CTTNBP 2 , but not CTTNBP 2 NL , regulates dendritic spinogenesis and synaptic distribution of the striatin – PP 2 A complex

Cortactin-binding protein 2 (CTTNBP2) interacts with cortactin to regulate cortactin mobility and control dendritic spine formation. CTTNBP2 has also been associated with autistic spectrum disorder. The regulation of dendritic spinogenesis could explain the association of CTTNBP2 with autism. Sequence comparison has indicated that CTTNBP2 N-terminal–like protein (CTTNBP2NL) is a CTTNBP2 homologue. To confirm the specific effect of CTTNBP2 on dendritic spinogenesis, here we investigate whether CTTNBP2NL has a similar function to CTTNBP2. Although both CTTNBP2 and CTTNBP2NL interact with cortactin, CTTNBP2NL is associated with stress fibers, whereas CTTNBP2 is distributed to the cortex and intracellular puncta. We also provide evidence that CTTNBP2, but not CTTNBP2NL, is predominantly expressed in the brain. CTTNBP2NL does not show any activity in the regulation of dendritic spinogenesis. In addition to spine morphology, CTTNBP2 is also found to regulate the synaptic distribution of striatin and zinedin (the regulatory B subunits of protein phosphatase 2A [PP2A]), which interact with CTTNBP2NL in HEK293 cells. The association between CTTNBP2 and striatin/zinedin suggests that CTTNBP2 targets the PP2A complex to dendritic spines. Thus we propose that the interactions of CTTNBP2 and cortactin and the PP2A complex regulate spine morphogenesis and synaptic signaling. INTRODUCTION Dendritic spines are tiny, actin-rich protrusions of ∼0.5–1 μm in width and 1–2 μm in length that extend from dendrites (Matus et al., 1982; Landis and Reese, 1983) and are the sites of most of the excitatory synapses in the mammalian CNS (Harris and Stevens, 1989). F-actin dynamics controls the morphology of dendritic spines (Penzes and Cahill, 2012). The signals derived from neurotransmitters also influence F-actin dynamics and alter the morphology or even the density of dendritic spines (Schubert and Dotti, 2007; Bosch and Hayashi, 2012). Many of the ubiquitously expressed actin-associated proteins, including cortactin, have been shown to regulate the morphology or density of dendritic spines. However, because dendritic spines are neuron-specific subcellular structures, it is possible that some of the neuron-specific proteins or signals control the formation of dendritic spines. Indeed, we recently showed that cortactinbinding protein 2 (CTTNBP2), a neuron-specific, F-actin–associated protein (Ohoka and Takai, 1998), regulates the formation and maintenance of dendritic spines (Chen and Hsueh, 2012). CTTNBP2 is also known as CortBP2 (cortactin-binding protein 2) or CBP90 (cortactin-binding protein at ∼90 kDa; Ohoka and Takai, 1998). It has been associated with autistic spectrum disorder (Cheung et al., 2001; Iossifov et al., 2012), indicating a critical role for CTTNBP2 in neural development and function. Through alternative splicing, a single CTTNBP2 gene encodes three different transcripts, namely short (S), long (L), and intron forms (Chen and Hsueh, 2012). The results of immunoblotting and reverse transcription PCR analyses indicated that CTTNBP2-S is the major product of the CTTNBP2 gene in neurons (Chen and Hsueh, 2012). An analysis of Monitoring Editor Paul Forscher Yale University Received: May 10, 2012 Revised: Aug 23, 2012 Accepted: Sep 17, 2012 This article was published online ahead of print in MBoC in Press (http://www .molbiolcell.org/cgi/doi/10.1091/mbc.E12-05-0365) on September 26, 2012. *Present address: Margaret M. Dyson Vision Research Institute, Department of Ophthalmology, Weill Medical College of Cornell University, New York, NY 10065. Address correspondence to: Yi-Ping Hsueh (yph@gate.sinica.edu.tw). © 2012 Chen et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0). “ASCB®,” “The American Society for Cell Biology®,” and “Molecular Biology of the Cell®” are registered trademarks of The American Society of Cell Biology. Abbreviations used: CTTNBP2, cortactin-binding protein 2; CTTNBP2NL, cortactinbinding protein 2 N-terminal–like protein; PP2A, protein phosphatase 2A.