HEY1 and pachyonychia congenita: In human PC cell lines, the downregulation of PTOV1 induced an upregulation of the endogenous HEY1 and HES1 genes, and reciprocally, the ectopic expression of PTOV1 in PC cells and HaCaT keratinocytes, where Notch acts as tumor suppressor, caused the inhibition of expression of HEY1 and HES1 genes [70, 71].