Mutational burden of hepatoblastomas: a role for the CX3CL1/CX3CR1 chemokine signaling pathway

Hepatoblastoma is an embryonal liver tumor supposed to arise from the impairment of hepatocyte differentiation during embryogenesis. CTNNB1 is the only recurrently mutated gene. In this study, we investigated by exome sequencing the burden of somatic mutations in a cohort of 10 hepatoblastomas, including a congenital case. Our data disclosed a low mutational background with only three recurrently mutated genes: CTNNB1 and two candidates, CX3CL1 and CEP164. The major finding was a recurrent mutation (A235G) identified in two hepatoblastomas at the CX3CL1 gene; evaluation of RNA and protein expression revealed up-regulation of CX3CL1 in tumors. The analysis was replicated in two independents cohorts, substantiating that an activation of the CX3CL1/CX3CR1 pathway occurs in hepatoblastomas, with a predominance of these proteins in the cytoplasm of tumor cells. These proteins were not detected in the infiltrated lymphocytes of inflammatory regions of the tumors, in which they should be expressed in normal conditions, whereas necrotic regions exhibited negative tumor cells, but strongly positive infiltrated lymphocytes. Our data suggested that CX3CL1/CX3CR1 upregulation may be a common feature of hepatoblastomas. In addition, three mutational signatures were identified in hepatoblastomas, two of them with predominance of either the COSMIC signatures 1 and 6, found in all cancer types, or the COSMIC signature 29, related only with tobacco chewing habit; a third novel mutational signature presented an unspecific pattern. Overall, we present here evidence that CX3CL1/CX3CR1 chemokine signaling pathway is involved with hepatoblastoma tumorigenesis or progression, besides reporting a novel mutational signature specific to a hepatoblastoma subset.