RPS6KA1 and cancer: Therefore, to explore whether the phosphorylation of MDM2 at serine 166 induced by p90RSK was important for the stability of p53 in the different cancer cell lines positive for p90RSK activation, as previously demonstrated for follicular thyroid cancer [32], these cells were incubated with different BI-D1870 concentrations (4 and 10 μM) for 1 h.