As shown in Figure 7, after transfection of siL21-1 and siL21-2 in PC cells, the expression of RPL21 is downregulated, resulting in decreased transcription of the transcription factor E2F1. It has been shown previously that the downregulation of CCND1 and CCNE1 also resulted in the inactivation of E2F1 due to the binding of non-phosphorylated Rb and E2F1 (43), which caused the suppression of proliferation and G1-S transition through the regulation of E2F1. Together it is suggested that RPL21 may control DNA replication and G1-S phase progression through E2F1 regulation in PC cells. Here, CCND1 is linked to pachyonychia congenita.