-mediated deletion of NMMIIA in our mouse model of GBM results in non-invasive tumors. Despite appearing encapsulated, the tumors are larger and more lethal, which is consistent with recent reports that NMMIIA is a tumor suppressor.
Aim 1 of this proposal seeks to investigate the function of NMMIIA both as a motility enhancer and as a tumor suppressor, using novel in vitro 2D and 3D migration assays, in situ brain tissue migration imaging, as well as comprehensive state-of-the-art proliferation, cytokinesis, and apoptosis assays.
Aim 2 focuses on S100A4, which may only be needed for NMMIIA motility functions that specifically require rapid filament disassembly/assembly dynamics. To investigate this hypothesis, S100A4 will be deleted from cre retrovirus-induced GBM tumors in our mouse model, and in vivo tumor survival and invasion will be assessed. In vitro studies will complement Aim 1 to determine the effect of S100A4 deletion on migration, proliferation, and apoptosis. The training for this fellowship will include intensive hands-on instruction in migration imaging, image analysis, and bioinformatics education for analyzing RNAseq data from NMMIIA-deleted tumors. Translating these findings into effective GBM therapies is our ultimate goal. However understanding the role of NMMIIA in cell biology is paramount to developing treatments and has the potential impact beyond GBM.
Glioblastoma is the most common type of malignant brain tumor and is uniformly lethal. Few treatment options are available and none effectively target glioma invasion into the rest of the brain, a key factor in morbidity and the poor survival. This project will identify alternative targets to block glioma cell migration and expand our understanding of how 'molecular motors' drive cell migration generally. Concepts gained from this research will identify new targets for drug development and create new considerations for patient therapy.
