Engineering CHO cell growth by stable manipulation of miRNA expression

Background MiRNAs are small non-coding RNAs involved in many biological functions such as cell proliferation and apoptosis (1), cell cycle (2), homeostasis (3) and cell metabolism (4). They are highly conserved between species. They are capable of regulating hundreds of genes in a post-transcriptional manner by translation repression and/or mRNA degradation (5). These characteristics make miRNAs attractive tools for CHO cell engineering as multiple genes may be targeted simultaneously and possibly entire biological pathways can be manipulated. After temperature-shifting CHO cell culture from 37°C to 31°C, several miRNAs were found differentially regulated of which miR-7 was found to be down-regulated. Our laboratory has previously demonstrated that transient overexpression of miR-7 using mimics of mature endogenous miR-7, leads to a significant decrease in cell growth (6). On the other hand, transient inhibition using inhibitors of mature endogenous miR-7 provoked increased cell growth, though to a lesser extent. As this antisense technology is transient, another strategy was chosen to study the impact of stable miR-7 inhibition on CHO phenotypes. “Sponge” technology is an effective tool to stably sequester endogenous miRNAs (7) by introducing a decoy target reporter gene. This approach can be used to understand post-transcriptional regulation in CHO cells and to identify cellular pathways related to cell growth, cell viability and cell productivity key phenotypes for cell bioprocess improvement.