Acute expression of constitutively active CREB in hippocampal neurons increased the protein levels of KIF17, NR2B, and NR2A (Figures

8C and 8D). The kif17 and nr2b mRNA levels were also increased, but the nr2a level was not ( Figures 8E and 8F). Inhibition of CREB activity by expression of a dominant-negative form of CREB caused significant decreases in the mRNA and protein levels for NR2B and in the mRNA level for KIF17 ( Figures 8E and 8F). These data suggest that activation of CREB upregulates KIF17 and NR2B by increasing the transcription of each coding gene, but that other mechanisms underlie the increase Sirolimus manufacturer in the level of NR2A. KIF17 has been implicated in the transport of NR2B subunits (Guillaud et al., 2003 and Setou et al., 2000). Consistently, our results revealed a decreased level of motility of NR2B-EGFP clusters (Figures 2G–2J; Movie S1), but normal motility of NR2A-EGFP clusters (Figures 2K–2N; Movie S2) in kif17−/− mouse neurons. These data suggest that KIF17 transports the NR2B subunit, but not the NR2A

subunit. The NR2A subunit is likely to be transported by a different molecular motor. Recent papers have shown data suggesting that Kv4.2 and other neurotransmitter receptors, namely GluR5 and KA2, might also be cargoes for KIF17 (Chu et al., 2006 and Kayadjanian et al., 2007). We studied the expression of Kv4.2, GluR5, and KA2 in the kif17−/− mouse hippocampus.

No significant differences in the levels of these proteins were observed buy GSI-IX between kif17+/+ and kif17−/− mice ( Figure 1B). One possibility is that some molecular motors other than KIF17 support the transport of these proteins, compensating for the loss of function of KIF17 in kif17−/− neurons. Interestingly, significant reductions in the levels of both NR2B and NR2A in kif17−/− mouse synapses were observed (Figures 1G, 2A–2F, and S2B). Further analysis revealed that the level of NR2A in kif17−/− mouse neurons is downregulated at a posttranslational level, but that of NR2B is downregulated at a transcriptional level (Figures 1B–1F and 3A–3C). The NR2A level is decreased in kif17−/− mouse unless neurons due to its accelerated degradation in dendrites ( Figures 3I and 3L). Consistent with this finding, other investigators have reported that NR2A-containing NMDA receptors are easily degraded ( Yashiro and Philpot, 2008), whereas the NR2B subunit is preferentially driven to a recycling pathway ( Lavezzari et al., 2004 and Scott et al., 2004). We also showed that the NR2A degradation is dependent on the ubiquitin-proteasome system ( Figures 3D–3F). Considering these data together with studies reporting KIF17-mediated NR2B transport (Guillaud et al., 2003 and Setou et al., 2000), it is plausible that the accelerated NR2A degradation is caused by the reduction in NR2B transport in kif17−/− mouse neurons.