Uncoupling the BMP receptor antagonist function from the WNT agonist function of R-spondin 2 using the inhibitory peptide dendrimer RW(d)

Signaling by bone morphogenetic proteins (BMPs) plays pivotal roles in embryogenesis, adult tissue homeostasis, and disease. Recent studies revealed that the well-established WNT agonist R-spondin 2 (RSPO2) is also a BMP receptor (BMPR1A) antagonist, with roles in early Xenopus embryogenesis and human acute myeloid leukemia (AML). To uncouple the BMP antagonist function from the WNT agonist function and to promote development of AML therapeutics, here we identified a 10-mer peptide (RW) derived from the Thrombospondin 1 (TSP1)-domain of RSPO2, which specifically prevents binding between RSPO2 and BMPR1A without altering WNT signaling. We also show a corresponding RW-dendrimer (RWd) exhibiting improved half-life relieves inhibition of BMP receptor signaling by RSPO2 in human AML cells, reducing cell growth and inducing differentiation. Moreover, microinjection of RWd in Xenopus embryos ventralizes the dorsoventral embryonic patterning by upregulating BMP signaling without affecting WNT signaling. Our study corroborates the function of RSPO2 as a BMP receptor antagonist and provides a proof-of-concept for pharmacologically uncoupling BMP antagonist from WNT agonist functions of RSPO2 using the inhibitor peptide RWd with enhanced target selectivity and limited side effects.