Abstract 924: GM-CSF induces CREB signaling pathways and modulates tobacco carcinogen-induced pancreatic tumorigenesis
Authors: Castellanos Jason , Honnenahally Kumaraswamy , Shi Chanjuan , Merchant Nipun , Nagathihalli Nagaraj 
Published: August 2015

Introduction: Nicotine and nitrosamine exposure from smoking causes pancreatic cell injury and contributes to a cascade of oncogenic events that may be contributing to the rising rate of pancreatic cancer (PDAC). Cytokines activate kinases and transcription factors including cyclic AMP response element binding (CREB) protein. CREB activation through phosphorylation regulates diverse cellular responses. We studied whether granulocyte-macrophage colony stimulating factor (GM-CSF)-dependent phosphorylated CREB plays a role in smoking-induced pathogenesis of PDAC.

Experimental procedure: Human tissue microarray analysis was performed to determine the significance of pCREB expression amongst smokers and non-smokers. Total RNA extracted from immortalized human pancreatic ductal cell (H6c7) and pancreatic intraepithelial neoplasia (PanIN) mouse cell lines (LSL-KrasG12D/+; Pdx1Cre/+) were treated with tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and RNA sequencing (RNA-seq) was performed. Network, pathway and functional analyses of the transcriptome were conducted. To analyze the signaling pathway involved in NNK-induced tumorigenicity, we performed a phospho-kinase antibody array and cytokine antibody array on NNK treated H6c7 and PanIN cells or conditioned media (CM) protein. Western blot and ELISA were used to validate the array data findings. NNK-induced activation of GM-CSF, G-CSF and IL-6 were blocked using monoclonal antibodies. PKT (Ptf1acre/+;LSL-KrasG12D/+;Tgfbr2flox/flox) mice and nude mice with MiaPaCa2 flank xenografts were treated with MEK inhibition (AZD6244) with or without NNK/in vivo smoking. Tumors from these mice were immunoblotted for phosphorylation of MEK1/2, MSK1/2, RSK and CREB. PDAC cells with CREB siRNA or human rGM-CSF were treated with NNK and analyzed for in vitro functional assays and EMT characteristics.

Results: Expression of pCREB was significantly higher (p&lt;0.001) in smokers when compared to non-smokers. Overall survival of smokers with high pCREB expression in their primary tumor was associated with significantly decreased median survival when compared to non-smokers with low pCREB expression. Exposure of cells to NNK resulted in phosphorylation of CREB, c-Jun and β-catenin, and release of GM-CSF, G-CSF and IL-6. RNA-seq analysis confirmed activation of MEK/ERK signaling. Studies were performed to elucidate the possible regulatory mechanism behind NNK mediated induction of GM-CSF and its downstream signaling. Importantly, blocking GM-CSF inhibited NNK-induced phosphorylation of CREB and it was mediated through MEK signaling. The in vivo and in vitro tumorigenicity assays showed an increase in the tumorigenic potential and EMT of NNK treated PDAC cells.

Conclusions: Our study demonstrates that NNK induces pancreatic tumorigenesis through GM-CSF mediated activation of CREB.

Citation Format: Jason Castellanos, Kumaraswamy Honnenahally, Chanjuan Shi, Nipun Merchant, Nagaraj Nagathihalli. GM-CSF induces CREB signaling pathways and modulates tobacco carcinogen-induced pancreatic tumorigenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 924. doi:10.1158/1538-7445.AM2015-924