Reversion of tumor hepatocytes to normal hepatocytes during liver tumor regression in an oncogene-expressing transgenic zebrafish model

Abstract

Tumors are frequently dependent on primary oncogenes to maintain their malignant properties (known as ‘oncogene addiction’). We have previously established several inducible hepatocellular carcinoma (HCC) models in zebrafish by transgenic expression of an oncogene. These tumor models are strongly oncogene addicted, as the induced and histologically proven liver tumors regress after suppression of oncogene expression by removal of a chemical inducer. However, the question of whether the liver tumor cells are eliminated or revert to normal cells remains unanswered. In the present study, we generated a novel Cre/loxP transgenic zebrafish line, Tg(fabp10: loxP-EGFP-stop-loxP-DsRed; TRE: CreERT2) (abbreviated to CreER), in order to trace tumor cell lineage during tumor regression after crossing with the xmrk (activated EGFR homolog) oncogene transgenic line, Tg(fabp10: rtTA; TRE: xmrk; krt4: EGFP). We found that, during HCC regression, restored normal liver contained both reverted tumor hepatocytes (RFP+) and newly differentiated hepatocytes (GFP+). RNA sequencing (RNA-seq) analyses of the RFP+ and GFP+ hepatocyte populations after tumor regression confirmed the conversion of tumor cells to normal hepatocytes, as most of the genes and pathways that were deregulated in the tumor stages were found to have normal regulation in the tumor-reverted hepatocytes. Thus, our lineage-tracing studies demonstrated the potential for transformed tumor cells to revert to normal cells after suppression of expression of a primary oncogene. This observation may provide a basis for the development of a therapeutic approach targeting addicted oncogenes or oncogenic pathways.

Evolutionarily novel genes are expressed in transgenic fish tumors and their orthologs are involved in development of progressive traits in humans

“…Thus we consider liver after tumor regression as a model of a «new» evolving organ. Such consideration is supported by a recent publication [31] that showed reversion of tumor hepatocytes to normal hepatocytes, although with somewhat different properties, during liver tumor regression in an oncogene transgenic zebrafish model. That is why we performed a study of expression of evolutionary novel genes in transgenic zebrafish tumors after their regression in experimental conditions.…”

“…In the recent paper of Li et al, [31] the authors have shown that after reversion of tumor hepatocytes to normal hepatocytes during liver tumor regression in an oncogene transgenic zebrafish model, some tumor signaling pathways remain activated in tumor-reverted hepatocytes, according to transcriptomes analysis. This is in accordance with the data obtained in the present article.…”

Resolution of Complex Issues in Genome Regulation and Cancer Requires Non-Linear and Network-Based Thermodynamics

“…Still more intriguing is the action of retinoic acid, which was initially demonstrated to promote reversion of teratocarcinoma [168], has been later recognized to induce a nearly complete differentiation of leukemogenic cells in acute promyelocytic leukemia through the induction of terminal differentiation into granulocytes [169], thus reversing cell fate from cancer to healthy fully differentiated state, which can, in turn, lead to partial or complete clinical remission. Recently [170], such a cell fate reversion was also observed for a solid tumour. The most recent achievement, the conversion of breast invasive cancer cells into adipocytes, was shown in a mouse model while using PPAR-gamma (member of nuclear receptors regulating adipocyte differentiation) agonist combined with the MEK inhibitor [171].…”

Inducible Liver Cancer Models in Transgenic Zebrafish to Investigate Cancer Biology

“…There are two possible mechanisms of tumour regression: (1) tumour hepatocytes undergo cell death and are eliminated while normal hepatocytes eventually replace these tumour hepatocytes via proliferation and differentiation, and (2) tumour hepatocytes might be directly reverted to normal hepatocytes. In order to test the two possibilities, we developed a CreER transgenic line that allowed us to trace liver cell lineage (Figure 1F) [82]. In this transgenic line, tamoxifen-activated Cre protein, CreER T2 , is expressed only in the presence of doxycycline.…”