Mutant actins that stabilise F-actin use distinct mechanisms to activate the SRF coactivator MAL.
Nuclear accumulation of the serum response factor coactivator MAL/MKL1 is controlled by its interaction with G-actin, which results in its retention in the cytoplasm in cells with low Rho activity. We previously identified actin mutants whose expression promotes MAL nuclear accumulation via an unknown mechanism. Here, we show that actin interacts directly with MAL in vitro with high affinity. We identify a further activating mutation, G15S, which stabilises F-actin, as do the activating actins S14C and V159N. The three mutants share several biochemical properties, but can be distinguished by their ability to bind cofilin, ATP and MAL. MAL interaction with actin S14C is essentially undetectable, and that with actin V159N is weakened. In contrast, actin G15S interacts more strongly with MAL than the wild-type protein. Strikingly, the nuclear accumulation of MAL induced by overexpression of actin S14C is substantially dependent on Rho activity and actin treadmilling, while that induced by actin G15S expression is not. We propose a model in which actin G15S acts directly to promote MAL nuclear entry.
Posern
Guido
G
Transcription Laboratory, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, London, UK.
Miralles
Francesc
F
Guettler
Sebastian
S
Treisman
Richard
R
D051339:Actin Depolymerizing Factors; D000199:Actins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D021581:Active Transport, Cell Nucleus / Q000235:genetics; D000255:Adenosine Triphosphate / Q000378:metabolism; D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002457:Cell Extracts; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism; D017930:Genes, Reporter; D005982:Glutathione Transferase / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism; D041681:NIH 3T3 Cells; D015514:Oncogene Proteins, Fusion / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010590:Phalloidine / Q000378:metabolism; D017354:Point Mutation; D011233:Precipitin Tests; D011485:Protein Binding; D026362:Serum Response Factor / Q000378:metabolism*; D015398:Signal Transduction; D015534:Trans-Activators; D020798:Two-Hybrid System Techniques
D051339:Actin Depolymerizing Factors; D000199:Actins; D002457:Cell Extracts; D004268:DNA-Binding Proteins; C431575:MRTFA protein, human; D008840:Microfilament Proteins; D015514:Oncogene Proteins, Fusion; D026362:Serum Response Factor; D015534:Trans-Activators; D010590:Phalloidine; D000255:Adenosine Triphosphate; D008156:Luciferases; D005982:Glutathione Transferase; D003850:Deoxyribonuclease I