Barbosa, A. C. | Search bioRxiv

bioRxiv2019

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

BackgroundHepatoblastoma is an embryonal liver tumor supposed to arise from the impairment of hepatocyte differentiation during embryogenesis. CTNNB1 is the only recurrently mutated gene, and this relative paucity of somatic mutations poses a challenge to risk stratification and development of targeted therapies. MethodsIn this study, we investigated by exome sequencing the burden of somatic mutations in a cohort of 10 hepatoblastomas, including a congenital case. ResultsOur data disclosed a low mutational background with only three recurrently mutated genes: CTNNB1 and two novel 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, potentially related to chemotherapy response and progression. 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 with an increase of C>A mutations. ConclusionsOverall, we present here evidence that CX3CL1/CX3CR1 chemokine signaling pathway is likely involved with hepatoblastoma tumorigenesis or progression, besides reporting a novel mutational signature specific to a hepatoblastoma subset.

cancer biology↗

bioRxiv2019

Budding yeast centromeric DNA and A+T rich bacterial DNA can function as centromeres in the fission yeast Schizosaccharomyces pombe.

Eukaryotic centromeric DNA is famously variable in evolution but currently, this cannot be reconciled with the conservation of eukaryotic centromere function. It seems likely that centromeric DNA from different organisms contains conserved functionally important features but the identity of these features is unknown. The point centromeres of the budding yeast Saccharomyces cerevisiae and the regional centromeres of the fission yeast Schizosaccharomyces pombe are separated by 350 million years of evolution and are canonical examples of the paradoxical relationship1 between centromeric DNA sequence and function. We have established a centromere-replacement strategy in Schizosaccharomyces pombe in order to resolve this paradox experimentally. Centromere-replacement shows that an A+T rich bacterial DNA sequence has weak centromere function and that elements of the Saccharomyces cerevisiae centromere embedded in short sequences from the non-centromeric S. pombe wee1 gene function almost as well as native S. pombe centromeric DNA. These observations demonstrate that determinants of centromere function are held in common by the budding and fission yeasts and that A+T rich DNA is both necessary and sufficient for function in S. pombe. Given the evolutionary distance between these yeasts, it is likely that A+T rich DNA has centromere function in a wide variety of eukaryotes. Centromere-replacement uses unidirectional serine recombinases that work well in many organisms2 3 and our experimental strategy should allow this idea to be tested in other eukaryotes.

genetics↗