Apparent up-regulation of stimulatory G-protein alpha subunits in the pregnant human myometrium is mimicked by elevated smoothelin expression.
Sensitization of adenylyl cyclase (AC) by increased expression of large isoforms of the stimulatory G-protein Galpha(s) has been suggested as a mechanism that governs uterine quiescence during pregnancy. We quantified several components of the AC pathway in pregnant (P, n=21) and nonpregnant human myometria (NP, n=10). AC activity was approximately sevenfold higher in P than in NP under basal and stimulated conditions (MnCl(2)/GTP/GTP + isoproterenol). In addition, relative stimulation (% of basal) by 5'-guanosine-betagamma-iminotriphosphate and forskolin was twofold higher in P. beta-Adrenoceptor density was low and unaltered in P. Galpha(s) mRNA splice variants did not differ in P. Using antisera against different epitopes of Galpha(s) (carboxyl-/more amino-terminal), we found unchanged expression of Galpha(s) short and long (45, 47 kDa) in P. Two additional proteins in P (51, 59 kDa) were detectable only by the carboxyl-terminal antiserum and lacked GTP binding properties. The 59 kDa protein could be identified as a recently discovered cytoskeletal protein, smoothelin, which was 10-fold increased in P. These data indicate that the apparent up-regulation of large Galpha(s) species in P is mimicked by elevated smoothelin. Therefore, the increase in AC cannot be attributed to changes in Galpha(s)- or beta-adrenoreceptors. Epitope sharing between Galpha(s) and smoothelin should be considered in experiments on smooth muscle tissues.
Gsell
S
S
Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Abteilung für Pharmakologie, Universitäts-Krankenhaus Eppendorf, 20246- Hamburg, Germany.
Eschenhagen
T
T
Kaspareit
G
G
Nose
M
M
Scholz
H
H
Behrens
O
O
Wieland
T
T
D015720:5'-Nucleotidase / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D005260:Female; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000378:metabolism*; D009215:Myometrium / Q000201:enzymology / Q000378:metabolism*; D011247:Pregnancy; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D015854:Up-Regulation
D003598:Cytoskeletal Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; C100762:SMTN protein, human; D015720:5'-Nucleotidase; D019205:GTP-Binding Protein alpha Subunits, Gs; D000262:Adenylyl Cyclases