TRPM7 transactivates the FOSL1 gene through STAT3 and enhances glioma stemness

Abstract

Introduction We previously reported that TRPM7 regulates glioma cells’ stemness through STAT3. In addition, we demonstrated that FOSL1 is a response gene for TRPM7, and the FOSL1 gene serves as an oncogene to promote glioma proliferation and invasion. Methods In the present study, we determined the effects of FOSL1 on glioma stem cell (GSC) markers CD133 and ALDH1 by flow cytometry, and the maintenance of stem cell activity by extreme limiting dilution assays (ELDA). To further gain insight into the mechanism by which TRPM7 activates transcription of the FOSL1 gene to contribute to glioma stemness, we constructed a FOSL1 promoter and its GAS mutants followed by luciferase reporter assays and ChIP-qPCR in a glioma cell line and glioma patient-derived xenoline. We further examined GSC markers ALDH1 and TRPM7 as well as FOSL1 by immunohistochemistry staining (IHC) in brain tissue microarray (TMA) of glioma patients. Results We revealed that FOSL1 knockdown reduces the expression of GSC markers CD133 and ALDH1, and FOSL1 is required to maintain stem cell activity in glioma cells. The experiments also showed that mutations of − 328 to − 336 and − 378 to − 386 GAS elements markedly reduced FOSL1 promoter activity. Constitutively active STAT3 increased while dominant-negative STAT3 decreased FOSL1 promoter activity. Furthermore, overexpression of TRPM7 enhanced while silencing of TRPM7 reduced FOSL1 promoter activity. ChIP-qPCR assays revealed that STAT3, present in nuclear lysates of glioma cells stimulated by constitutively activated STAT3, can bind to two GAS elements, respectively. We demonstrated that deacetylation of FOSL1 at the Lys-116 residue located within its DNA binding domain led to an increase in FOSL1 transcriptional activity. We found that the expression of TRPM7, ALDH1, and FOSL1 protein is associated with grades of malignant glioma, and TRPM7 protein expression correlates to the expression of ALDH1 and FOSL1 in glioma patients. Conclusions These combined results demonstrated that TRPM7 induced FOSL1 transcriptional activation, which is mediated by the action of STAT3, a mechanism shown to be important in glioma stemness. These results indicated that FOSL1, similar to GSC markers ALDH1 and TRPM7, is a diagnostic marker and potential drug target for glioma patients.

FOSL1’s Diverse Roles in Glioma/Glioma Stem Cells and Tu-morigenesis: A Comprehensive Review

“…To further gain insight into the mechanism by which TRPM7 activates transcription of the FOSL1 gene to contribute to glioma stemness, we constructed a FOSL1 promoter and its GAS mutants followed by luciferase reporter assays and ChIP-qPCR. These combined results demonstrated that TRPM7 induced FOSL1 transcriptional activation, which is mediated by the action of STAT3, a mechanism shown to be important in glioma stemness [16].…”

“…This modification results in the cancer cells acquiring stemness properties, which represents a critical step in the development and progression of cancer [41]. Our most recent studies demonstrated that deacetylation of FOSL1 at the Lys-16 residue located within its DNA binding domain leads to an increase in FOSL1 transcriptional activity [16].…”

“…Consequently, the rebound led to increased transcription levels of five FOSL1 target genes, SPRY2, MMP2, JUN, PLAUR, MMP1, and IL-6, contributing to resistance against kinase inhibitors [44][45][46][47][48][49][50]. FOSL1 serves as a clinical prognostic marker for glioma [16,21,51].…”

“…Although a similar tendency was displayed in the proneural subtype, it did not reach a significant difference. To determine whether FOSL1 gene expression is related to patient survival, all GBM patients from The Human Protein Atlas were analyzed in a pooled setting; the 7-year overall survival (OS) rate, as revealed by the Kaplan-Meier survival curves, was significantly higher (p<0.001; log-rank test) in those with low FOSL1 transcript levels compared with those with high expression [16]. Recently, several new binding partners of FOSL1were identified in human Th17 cells, which include HDAC2, XRN1, AP2A1, PCBP1, ILF3, TRIM21, and HNRNPH1 [103].…”

FOSL1’s Oncogene Roles in Glioma/Glioma Stem Cells and Tumorigenesis: A Comprehensive Review

“…The collective findings indicate that TRPM7 triggers the activation of FOSL1 transcription, which is facilitated by the activity of STAT3. This process has been identified as crucial in maintaining the stemness of glioma cells [21].…”