Inhibition of capacitative Ca2+ entry into cells by farnesylcysteine analogs

Capacitative Ca2+ influx, which occurs in response to mobilization of intracellular Ca2+ stores, is a general feature of many cell types. Although the mechanism of capacitative Ca2+ entry is not known, evidence suggests the involvement of small G proteins that are prenylated on a cysteine residue near their carboxyl termini. We have investigated the actions of farnesylcysteine analogs on capacitative Ca2+ influx. Using human embryonic kidney 293 cells, we found that S-farnesylthioacetic acid, N-acetyl-S-farnesyl-L-cysteine, N-pivaloyl-S-farnesyl-L-cysteine, and N-acetyl-S-gernylgemyl-L-cysteine blocked the activation of capacitative Ca2+ influx, whereas N-benzoyl-S-farnesyl-S-cysteine had no effect on capacitative Ca2+ entry. Inhibition by S-farnesylthioacetic acid was concentration dependent (5-20 mu M) and specific for Ca2+ influx through non-voltage-gated Ca2+ channels. A single protein band of 26-28 kDa was labeled specifically with a photoaffinity analog of farnesylcysteine. GTP binding to the photoaffinity-labeled band was demonstrated. These findings suggest, but do not prove, that a prenylated substrate, possibly a small G protein, is linked functionally to capacitative Ca2+ entry in human embryonic kidney 293 cells.