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SMAD4 represses FOSL1 expression and pancreatic cancer metastatic colonization

ABSTRACT: Less than 8% of patients diagnosed with pancreatic ductal adenocarcinomas (PDAC) survive more than five years in part due to late stage diagnosis. Approximately half of PDAC patients exhibit loss of SMAD4, which correlates with increased metastatic disease. Here we demonstrate that SMAD4 is a suppressor of metastatic colonization. Using isogenic human PDAC cell lines expressing or lacking SMAD4, both in vitro and in vivo, we define SMAD4-dependent gene expression changes in metastatic lesions. We performed a pooled in vivo open reading frame (ORF) screen of SMAD4 transcriptional targets and identified genes that, induce tumor seeding and growth at secondary sites. We found that expression of the transcription factor FOSL1 was sufficient to drive metastatic colonization. SMAD4 directly binds and represses the activity of the FOSL1 enhancer. These studies demonstrate a direct role for SMAD4 in regulating metastatic colonization and identify FOSL1 as a SMAD4-regulated gene involved in PDAC progression.

ORGANISM(S): Homo sapiens

PROVIDER: GSE148248 | GEO | 2021/08/02

REPOSITORIES: GEO

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Project description:Chemoresistance to gemcitabine limits its clinical implementation for pancreatic ductal adenocarcinoma (PDAC). We previously generated an antibody drug conjugate (ADC) -like agent, EGFR/HER2 dual-targeting ligand-based lidamycin (DTLL), and studied the effect of DTLL combined with gemcitabine and the potential role of SMAD4 in the chemoresistance of PDAC. On the basis of SMAD4 profiles in in vitro and in vivo models, we investigated the antitumor effects of DTLL, gemcitabine and their combination, followed with mechanistic characterization. The results suggested that DTLL combination treatment with gemcitabine significantly repressed tumors with remarkably enhanced efficacy as compared to gemcitabine or DTLL alone given in either SMAD4-deficient/gemcitabine-resistant or SMAD4-sufficient/gemcitabine-sensitive cell line derived xenograft (CDX) and patient derived xenograft (PDX) tumors, respectively. Functional studies indicated that SMAD4 genetic status is responsible for SMAD4 protein level which determines different cellular susceptibility of PDAC. R100T mutation contributes to loss of SMAD4 protein and function with rapid protein degradation, leading to resistance to gemcitabine in PDAC cells. Moreover, DTLL significantly altered the protein half-life time and level of mutant and wild-type SMAD4 by inhibiting protein degradation at different velocities and distinctly changing the interaction of SMAD4 with TRIM33. Mechanism studies implied that DTLL combinational treatment might not only prevent from neoplastic proliferation via blockage of ATK/mTOR signaling and anti-apoptotic proteins (Bcl-2 and MCL1) mediated by impaired NF-B function in SMAD4-sufficient/gemcitabine-sensitive PDAC cells, but also restore the bioactivity of SMAD4 as a tumor suppressor to trigger its downstream NF-B-regulated signaling of cell apoptosis in SMAD4-deficient/gemcitabine-resistant tumors. In conclusion, SMAD4 is the key central mediator of not only the occurrence and development but also susceptibility in PDAC. DTLL sensitized gemcitabine efficacy via distinct action mechanisms based on SMAD4 profiles in SMAD4-sufficient/gemcitabine-sensitive and SMAD4-deficient/-resistant PDAC, respectively. Our findings provide insight into a rational SMAD4-directed precision treatment strategy and reveal a promising DTLL combination therapy to overcome chemoresistance in gemcitabine-resistant PDAC.

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SMAD4 represses FOSL1 expression and pancreatic cancer metastatic colonization

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