The H1 and H2 polypeptides associate to form the asialoglycoprotein receptor in human hepatoma cells

Antibody-induced degradation and chemical cross-linking experiments have been carried out to assess the nature of the interaction between the two asialoglycoprotein-receptor polypeptides, H1 and H2, synthesized in HepG2 cells. Incubation of HepG2 cell monolayers with anti-H1 antibody caused a specific and equal loss of both H1 and H2 polypeptides. The same result was obtained with anti-H2 antibody. Control serum did not affect the level of H1 or H2 not did anti-H1 or anti-H2 antibodies affect the level of the transferrin receptor. The chemical cross-linking reagent, difluorodinitrobenzene, has been used to demonstrate that H1 can be cross-linked to H2 in HepG2 cell microsomal membranes. Dimer and trimer species with apparent molecular masses of 93 and 148 kD, respectively, were readily observed upon chemical cross-linking and some dimers and trimers were immunoreactive with both anti-H1 and anti-H2 antibodies. The putative trimer, possibly two H1 and one H2 molecules, is a minimum estimate of the true size of the asialoglycoprotein receptor in intact HepG2 cell, and it is possible that larger hetero-oligomeric forms of the receptor exist. The results of both types of experiments indicate that H1 and H2 form an oligomeric complex in HepG2 cells and thus, both polypeptides constitute the human asialoglycoprotein receptor.