TY - JOUR
T1 - Stargazin modulates neuronal voltage-dependent Ca2+ channel Cav2.2 by a Gβγ-dependent mechanism
AU - Tselnicker, Isabella
AU - Tsemakhovich, Vladimir A.
AU - Dessauer, Carmen W.
AU - Dascal, Nathan
PY - 2010/7/2
Y1 - 2010/7/2
N2 - Loss of neuronal protein stargazin (γ2) is associated with recurrent epileptic seizures and ataxia in mice. Initially, due to homology to the skeletal muscle calcium channel γ1 subunit, stargazin and other family members (γ3-8) were classified as γ subunits of neuronal voltage-gated calcium channels (such as CaV2.1-Ca V2.3). Here, we report that stargazin interferes with G protein modulation of CaV2.2 (N-type) channels expressed in Xenopus oocytes. Stargazin counteracted the Gβγ-induced inhibition of Ca V2.2 channel currents, caused either by coexpression of the Gβγ dimer or by activation of a G protein-coupled receptor. Expression of high doses of Gβγ overcame the effects of stargazin. High affinity Gβγ scavenger proteins m-cβARK and m-phosducin produced effects similar to stargazin. The effects of stargazin and m-cβARK were not additive, suggesting a common mechanism of action, and generally independent of the presence of the CaVβ3 subunit. However, in some cases, coexpression of CaVβ3 blunted the modulation by stargazin. Finally, the Gβγ-opposing action of stargazin was not unique to CaV2.2, as stargazin also inhibited the Gβγ-mediated activation of the G protein-activated K+ channel. Purified cytosolic C-terminal part of stargazin bound Gβγ in vitro. Our results suggest that the regulation by stargazin of biophysical properties of CaV2.2 are not exerted by direct modulation of the channel but via a Gβγ-dependent mechanism.
AB - Loss of neuronal protein stargazin (γ2) is associated with recurrent epileptic seizures and ataxia in mice. Initially, due to homology to the skeletal muscle calcium channel γ1 subunit, stargazin and other family members (γ3-8) were classified as γ subunits of neuronal voltage-gated calcium channels (such as CaV2.1-Ca V2.3). Here, we report that stargazin interferes with G protein modulation of CaV2.2 (N-type) channels expressed in Xenopus oocytes. Stargazin counteracted the Gβγ-induced inhibition of Ca V2.2 channel currents, caused either by coexpression of the Gβγ dimer or by activation of a G protein-coupled receptor. Expression of high doses of Gβγ overcame the effects of stargazin. High affinity Gβγ scavenger proteins m-cβARK and m-phosducin produced effects similar to stargazin. The effects of stargazin and m-cβARK were not additive, suggesting a common mechanism of action, and generally independent of the presence of the CaVβ3 subunit. However, in some cases, coexpression of CaVβ3 blunted the modulation by stargazin. Finally, the Gβγ-opposing action of stargazin was not unique to CaV2.2, as stargazin also inhibited the Gβγ-mediated activation of the G protein-activated K+ channel. Purified cytosolic C-terminal part of stargazin bound Gβγ in vitro. Our results suggest that the regulation by stargazin of biophysical properties of CaV2.2 are not exerted by direct modulation of the channel but via a Gβγ-dependent mechanism.
UR - http://www.scopus.com/inward/record.url?scp=77954222145&partnerID=8YFLogxK
U2 - 10.1074/jbc.M110.121277
DO - 10.1074/jbc.M110.121277
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AN - SCOPUS:77954222145
SN - 0021-9258
VL - 285
SP - 20462
EP - 20471
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 27
ER -