PDE4D and nasopharyngeal carcinoma: As demonstrated by MTT assay (Fig 2B), following treatment with 100 ng/ml recombinant human EGF, the LV-PDE4D shRNA-infected CNE2 and 5–8F cells exhibited increased cell proliferation compared with the untreated cells, which reversed the effect of LV-PDE4D shRNA on the NPC cells.