[Report] Nuclear Actin Network Assembly by Formins Regulates the SRF Coactivator MAL

Christian Baarlink, Haicui Wang, Robert Grosse*

Institute of Pharmacology, Biochemical-Pharmacological Center (BPC), University of Marburg, Germany?*Corresponding author. E-mail: robert.grosse{at}staff.uni-marburg.deFormins are potent activators of actin filament assembly in the cytoplasm. In turn, cytoplasmic actin polymerization can promote release of actin from megakaryocytic acute leukemia (MAL) for serum response factor (SRF) transcriptional activity. Here, we found that formins polymerized actin inside the mammalian nucleus to drive serum-dependent MAL/SRF activity. Serum stimulated rapid assembly of actin filaments within the nucleus in a formin-dependent manner. Endogenous mDia was regulated using a optogenetic tool, which allowed for photoreactive release of nuclear formin autoinhibition. Activated mDia promoted rapid and reversible nuclear actin network assembly, subsequent MAL nuclear accumulation, and SRF activity. Thus, a dynamic polymeric actin structure within the nucleus is part of the serum response.

Received for publication 11 January 2013. Accepted for publication 26 March 2013.

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