PDPK1 and plasma cell myeloma: Furthermore, the inactivation of RSK2-NTKD causes apoptosis in myeloma cells regardless of their cytogenetic/molecular features [32], while there is a compensative interaction between RAS/ERK/RSK2-mediated signal and AKT, which is another major oncogenic substrate of PDPK1 in various types of cancer cells [33,34,35,36].