Al. Schneyer et al., FOLLISTATIN ACTIVIN COMPLEXES IN HUMAN SERUM AND FOLLICULAR-FLUID DIFFER IMMUNOLOGICALLY AND BIOCHEMICALLY, Endocrinology, 137(1), 1996, pp. 240-247
Follistatin (FS) is the principle high affinity activin-binding protei
n in tissues such as the pituitary and ovary as well as in serum. In a
ddition, the activin-binding peaks identified after gel filtration of
serum or human follicular fluid (hFF) exhibited high affinity and low
reversibility binding kinetics, with higher concentrations in hFF than
serum. This extremely low reversibility was also observed for recombi
nant human follistatin 288 (rhFS288) under a variety of incubation con
ditions, further supporting the identification of the serum and hFF ac
tivin-binding proteins as FS. Using enhanced resolution gel filtration
, immunoprecipitation with monoclonal antibodies to rhFS288, and sulfa
ted carbohydrate binding, activin-FS complexes in hFF and serum differ
ed. The activin-FS complex in hFF elutes at approximately 200-300 kDa,
is immunoprecipitated by anti-hFS288 monoclonal antibodies, and binds
to sulfate Cellufine matrix, all characteristics similar to those of
recombinant human FS288. In contrast, the activin binding peak in huma
n serum elutes at an apparent M(r) of 60-70 kDa, is not precipitated b
y anti-rhFS288 monoclonal antibodies, and is weakly bound by sulfate C
ellufine matrix, characteristics shared by rhFS315 conditioned medium.
As the forms of FS that bind sulfate-containing matrices also bind to
cell surface proteoglycans, the molecular differences reported here f
or serum and hFF activin-binding proteins have implications for potent
ial tissue-specific forms of FS that may well have distinct biological
functions.