Nucleophosmin 1 induction is an early event in a Phenobarbital induced proliferation response in rat but not human liver 3D microtissues

A key event in the process of rat but not human liver carcinogenesis caused by constitutive androstane receptor activators such as phenobarbital (PB) is hepatocyte proliferation, but the mechanism(s) underpinning this response is not fully understood. Previously we showed that rat liver microtissues (LiMTs) can recapitulate a PB-induced hepatocyte proliferation response (1). In this follow up study we used our microTMA technology coupled with transcriptomics and immunofluorescence (IF) staining to elucidate mechanisms of rat liver carcinogenesis in this model. We performed gene set enrichment analysis (GSEA) on transcriptomics data generated from laser microdissected liver microtissue microTMA FFPE sections from control and PB-treated LiMTs against custom liver cell proliferation and constitutive androstane receptor (CAR) activation signatures (2) and found that the former signature was significantly (q<0.25) enriched in rat but not human LiMT differentially expressed gene lists. This process also identified the cell proliferation gene nucleophosmin 1 (NPM1) as being significantly induced (p < 0.05) in rat but not human LiMTs. IF staining of parallel microTMA FFPE sections coupled with quantitative image analysis confirmed that the NPM1 protein was induced by PB treatment in rat but not human liver microtissues after 24 and 48 hrs PB treatment. In conclusion we have identified induction of nuclear NPM1 expression as an early event in PB-induced rat hepatocyte cell proliferation.