MAPK3 and acute lymphoblastic leukemia: Importantly, the signaling pathway is intact, at least in HPB-ALL cells from RAF onwards, as evidenced by induction of phospho-ERK1/2 by the phorbol ester PMA which acts via PKC to RAF[34] (S8C Fig), and the RAS(G12D) construct itself functions properly as shown by induction of phospho-ERK1/2 in 293T cells (S9 Fig).