Molecular and Cellular Endocrinology, 12 (1990) 55-61 Elsevier Scientific Publishers Ireland, Ltd. 55 MOLCEL 02322 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Human relaxin inhibits division but not differentiation of zyxwvutsrqponmlkjihgfed 3T3-Ll cells Wojciech Pawlina ‘, Lynn H. Larkin ‘, Susan Ogilvie ‘** and Susan C. Frost ’ Departments of ’ Anatomy and Cell Biology, and ’ Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, U.S.A. (Received 20 March 1990; accepted 2 May 1990) Key words; Relaxin; Cell division; Differentiation; (3T3-Ll cells) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF Summary For the first time, we demonstrate here the ability of human relaxin to block cell division. During the induction of differentiation of 3T3-Ll fibroblasts to adipocytes, the cells typically undergo two rounds of cell division followed by accumulation of lipid droplets and expression of insulin-stimulated glucose transport as the cells attain the adipocyte phenotype. Human relaxin added during induction had no effect on the development of the adipocyte phenotype or insulin-stimulated glucose transport. However, it blocked cell division at a half-maximal concentration of 1.25 nM, well within physiological range. This could be reversed by the addition of antibodies specific for human relaxin. Thus relaxin joins a select number of hormones with growth inhibitory properties such as transforming growth factor-p (TGFP) and mammastatin. Potentially, this is an important but until now unidentified function of relaxin. Unlike other inhibitory polypeptides, like TGF/3, relaxin does not prevent differentiation but rather uncouples it from cell division. Introduction Relaxin has been recognized as a hormone of pregnancy and parturition for many years. Since determination of porcine relaxin’s amino acid composition and its structural similarity to insulin, it has been considered a member of the insulin family which includes insulin and insulin-like growth factors I and II (IGF-I, -11) (James et al., Address for correspondence: Dr. Susan C. Frost, Depart- ment of Biochemistry and Molecular Biology, Box J 245 JHMHC, University of Florida, Gainesville, FL 32610, U.S.A. * Present address: Department of Pharmacology and Ther- apeutics, University of Florida, Gainesville, FL 32610, U.S.A. 1977; Blundell and Humbel, 1980). Relaxin’s simi- larity to insulin has led to many studies which indicate that relaxin and insulin have few func- tional and no antigenic traits in common (Kemp and Niall, 1984; Sherwood, 1988). However, stud- ies with isolated rat adipocytes and 3T3-Ll adipocytes have shown that relaxin potentiates insulin-stimulated glucose transport (ISGT) (Olef- sky et al., 1982; Pawlina et al., 1987) by increasing the affinity of the insulin receptor for insulin (Olefsky et al., 1982). Although relaxin’s primary targets are the female reproductive organs, there is recent evi- dence suggesting that it may also be involved in the differentiation of preadipocytes during mam- mary tissue development (Bianchi et al., 1986; Bani-Sacchi et al., 1987). The 3T3-Ll cell line, 0303-7207/90/$03.50 0 1990 Elsevier Scientific Publishers Ireland, Ltd.