RPS6 and Miyoshi myopathy: We found that MM cell-induced mTORC1 activity, as measured by phosphorylation of the downstream ribosomal S6 protein, was lower in ARI2hIL-15 cells than in either ARI2hIL-2 or ARI2hIL-15/IL-7 cells, which exhibited similar levels of S6 protein phosphorylation (Figure 4E).