A common variant of the pregnancy-associated plasma protein-A (PAPPA) gene encodes a protein with reduced proteolytic activity towards IGF-binding proteins

Jane Alrø Bøtkjær,Claus Yding Andersen,Claus Oxvig,Pernille Rimmer Noer

doi:10.1038/s41598-019-49626-8

Abstract

Pregnancy-associated plasma protein-A (PAPP-A) is a key regulator of insulin-like growth factor (IGF) bioactivity, by releasing the IGFs from their corresponding IGF-binding proteins (IGFBPs). The minor allele of the single nucleotide polymorphism (SNP), rs7020782 (serine < tyrosine), in PAPPA has previously been associated with recurrent pregnancy loss as well as with significant reduced levels of PAPP-A protein in human ovarian follicles. The aim of the present study was to reveal a possible functional effect of the rs7020782 SNP in PAPPA by comparing recombinant PAPP-A proteins from transfected human embryonic kidney 293 T cells. The proteolytic cleavage of IGFBP-4 was shown to be affected by the rs7020782 SNP in PAPPA, showing a significantly reduced cleavage rate for the serine variant compared to the tyrosine variant (p-value < 0.001). The serine variant also showed a trend towards reduced cleavage rates, that was not significant, towards IGFBP-2 and IGFBP-5 compared to the tyrosine variant. No differences were found when analysing cell surface binding, complex formation between PAPP-A and STC2 or proMBP, nor when analysing STC1 inhibition of PAPP-A-mediated IGFBP-4 cleavage. Regulation of IGF bioactivity in reproductive tissues is important and the rs7020782 SNP in PAPPA may disturb this regulation by altering the specific activity of PAPP-A.

Highlights

Pregnancy-associated plasma protein-A (PAPP-A) is a key regulator of insulin-like growth factor (IGF) bioactivity, by releasing the IGFs from their corresponding IGF-binding proteins (IGFBPs)
No statistically significant difference was observed between human embryonic kidney 293 T (HEK293T) cells incubated with supernatant containing the serine variant (rPA_1144(Ser)) and HEK293T cells incubated with supernatant containing the tyrosine variant (rPA_1144(Tyr)) (Fig. 1)
The results showed a trend towards reduced cleavage rates of radiolabelled IGFBP-2 and IGFBP-5 (Fig. 3, lower panel) for the serine variant compared to the tyrosine variant, which were derived from three independent proteinase assays

Summary

Introduction

Pregnancy-associated plasma protein-A (PAPP-A) is a key regulator of insulin-like growth factor (IGF) bioactivity, by releasing the IGFs from their corresponding IGF-binding proteins (IGFBPs). The minor allele of the single nucleotide polymorphism (SNP), rs7020782 (serine < tyrosine), in PAPPA has previously been associated with recurrent pregnancy loss as well as with significant reduced levels of PAPP-A protein in human ovarian follicles. Functional in vitro studies revealed that the ability of this variant to bind and inhibit PAPP-A-mediated IGFBP-4 cleavage was reduced, suggesting higher levels of bioactive IGFs that promote growth[28]. These earlier studies highlight the tremendous phenotypic effect small genetic variations may have. A recent study revealed a significant effect of this SNP on the level of PAPP-A protein in human ovarian follicles and suggested a possible adverse effect on IGF bioactivity[33]. The glycosylation of these two variants may differ because the site of variation encodes a potential N-glycosylation motif[22,23] and may hereby affect the properties of the protein, such as ability to bind substrates

Objectives

Methods

Results

Conclusion