Abstract 3085: Upregulation of TAGLN2-PI3K-AKT signaling promotes therapeutic resistance in glioblastoma through a positive feedback mechanism

Abstract Objective: Despite aggressive treatment with surgery, radiation and temozolomide chemotherapy glioblastoma (GBM) remains the most lethal tumor of the human brain, which is largely due to inevitable recurrence of treatment refractory tumor. Studies have shown that aberrant activation of AKT significantly contributes to the development of treatment resistance in GBM. Molecular profiling and in vitro studies from our group identified TAGLN2, an actin binding cytoskeletal protein, as a top upregulated gene in GBM. In other cancer types, TAGLN2 has been shown to activate the PI3K-AKT pathway resulting in treatment resistance. This study aims to explore how TAGLN2 drives treatment resistance in GBM. Methods: PDX primary human GBM cell lines (08-387 and GBM 3359) were used. Co-immunoprecipitation (Co-IP) assays were performed to study the interaction of PTEN with TAGLN2 in vitro. Biacore/Surface plasmon resonance (SPR) analyses were performed to study binding affinity and kinetics of their interaction. Protein-protein interactions were validated by in silico (AlphaFold2) analysis. Protein expression was quantified by WB analysis. Cell viability was assessed by MTS assays. Results: We have previously shown that RNAi-mediated knockdown (KD) of TAGLN2 significantly reduced cell proliferation, survival, clonal expansion and the invasive potential of GBM PDX cell lines in vitro and reduced tumor growth using preclinical in vivo models. We found that KD of TAGLN2 reduced the levels of activated/phosphorylated AKT (pAKT) in GBM cells resulting in downregulation of this pathway. Subsequently, we found that TAGLN2 physically associated with PTEN as evidenced by Co-IP, SPR and in silico analysis. Binding of TAGLN2 to PTEN may attenuate PTEN function resulting in the activation of downstream oncogenic pathways. mTORC2 and DNA-PK are known to phosphorylate and activate AKT resulting in the upregulation of downstream signaling. Here, we show that inhibition of these kinases either individually or in combination reduced TAGLN2 protein levels in GBM cells in vitro. Importantly, direct inhibition of Akt phosphorylation also resulted in the reduction of TAGLN2 protein levels indicating that activated Akt stabilized TAGLN2 (likely by phosphorylation), which in turn promoted oncogenic pathways via a positive feedback mechanism. Also, KD of TAGLN2 increased the sensitivity of GBM cells to both TMZ and RT as assessed by multiple in vitro models. Conclusion: Taken together, our data suggest that Transgelin-2 promotes chemo-radiation treatment resistance in GBM through a novel positive feedback mechanism that involves the TAGLN2-PTEN-PI3K-AKT axis. Therefore, TAGLN2 may serve as potential therapeutic target in GBM and to this end, development of small molecule inhibitors of TAGLN2 is actively underway in our laboratory. Citation Format: Ashok Kumar, Sasha Beyer, Bryan Pérez-Soto, Anca-Ligia Grosu, Steffen Lindert, Heather R. Manring, Saikh Jaharul Haque, Arnab Chakravarti. Upregulation of TAGLN2-PI3K-AKT signaling promotes therapeutic resistance in glioblastoma through a positive feedback mechanism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3085.