MAPK-mediated phosphorylation of MKL2 regulates nuclear localization and transcriptional activity in striatal neurons

[Speaker] Anthony Ariza:1
[Co-author] Yasuhiro Funahashi:1, Keiichiro Okuda:1, Sachi Kozawa:1, Kozo Kaibuchi:1
1:Cell Pharmacology, Nagoya University Graduate School of Medicine, Japan

Dopamine (DA) type 1 receptor (D1R) signaling activates cAMP/Protein kinase A (PKA), which then activates Mitogen-Activated Protein Kinase (MAPK) through Rap1 finally activating transcription factors (TFs) in striatal medium spiny neurons (MSNs). These neurons play a pivotal role in reward-related behavior (Nagai T. et al. Neuron, 89, 1-16 (2016)). However, how D1R signaling regulates behavior through phosphorylation of these TFs is still largely unknown. It's known that CREB-binding protein (CBP) promotes transcription through the interaction with hundreds of different TFs and cofactors, and is also important for reward-related behavior. To isolate TFs regulated by DA signaling in MSNs, we performed a proteomic analysis for CBP-interacting proteins and identified more than 300 novel candidates in the mouse striatum. We focused on Myocardin Like 2 (MKL2) protein, which is a transcriptional co-activator of Serum Response Factor (SRF) highly expressed in the brain and known to regulate dendritic complexity. We found that interaction of CBP and MKL2 increased by cocaine administration. Furthermore, MKL2 formed a ternary complex with CBP and SRF in vivo. The C-terminal domain of MKL2, which can interact with KIX domain of CBP, was phosphorylated by MAPK at Serine 913. MAPK signaling induced MKL2 nuclear localization in striatal neurons and also increased SRF-response element promoter activity. These results demonstrate that MAPK downstream of DA signaling phosphorylates MKL2 and promotes MKL2 nuclear import facilitating interaction with CBP and regulating SRF-dependent gene expression.
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