Protein kinase C (PKC) is a family of
serine/threonine kinases implicated in a variety of physiological processes. We have shown previously that sustained activation of the classical PKCα and PKCβII induces their
phospholipase D (
PLD)-dependent internalization and translocation to a subset of the recycling endosomes defined by the presence of PKC and
PLD (the pericentrion), which results in significant differences in phosphorylation of PKC substrates. Here, we have investigated the
biological consequences of sustained PKC activity and the involvement of
PLD in this process. We find that sustained activation of PKC results in activation of the
mammalian target of rapamycin (mTOR)/
S6 kinase pathway in a
PLD- and endocytosis-dependent manner, with both pharmacologic inhibitors and
siRNA implicating the PLD2
isoform. Notably, dysregulated overexpression of PKCβII in A549
lung cancer cells was necessary for the enhanced proliferation and migration of these
cancer cells. Inhibition of PKCβII with
enzastaurin reduced A549 cell proliferation by >60% (48 h) and migration by >50%. These
biological effects also required both
PLD activity and mTOR function, with both the
PLD inhibitor FIPI and
rapamycin reducing cell growth by >50%. Reciprocally, forced overexpression of wild-type PKCβII, but not an F666D mutant that cannot interact with
PLD, was sufficient to enhance cell growth and increase migration of noncancerous HEK cells; indeed, both properties were almost doubled when compared to vector control and PKC-F666D-overexpressing cells. Notably, this condition was also dependent on both
PLD and mTOR activity. In summary, these data define a PKC-driven oncogenic signaling pathway that requires both
PLD and mTOR, and suggest that inhibitors of
PLD or mTOR would be beneficial in
cancers where PKC overexpression is a contributing or driving factor.