RPS6KB1 and B-cell chronic lymphocytic leukemia: Interestingly, ERK➔AKT cross-talk appeared to operate in CLL cells, but not RL cells, as U0126 reduced phosphorylation of ERK1/2 and p90RSK, as well as p70S6K, and this may have contributed to the inability of single kinase inhibitors to fully reverse anti-IgM-induced PDCD4 down-regulation.