Spontaneously slow-cycling subpopulations of human cells originate from activation of stress response pathways

Slow-cycling subpopulations exist in bacteria, yeast, and mammalian systems. In the case of cancer, slow-cycling subpopulations have been proposed to give rise to drug resistance. However, the origin of slow-cycling human cells is poorly studied, in large part due to lack of markers to identify these rare cells. Slow-cycling cells pass through a non-cycling period marked by low CDK2 activity and high p21 levels. Here, we use this knowledge to isolate these naturally slow-cycling cells from a heterogeneous population and perform RNA-sequencing to delineate the transcriptome underlying the slow-cycling state. We show that cellular stress responses – the p53 transcriptional response and the integrated stress response – are the most salient causes of spontaneous entry into the slow-cycling state. mRNA profiling of spontaneously quiescent human cells and cells forced into quiescence by four different methods