Either qRT-PCR or Western blot demonstrated that Sp1 knockdown obviously up-regulated the levels of p27 and p21, but had no effect on the expression levels of CDK4 (Figure 4C and D), indicating Sp1 knockdown blocked the G1/S transition through induction of p27 and p21 in NPC cells. The gene discussed is SP1; the disease is nasopharyngeal carcinoma.