Hepatitis B virus x (HBx) protein increases cellular OCT3/4 and MYC and facilitates cellular reprogramming

Abstract

HBx is a multifunctional protein coded by the Hepatitis B virus which is involved in various cellular processes such as proliferation, cell survival or apoptosis, and histone methylation. HBx was reported to be associated with liver cancer stem cells. The stemness inducing properties of HBx could also facilitate the generation of pluripotent stem cells from somatic cells. It is well established that somatic cells can be reprogrammed to induced pluripotent stem cells (iPSC) using a cocktail of transcription factors called Yamanakas factors (OCT4, SOX2, KLF4, and MYC). The reprogramming process proceeds step-by-step with reprogramming factor chromatin interactions, transcription and chromatin states changing during transitions. HBx is a broad-spectrum trans-activator and therefore could facilitate these transitions. We electroporated low passage and high passage (difficult to reprogram) fibroblasts using Yamanakas factors (YF) with and without HBx and evaluated the reprogramming efficiency. We also investigated the tri-lineage and terminal differentiation potential of iPSC derived using HBx. We found, addition of HBx to YF, improves iPSC derivation, and increases the efficiency of iPSC generation from difficult or hard-to-reprogram samples such as high passage/senescent fibroblasts. Furthermore, we show that HBx can substitute the key transcription factor MYC in the YF cocktail to generate iPSC. Our results have practical value in improving the efficiency of pluripotent stem cell derivation from difficult to reprogram somatic cells in addition to providing some insights into the mechanisms of liver carcinogenesis in chronic hepatitis B. To conclude, HBx improves the reprogramming efficiency of YFs. HBx increases the cellular levels of OCT3/4 and MYC. Lay summary: HBx is a protein made by hepatitis B virus. Yamanakas Factors (YF) are a mixture of master-proteins which are used to convert adult cells to embryonic stem cells. We found that HBx protein can augment the efficiency of YF in generating these stem cells (concept summary figure).