Genetic alterations that activate protein kinase A (PKA) are found in many tumor types. Yet, their downstream oncogenic signaling mechanisms are poorly understood. We used global phosphoproteomics and kinase activity profiling to map conserved signaling outputs driven by a range of genetic changes that activate PKA in human cancer. Two signaling networks were identified downstream of PKA: RAS/MAPK components, and an Aurora Kinase A (AURKA) /glycogen synthase kinase (GSK3) sub-network with activity toward MYC oncoproteins. Findings were validated in two PKA-dependent cancer models: a novel, patient-derived fibrolamellar liver cancer (FLC) line that expresses a DNAJ-PKAc fusion, and a PKA-addicted melanoma model with a mutant Type I PKA regulatory subunit. We identify PKA signals that can influence both de novo translation and stability of the proto-oncogene c-MYC. However, the primary mechanism of PKA effects on MYC in our cell models was translation and could be blocked with the eIF4A inhibitor zotatifin. This compound dramatically reduced c-MYC expression and inhibited FLC cell line growth in vitro. Thus, targeting PKA effects on translation is a potential treatment strategy for FLC and other PKA-driven cancers.

Genetic alterations that activate protein kinase A (PKA) signaling are found across many tumor types, but their downstream oncogenic mechanisms are poorly understood. We used global phosphoproteomics and kinome activity profiling to map the conserved signaling outputs driven by diverse genetic changes that activate PKA in human cancer, including melanoma and fibrolamellar carcinoma (FLC). We define two consensus networks of effectors downstream of PKA in cancer models. One is centered on RAS/MAPK components, and a second involves Aurora Kinase A (AURKA). We find that AURKA stabilizes c-MYC and n-MYC protein levels and expression programs in PKA-dependent tumor models, in part via a positive feedback loop mediated by the oncogenic kinase PIM2. This process can be suppressed by conformation-disrupting AURKA inhibitors such as CD-532. Our findings elucidate two independent mechanisms of PKA-driven tumor cell growth and offer insight into drug targets for study in FLC and other PKA-dependent malignancies.