title: PSD-95 and SAP97 exhibit distinct mechanisms for regulating K(+) channel surface expression and clustering.
abstract: Mechanisms of ion channel clustering by cytoplasmic membrane-associated guanylate kinases such as postsynaptic density 95 (PSD-95) and synapse-associated protein 97 (SAP97) are poorly understood. Here, we investigated the interaction of PSD-95 and SAP97 with voltage-gated or Kv K(+) channels. Using Kv channels with different surface expression properties, we found that clustering by PSD-95 depended on channel cell surface expression. Moreover, PSD-95-induced clusters of Kv1 K(+) channels were present on the cell surface. This was most dramatically demonstrated for Kv1.2 K(+) channels, where surface expression and clustering by PSD-95 were coincidentally promoted by coexpression with cytoplasmic Kvbeta subunits. Consistent with a mechanism of plasma membrane channel-PSD-95 binding, coexpression with PSD-95 did not affect the intrinsic surface expression characteristics of the different Kv channels. In contrast, the interaction of Kv1 channels with SAP97 was independent of Kv1 surface expression, occurred intracellularly, and prevented further biosynthetic trafficking of Kv1 channels. As such, SAP97 binding caused an intracellular accumulation of each Kv1 channel tested, through the accretion of SAP97 channel clusters in large (3-5 microm) ER-derived intracellular membrane vesicles. Together, these data show that ion channel clustering by PSD-95 and SAP97 occurs by distinct mechanisms, and suggests that these channel-clustering proteins may play diverse roles in regulating the abundance and distribution of channels at synapses and other neuronal membrane specializations.
authors.affiliation: Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York 11794-5215, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Tiffany
authors.forename: L N
authors.initials: LN
authors.lastname: Manganas
authors.forename: E
authors.initials: E
authors.lastname: Kim
authors.forename: Y P
authors.initials: YP
authors.lastname: Hsueh
authors.forename: M
authors.initials: M
authors.lastname: Sheng
authors.forename: J S
authors.initials: JS
authors.lastname: Trimmer
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D000074288:Discs Large Homolog 1 Protein; D000076122:Disks Large Homolog 4 Protein; D051528:Guanylate Kinases; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051662:Kv1.1 Potassium Channel; D051663:Kv1.2 Potassium Channel; D051665:Kv1.4 Potassium Channel; D008565:Membrane Proteins; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D015221:Potassium Channels / Q000096:biosynthesis / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D013347:Subcellular Fractions
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C513314:DLG1 protein, human; D000074288:Discs Large Homolog 1 Protein; D000076122:Disks Large Homolog 4 Protein; C000614189:Dlg1 protein, mouse; C501447:Dlg4 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; C496946:KCNA1 protein, human; C496969:KCNA2 protein, human; C496977:KCNA4 protein, human; C496947:Kcna1 protein, mouse; C496970:Kcna2 protein, mouse; C496978:Kcna4 protein, mouse; D051663:Kv1.2 Potassium Channel; D051665:Kv1.4 Potassium Channel; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; C033652:postsynaptic density proteins; D051662:Kv1.1 Potassium Channel; D051528:Guanylate Kinases