Secretion of recombinant rat annexin 5 by insect cells in a baculovirus expression system

Rat annexin 5 was expressed in insect cells using a baculovirus vector, Autographa californica nuclear polyhedrosis virus. The rat annexin 5 cDNA was prepared by a polymerase chain reaction using mRNA from rat pituitary glands and placed under the control of the polyhedrin promoter. The gene product was 36 k dalton and was recognized by anti-rat annexin 5 serum. The calcium dependent binding of the recombinant annexin 5 to membranes was confirmed. The recombinant protein appeared in the medium by 21 hours post-inoculation in high amount and this was specific to this recombinant virus. High potassium milieu (20 mM KCl) for two hours increased the release of the recombinant protein but not for the recombinant beta-galactosidase prepared for a control. These results reveal that the product of the annexin 5 gene, which lacks a signal sequence, follows a secretory pathway in insect cells.