Expression of human placental G proteins during pregnancy

Regulatory guanine nucleotide-binding proteins (G proteins) play key roles in the stimulus-response coupling of many important biological systems. Recent studies from our laboratory suggest a functional role for many G proteins in the human placenta. However, the expression of these proteins has not yet been reported. Therefore, the aims of this investigation were to identify the expression of placental G protein alpha subunits in human placenta, and to study their level of variation during pregnancy.

Western and Northern blot analyses were performed on membrane protein and mRNA preparations, respectively, of human placentas from the first (7-11 weeks), second (16-19 weeks), and third (term) trimesters.

The autoradiographs of both proteins and mRNA showed differential expression of placental G proteins during pregnancy. Thus, the relative levels of G alpha i2 and G alpha i3 subunits were highest during the first trimester, whereas no differences were observed between second-trimester and term placentas for both subunits. The levels of placental G alpha o and G alpha s subunits stayed relatively stable during pregnancy.

The demonstration of human placental G alpha protein expression during pregnancy provides new insight into the components of the signal transduction machinery within trophoblast. However, the physiologic significance of the variations of placental G alpha i protein expression during pregnancy remains to be investigated.