RA-induced phosphorylation of the S6 ribosomal protein (rpS6). (A) NB-4 cells were incubated with RA (1 μM) for the indicated times. Equal amounts of total cell lysates were analyzed by SDS-PAGE and immunoblotted with an antibody against the phosphorylated form of rpS6 on Ser240/244. (B) The blot shown in panel A was stripped and reprobed with an anti-rpS6 antibody, to control for protein loading. (C) NB-4 cells were incubated with RA (1 μM) for the indicated times. Equal amounts of total cell lysates were analyzed by SDS-PAGE and immunoblotted with an antibody against the phosphorylated form of rpS6 on Ser235/236. (D) The blot shown in panel C was stripped and reprobed with an anti-rpS6 antibody, to control for protein loading. (E) HL60 cells were incubated with RA (1 μM) for 48 hours. Equal amounts of total cell lysates were analyzed by SDS-PAGE and immunoblotted with an antibody against the phosphorylated form of rpS6 on Ser240/244. (F) The blot shown in panel E was stripped and reprobed with an anti-rpS6 antibody, to control for protein loading. (G) NB-4 cells were incubated with RA (1 μM) for indicated times. Equal amounts of total cell lysates were analyzed by SDS-PAGE and immunoblotted with an antibody against the phosphorylated form of rpS6 on Ser235/236. (H) The blot shown in panel G was stripped and reprobed with an anti-rpS6 antibody, to control for protein loading. (I) NB-4 cells were incubated with RA for indicated times and 2.5 hours prior to cell lysis indicated inhibitors were added in the cultures. Equal amounts of total cell lysates were analyzed by SDS-PAGE and immunoblotted with an antibody against the phosphorylated form of rpS6 on Ser240/244. (J) The blot shown in panel I was stripped and reprobed with an anti-rpS6 antibody, to control for protein loading.