Uncovering pathogenesis of the DNAJ-PKAc fusion in fibrolamellar carcinoma

Abstract

Fibrolamellar carcinoma (FLC) is a rare liver cancer that occurs in healthy adolescents and young adults. FLCs uniquely produce DNAJ-PKAc, a de novo chimeric enzyme consisting of a chaperonin-binding domain fused to the Cα subunit of protein kinase A. FLC patients do not consistently respond to conventional chemotherapy, or to any directed agents that have been tested to date; the search for new therapies for these patients is hindered by the limited availability of clinical samples and a lack of disease relevant cell lines or viable animal models that faithfully recapitulate the pathogenesis of FLC. We performed gene-editing on non-transformed mouse hepatocytes to generate disease-relevant cell lines (AML12DNAJ-PKAc cells). Biochemical analyses of clinical samples and disease-relevant cell lines reveal that a unique property of DNAJ-PKAc is its ability to recruit and bind heat shock protein 70 (Hsp70). Drug screening reveals that Hsp70 and MEK kinase inhibitor combinations that selectively block proliferation of AML12DNAJ-PKAc cells. Further analyses indicate that the proto-oncogene A-kinase anchoring protein (AKAP)-Lbc is up-regulated in FLC and functions to cluster DNAJ-PKAc/Hsp70 sub-complexes with a RAF-MEK-ERK kinase module. Phosphoproteomic profiling of AML12DNAJ-PKAc cells demonstrates that DNAJ-PKAc biases the signaling landscape toward ERK activation, and mobilizes other downstream kinase cascades. Thus we propose the oncogenic action of DNAJ-PKAc proceeds through an acquired scaffolding function that permits recruitment of Hsp70 and local ERK signaling.