Lin28 Enhances Tumorigenesis and is Associated With Advanced Human Malignancies

Multiple members of the let-7 family of miRNAs are often repressed in human cancers 1 , 2 , thereby promoting oncogenesis by de-repressing the targets K-Ras, c-Myc, and HMGA2 3 , 4 . However, the mechanism by which let-7 miRNAs are coordinately repressed is unclear. The RNA-binding proteins Lin28 and Lin28B block let-7 precursors from being processed to mature miRNAs 5 – 8 , suggesting that over-expression of Lin28/Lin28B might promote malignancy via repression of let-7. Here we show that LIN28 and LIN28B are over-expressed in primary human tumors and human cancer cell lines (overall frequency ∼15%), and that over-expression is linked to repression of let-7 family miRNAs and de-repression of let-7 targets. Lin28/Lin28B facilitate cellular transformation in vitro , and over-expression is associated with advanced disease across multiple tumor types. Our work provides a mechanism for the coordinate repression of let-7 miRNAs observed in a subset of human cancers, and associates activation of LIN28/LIN28B with poor clinical prognosis.