Kjaer-Sorensen, K., Engholm, D.H., Kamei, H., Morch, M.G., Kristensen, A.O., Zhou, J., Conover, C.A., Duan, C., and Oxvig, C. (2013) Pregnancy-associated plasma protein-A (PAPP-A) modulates early developmental rate in zebrafish independent of its proteolytic activity. The Journal of biological chemistry. 288(14):9982-92.
Pregnancy-associated plasma protein-A (PAPP-A) is a large metalloproteinase specifically cleaving IGF binding proteins, causing
increased IGF bioavailability and hence local regulation of IGF receptor activation. We have identified two highly conserved
zebrafish homologs of the human PAPP-A gene. Expression of zebrafish Papp-a, one of the two paralogs, begins during gastrulation
and persists throughout the first week of development, and analyses demonstrate highly conserved patterns of expression between
adult zebrafish, humans, and mice. We show that the specific knockdown of zebrafish papp-a limits the developmental rate beginning
during gastrulation without affecting the normal patterning of the embryo. This phenotype is different from those resulting
from deficiency of Igf receptor or ligand in zebrafish, suggesting a function of Papp-a outside the Igf system. Biochemical
analysis of recombinant zebrafish Papp-a demonstrates conservation of proteolytic activity, specificity, and intrinsic regulatory
mechanism. However, in vitro transcribed mRNA, which encodes a proteolytically inactive Papp-a mutant, recues the papp-a knockdown
phenotype as efficient as wild-type Papp-a. Thus, the developmental phenotype of papp-a knockdown is not a consequence of
lacking Papp-a proteolytic activity. We conclude that Papp-a possesses biological functions independent of its proteolytic
activity. Our data represent the first evidence for a non-proteolytic function of PAPP-A.