MicroRNA expression in E6/E7 HPV-transformed human keratinocytes. Effects of IFN beta treatment

Background: MicroRNAs (miRNAs) represent a class of small ( 22 nt), non-codifying RNAs involved in the negative regulation of mRNAs expression. They normally bind the 3' UTR region of mRNAs, either inhibiting translation or promoting mRNA specific degradation. They are involved in the regulation of several cellular processes including proliferation, differentiation, embryonic development and apoptosis. Accumulating evidence indicates a role of miRNAs also in tumorigenesis as it is well known that tumor cells bear a specific and altered pattern of miRNAs expression. Objectives: In an initial attempt, we sought to check the levels of three HPV-associated miRNAs (miR-126, miR-155 and miR-223). We also tested the effect of IFN b treatment on the miRNAs expression and on the putative miRNAs targets expression. Methods: We used primary keratinocytes transformed by both E6 and E7 proteins derived from mucosal or cutaneous HPV (HPV-16 and -38, respectively named K16 and K38). We also used HPV-positive (CaSki, SiHa) or -negative (primary keratinocytes and C33A) cells. MiRNAs expression was checked using a specific TaqMan Small RNA Assay from Applied Biosysthems, mRNAs expression by Sybr-green based RT-PCR and protein expression by Western Blot. Results and Conclusions: Preliminary miRNAs analysis revealed that, if compared to normal keratinocytes, miR-126 and miR-155 are differentially expressed in K16 and K38, being miR-126 under-expressed in K16 and over-expressed in K38; miR-155 is, instead, over-expressed in K16 and under-expressed in K38. Putative miRNA-155 target K-Ras is over-expressed in all HPV positive cells tested, compared to HPV negative C33A squamous carcinoma cell line. IFN b treatment has no effects on K-Ras expression in K16 and, surprisingly, downregulates K-Ras expression in the other HPV positive cells whereas upregulates K-Ras expression in C33A cells. These results indicate a correlation between HPV genotypes and miRNAs expression profiles evidentiating also the ability of the antitumoral agent IFN b to interfere with E6 and/ or E7-induced miRNAs dysregulation.