Oncogenic PKA signaling increases c-MYC protein expression through multiple targetable mechanisms

Abstract

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.

Recruitment of BAG2 to DNAJ-PKAc scaffolds promotes cell survival and resistance to drug-induced apoptosis in fibrolamellar carcinoma

“…We have previously demonstrated an association between oncogenic PKA signaling and mRNA translation. 40 Consistent with these findings, examination of the STRING network for phosphopeptides with increased DNAJ-PKAc association revealed Gene Ontology (GO) enrichment of biological processes often increased in cancer (i.e., mRNA processing, ribosome biogenesis, and translation) as well as members of the TORC1 signaling complex (Rps6, Akt, and Raptor; Figure S2D ). 41 – 44 Network propagation was performed on both the proximity proteomics (node fill color) and proximity phosphoproteomics (node border color) datasets to assess the links between alterations in DNAJ-PKAc localization and substrate phosphorylation.…”

“…This further supported an increase in cap-dependent translation, likely impacting genes such as MYC . 40 , 47 Finally, to determine the impact of the kinase activity of the fusion on protein synthesis, we treated cells with BLU2864 to selectively inhibit PKA activity 1 h prior to addition of puromycin. These experiments revealed a dose-dependent decrease in translation corresponding to degree of PKA inhibition by BLU2864, with greater inhibition occurring at the higher dose ( Figures 4I and 4J ).…”

Integration of metabolic flux with hepatic glucagon signaling and gene expression profiles in the conscious dog

“…6B, 6C). Indeed, elevated cAMP-PKA signaling was shown to augment MYC protein expression in vitro (9), and MYC directly regulates genes that promote mitochondrial biogenesis and oxidative metabolism (39). In support of this, GO terms associated with leading edge genes underlying positive enrichment of the MYC Targets geneset included ribonucleoprotein complex biogenesis, translational initiation, peptide biosynthetic processes, spliceosomal complex assembly, and RNA binding.…”

Discovery of a Cushing’s syndrome protein kinase A mutant that biases signaling through type I AKAPs

“…In comparison to type II PKA, the type I holoenzyme is activated at sevenfold lower levels of second messenger (43)(44)(45). Thus, an increased RI to RII ratio should sensitize tumors to cAMP.…”