A study showed that HIF-1α upregulated p21 expression and induced G2/M arrest and fibrogenesis in HK-2 cells treated with aristolochic acid, and the inhibition of p21 prevented G2/M phase arrest and fibrogenesis in those cells, suggesting that there is a connection between G2/M phase arrest of PTECs and renal fibrosis, and that p21 modulates the process [52]. Here, CDKN1A is linked to renal fibrosis.