A Diaphanous-related formin links Ras signaling directly to actin assembly in macropinocytosis and phagocytosis.
Phagocytosis and macropinocytosis are Ras-regulated and actin-driven processes that depend on the dynamic rearrangements of the plasma membrane that protrudes and internalizes extracellular material by cup-shaped structures. However, the regulatory mechanisms underlying actin assembly in large-scale endocytosis remain elusive. Here, we show that the Diaphanous-related formin G (ForG) from the professional phagocyte Dictyostelium discoideum localizes to endocytic cups. Biochemical analyses revealed that ForG is a rather weak nucleator but efficiently elongates actin filaments in the presence of profilin. Notably, genetic inactivation of ForG is associated with a strongly impaired endocytosis and a markedly diminished F-actin content at the base of the cups. By contrast, ablation of the Arp2/3 (actin-related protein-2/3) complex activator SCAR (suppressor of cAMP receptor) diminishes F-actin mainly at the cup rim, being consistent with its known localization. These data therefore suggest that ForG acts as an actin polymerase of Arp2/3-nucleated filaments to allow for efficient membrane expansion and engulfment of extracellular material. Finally, we show that ForG is directly regulated in large-scale endocytosis by RasB and RasG, which are highly related to the human proto-oncogene KRas.
Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany.
Alexander
A
Junemann
Division of Molecular Biology, Ruđer Bošković Institute, 10000 Zagreb, Croatia.
Vedrana
V
Filić
Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany.
Moritz
M
Winterhoff
Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany.
Benjamin
B
Nordholz
Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany.
Christof
C
Litschko
Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany.
Helena
H
Schwellenbach
Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany.
Till
T
Stephan
Division of Molecular Biology, Ruđer Bošković Institute, 10000 Zagreb, Croatia.
Igor
I
Weber
Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany; faix.jan@mh-hannover.de.
Jan
J
Faix
D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D004023:Dictyostelium / Q000378:metabolism / Q000502:physiology*; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010587:Phagocytosis; D010873:Pinocytosis; D000090063:Proto-Oncogene Mas; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D018631:ras Proteins / Q000378:metabolism*
D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; C000715470:MAS1 protein, human; D008840:Microfilament Proteins; D000090063:Proto-Oncogene Mas; D015800:Protozoan Proteins; D018631:ras Proteins
Arp2/3 complex; Ras; formin; macropinocytosis; phagocytosis