RPS6KA1 and breast cancer: In breast cancer, inhibition of p90 RSK, a major kinase involved in YB-1 phosphorylation; see section “Post-Translational Modification in the Control of YB-1 Activity and Localization”) using the small molecule LJI308 eradicated the population of breast CSCs and induced apoptosis in breast cancer cells (Davies et al., 2015).