Abstract 2618: IQGAP3 regulates intra-cellular Ras signaling and intra-tumoral malignant cycles via TGFβ signaling

Abstract Scaffold protein IQ motif-containing GTPase-activating protein 3 (IQGAP3; IQ3) is a member of the multifunctional IQGAP family. The interaction between IQ3 and Ras-ERK signaling has been reported, but how IQ3 regulates Ras-ERK signaling in malignancies is still unclear. The purpose of this study is to elucidate the role of IQ3 in coordinating diverse pathways, such as ERK-Ras and TGFβ in gastric cancer (GC).According to Stomach Adenocarcinoma of TCGA Pan-Cancer Atlas, the frequency of gene mutations is high in TP53 (60.1%), RTK-Ras (51.8%), and TGFβ pathways (36.4%). Gene Set Enrichment Analysis (GSEA) indicated that KRAS signaling was significantly downregulated after IQ3 knockdown (KD) in three GC cell lines (AGS, NUGC3, Hs746T). Ingenuity upstream regulator analysis (IPA) of RNA sequencing data revealed that TGFβ1, the top-ranked growth factor, is significantly inhibited after IQ3 KD. Immunoblot analysis showed that IQ3 KD led to suppression of TGFβ-induced phosphorylation of MEK/ERK in three GC cell lines, particularly NUGC3. While TGFβ treatment promoted invasion and migration in transwell migration assays, IQ3 KD significantly diminished TGFβ-mediated cell migration. In vivo, the size and volume of subcutaneous tumors from IQ3 KD NUGC3 cells were significantly smaller than that from Control (Ctrl) cells. According to RNA sequencing using bulk tumors, mouse stromal cells in Ctrl tumors showed significantly higher expression of acta2, fap, pdgfa, which are the markers of cancer-associated fibroblasts, than in IQ3 KD tumors. The TGFβ1 expression levels in the NUGC3 xenograft and mouse stromal cells harvested from Ctrl were significantly higher than that from IQ3 KD, respectively. Additionally, digital spatial profiler (DSP) GeoMx evaluation of the intra-tumoral expressions from the human xenograft and mouse stromal cells showed that the mouse stromal cells from Ctrl expressed significantly higher acta2 and tgfβ1 than that from IQ3 KD. Furthermore, metastasis assays via tail vein injection in vivo showed dramatically lesser lung metastases from IQ3 KD cells than that from Ctrl cells. This study shows that IQ3 KD suppressed Ras signaling and blocked upstream regulator TGFβ1 in vitro. The stromal cells in the IQ3 KD xenografts showed a reduced population of cancer-associated fibroblasts in vivo. Consequently, tumorigenesis and metastasis were strongly suppressed after IQ3 KD. IQ3 is thus a highly relevant therapy target in GC. Citation Format: Mitsuhiro Shimura, Pang SHUCHIN, Junichi Matsuo, Linda Shyue Chuang, Yoshiaki Ito. IQGAP3 regulates intra-cellular Ras signaling and intra-tumoral malignant cycles via TGFβ signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2618.