DNMT1 and infection: At every 24 hours within 4 days after lentiviruses infection of SiHa and CaSki, we used Q-PCR to analyze the expression of E6, E7, DNA methyltransferase genes (DNMT1, DNMT3A, DNMT3B and DNMT3L) [37], and tumor suppressor genes (MT1G, NMES1, RRAD, SFRP1, SPARC and TFPI2).