MicroRNAs (miRNA) play pivotal roles in controlling cell proliferation and differentiation. Aberrant miRNA expression in human is becoming recognized as a new molecular mechanism of carcinogenesis. However, the causes for alterations in miRNA expression remain largely unknown. Infection with oncogenic human papillomavirus types 16 (HPV16) and 18 (HPV18) can lead to cervical and other ano-genital cancers. Here, we have demonstrated that cervical cancer tissues and cervical cancer- derived cell lines containing oncogenic HPVs display reduced expression of tumor-suppressive miR-34a. The reduction of miR-34a expression in organotypic tissues derived from HPV-containing primary human keratinocytes correlates with the early productive phase and is attributed to the expression of viral E6, which destabilizes the tumor suppressor p53, a known miR-34a transactivator. Knockdown of viral E6 expression in HPV16+ and HPV18+ cervical cancer cell lines by siRNAs leads to an increased expression of p53 and miR-34a and accumulation of miR-34a in G 0/G1 phase cells. Ectopic expression of miR-34a in HPV18+ HeLa cells and HPV- HCT116 cells results in a substantial induction of cell growth retardation and a moderate cell apoptosis. Together, this is the first time a viral oncoprotein has been shown to regulate cellular miRNA expression. Our data have provided new insights into mechanisms by which high-risk HPVs contribute to the development of cervical cancer. Copyright © 2009 RNA Society.