Secretion of glycosylated human recombinant haptoglobin in baculovirus-infected insect cells

Human haptoglobin (Hp alpha 2 beta) was synthesized in insect cells using the baculovirus Autographa californica nuclear polyhedrosis virus (AcNPV) as an expression vector. Viruses carrying the proHp alpha 2 beta cDNA, either fused or non fused to viral polyhedrin DNA sequences, expressed intracellularly low levels of unglycosylated and non maturated haptoglobin. On the contrary, recombinant viruses containing the preproHp alpha 2 beta cDNA directed the expression of high levels of prohaptoglobin. To a large extent, the uncleaved product was found in the culture medium as a glycosylated molecule. Despite the lack of maturation into subunits, the secreted recombinant prohaptoglobin was able to bind hemoglobin in vitro, although less efficiently than plasma-derived haptoglobin.