Galphaz inhibits serum response factor-dependent transcription by inhibiting Rho signaling.
Galpha12/13 or Galphaq signals induce activation of Rho GTPase, leading to serum response factor (SRF)-mediated gene transcription and actin cytoskeletal organization; however, less is known regarding how Rho pathway signals are down-regulated. Here we report that Galphaz signals inhibit serum response factor (SRF)-dependent transcription. Galphaz expression inhibits Galpha12/13-, Galphaq-, and Rho guanine nucleotide exchange factor (GEF)-induced serum response element (SRE) reporter activation in human embryonic kidney 293T and PC-12 cells. Expression of Galphaz mutants with defective fatty acylation has no inhibitory effect. Expression of Galphaz, but not Galphai, attenuates serum-induced SRE reporter activation, suggesting that Galphaz can down-regulate endogenous signals leading to SRF. Whereas Galphaz also blocks SRE reporter induction by the activated mutant RhoAL63, it does not affect Galpha12- or Rho GEF-induced RhoA activation or RhoAL63-GTP binding in vivo. Moreover, Galphaz does not inhibit SRE reporter induction by an activated form of Rho kinase. Because Galphaz inhibits RhoAL63/A188-induced reporter activation, phosphorylation of RhoA on serine 188 does not seem to be involved; furthermore, RhoA subcellular localization was not affected. Use of pharmacologic inhibitors implies that Galphaz-induced reduction of SRE reporter activation occurs via a mechanism other than adenylate cyclase modulation. These findings suggest that Galphaz signals may attenuate Rho-induced stimulation of SRF-mediated transcription.
Physiology Department, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
Parmesh
P
Dutt
Aron B
AB
Jaffe
Keith D
KD
Merdek
Alan
A
Hall
Deniz
D
Toksoz
D019943:Amino Acid Substitution; D002460:Cell Line; D044385:GTP-Binding Protein alpha Subunits / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology; D017930:Genes, Reporter; D006801:Humans; D007668:Kidney; D016297:Mutagenesis, Site-Directed; D010957:Plasmids; D011994:Recombinant Proteins / Q000378:metabolism; D012234:Rho Factor / Q000037:antagonists & inhibitors*; D026362:Serum Response Factor / Q000037:antagonists & inhibitors*; D015398:Signal Transduction; D014158:Transcription, Genetic / Q000502:physiology*; D014162:Transfection
C099387:GNAZ protein, human; D044385:GTP-Binding Protein alpha Subunits; D011994:Recombinant Proteins; D012234:Rho Factor; D026362:Serum Response Factor