Regulation of FSHβ induction in LβT2 cells by BMP2 and an Activin A/BMP2 chimera, AB215

Abstract

Activins and bone morphogenetic proteins (BMPs) share activin type 2 signaling receptors but utilize different type 1 receptors and Smads. We designed AB215, a potent BMP2-like Activin A/BMP2 chimera incorporating the high-affinity type 2 receptor-binding epitope of Activin A. In this study, we compare the signaling properties of AB215 and BMP2 in HEK293T cells and gonadotroph LbT2 cells in which Activin A and BMP2 synergistically induce FSHb. In HEK293T cells, AB215 is more potent than BMP2 and competitively blocks Activin A signaling, while BMP2 has a partial blocking activity. Activin A signaling is insensitive to BMP pathway antagonism in HEK293T cells but is strongly inhibited by constitutively active (CA) BMP type 1 receptors. By contrast, the potencies of AB215 and BMP2 are indistinguishable in LbT2 cells and although AB215 blocks Activin A signaling, BMP2 has no inhibitory effect. Unlike HEK293T, Activin A signaling is strongly inhibited by BMP pathway antagonism in LbT2 cells but is largely unaffected by CA BMP type 1 receptors. BMP2 increases phospho-Smad3 levels in LbT2 cells, in both the absence and the presence of Activin A treatment, and augments Activin A-induced FSHb. AB215 has the opposite effect and sharply decreases basal phospho-Smad3 levels and blocks Smad2 phosphorylation and FSHb induction resulting from Activin A treatment. These findings together demonstrate that while AB215 activates the BMP pathway, it has opposing effects to those of BMP2 on FSHb induction in LbT2 cells apparently due to its ability to block Activin A signaling. Key Words" transforming growth factor beta (TGFb)" activin " bone morphogenetic protein (BMP)" protein structure " signal transduction

A Survey of Strategies to Modulate the Bone Morphogenetic Protein Signaling Pathway: Current and Future Perspectives

“…Part of the high cost of rhBMPs is related to the fact that large amounts of protein have been required for clinical use, leading multiple groups to engineer versions that have higher activity than the naturally-occurring ligand ( Table 1 ). For instance, BMP2 chimerae containing segments from Activin A have been shown to be resistant to sequestration by the antagonist Noggin [ 35 , 42 – 47 ], leading to greater signaling activity. Noggin-resistant versions of BMP7 and GDF5 bearing enhanced activity have also been described [ 48 – 50 ].…”

Design-augmented (DA) biologics: BMP chimeras for bone and cartilage regeneration

“…These activin A/ BMP2 chimeras also act as potent activin antagonists and one was shown to block activin A induction of FSHb production in a pituitary gonadotrope cell line. 9 AB204 for bone regeneration AB204 is a well-studied DA chimera that combines type I receptor binding sequences of BMP2 with the high-affinity type II receptor-binding sequences of activin A (Fig. 1 and Table I) 6 .…”