Mutations in GDF5 reveal a key residue mediating BMP inhibition by NOGGIN.
Signaling output of bone morphogenetic proteins (BMPs) is determined by two sets of opposing interactions, one with heterotetrameric complexes of cell surface receptors, the other with secreted antagonists that act as ligand traps. We identified two mutations (N445K,T) in patients with multiple synostosis syndrome (SYM1) in the BMP-related ligand GDF5. Functional studies of both mutants in chicken micromass culture demonstrated a gain of function caused by a resistance to the BMP-inhibitor NOGGIN and an altered signaling effect. Residue N445, situated within overlapping receptor and antagonist interfaces, is highly conserved among the BMP family with the exception of BMP9 and BMP10, in which it is substituted with lysine. Like the mutant GDF5, both BMPs are insensitive to NOGGIN and show a high chondrogenic activity. Ectopic expression of BMP9 or the GDF5 mutants resulted in massive induction of cartilage in an in vivo chick model presumably by bypassing the feedback inhibition imposed by endogenous NOGGIN. Swapping residues at the mutation site alone was not sufficient to render Bmp9 NOG-sensitive; however, successive introduction of two additional substitutions imparted high to total sensitivity on customized variants of Bmp9. In conclusion, we show a new mechanism for abnormal joint development that interferes with a naturally occurring regulatory mechanism of BMP signaling.
Seemann
Petra
P
Research Group Development and Disease, Max-Planck-Institut für Molekulare Genetik, Berlin, Germany. petra.seemann@charite.de
Brehm
Anja
A
König
Jana
J
Reissner
Carsten
C
Stricker
Sigmar
S
Kuss
Pia
P
Haupt
Julia
J
Renninger
Stephanie
S
Nickel
Joachim
J
Sebald
Walter
W
Groppe
Jay C
JC
Plöger
Frank
F
Pohl
Jens
J
Schmidt-von Kegler
Mareen
M
Walther
Maria
M
Gassner
Ingmar
I
Rusu
Cristina
C
Janecke
Andreas R
AR
Dathe
Katarina
K
Mundlos
Stefan
S
D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors*; D002352:Carrier Proteins / Q000502:physiology*; D002356:Cartilage; D002478:Cells, Cultured; D002645:Chickens; D025461:Feedback, Physiological; D055428:Growth Differentiation Factor 5 / Q000235:genetics*; D006801:Humans; D051379:Mice; D009154:Mutation; D013580:Synostosis / Q000235:genetics; D000099176:Noggin Protein
D019485:Bone Morphogenetic Proteins; D002352:Carrier Proteins; D055428:Growth Differentiation Factor 5; D000099176:Noggin Protein; C525893:GDF5 protein, human