Paracrine effects of a uterine agglutinin are mediated via the sialic acids present in the rat uterine endometrium

A 32 kDa estrogen-induced, sialic acid-specific agglutinin (P-SAS) was isol ated from rat endometrium in its proestrus stage [1]. To investigate the fu nctional importance of P-SAS in the uterine milieu, specific binding assays were carried out with I-125-labeled P-SAS and different cellular component s of the uterus (epithelial, stromal and myometrial cells), that were isola ted from different stages of the estrus cycle. The results indicate that al though the protein is secreted from the epithelial cells in the estrogenic phase, it binds specifically to the stromal cells, especially to those isol ated from the diestrus stage of the estrus cycle. The specific binding, how ever, is seen to decrease with the progression of pregnancy. Scatchard anal ysis performed with varying amounts of I-125-P-SAS in the presence of exces s cold P-SAS revealed that the binding occurs with a Ka = 1.69 x 10(8) M-1. As P-SAS binds specifically to sialic acids on the stromal cell surface, f urther characterization of the sialic acid molecule to which P-SAS binds wa s carried out by gas liquid chromatography (GLC). The studies revealed that P-SAS preferentially binds to N-glycolylneuraminic acid, which is attached to the penultimate sugar of the stromal cell surface glycoprotein chain vi a alpha2,6 linkage. As P-SAS is further known to be mitogenic [2], the effe ct of P-SAS on cultured stromal cells was studied in vitro. The growth regu latory assays revealed that P-SAS induced H-3-thymidine uptake by stromal c ells in culture. Thus, from the above observations, paracrine effects of P- SAS on the stromal cells and on the subsequent growth and development of th e uterus can be assumed.