DnaJ-PKAc fusion induces liver inflammation in a zebrafish model of Fibrolamellar Carcinoma

Abstract

Fibrolamellar Carcinoma (FLC) is a rare liver cancer that affects adolescents and young adults. Genomic analysis in FLC has revealed a 400 kB deletion in chromosome 19 that leads to a fusion protein, DNAJB1-PRKACA (DnaJ-PKAc) comprised of the first exon of the heat shock protein 40 (DNAJB1) and exons 2–10 of the catalytic subunit of protein kinase A (PRKACA). Here, we report a new zebrafish model of FLC induced by ectopic expression of zebrafish DnaJa-Pkaca (zfDnaJ-Pkaca) in hepatocytes that is amenable to live imaging of early innate immune inflammation. Expression of zfDnaJ-Pkaca in hepatocytes induces hepatomegaly and increased hepatocyte size. In addition, FLC larvae exhibit early innate immune inflammation characterized by early infiltration of neutrophils and macrophages into the liver microenvironment. Increased caspase-a activity was also found in the liver of FLC larvae, and pharmacological inhibition of TNFα and caspase-a decreased liver size and inflammation. Overall, these findings show that innate immune inflammation is an early feature in a zebrafish model of FLC and that that pharmacological inhibition of TNFα or caspase-1 activity might be targets to treat inflammation and progression in FLC.

Inflammatory Responses during Tumour Initiation: From Zebrafish Transgenic Models of Cancer to Evidence from Mouse and Man

“…In support of the latter, leukocyte heterogeneity was observed in zebrafish studies of tumour initiation; only 20% of leukocytes recruited to PNCs in the skin expressed PGE synthase, whilst minor populations of macrophages were positive for either M1 (TNFα) or M2 (arginase-1) markers [6,7]. Furthermore, in response to oncogenic transformation in the liver, only 35% of macrophages were TNFα positive [146].…”

“…Whilst the independent influence of oncogene-dependent inflammation is yet to be determined in this model, a combination of β-catenin expression and high fat diet induced a strong tumour-promoting inflammatory response, which was associated with TNFα positive macrophages. Finally, modelling a rare type of liver cancer (fibromellar carcinoma), by transgenic expression of a DnaJ-PKAc fusion protein, resulted in leukocyte recruitment to the liver [146]. Here too, an increase of TNFα positive macrophages was observed, alongside a liver-wide activation of caspase-1, indicating inflammasome activation and IL-1β release.…”

“…Zebrafish skin and liver cancer models showed an upregulation of the pro-inflammatory cytokines IL-1β and TNFα in response to tumour initiation [6,7,68,78,140,146]. Both of these inflammatory cytokines were important for the recruitment of leukocytes to the liver [146].…”

“…Dichotomously, TNFα signalling can also directly induce apoptosis of cancer cells, or promote cell survival through activation of NF-κB signalling [165]. Although the direct effect of TNFα upon PNCs has not been explored in zebrafish models of tumour initiation, the latter mechanism is more likely since no signs of leukocyte-mediated cell death have been recorded and TNFα positive macrophages promote tumourigenesis in zebrafish liver cancer models [140,146]. Figure 1.…”

“…Promotes neoplasm formation and leukocyte recruitment in the skin and colon [152][153][154]. Promotes PNC proliferation and leukocyte recruitment in the liver [146].…”