Expression and preliminary characterization of recombinant human tissue kallikrein in egg white of laying hens

Human tissue kallikrein (hK1) plays an important role in regulation of blood pressure, electrolyte and glucose transport, and renal function. To evaluate the feasibility of expression of recombinant human tissue kallikrein (rhK1) in the egg whites of laying hens, human tissue kallikrein gene (hKLK1) cDNA was subcloned into the chicken oviduct-specific expression vector (pOV3), and the resultant recombinant vector pOV3K was injected into laying hens via wing vein after mixing with polyethyleneimine. Following injection twice with the recombinant vector, the enzymatic activity at a maximal level of 59 U/mL was detected in the egg whites, which lasted for more than 7 d. The expression level of rhK1 in the egg whites in the 3-mg group was relatively higher than that in the 2-mg group, but the significant differences were identified on d 7 and 8 (P < 0.05). Ten days after the primary injection, the hens were reinjected with the same dose of the vector, and even higher enzymatic activity was detected in their egg whites. Two different breeds of hen were tested with no difference in expression level found (P > 0.05). Western blot analysis of the egg whites from vector-injected hens showed the rhK1 was recognized by a polyclonal antibody specific for hK1 with molecular weights of 37 and 43 kDa, which probably corresponded to the mature and preenzyme, respectively. Biochemical studies showed that the recombinant enzyme had a similar thermostability, optimal pH, hypotensive effect, and sensitivity to different ions to the natural enzymes in human and porcine tissues. These data indicate that the chicken oviduct-specific transient expression system can produce relatively high level and authentic recombinant enzyme with a potential for further development for therapeutic use.