title: Involvement of dominant-negative spliced variants of the intermediate conductance Ca2+-activated K+ channel, K(Ca)3.1, in immune function of lymphoid cells.
abstract: The intermediate conductance Ca(2+)-activated K(+) channel (IK(Ca) channel) encoded by K(Ca)3.1 is responsible for the control of proliferation and differentiation in various types of cells. We identified novel spliced variants of K(Ca)3.1 (human (h) K(Ca)3.1b) from the human thymus, which were lacking the N-terminal domains of the original hK(Ca)3.1a as a result of alternative splicing events. hK(Ca)3.1b was significantly expressed in human lymphoid tissues. Western blot analysis showed that hK(Ca)3.1a proteins were mainly expressed in the plasma membrane fraction, whereas hK(Ca)3.1b was in the cytoplasmic fraction. We also identified a similar N terminus lacking K(Ca)3.1 variants from mice and rat lymphoid tissues (mK(Ca)3.1b and rK(Ca)3.1b). In the HEK293 heterologous expression system, the cellular distribution of cyan fluorescent protein-tagged hK(Ca)3.1a and/or YFP-tagged hK(Ca)3.1b isoforms showed that hK(Ca)3.1b suppressed the localization of hK(Ca)3.1a to the plasma membrane. In the Xenopus oocyte translation system, co-expression of hK(Ca)3.1b with hK(Ca)3.1a suppressed IK(Ca) channel activity of hK(Ca)3.1a in a dominant-negative manner. In addition, this study indicated that up-regulation of mK(Ca)3.1b in mouse thymocytes differentiated CD4(+)CD8(+) phenotype thymocytes into CD4(-)CD8(-) ones and suppressed concanavalin-A-stimulated thymocyte growth by down-regulation of mIL-2 transcripts. Anti-proliferative effects and down-regulation of mIL-2 transcripts were also observed in mK(Ca)3.1b-overexpressing mouse thymocytes. These suggest that the N-terminal domain of K(Ca)3.1 is critical for channel trafficking to the plasma membrane and that the fine-tuning of IK(Ca) channel activity modulated through alternative splicing events may be related to the control in physiological and pathophysiological conditions in T-lymphocytes.
authors.affiliation: Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Ohya
authors.forename: Satomi
authors.initials: S
authors.lastname: Niwa
authors.forename: Ayano
authors.initials: A
authors.lastname: Yanagi
authors.forename: Yuka
authors.initials: Y
authors.lastname: Fukuyo
authors.forename: Hisao
authors.initials: H
authors.lastname: Yamamura
authors.forename: Yuji
authors.initials: Y
authors.lastname: Imaizumi
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D005799:Genes, Dominant; D006801:Humans; D007107:Immune System / Q000378:metabolism; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000737:chemistry; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology; D024681:Potassium Channels, Calcium-Activated / Q000737:chemistry*; D020033:Protein Isoforms; D051381:Rats; D013601:T-Lymphocytes / Q000166:cytology*; D014982:Xenopus laevis
chemical_list: D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; D024681:Potassium Channels, Calcium-Activated; D020033:Protein Isoforms