MicroRNA Regulation of Cholesteatoma Growth

Objectives: Identify novel regulatory mechanisms controlling growth and proliferation of cholesteatoma. Specifically, the potential role of microRNAs and downstream proteins was studied in cholesteatoma. Study Design: This study represents a molecular biological investigation characterizing and comparing microRNA and protein expression. Methods: Cholesteatoma and normal skin were taken from patients at the time of surgery. Tissue was processed for RNA and protein extraction. Real-time RT-PCR was used to assess levels of human microRNAs. Western blot analyses were used to assess levels of upstream and downstream regulatory proteins. Results: Several microRNAs were found to be up-regulated in cholesteatoma as compared to normal skin, especially microRNA-21 (hsa-mir-21), which has been associated with numerous other human neoplasms. Further characterization of hsa-mir-21 showed a greater than 4-fold higher expression in cholesteatoma. The downstream targets of hsa-mir-21, PTEN and PDCD4, were found to be reduced in cholesteatoma compared to normal skin. Activators of hsa-mir-21 expression were also differentially regulated between the tissues. Conclusions: Hsa-mir-21 causes down-regulation of the potent tumor suppressor gene PTEN which regulates apoptosis, proliferation, invasion and migration. It also regulates PDCD4 which has been implicated in cutaneous neoplasms. This study has identified differential regulation of these factors in cholesteatoma when compared to normal skin. The presence of microRNA regulators provides pharmacological targets for the adjunctive or primary treatment of cholesteatoma.