HDAC4 and pachyonychia congenita: In addition, recent basic research uncovered that cigarette smoke extract (CSE) exposure can not only significantly promote PC attributable to smoking progression by upregulating of Chromobox protein homolog 3 (CBX3) via promoting the overexpression of Y-box-binding protein 1 (YBX1) but also the invasion and metastasis of the cancer cells by inducing histone deacetylase 4 (HDAC4) (10, 11).