Interactions of the PKA pathway with other signaling systems
are well documented [34], including the potential action(s) of
cAMP independent of PKA, e.g. via the exchange protein directly
activated by cAMP (EPAC) [35]. Also, in addition to the phosphorylation
of CREB as mentioned above, PKC signaling can impact
on PKA-mediated actions via the receptor for activated C kinase 1
(RACK1), a scaffold protein for PKC and the cAMP-specific phosphodiesterase,
PDE4D5 [36]. Interestingly, one isoform of PKC activates
PDE4D5 when it is bound to RACK1, thus reducing cellular
cAMP. The roles of EPAC and RACK1 in MA-10 cells have not, to the
best of our knowledge, been explored.