PT  - JOURNAL ARTICLE
AU  - Hironori Nishino
AU  - Taro Saito
AU  - Ran Wei
AU  - Tetsuya Takano
AU  - Koji Tsutsumi
AU  - Makoto Taniguchi
AU  - Kanae Ando
AU  - Mineko Tomomura
AU  - Mitsunori Fukuda
AU  - Shin-ichi Hisanaga
TI  - The LMTK1—TBC1D9B—Rab11A cascade regulates dendritic spine formation via endosome trafficking
AID  - 10.1523/JNEUROSCI.3209-18.2019
DP  - 2019 Oct 18
TA  - The Journal of Neuroscience
PG  - 3209-18
4099  - http://www.jneurosci.org/content/early/2019/10/18/JNEUROSCI.3209-18.2019.short
4100  - http://www.jneurosci.org/content/early/2019/10/18/JNEUROSCI.3209-18.2019.full
AB  - Dendritic spines are postsynaptic protrusions at excitatory synapses that are critical for proper neuronal synaptic transmission. While lipid and protein membrane components are necessary for spine formation, it is largely unknown how they are recruited to developing spines. Endosomal trafficking is one mechanism that may influence this development. We recently reported that Lemur kinase 1A (LMTK1A), a membrane-bound Ser/Thr kinase, regulates trafficking of endosomes in neurons. LMTK1 has been shown to be a p35 Cdk5 activator-binding protein and a substrate for Cdk5-p35, however, its neuronal function has not been sufficiently studied. Here, we investigate the role of LMTK1 in spine formation. Depletion of LMTK1 increases spine formation, maturation and density in primary cultured neurons and in mouse brain of either sex. Additionally, expression of kinase negative (kn) LMTK1 stimulates spine formation in primary neurons and in vivo. LMTK1 controls spine formation through Rab11, a regulator of recycling endosome trafficking. We identify TBC1D9B—a Rab11A GTPase-activating protein (Rab11A GAP)—as a LMTK1 binding protein, and find that TBC1D9B mediates LMTK1 activity on Rab11A. TBC1D9B inactivates Rab11A under the control of LMTK1A. Further, by analyzing the effect of decreased TBC1D9B expression in primary neurons, we demonstrate that TBC1D9B indeed regulates spine formation. This is the first demonstration of the biological function of TBC1D9B. Together, with the regulation of LMTK1 by Cdk5-p35, we propose the Cdk5—LMTK1—TBC1D9B—Rab11A cascade as a novel signaling mechanism regulating endosomal transport for synapse formation and function.SIGNIFICANCE STATEMENTDendritic spines are post-synaptic specializations essential for synaptic transmission. However, it is not known how critical membrane components are recruited to spines for their formation. Endosomal trafficking is one such mechanism that may mediate this process. Here we investigate regulators of endosomal trafficking and their contribution to spine formation. We identify two novel factors, LMTK1 and TBC1D9B, which regulate spine formation upstream of Rab11A, a small GTPase. LMTK1 is a membrane bound Ser/Thr kinase regulated by Cdk5-p35, and TBC1D9B is a recently identified Rab11 GAP. LMTK1 controls the GAP activity of TBC1D9B on Rab11A, and TBC1D9B mediates the LMTK1 activity on Rab11A. We propose the Cdk5—LMTK1—TBC1D9B—Rab11A cascade as a novel mechanism controlling spine formation and function.