Expression of protein kinase A holoenzymes in human myometrium during pregnancy and labour
There is substantial data indicating that components of the cAMP signalling pathway are differentially expressed in the human myometrium during pregnancy. The effects of cAMP in most tissues and cell types are mainly modulated via protein kinase A, a heterotetrameric protein complex consisting of two regulatory (R) and two catalytic (C) subunits. In this thesis Western-blotting/immuno-precipitation, RT-PCR and functional PKA phosphorylation assays. have been used to determine the PKA holoenzymes that are expressed in the human myometrium throughout pregnancy and labour. As early as the second trimester of pregnancy a significant increase in expression of the regulatory RIIct protein subunit of PKA in the myometrium was seen. This increase in protein expression is also mirrored at the mRNA level indicating transcriptional control throughout pregnancy, whereas during parturition both transcript and protein are significantly decreased. This increase in RIIa protein also resulted in increased particulate PKA activity in the myometrium during gestation, which was subsequently decreased during labour. The RIIa subunit is associated with A kinase anchoring proteins thus directing the cAMP quiescence signal to specific sub-cellular loci within myometrial smooth muscle cells including the contractile machinery at the cytoskeleton, this effect is then removed during parturition.