title: Canonical transient receptor potential channel 2 (TRPC2) as a major regulator of calcium homeostasis in rat thyroid FRTL-5 cells: importance of protein kinase C δ (PKCδ) and stromal interaction molecule 2 (STIM2).
abstract: Mammalian non-selective transient receptor potential cation channels (TRPCs) are important in the regulation of cellular calcium homeostasis. In thyroid cells, including rat thyroid FRTL-5 cells, calcium regulates a multitude of processes. RT-PCR screening of FRTL-5 cells revealed the presence of TRPC2 channels only. Knockdown of TRPC2 using shRNA (shTRPC2) resulted in decreased ATP-evoked calcium peak amplitude and inward current. In calcium-free buffer, there was no difference in the ATP-evoked calcium peak amplitude between control cells and shTRPC2 cells. Store-operated calcium entry was indistinguishable between the two cell lines. Basal calcium entry was enhanced in shTRPC2 cells, whereas the level of PKCβ1 and PKCδ, the activity of sarco/endoplasmic reticulum Ca(2+)-ATPase, and the calcium content in the endoplasmic reticulum were decreased. Stromal interaction molecule (STIM) 2, but not STIM1, was arranged in puncta in resting shTRPC2 cells but not in control cells. Phosphorylation site Orai1 S27A/S30A mutant and non-functional Orai1 R91W attenuated basal calcium entry in shTRPC2 cells. Knockdown of PKCδ with siRNA increased STIM2 punctum formation and enhanced basal calcium entry but decreased sarco/endoplasmic reticulum Ca(2+)-ATPase activity in wild-type cells. Transfection of a truncated, non-conducting mutant of TRPC2 evoked similar results. Thus, TRPC2 functions as a major regulator of calcium homeostasis in rat thyroid cells.
authors.affiliation: Department of Biosciences, Åbo Akademi University, Tykistökatu 6A, 20520 Turku, Finland.
authors.forename: Pramod
authors.initials: P
authors.lastname: Sukumaran
authors.forename: Christoffer
authors.initials: C
authors.lastname: Löf
authors.forename: Kati
authors.initials: K
authors.lastname: Kemppainen
authors.forename: Pasi
authors.initials: P
authors.lastname: Kankaanpää
authors.forename: Ilari
authors.initials: I
authors.lastname: Pulli
authors.forename: Johnny
authors.initials: J
authors.lastname: Näsman
authors.forename: Tero
authors.initials: T
authors.lastname: Viitanen
authors.forename: Kid
authors.initials: K
authors.lastname: Törnquist
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D005786:Gene Expression Regulation; D006706:Homeostasis; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism; D000071738:Stromal Interaction Molecule 2; D050052:TRPC Cation Channels / Q000235:genetics / Q000378:metabolism*; D013961:Thyroid Gland / Q000201:enzymology / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D008565:Membrane Proteins; C560435:STIM2 protein, rat; D000071738:Stromal Interaction Molecule 2; D050052:TRPC Cation Channels; C491857:Trpc2 protein, rat; D051745:Protein Kinase C-delta; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium