GNAS‐PKA Oncosignaling Network in Colorectal Cancer
Authors: Steffen Dana Jean , Amornphimoltham Panomwat , Valera Juan Luis Callejas , Taylor Susan , Hunter Tony , Tamayo Pablo , Gutkind J. Silvio 
Published: November 2023

Despite the successes of early detection and polyp removal, colorectal cancer (CRC) remains the second leading cause of cancer death in the United States. Substantial evidence supports the efficacy of nonsteroidal anti‐inflammatory drugs (NSAIDs), like aspirin and ibuprofen, for the prevention of CRC. NSAIDs inhibit cyclooxygenase‐2 (COX2), an enzyme that converts arachidonic acid to prostaglandins, including prostaglandin E2 (PGE2). Increased synthesis of PGE2 due to COX2 overexpression is consistently observed in patients with colorectal neoplasia and has been shown to promote CRC. Activation of Gαs‐linked, G protein‐coupled receptors by PGE2 has also been linked to CRC progression. Furthermore, analysis of cancer genomes reveals that activated GNAS mutants, encoding a constitutively active, GTPase defective Gαs, can be identified in approximately 5% of all sequenced tumors, including 4% of CRC. By stimulating adenylyl cyclases, GNAS activation leads to the intracellular accumulation of cyclic adenosine monophosphate (cAMP), a central second messenger, which in turn, activates protein kinase A (PKA). Similarly, 10% of CRC patients harbor gene amplification of GNAS, and another 45% have mutations in PKA subunits, adenylyl cyclase genes, or homozygous deletions of phosphodiesterases (which inhibit cAMP accumulation). These findings highlight the potential oncogenic role of GNAS‐PKA signaling. The aim of our study is to define the contribution of the GNAS‐PKA pathway in CRCs and explore the cancer‐associated GNAS‐PKA signaling network. We hypothesize that increased PKA activity downstream of GNAS mutations plays a central role in the growth and progression of CRCs. We utilized human colorectal cancer cell lines, genetic mouse models of colorectal cancer, and organoids derived from mouse and human tumor samples. We are able to precisely modulate GNAS‐PKA pathway activity in our in vitro and in vivo models with genetically encoded, inducible expression systems. We performed RNA sequencing, phospho‐proteomics, and computational analysis to identify candidate signaling modalities downstream of GNAS‐PKA. We have demonstrated the ability of the activating GNASR201C mutation to drive a greater than 3‐fold increase in cell proliferation and the ability of PKA inhibition to significantly reduce tumor burden in xenograft mouse models. Preliminary analysis of genomic, transcriptomic, and proteomic data suggest a signaling interaction between GNAS‐PKA and RAS. Emerging results from our studies will be presented. We have demonstrated the ability of GNAS‐PKA signaling to promote growth and identified a potential signaling connection between GNAS‐PKA and RAS.

Support or Funding Information

Dana Steffen was supported by the UCSD Graduate Training Program in Cellular and Molecular Pharmacology through an institutional training grant from the National Institute of General Medical Sciences (T32 GM007752) and the San Diego NCI Cancer Centers Council (C3) Collaborative Translational Cancer Research Pilot Grant.