Dopamine D1-like receptors, composed of D1 and D5 receptors, have been documented to modulate glutamate-mediated fast excitatory synaptic neurotransmission. Here, we report that dopamine D1 receptors modulate NMDA glutamate receptor-mediated functions through direct protein-protein interactions. Two regions in the D1 receptor carboxyl tail can directly and selectively couple to NMDA glutamate receptor subunits NR1-1a and NR2A. While one interaction is involved in the inhibition of NMDA receptor-gated currents, the other is implicated in the attenuation of NMDA receptor-mediated excitotoxicity through a PI-3 kinase-dependent pathway.

Epigenetic inheritance in mammals is characterized by high-fidelity replication of CpG methylation patterns during development. UHRF1 (also known as ICBP90 in humans and Np95 in mouse) is an E3 ligase important for the maintenance of global and local DNA methylation in vivo. The preferential affinity of UHRF1 for hemi-methylated DNA over symmetrically methylated DNA by means of its SET and RING-associated (SRA) domain and its association with the maintenance DNA methyltransferase 1 (DNMT1) suggests a role in replication of the epigenetic code. Here we report the 1.7 A crystal structure of the apo SRA domain of human UHRF1 and a 2.2 A structure of its complex with hemi-methylated DNA, revealing a previously unknown reading mechanism for methylated CpG sites (mCpG). The SRA-DNA complex has several notable structural features including a binding pocket that accommodates the 5-methylcytosine that is flipped out of the duplex DNA. Two specialized loops reach through the resulting gap in the DNA from both the major and the minor grooves to read the other three bases of the CpG duplex. The major groove loop confers both specificity for the CpG dinucleotide and discrimination against methylation of deoxycytidine of the complementary strand. The structure, along with mutagenesis data, suggests how UHRF1 acts as a key factor for DNMT1 maintenance methylation through recognition of a fundamental unit of epigenetic inheritance, mCpG.

SUMMARY A fundamental challenge in mammalian biology has been elucidating mechanisms linking DNA methylation and histone post-translational modifications. Human UHRF1 (ubiquitin-like, PHD and RING finger containing 1) has multiple domains that bind chromatin and is implicated genetically in DNA methylation maintenance. However, molecular mechanisms underlying DNA methylation regulation by UHRF1 are poorly defined. Here we show that UHRF1 association with methylated histone H3 lysine 9 (H3K9) is required for DNA methylation maintenance. We further show that UHRF1 association with H3K9 methylation is insensitive to adjacent H3 serine 10 phosphorylation – a known mitotic ‘phospho/methyl switch.’ Importantly, we demonstrate that UHRF1 mitotic chromatin association is necessary for DNA methylation maintenance through regulation of DNMT1 stability. Collectively, our results define a novel link between H3K9 methylation and the faithful epigenetic inheritance of DNA methylation, establishing an unexpected mitotic role for UHRF1 in this process.