Thrombospondin-1 (TSP-1), a new bone morphogenetic protein-2 and -4 (BMP-2/4) antagonist identified in pituitary cells

Céline Sallon,Isabelle Callebaut,Ida Boulay,Joel Fontaine,Delphine Logeart-Avramoglou,Corinne Henriquet,Martine Pugnière,Xavier Cayla,Philippe Monget,Grégoire Harichaux,Valérie Labas,Sylvie Canepa,Catherine Taragnat

doi:10.1074/jbc.m116.736207

Abstract

Bone morphogenetic proteins (BMPs) regulate diverse cellular responses during embryogenesis and in adulthood including cell differentiation, proliferation, and death in various tissues. In the adult pituitary, BMPs participate in the control of hormone secretion and cell proliferation, suggesting a potential endocrine/paracrine role for BMPs, but some of the mechanisms are unclear. Here, using a bioactivity test based on embryonic cells (C3H10T1/2) transfected with a BMP-responsive element, we sought to determine whether pituitary cells secrete BMPs or BMP antagonists. Interestingly, we found that pituitary-conditioned medium contains a factor that inhibits action of BMP-2 and -4. Combining surface plasmon resonance and high-resolution mass spectrometry helped pinpoint this factor as thrombospondin-1 (TSP-1). Surface plasmon resonance and co-immunoprecipitation confirmed that recombinant human TSP-1 can bind BMP-2 and -4 and antagonize their effects on C3H10T1/2 cells. Moreover, TSP-1 inhibited the action of serum BMPs. We also report that the von Willebrand type C domain of TSP-1 is likely responsible for this BMP-2/4-binding activity, an assertion based on sequence similarity that TSP-1 shares with the von Willebrand type C domain of Crossveinless 2 (CV-2), a BMP antagonist and member of the chordin family. In summary, we identified for the first time TSP-1 as a BMP-2/-4 antagonist and presented a structural basis for the physical interaction between TSP-1 and BMP-4. We propose that TSP-1 could regulate bioavailability of BMPs, either produced locally or reaching the pituitary via blood circulation. In conclusion, our findings provide new insights into the involvement of TSP-1 in the BMP-2/-4 mechanisms of action.

Highlights

Bone morphogenetic proteins (BMPs) regulate diverse cellular responses during embryogenesis and in adulthood including cell differentiation, proliferation, and death in various tissues
We report that the von Willebrand type C domain of TSP-1 is likely responsible for this BMP-2/4-binding activity, an assertion based on sequence similarity that TSP-1 shares with the von Willebrand type C domain of Crossveinless 2 (CV-2), a BMP antagonist and member of the chordin family
Based on the similarity we observed with the CV-2: BMP-2 interaction, we suggest that the von Willebrand type C domain (VWC) domain of TSP-1 behaves as a paperclip relative to the BMP-4 3D structure, with on the one hand the N-terminal clip folding into the BMP-4 wrist epitope and on another hand the SD1 interacting with the BMP-4 knuckle epitope (Fig. 7C, top and bottom left)

Summary

Introduction

Bone morphogenetic proteins (BMPs) regulate diverse cellular responses during embryogenesis and in adulthood including cell differentiation, proliferation, and death in various tissues. Bone morphogenetic proteins (BMPs), members of the transforming growth factor ␤ (TGF␤) superfamily, were originally identified by their ability to induce endochondral bone formation [1, 2] They are known to regulate diverse cellular responses during embryogenesis and in adulthood including cell differentiation, proliferation, and death in various tissues. ALK3, ALK6, and BMPR-II are found on different cell types including gonadotropes and corticotropes [10] These data suggest that pituitary BMPs can exert paracrine/autocrine actions on hormone synthesis and release. BMP-4, BMP-6, and BMP-9 were found in bovine serum [27], suggesting a potential endocrine role for BMPs at pituitary level

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