Calcium-phospholipid enhanced protein phosphorylation in human placenta

Area of Science:

• Biochemistry
• Cell Biology
• Reproductive Biology

Background:

• Calcium-activated, phospholipid-dependent protein phosphorylation is a key cellular process.
• This mechanism had not been previously investigated in human placental tissue.

Purpose of the Study:

• To investigate calcium-activated, phospholipid-dependent protein phosphorylation in human placental cytosol.
• To identify specific phosphoproteins modulated by these signaling molecules.

Main Methods:

• Human placental cytosol was used for endogenous protein phosphorylation assays.
• Assays involved [gamma-32P]ATP, calcium (Ca2+), and phosphatidylserine.
• Phosphorylation was analyzed using SDS-PAGE and autoradiography.

Main Results:

• Calcium and phosphatidylserine significantly enhanced phosphorylation of 47,000, 43,000, and 37,000 mol wt phosphoproteins.
• Half-maximal phosphorylation occurred at 3.5 X 10(-7) M Ca2+.
• Tetracaine inhibited this calcium-activated, phospholipid-dependent phosphorylation.
• Calcium alone enhanced a 98,000 mol wt phosphoprotein, an effect suppressed by phosphatidylserine.
• Calmodulin did not enhance phosphorylation beyond calcium alone, but its inhibitor affected the 98,000 mol wt phosphoprotein.

Conclusions:

• Human placental cytosol contains calcium-activated, phospholipid-dependent phosphoproteins.
• The presence of calcium-activated, calmodulin-dependent phosphoproteins remains to be elucidated.