Abstract C041: Oncostatin-M and transforming growth factor-beta promote loss of PTEN in PDAC cancer associated fibroblasts

Abstract

Abstract Pancreatic Ductal Adenocarcinoma (PDAC) is a deadly malignancy with poor prognosis and treatment options. Cancer associated fibroblasts (CAFs) play a complex role in the PDAC tumor microenvironment (TME), contributing significantly to the progression of the tumor and the dense desmoplastic stroma. Phosphatase and tensin homolog (PTEN) is a tumor suppressor and its loss in both the tumor and in CAFs is associated with increased tumor aggressiveness and resistance to therapy. Our group previously demonstrated PTEN loss occurs in CAFs in ~25% of PDAC patient samples, which correlated with worsened outcomes. In addition, PTEN expression was lost in 80% of SMA+ CAFs in mouse PDAC models. Genetic or pharmacologic inhibition of the hedegehog pathway leads to ubiquitin-dependent destruction of PTEN by the proteosome. However, little is known of the signals produced by tumor cells that trigger PTEN degradation in CAFs. In order to address this problem, we developed an in vitro assay system based on wild type murine PDAC-CAFs that expresses a PTEN-GFP fusion protein. Initially, we focused on IL6 and IL6 family members Leukemia Inhibitory Factor (LIF) and Oncostatin-M (OSM) and Transforming Growth Factor beta 1 (TGFb1). The SMO inhibitor GDC-0449 was used as a positive control. PTEN stability was evaluated using the LSM 880 confocal microscope and GFP+ cells were quantified with QuPath-0.4.3 and analyzed with GraphPad Prism. Among the repertoire of secreted factors, we found that only OSM and TGFb1 could destabilize PTEN after 48H of treatment. When queried against the single cell RNA sequence dataset produced by our lab, we observed that CD45+ leukocytes were the likely source of OSM whereas TGFb1 was produced by tumor cells, fibroblasts, and immune cells. In conclusion, OSM and TGFb1 can downregulate PTEN in CAFs in vitro. Current efforts are aimed at testing whether inhibition of these pathways can restore PTEN expression in mouse PDAC models, and in identifying signaling pathways and E3-ligases that mediate PTEN destruction. These pathways and interactions could be further exploited for selective inhibition aimed at therapeutic benefits in curbing PDAC progression. Citation Format: Ivo N. Woogeng, Lu Han, Samaneh Saberi, Cameron Bumbleburg, Joseph Beaudet, Sudarshana Sharma, Michael Ostrowski. Oncostatin-M and transforming growth factor-beta promote loss of PTEN in PDAC cancer associated fibroblasts [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C041.