Scientists at the Icahn School of Medicine at Mount Sinai have identified a protein called TEAD1 that appears to regulate the migration of human glioblastoma cells away from the primary brain tumor mass, into other areas of the brain. Their studies, reported in Nature Communications, found that knocking out the TEAD1 gene in patient-derived glioblastoma multiforme (GBM) cells grown in vitro and transplanted into mice inhibited the cancer cells’ ability to proliferate and reduced the rate of cell migration. The researchers suggest that the findings could feasibly lead to new therapeutic approaches that either increase the success of surgery to remove the tumor, or at least help to hold back tumor recurrence.
“Our study is one of the first to take human patient glioblastoma cells directly from the tumor immediately after surgery and isolate the most aggressive tumor subclones—the glioma stem cells—to specifically characterize the machinery responsible for tumor migration,” comments Nadejda Tsankova, M.D., Ph.D., associate professor of pathology and neuroscience at the Icahn School of Medicine at Mount Sinai. “We found that the transcription factor TEAD1 directs the activity of genes responsible for tumor migration and, particularly, our research implicates the AQP4 gene as one of TEAD1's direct pro-migratory partners.”
Dr. Tsankova is senior author of the team’s published paper, which is titled, “Analysis of chromatin accessibility uncovers TEAD1 as a regulator of migration in human glioblastoma.”
Glioblastoma is the most common primary brain tumor in adults, and is associated with what the authors term a “dismal prognosis, despite aggressive treatment.” Some tumor cells are able to migrate away from the primary mass beyond the edge of the site of surgical resection, and so escape the knife. Glioma cells that move away from the tumor core also tend to respond poorly to chemotherapy, and these cells that have been implicated in tumor recurrence, the authors add. It’s likely, they suggest, that different mechanisms regulate these migratory and tumor core cells. “Given the unique microenvironment and transcriptional signatures of tumor cells at the infiltrative edge vs. those at the tumor core, the two populations are likely regulated by distinct molecular pathways.”
Although prior in vitro research and studies of patient-derived grafts in mice have implicated a number of transcription factors in the regulation of glioblastoma tumor growth and migration, the tumor microenvironment in the human brain is very different to that of tumor cells growing in laboratory petri dishes or transplanted into mice, so we still don't really understand how cell migration is controlled in clinical cases of glioblastoma.
To try and derive new insights into glioma cell migration, the team exploited a recently developed protocol for isolating glioblastoma stem cells directly from human GBM tissue, and investigated the epigenetic landscape of this aggressive type of brain cancer. The results highlighted gene signatures that related to tumor migration, and identified TEAD1 overexpression as a key feature of these migratory signatures. TEAD1 is one of a family of four TEAD genes, and when the team then analyzed the expression levels of all four TEAD family genes in RNA sequencing data from The Cancer Genome Atlas (TCGA), they found that TEAD1 was the most highly expressed across 150 different primary GBM samples. TEAD1 overexpression was also associated with the overexpression of known migratory genes. “Of note, genes significantly coexpressed with TEAD1 in TCGA GBM samples were highly enriched for terms related to cell migration and cell adhesion,” they write. “… this analysis prioritized TEAD1 as the most highly and widely expressed TEAD family member across GBM tumors.”
To test the role of TEAD1 in GBM migration the team then used CRISPR-Cas9 gene editing to effectively knock out the gene in patient-derived GBM cells. In vitro tests confirmed that TEAD1 knockout cells (TEAD1KO) demonstrated reduced proliferative and migratory capabilities when compared with sham-engineered cells. TEAD1KO cells then provided with TEAD1 regained some of their migratory capacity.
TEAD1 knockout cells transplanted into live mice were also less able to infiltrate into the brain from the initial injection site than the sham-engineered cells. “While sham cells had infiltrated extensively into the striatum, away from the tumor injection site, and across the corpus callosum, TEAD1KO cells were found primarily around the site of injection with only occasional infiltrative cells counted throughout the rest of the brain,” the authors write.
The researchers' subsequent analyses, including comparing RNA sequencing data for TEAD1KO and sham cells, were designed to look for potential binding targets of TEAD1. The results highlighted the gene encoding AQP4, a protein that plays a role in controlling water movement that allows cells to change their shape as they penetrate through the brain. Their analyses showed that the AQP4 gene was turned off in TEAD1 knockout cells with reduced migratory capacity. Tests also indicated that AQP4 was also a direct binding target of TEAD1 in GBM, in vivo.
Interestingly, the migratory capacity of TEAD1-deficient cells could be restored by overexpression of either TEAD1 or AQP4. “TEAD1 overexpression restores AQP4 expression, and both TEAD1 and AQP4 overexpression rescue migratory deficits in TEAD1-knockout cells, implicating a direct regulatory role for TEAD1–AQP4 in GBM migration,” the team states.
“Our study data provides convincing evidence that TEAD1 signals through AQP4 to promote tumor migration and furthermore, that if we can inhibit the activity of TEAD1, we can potentially stop tumor cells from migrating away from the main tumor mass,” comments Dr. Tsankova. “This newfound information has important implications for brain tumor treatment, potentially increasing the success rate of removing the entire tumor during surgery or at least prolonging the time it takes for the tumor to come back.”
The team is now working to test potential TEAD1 inhibitors and see if they can stop glioblastoma cells from migrating both in vitro, and in animal models.