Fenster Catherine P, Fenster Steven D, Leahy Hannah P, Kurschner Cornelia, Blundon Jay A
Department of Biology, Rhodes College, Memphis, TN 38112, USA.
Brain Res. 2007 Aug 8;1162:19-31. doi: 10.1016/j.brainres.2007.05.051. Epub 2007 Jun 8.
Neuronal interleukin-16 (NIL-16) is a multi-PDZ domain protein expressed in post-mitotic neurons of the hippocampus and cerebellum. NIL-16 contains four PDZ domains, two of which are located within the neuron-specific N-terminal region. In yeast two-hybrid systems, the N-terminus of NIL-16 interacts with several ion channel proteins, including the Kv4.2 subunit of A-type K(+) channels. Here we provide evidence that NIL-16, through interactions with Kv4.2, influences Kv4.2 channel function and subcellular distribution. Specifically, coexpression of NIL-16 with Kv4.2 in COS-7 cells results in a significant reduction in whole-cell A-type current densities; however, when the Kv4.2 PDZ-ligand domain is mutated, Kv4.2 current densities are not affected by NIL-16 coexpression. Moreover, single-channel conductance was not influenced by the presence of NIL-16. In hippocampal neurons, A-type current densities are increased by conditions that inhibit interactions between NIL-16 and Kv4.2, such as overexpression of the Kv4.2 C-terminal PDZ-ligand domain and treatment with small-interfering RNA duplexes that reduce NIL-16 expression. Results of surface biotinylation assays using COS-7 cells suggest that Kv4.2 surface expression levels are reduced by coexpression with NIL-16. In addition, coexpression of NIL-16 with Kv4.2 induces Kv4.2 to form dense intracellular clusters; whereas without NIL-16, Kv4.2 channels cells are dispersed. Taken together, these data suggest that interactions between Kv4.2 and NIL-16 may reduce the number of functional Kv4.2-containing channels on the cell surface. In summary, NIL-16 may provide a novel form of A-type K(+) channel modulation that is localized specifically to neurons of the hippocampus and cerebellum.
神经元白细胞介素-16（NIL-16）是一种多PDZ结构域蛋白，在海马体和小脑的有丝分裂后神经元中表达。NIL-16包含四个PDZ结构域，其中两个位于神经元特异性N端区域。在酵母双杂交系统中，NIL-16的N端与几种离子通道蛋白相互作用，包括A型钾通道的Kv4.2亚基。在此，我们提供证据表明，NIL-16通过与Kv4.2相互作用，影响Kv4.2通道功能和亚细胞分布。具体而言，NIL-16与Kv4.2在COS-7细胞中共表达导致全细胞A型电流密度显著降低；然而，当Kv4.2的PDZ配体结构域发生突变时，Kv4.2电流密度不受NIL-16共表达的影响。此外，单通道电导不受NIL-16存在的影响。在海马神经元中，抑制NIL-16与Kv4.2之间相互作用的条件，如Kv4.2 C端PDZ配体结构域的过表达和用降低NIL-16表达的小干扰RNA双链体处理，会增加A型电流密度。使用COS-7细胞进行的表面生物素化分析结果表明，与NIL-16共表达会降低Kv4.2的表面表达水平。此外，NIL-16与Kv4.2共表达诱导Kv4.2形成密集的细胞内簇；而没有NIL-16时，Kv4.2通道在细胞中分散分布。综上所述，这些数据表明Kv4.2与NIL-16之间的相互作用可能会减少细胞表面含功能性Kv4.2通道的数量。总之，NIL-16可能提供一种新型的A型钾通道调节方式，这种调节方式特异性地定位于海马体和小脑的神经元。
