DNAJB1-PRKACA Fusion Drives Fibrolamellar Liver Cancer through Impaired SIK Signaling and CRTC2/p300-Mediated Transcriptional Reprogramming

Fibrolamellar carcinoma (FLC) is a liver cancer of adolescents and young adults characterized by fusions of the genes encoding the protein kinase A catalytic subunit, PRKACA, and heat shock protein, DNAJB1. The chimeric DNAJB1-PRKACA protein has increased kinase activity and is essential for FLC xenograft growth. Here, we explore the critical oncogenic pathways controlled by DNAJB1-PRKACA using patient-derived FLC models, engineered systems, and patient samples. We show that a core function of DNAJB1-PRKACA is the phosphorylation and inactivation of salt-inducible kinases (SIKs). This leads to deregulation of the CRTC2 transcriptional coactivator and p300 acetyltransferase, resulting in transcriptional reprogramming and increased global histone acetylation, driving malignant growth. Our studies establish a central oncogenic mechanism of DNAJB1-PRKACA and suggest the potential of targeting CRTC2/p300 in FLC. Notably, these findings link this rare cancer’s signature fusion oncoprotein to more common cancer gene alterations involving STK11 and GNAS, which also function via SIK suppression. Sge: This work combines functional studies in model systems and examination of human tumor specimens to define a central oncogenic pathway driven by DNAJB1-PRKACA fusions in FLC. DNAJB1-PRKACA-mediated inactivation of the SIK stimulates CRTC2-p300-mediated transcription to drive tumor growth. The findings illuminate pathogenic mechanisms and inform therapeutic development.