J. Hamid et al., Identification of an integration center for cross-talk between protein kinase C and G protein modulation of N-type calcium channels, J BIOL CHEM, 274(10), 1999, pp. 6195-6202
The modulation of presynaptic calcium channel activity by second messengers
provides a fine tuning mechanism for neurotransmitter release. In neurons,
the activation of certain G protein-coupled receptors reduces N-type chann
el activity by similar to 60%. In contrast, activation of protein kinase C
(PKC) results in an approximately 50% increase in N-type channel activity,
and subsequent G protein inhibition is antagonized. Here, we describe the m
olecular determinants that control the dual effects of PKC-dependent phosph
orylation. The double substitution of two adjacent PKC consensus sites in t
he calcium channel domain I-II linker (Thr(422), Ser(425)) to alanines abol
ished both PKC-dependent up-regulation and the PKC-G protein cross-talk. Th
e single substitution of Ser(425) to glutamic acid abolished PRC up-regulat
ion but had no effect on G protein modulation. Replacement of Thr(422) With
glutamic acid eliminated PKC-dependent up-regulation and mimicked the effe
cts of PKC phosphorylation on G protein inhibition. Our data suggest that T
hr(422) mediates the antagonistic effect of PKC on G protein modulation, wh
ile phosphorylation of either Thr(422) or Ser(425) are sufficient to increa
se N-type channel activity. Thus, Thr(422) serves as a molecular switch by
which PKC is able to simultaneously trigger the upregulation of channel act
ivity and antagonize G protein inhibition.