PROLIFERATIVE STIMULATION OF LYMPHOCYTES BY CALMODULIN-BINDING PROTEINS ISOLATED FROM AMNIOTIC-FLUID

In view of the role of calmodulin and calmodulin binding proteins in m odulating the second messenger functions of Ca2+, we studied the prese nce of such proteins in amniotic fluid, which may be considered as a d ynamic medium for promoting foetal growth. Affinity chromatography of amniotic fluid proteins revealed the presence of calmodulin binding pr oteins in samples obtained either at 28 or 36 wk of pregnancy. The rel ative content of these proteins increased in amniotic fluid from 1.5 m g/g total protein at 28 wk to 3.6 mg/g at full term of pregnancy. Cult uring murine splenocytes in presence of the isolated calmodulin bindin g proteins (10 mu g protein/10(6) cells) resulted in nearly 4-fold enh ancement of H-3-thymidine incorporation into them as compared to contr ols. in comparison, similar incorporation of the radiolabel inter lymp hocytes obtained from ford blood was enhanced only by 2 fold in presen ce of calmodulin binding proteins, though at a much lower protein conc entration (50 ng/10(6) cells). SDS-PAGE on 12.5 per cent gels of eluat es obtained from calmodulin-agarose columns, followed by overlay of co rresponding western blots with biotinylated calmodulin revealed the pr esence of a 68 kDa calmodulin binding protein in samples collected eit her at 28 wk or at full-term of pregnancy. In addition, the amniotic f luid also contained 83 kDa calmodulin binding protein at 28 wk. This f irst-time demonstration of mitogenic, calmodulin binding proteins in a mniotic fluid suggests that such mitogens may participate in promoting foetal growth.