Abstract A02: SYK kinase inhibition causes autophagy pathway activation via suppression of mTORC1 in KRAS-mutant pancreatic cancer cells

Abstract

Abstract The spleen tyrosine kinase (SYK) is highly expressed in a subset of KRAS-mutant pancreatic ductal adenocarcinoma (PDAC) cell lines. This prompted our interest in investigating SYK as a candidate therapeutic target in PDAC cell lines. Here, we use a selective SYK kinase inhibitor (PRT-062607) in pharmacologic and mechanistic studies of SYK kinase signaling in PDAC cell lines. SYK kinase inhibition causes dose-dependent decreases in cell proliferation of “SYK-high” PDAC cell lines YAPC and DAN-G. Furthermore, combined SYK and MEK inhibition causes additive effects on reducing cell proliferation. Mechanistically, SYK inhibition causes reduced S6K and rpS6 phosphorylation, which is independent of MEK/ERK and PI3K/AKT signaling. Therefore, SYK activates mTORC1 activity through an unknown mechanism. The mTORC1 complex is a key activator of the macroautophagy pathway (autophagy), which is implicated as a driver of PDAC progression. However, autophagy can cause tumor suppression in some contexts. We demonstrate that SYK inhibition or shRNA-mediated depletion results in increased autolysosomal biogenesis and autophagic flux that occur with latency following treatment of cells with the SYK inhibitor. These effects are partly mediated by the nuclear localization and activation of MITF, which is a key transcriptional regulator of genes that control lysosomal biogenesis and autophagy. Taken together, our results demonstrate that SYK is a positive regulator of mTORC1 activity in a subset of PDAC cell lines. SYK kinase inhibition or shRNA-mediated depletion causes a strong reduction in mTORC1 activity and subsequent MITF activation and nuclear localization. The net effect is increased autolysosomal biogenesis and autophagic flux in YAPC and DAN-G PDAC cell lines. Therefore, SYK inhibition in combination with KRAS pathway inhibitors may serve as a potential therapeutic strategy to perturb autophagy pathway homeostasis and pancreatic cancer cell survival. Citation Format: Kevin L. Hua, Michelle Pan, Minoo Rafati, Anurag Singh. SYK kinase inhibition causes autophagy pathway activation via suppression of mTORC1 in KRAS-mutant pancreatic cancer cells [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr A02.