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Structural and Immunological Characterization of Insulin-Like Growth Factor II Binding to IM-9 Cells^*

PRATIMA MISRA, RAYMOND L. HINTZ and RON G. ROSENFELD

Department of Pediatrics, Stanford University School of Medicine Stanford, California 94305

The structural and immunological properties of the insulin-like growth factor II (IGF-II) receptor on IM-9 lymphoblasts were studied using a combination of competitive binding and affinity cross-linking techniques as well as with a panel of polyclonal and monoclonal antireceptor antibodies. Unlike (IGF-II) binding to the classical type II IGF receptor, [¹²⁵I] IGF-II binding to IM-9 cells was potently inhibited not only by unlabeled IGF-II, but also by insulin (50Ü inhibition of binding at 2.5 and 1.5 nM, respectively). Affinity cross-linking of [¹²⁵I] IGF-II to intact cells, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, demonstrated that the over-whelming majority of IGF-II binding was to a type I receptor (apparent mol wt, >300,000 unreduced and 135,000 reduced), with minimal binding to a type II receptor (apparent mol wt,220,000 unreduced and 240,000 reduced). After preincubation with five different antireceptor antibodies, inhibition of [¹²⁶] IIGF-II binding was comparable to inhibition of [¹²⁵I]insulinbinding. These studies demonstrate that in IM-9 cells, the majority of IGF-II binding is to a type I receptor with high affinity for both insulin and IGF-II. Whether this is an atypical insulinreceptor or a unique type I receptor remains to be established.

^* This work was supported in part by Grants AM-24085 (to R.L.H.) and AM-28229 (to R.G.R.) from the NIH.

Recipient of Research Career Development Award AM-01275 from the USPHS. To whom all correspondence and requests for reprints should be addressed.

Received January 13, 1986.

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