The HDAC inhibitor domatinostat induces type I interferon α in Merkel cell carcinoma by HES1 repression

by Selleckchem | Jun 15 2023

Background: Class I selective histone deacetylase inhibitors (HDACi) have been previously demonstrated to not only increase major histocompatibility complex class I surface expression in Merkel cell carcinoma (MCC) cells by restoring the antigen processing and presentation machinery, but also exert anti-tumoral effect by inducing apoptosis. Both phenomena could be due to induction of type I interferons (IFN), as has been described for HDACi. However, the mechanism of IFN induction under HDACi is not fully understood because the expression of IFNs is regulated by both activating and inhibitory signaling pathways. Our own preliminary observations suggest that this may be caused by suppression of HES1.

Methods: The effect of the class I selective HDACi domatinostat and IFNα on cell viability and the apoptosis of MCPyV-positive (WaGa, MKL-1) and -negative (UM-MCC 34) MCC cell lines, as well as, primary fibroblasts were assessed by colorimetric methods or measuring mitochondrial membrane potential and intracellular caspase-3/7, respectively. Next, the impact of domatinostat on IFNA and HES1 mRNA expression was measured by RT-qPCR; intracellular IFNα production was detected by flow cytometry. To confirm that the expression of IFNα induced by HDACi was due to the suppression of HES1, it was silenced by RNA interference and then mRNA expression of IFNA and IFN-stimulated genes was assessed.

Results: Our studies show that the previously reported reduction in viability of MCC cell lines after inhibition of HDAC by domatinostat is accompanied by an increase in IFNα expression, both of mRNA and at the protein level. We confirmed that treatment of MCC cells with external IFNα inhibited their proliferation and induced apoptosis. Re-analysis of existing single-cell RNA sequencing data indicated that induction of IFNα by domatinostat occurs through repression of HES1, a transcriptional inhibitor of IFNA; this was confirmed by RT-qPCR. Finally, siRNA-mediated silencing of HES1 in the MCC cell line WaGa not only increased mRNA expression of IFNA and IFN-stimulated genes but also decreased cell viability.

Conclusion: Our results demonstrate that the direct anti-tumor effect of HDACi domatinostat on MCC cells is at least in part mediated via decreased HES1 expression allowing the induction of IFNα, which in turn causes apoptosis.

Comments:

The background information suggests that class I selective histone deacetylase inhibitors (HDACi), such as domatinostat, can increase major histocompatibility complex class I surface expression in Merkel cell carcinoma (MCC) cells and induce apoptosis. It is believed that these effects may be due to the induction of type I interferons (IFNs), although the exact mechanism is not fully understood. Preliminary observations indicate that the suppression of HES1, a transcriptional inhibitor of IFNA, may be responsible for the induction of IFNα by HDACi.

To investigate this further, the researchers in the study conducted several experiments. They assessed the effect of domatinostat and IFNα on cell viability and apoptosis in MCC cell lines and primary fibroblasts. They measured the expression of IFNA and HES1 mRNA using RT-qPCR and detected intracellular IFNα production using flow cytometry. To confirm the involvement of HES1 in IFNα induction, they used RNA interference to silence HES1 and assessed the expression of IFNA and IFN-stimulated genes.

The results of the study showed that inhibition of HDAC by domatinostat reduced the viability of MCC cell lines and increased the expression of IFNα at both mRNA and protein levels. Treatment with external IFNα inhibited the proliferation of MCC cells and induced apoptosis. Re-analysis of single-cell RNA sequencing data indicated that domatinostat induced IFNα expression by suppressing HES1. This was confirmed by RT-qPCR. Silencing HES1 in MCC cells increased the expression of IFNA and IFN-stimulated genes while decreasing cell viability.

In conclusion, the study demonstrated that the anti-tumor effect of HDACi domatinostat on MCC cells involves decreased HES1 expression, leading to the induction of IFNα and subsequent apoptosis. This suggests a potential mechanism by which HDACi can regulate the antigen processing and presentation machinery and exert anti-tumoral effects in MCC.