STAT6 expression in glioblastoma promotes invasive growth
Signal Transducers and Activators of Transcription (STATs) were initially identified as modulators of the immune response, but more recently have been ascribed numerous roles in the regulation of carcinogenesis, tumor maintenance and tumor progression. Reports indicate that STATs 3, 5A and 5B play important roles in the regulation of GBM pathophysiology. In this study, we investigated the expression, activation status and physiological effects of STAT6 in glioblastoma (GBM), and correlated its expression with patient survival.
First, we utilized GBM cell lines and human patient tissue specimens to demonstrate increased STAT6 expression relative to non-malignant cells and normal brain tissue at the protein and mRNA level by Western blot, immunohistochemistry and real-time (quantitative) PCR. Next, we assessed the effects of lentiviral STAT6 knockdown by shRNA on the proliferation and invasion of two STAT6-positive GBM cell lines. STAT6-deficient GBM cells showed a reduction in 3H-Thymidine uptake compared to the wild-type, ranging from 35%–70% in U-1242MG and 40–50% in U-87MG cells. Additionally, STAT6-depleted cells were less invasive than controls in our in vitro transmembrane invasion assay. Invasiveness was decreased by 25–40% and 30–75% in U-1242MG and U-87MG cells, respectively. A microarray analysis comparing wild type U-87MG and U-1242MG to their respective STAT6 knockdown clones identified several potential downstream mediators of STAT6 signaling.
We utilized the National Cancer Institute (NCI) Rembrandt public data depository (NCI, 2005) to generate Kaplan-Meyer survival curves showing the relationship between STAT6 gene expression and survival times for glioma patients. In a dataset of 343 glioma patients—including grades II–IV (GBM)—there was a significant difference in survival (p < 0.05) between patients with up- and down-regulated STAT6 (NCI, 2005). Decreased STAT6 expression correlated with longer survival times. When patient data was separated into lower grade gliomas and GBM (grade IV), a similar but non-significant trend was observed.
Taken together, these findings suggest a role for STAT6 in enhancing cell proliferation and invasion in GBM, which may explain why up-regulation of STAT6 correlates with shorter survival times in glioma patients. This report thus identifies STAT6 as a new and potentially promising therapeutic target.