PIK3CB and fibrosarcoma: Analysis of transfected cell lysates cultured either in the presence of serum or in serum-starved conditions revealed that overexpression of myc-p110β in Rat2 cells to a level approximately 35-fold higher than that of the endogenous protein in Rat2 cells and a human fibrosarcoma cell line (Supplementary Figure 2) resulted in increased endogenous phosphorylation of AKT (p-AKT), proline-rich AKT1 substrate (p-PRAS40) and S6 ribosomal protein (p-S6) in the PI3K signaling pathway (Figure 2a).