Cryptic lncRNA-encoded ORFs: A hidden source of regulatory proteins.

A majority of the human genome is transcribed into noncoding RNAs, of which long noncoding RNAs (lncRNAs) form a large and heterogeneous fraction. While lncRNAs are mostly noncoding, recent evidence suggests that cryptic translation within some lncRNAs may produce proteins with important regulatory functions. In this issue of the JCI, Zheng, Wei, and colleagues used an integrative functional genomic strategy to systematically identify cryptic lncRNA-encoded ORFs that play a role in estrogen receptor-positive (ER+) breast cancer (BC). They identified 758 cryptic lncRNA-encoded ORFs undergoing active translation, of which 28 had potential functional and clinical relevance in ER+ BC. The LINC00992-encoded polypeptide GT3-INCP was upregulated in ER+ BC and drove tumor growth. GT3-INCP was regulated by estrogen and the ER and acted via the transcription factor GATA3 to regulate BC susceptibility and risk genes. These findings discern a largely unexplored class of molecules and have implications for many pathologies, including cancer.