Gebr-7b counteracts the epithelial-to-mesenchymal transition by modulating transcription of the IGF2/H19 cluster in HCC cell lines

The epithelial-to-mesenchymal transition (EMT) is associated with metastasis and chemoresistance in many types of cancers including hepatocellular carcinoma (HCC). In a few tumours, a connection between EMT activation and disruption of the cAMP pathway has been found. Moreover, overexpression of phosphodiesterase 4D (PDE4D) seems to be involved in this process. Our previous study1 showed that PDE4D is overexpressed in HCC cell lines and tissues, and its depletion/inhibition reduced the growth of HCC cells by causing apoptosis and interfering with the expression of various cell cycle effectors and other pro-oncogenic genes, such as the insulin growth factor 2 (IGF2) gene. However, regulation of the PDE4D-IGF2 network and its role in the EMT remain to be explored. IGF2 is an imprinted gene whose transcription is regulated in a cluster with the H19 gene, which produces a non-coding RNA. After PDE4D silencing/inhibition we found a significant downregulation of IGF2 gene and protein expression in HCC, and in this tumour IGF2 protein expression positively correlated with cell proliferation, migration and invasion. Here, we also show that selective pharmacological inhibition of PDE4D, using Gebr-7b, induces cell-cell adhesion proteins, such as E-cadherin, and decreases mesenchymal markers, including Snail and Twist, in Western Blot experiments. Gebr-7b treatment also significantly reduced HCC cell migration, as revealed by Incucyte® Scratch Wound Assays. In addition, Gebr-7b treatment induces deregulation of the IGF2/H19 cluster. It is conceivable that this PDE4D-dependent modulation of the IGF2/H19 cluster could be crucial in the control of the EMT in HCC. These preliminary data suggest that targeting of PDE4D may reverse the EMT, thus preventing metastatic dissemination of HCC by acting on the IGF2/H19 cluster. (1) Ragusa F. et al. Cancers 2021, 13(9), 2182.