ABSTRACT
Medulloblastoma (MB) encompasses diverse subgroups, and leptomeningeal disease/metastasis (LMD) plays a substantial role in associated fatalities. Despite extensive exploration of canonical genes in MB, the molecular mechanisms underlying LMD and the involvement of the orthodenticle homeobox 2 (OTX2) gene, a key driver in aggressive MB Group 3, remain insufficiently understood. Recognizing OTX2's pivotal role, we investigated its potential as a catalyst for aggressive cellular behaviors, including migration, invasion, and metastasis. OTX2 overexpression heightened cell growth, motility, and polarization in Group 3 MB cells. Orthotopic implantation of OTX2-overexpressing cells in mice led to reduced median survival, accompanied by the development of spinal cord and brain metastases. Mechanistically, OTX2 acted as a transcriptional activator of the Mechanistic Target of Rapamycin (mTOR) gene's promoter and the mTORC2 signaling pathway, correlating with upregulated downstream genes that orchestrate cell motility and migration. Knockdown of mTOR mRNA mitigated OTX2-mediated enhancements in cell motility and polarization. Analysis of human MB tumor samples (N = 952) revealed a positive correlation between OTX2 and mTOR mRNA expression, emphasizing the clinical significance of OTX2's role in the mTORC2 pathway. Our results reveal that OTX2 governs the mTORC2 signaling pathway, instigating LMD in Group 3 MBs and offering insights into potential therapeutic avenues through mTORC2 inhibition.
Subject(s)
Gene Expression Regulation, Neoplastic , Mechanistic Target of Rapamycin Complex 2 , Medulloblastoma , Meningeal Neoplasms , Otx Transcription Factors , Animals , Female , Humans , Male , Mice , Cell Line, Tumor , Cell Movement/genetics , Cell Proliferation/genetics , Cerebellar Neoplasms/genetics , Cerebellar Neoplasms/pathology , Cerebellar Neoplasms/metabolism , Mechanistic Target of Rapamycin Complex 2/metabolism , Mechanistic Target of Rapamycin Complex 2/genetics , Medulloblastoma/genetics , Medulloblastoma/pathology , Medulloblastoma/metabolism , Meningeal Neoplasms/genetics , Meningeal Neoplasms/pathology , Meningeal Neoplasms/metabolism , Meningeal Neoplasms/secondary , Otx Transcription Factors/metabolism , Otx Transcription Factors/genetics , Signal TransductionABSTRACT
Breast cancer brain metastasis marks the most advanced stage of breast cancer no longer considered curable with a median survival period of â¼4-16 months. Apart from the genetic susceptibility (subtype) of breast tumors, brain metastasis is also dictated by the biophysical/chemical interactions of tumor cells with native brain microenvironment, which remain obscure, primarily due to the lack of tunable biomimetic in vitro models. To address this need, we utilized a biomimetic hyaluronic acid (HA) hydrogel platform to elucidate the impact of matrix stiffness on the behavior of MDA-MB-231Br cells, a brain metastasizing variant of the triple negative breast cancer line MDA-MB-231. We prepared HA hydrogels of varying stiffness (0.2-4.5 kPa) bracketing the brain relevant stiffness range to recapitulate the biophysical cues provided by brain extracellular matrix. In this system, we observed that the MDA-MB-231Br cell adhesion, spreading, proliferation, and migration significantly increased with the hydrogel stiffness. We also demonstrated that the stiffness based responses of these cells were mediated, in part, through the focal adhesion kinase-phosphoinositide-3 kinase pathway. This biomimetic material system with tunable stiffness provides an ideal platform to further the understanding of mechanoregulation associated with brain metastatic breast cancer cells. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1832-1841, 2018.
