Fig. 4.

S6K1 confers resistance to palbociclib in breast cancer cell lines. A, B The expression of S6K1 was measured in four breast cancer cell lines, including MCF-7, MDA-MB-231, MDA-MB-468, and T47D, using RT-qPCR (A) and western blotting (B), respectively. C, D MCF-7 (C) or T47D (D) cells were treated with increasing doses of palbociclib, as indicated, for 5 days. The cell viability was then detected using CCK-8 assay. E, F MCF-7 cells were transfected with two specific S6K1 siRNAs (siS6K1-1/− 2) or non-sense control siRNA (siNC), followed by CCK-8 assay (E) or clonogenic assay (F) upon treatment with increasing doses of palbociclib as indicated. G, H Exogenous S6K1-expressed T47D cells or control cells were subjected to CCK-8 assay (G) or clonogenic assay (H) with the indicated doses of palbociclib. I, J MCF-7 cells transfected with two specific S6K1 siRNAs or non-sense control siRNA (I) as well as exogenous S6K1-expressed T47D cells or control cells (J) were treated with or without palbociclib (10 μM for MCF-7 cells, 1 μM for T47D cells). The xCELLigence system was used for examining proliferation of these cells