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. Al though 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 th e actions of farnesylcysteine analogs on capacitative Ca2+ influx. Usi ng human embryonic kidney 293 cells, we found that S-farnesylthioaceti c acid, N-acetyl-S-farnesyl-L-cysteine, N-pivaloyl-S-farnesyl-L-cystei ne, and N-acetyl-S-gernylgemyl-L-cysteine blocked the activation of ca pacitative 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+ in flux through non-voltage-gated Ca2+ channels. A single protein band of 26-28 kDa was labeled specifically with a photoaffinity analog of far nesylcysteine. GTP binding to the photoaffinity-labeled band was demon strated. These findings suggest, but do not prove, that a prenylated s ubstrate, possibly a small G protein, is linked functionally to capaci tative Ca2+ entry in human embryonic kidney 293 cells.