Transmembrane delivery of polypeptide growth factors bypassing the intrinsic cell surface receptors: Synthesis and biological activity of a conjugate of epidermal growth factor with .ALPHA.2-macroglobulin.

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Abstract
Epidermal growth factor (EGF) was derivatized at the amino terminus with N-succinimidyl 3-(2-pyridyldithio)propionate and then cross-linked to the cysteinyl residues of α2-macroglobulin (α2M) via disulfide bonds. The EGF-α2M conjugate delivered EGF into dense lysosomal fractions through binding to α2M receptors in a variant of mouse Swiss/3T3 fibroblasts, NR-6, which are deficient in EGF receptors. The conjugate stimulated DNA synthesis in Swiss/ 3T3 cells, but it did not stimulate DNA synthesis in NR-6 cells. This differential stimulation was due to the conjugate's binding to EGF receptors since bacitracin, which completely inhibits [125I]α2M binding to its receptors, inhibited conjugate binding by 80%. Thus, EGF bound to and internalized through α2M receptors does not function as a mediator for DNA stimulation. The mechanisms of action of the conjugate are discussed in relation to the role of receptor-mediated endocytic pathways.

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