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Insulin-Like Growth Factor Receptors in Rat Placental Membranes^*

SYDNE J. PILISTINE, ALAN C. MOSES and HAMISH N. MUNRO

Massachusetts Institute of Technology Cambridge, Massachusetts 02139
Diabetes Unit, Department of Medicine, Beth Israel Hospital, the Charles A. Dana Research Institute and the Harvard-Thorndike Laboratory of Beth Israel Hospital Boston, Massachusetts 02215
USDA Human Nutrition Research Center on Aging at Tufts University Boston, Massachusetts 02111

Address all correspondence and requests for reprints to: Alan C. Moses, M.D., Department of Medicine, Beth Israel Hospital, 330 Brookline Avenue, Boston, Massachusetts 02215.

Abstract

The nature and relative quantity of insulin-like growth factor (IGF) receptors in rat placental microsomal membranes was investigated by competitive binding studies and covalent cross-linking followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Binding studies revealed that 100 fig membrane protein specifically bound 26.5% of [¹²⁵I]iodo-IGF-II, 19.6% of [¹²⁵I]iodomultiplication-stimulating activity III-2 ([¹²⁵I]iodo-MSA-III-2), and 11.5% [¹²⁵I]iodo-IGF-I. IGF-II was equipotent with MSA-III-2, and both were approximately twice as potent as IGF-I in competing with [¹²⁵I]iodo-IGF-I for binding. In contrast, IGF-I competed for the binding of [1Z5I]iodo- MSA and [¹²⁵I]iodo-IGF-II with only 5–20% the potency of unlabeled MSA and IGF-II. Insulin competed weakly with [126I] iodo-IGF-I for binding (achieving half-maximal displacement at 20 µg/ml), but did not compete with [¹²⁵I]iodo-MSA for binding. This evidence suggested that while IGF-I binds to both IGF-I and IGF-II receptors, the majority of IGF-I binding is due to an interaction with IGF-II receptors. Studies using [¹²⁵I]iodo-IGFI covalently cross-linked to placental membrane receptors followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis confirmed that molecular species characteristic of the subunits of IGF-I receptors are present in rat placenta. It is concluded that rat placenta, like human placenta, contains receptors for both types of IGFs. Unlike human placenta, the majority of the receptors are of the IGF-II type. (Endocrinology 115: 1060–1065, 1984)

Footnotes

^* This work was supported in part by a grant from the Juvenile Diabetes Foundation.

Recipient of the Capps Fund Scholarship from the Harvard Medical School.

Received July 11, 1983.