Proliferative stimulation of lymphocytes by calmodulin binding proteins isolated from amniotic fluid

In view of the role of calmodulin and calmodulin binding proteins in modulating the second messenger functions of Ca2+, we studied the presence of such proteins in amniotic fluid, which may be considered as a dynamic medium for promoting foetal growth. Affinity chromatography of amniotic fluid proteins revealed the presence of calmodulin binding proteins in samples obtained either at 28 or 36 wk of pregnancy. The relative content of these proteins increased in amniotic fluid from 1.5 mg/g total protein at 28 wk to 3.6 mg/g at full term of pregnancy. Culturing murine splenocytes in presence of the isolated calmodulin binding proteins (10 micrograms protein/10(6) cells) resulted in nearly 4-fold enhancement of 3H-thymidine incorporation into them as compared to controls. In comparison, similar incorporation of the radiolabel into lymphocytes obtained from cord blood was enhanced only by 2 fold in presence of calmodulin binding proteins, though at a much lower protein concentration (50 ng/10(6) cells). SDS-PAGE on 12.5 per cent gels of eluates obtained from calmodulin-agarose columns, followed by overlay of corresponding western blots with biotinylated calmodulin revealed the presence of a 68 kDa calmodulin binding protein in samples collected either at 28 wk or at full-term of pregnancy. In addition, the amniotic fluid also contained 83 kDa calmodulin binding protein at 28 wk. This first-time demonstration of mitogenic, calmodulin binding proteins in amniotic fluid suggests that such mitogens may participate in promoting foetal growth.