Less than 5% of patients diagnosed with pancreatic ductal adenocarcinomas (PDAC) survive more than 5 years, largely due to therapeutic resistance and metastatic disease. Half of all PDAC patients have been shown to have loss of SMAD4, which has been shown to correlate with metastasis. Here we functionally demonstrate that SMAD4 is a key suppressor of metastatic colonization of PDAC. Using an in vitro and in vivo multi-component RNA-seq analysis on isogenic human PDAC cell lines, we defined SMAD4-dependent gene expression changes. Specifically, we identified genes that were suppressed in the presence of SMAD4. These genes could contribute to tumor metastasis. To test this, we performed a pooled open reading frame (ORF) overexpression lung colonization assay with the identified genes. We found that expression of the transcription factor FOSL1 is sufficient for metastatic colonization. Mechanistically, SMAD4 directly binds and modulates the activity of the FOSL1 enhancer. Taken together, these studies demonstrate a direct role for SMAD4 in regulating metastatic colonization and identify FOSL1 as a direct SMAD4-regulated gene involved in distant site colonization.

Citation Format: Jonathan P. Rennhack, Chao Dai, Andrew Aguirre, John Doench, David Root, William C. Hahn. SMAD4 represses PDAC metastatic colonization through binding FOSL1 enhancer regions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2402.