The long intergenic non-coding RNA CCR492 functions as a let-7 competitive endogenous RNA to regulate c-Myc expression

In mammals the cell-cycle progression through the G1 phase is a tightly regulated process mediated by the transcriptional activation of early genes in response to mitogenic stimuli, whose dysregulation often leads to tumorigenesis. We here report the discovery by RNA-seq of cell-cycle regulated (CCR) long intergenic non-coding RNAs (lincRNAs), potentially involved in the control of the cell-cycle progression. We identified 10 novel lincRNAs expressed in response to serum treatment in mouse embryonic fibroblasts (MEFs) and in BALB/c fibroblasts, comparably to early genes. By loss-of-function experiments we found that lincRNA CCR492 is required for G1/S progression, localizes in the cell cytoplasm and contains 4 let-7 microRNA recognition elements (MREs). Mechanistically, CCR492 functions as a competing endogenous RNA (ceRNA) to antagonize the function of let-7 microRNAs, leading to the de-repression of c-Myc. Moreover, we show that ectopic expression of CCR492 along with a constitutively active H-Ras promotes cell transformation. Thus, we identified a new lincRNA expressed as an early gene in mammalian cells to regulate the cell-cycle progression by upregulating c-Myc expression.