Myocardin-related transcription factor A regulates expression of Bok and Noxa and is involved in apoptotic signalling.

The myocardin-related transcription factor MAL/MRTF-A relates changes in G-actin to SRF-mediated gene expression. The set of G-actin-controlled SRF target genes includes components of the cytoskeleton and cell migration machinery as well as various signal transducers. Our previous screen for G-actin regulated genes identified a number of targets with well-established anti-proliferative and proapoptotic functions. Here, we report that the two proapoptotic Bcl-2 family members Bok and Noxa/Pmaip are directly transcriptionally induced by activated MAL and upon activation of the actin-MAL-SRF pathway. This activation depends on MRTFs and is sensitive to the actin drug latrunculin but insensitive to p53 depletion. A cis-regulatory element comprising a CArG-like box in the Bok promoter is required and inducibly recruits MAL and SRF. Moreover, MAL/MRTF-dependent transcriptional activity and target gene expression is upregulated upon stimulation of fibroblasts with TNF and staurosporin. This is accompanied by nuclear accumulation of MRTFs. The results suggest a role for MAL in TNF signaling and implicate the MAL-SRF transcription module in regulating the proapoptotic Bcl-2 family network.