Dynamin-dependent endocytosis of Bone Morphogenetic Protein2 (BMP2) and its receptors is dispensable for the initiation of Smad signaling.
Bone Morphogenetic Protein (BMP) signal transduction via the canonical Smad158 pathway has previously been linked to dynamin-dependent endocytosis, since the application of chemical inhibitors of clathrin or dynamin in functional cell culture based assays negatively affects initiation and propagation of the Smad response. More recent studies, however, demonstrated efficient Smad signaling by non-internalizable BMP2. The role of endocytosis in BMP signal transduction thus remained controversial. In our study we aimed to refine cell biological assays and to apply novel tools, including a new site-directed fluorescently labeled BMP2 ligand, to revisit key steps in BMP Smad signaling. We found that dynamin2 function was required for BMP2 uptake but was dispensable for C-terminal phosphorylation, nuclear translocation and transcriptional activity of BMP-dependent Smads. Furthermore, we demonstrated a role of dynamin2 in the regulation of steady-state and surface BMP receptor levels, as well as an impact on Smad1 protein level. Thus, dynamin2 allows for modulation of basal and ligand-dependent Smad signaling capacity. High levels of functional dynamin2 enhanced the myogenic differentiation of precursor cells. From our study we conclude that dynamin-dependent endocytosis serves as a regulatory mechanism to fine-tune Smad signaling, but it is not a prerequisite for signal initiation and propagation. Our findings contribute to the understanding of fundamental mechanisms of BMP signaling and thus provide important information for future consideration in the context of therapeutic applications of BMPs.
Institute for Chemistry and Biochemistry, Freie Universität Berlin, Thielallee 63, 14195 Berlin, Germany.
Pia
P
Paarmann
Institute for Chemistry and Biochemistry, Freie Universität Berlin, Thielallee 63, 14195 Berlin, Germany.
Gina
G
Dörpholz
Department for Molecular Plant Physiology and Biophysics, Biozentrum Universität Würzburg, Julius-von-Sachs Institute, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany.
Juliane
J
Fiebig
Department of Neurobiology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
Ayelet R
AR
Amsalem
Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
Marcelo
M
Ehrlich
Department of Neurobiology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
Yoav I
YI
Henis
Department for Molecular Plant Physiology and Biophysics, Biozentrum Universität Würzburg, Julius-von-Sachs Institute, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany.
Thomas
T
Müller
Institute for Chemistry and Biochemistry, Freie Universität Berlin, Thielallee 63, 14195 Berlin, Germany. Electronic address: knaus@chemie.fu-berlin.de.
Petra
P
Knaus
D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D002454:Cell Differentiation / Q000502:physiology*; D002522:Chlorocebus aethiops; D034285:Dynamin II / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D051379:Mice; D024510:Muscle Development / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D051898:Smad1 Protein / Q000235:genetics / Q000378:metabolism*
C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D051898:Smad1 Protein; C497401:Smad1 protein, mouse; D034285:Dynamin II
BMP signaling; Dynamin; Endocytosis; Smad