The major obstacle for oral delivery of administered therapeutic proteins is malabsorption in the intestine. This malabsorption could be overcome by induction of neonatal FcRn [Fc (CH2 and CH3 domains of human IgG1 antibody) receptor]-mediated transcytosis in the intestine using recombinant fusion of CH2 and CH3 moieties of human IgG to a therapeutic protein. To this end we developed recombinant hGH (human growth hormone) fused to the N-terminus of Fc moieties [CH2-CH3 or h (hinge)-CH2-CH3] from human IgG1. These recombinant proteins secreted by the methylotrophic yeast Pichia pastoris functionally induced secretion of insulin-like growth factor 1 by HepG2 cells in the response to hGH moiety in the fusion proteins. In a transport study using polarized T84 cells, 3.7% of added dimeric hGH-h-Fc was transported in the apical-to-basolateral direction within 1 h by FcRn-mediated transcytosis of 1 cm(2) monolayers. However, transport of monomeric hGH-Fc (only 0.43%) was much less effective, yet its transport was 2.3 times higher than that of hGH. Finally, we concluded that, upon recombinant fusion, maintenance of dimeric structure of Fc moieties is crucial for the induction of FcRn-mediated transcytosis.