Figure 1.

MicroRNA oncogenes and tumor suppressors. (A) Normally, microRNA (miRNA) binding to target mRNA represses gene expression by blocking protein translation or inducing miRNA degradation, contributing to homeostasis of growth, proliferation, differentiation, and apoptosis. (B) Reduced miRNA levels, reflecting defects at any stage of miRNA biogenesis (indicated by question marks), produce inappropriate expression of target oncoproteins (purple squares). The resulting defects in homeostasis increase proliferation, invasiveness or angiogenesis, or decrease levels of apoptosis or differentiation, potentiating tumor formation. (C) Conversely, overexpression of an oncogenic miRNA eliminates the expression of tumor‐suppressor genes (pink), leading to cancer progression. Increased levels of mature miRNA could reflect amplification of the miRNA gene, a constitutively active promoter, increased efficiency in miRNA processing or increased stability of the miRNA (indicated by question marks). ORF, open reading frame. Figure reproduced from Esquela‐Kerscher and Slack. ⁴