Noncoding microRNAs act as posttranscriptional repressors of gene function and 
are often deregulated in cancers and other diseases. Here we review recent 
findings on microRNA roles in tumorigenesis and report a microRNA profiling 
screen in transforming growth factor-beta1 (TGF-beta)-induced 
epithelial-mesenchymal transition (EMT) in human keratinocytes, a model of 
epithelial cell plasticity underlying epidermal injury and skin carcinogenesis. 
We describe a novel EMT-specific microRNA signature that includes induction of 
miR-21, a candidate oncogenic microRNA associated with carcinogenesis. By 
integrating the microRNA screen results with target prediction algorithms and 
gene expression profiling data, we outline a framework for TGF-beta-directed 
microRNA:messenger RNA (mRNA) regulatory circuitry and discuss its biological 
relevance for tumor progression.