CDK4 and pachyonychia congenita: To further investigate the relevance, we examined the cell cycle checkpoint markers expression, CDK1, CDK2, CDK4, CDK6, CyclinA1, CyclinD1, CyclinE1, and CDC25A. As a result, the majority of the checkpoint markers were altered in both shZNF507 treated PC cell lines (Fig. 3C, D).