Pm. Jones et al., Cyclic AMP-induced expression of steroidogenic acute regulatory protein isdependent upon phosphoprotein phosphatase activities, J MOL ENDOC, 24(2), 2000, pp. 233-239
In addition to the well-documented role of protein kinases in the regulatio
n of steroid production, phosphoprotein phosphatase (PP) activity is requir
ed for steroidogenesis. In the present study, we have used the mouse Y1 adr
enocortical cell line to identify the site of action of PPs on steroid prod
uction by measuring the effects of PP inhibition on the expression of the s
teroidogenic acute regulatory (StAR) protein and on steroid production. For
skolin-induced activation of cyclic AMP-dependent protein kinase (PKA) enha
nced steroidogenesis and this was accompanied by an increased expression of
StAR protein. Both steroidogenesis and StAR protein expression were inhibi
ted by two structurally dissimilar inhibitors of PP1 and PP2A activities, o
kadaic acid and calyculin A. These results suggest that inhibition of PP1 a
nd PP2A inhibits steroid production by preventing the expression of the StA
R protein, implicating PP1/2A dephosphorylation reactions as important regu
lators of stimulus-dependent StAR protein expression, and thus of steroidog
enesis.