Aberrant expression of the epidermal growth factor receptor (EGFR) and/or human epidermal growth factor receptor 2 (HER2) is a feature of many human tumors and is associated with disease progression, treatment resistance, and poor prognosis. Protein kinase B/Akt, an important downstream effector of these receptor tyrosine kinases, induces signaling pathways that control cancer cell proliferation, invasion, angiogenesis, and apoptosis resistance. MicroRNAs (miRNAs), small noncoding RNAs that bind to the 3′-untranslated region of target mRNAs, are now recognized to play key roles in the regulation of gene expression, particularly in tumor development and metastasis. We have shown that miRNA-7 (miR-7) and miRNA-331-3p (miR-331-3p) directly regulate expression of EGFR and HER2, respectively, in glioblastoma and prostate cancer cell lines. As a consequence, miR-7 and miR-331-3p reduce Akt activity and thus have the capacity to regulate a signaling pathway critical to the development and progression of glioblastoma and prostate cancer. This chapter provides a detailed approach outlining how to confirm that a putative target of a miRNA is a direct target, and subsequent assessment of downstream signaling mediators.
