Regulation of the mouse epithelial Ca2(+) channel TRPV6 by the Ca(2+)-sensor calmodulin

• Published in: The Journal of biological chemistry 2004-07, Vol.279 (28), p.28855-28861
• Main Authors: Lambers, Tim T, Weidema, A Freek, Nilius, Bernd, Hoenderop, Joost G J, Bindels, René J M
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Binding Sites; Calcium - metabolism; Calcium Channels - chemistry; Calcium Channels - genetics; Calcium Channels - metabolism; Calmodulin - genetics; Calmodulin - metabolism; Cell Line; Epithelial Cells - metabolism; Humans; Mice; Molecular Sequence Data; Oocytes - physiology; Patch-Clamp Techniques; Protein Binding; Rabbits; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Sequence Alignment; TRPV Cation Channels; Xenopus
• ISSN: 0021-9258

TRPV5 and TRPV6 are members of the superfamily of transient receptor potential (TRP) channels and facilitate Ca(2+) influx in a variety of epithelial cells. The activity of these Ca(2+) channels is tightly controlled by the intracellular Ca(2+) concentration in close vicinity to the channel mouth. The molecular mechanism underlying the Ca(2+)-dependent activity of TRPV5/TRPV6 is, however, still unknown. Here, the putative role of calmodulin (CaM) as the Ca(2+) sensor mediating the regulation of channel activity was investigated. Overexpression of Ca(2+)-insensitive CaM mutants (CaM(1234) and CaM(34)) significantly reduced the Ca(2+) as well as the Na(+) current of TRPV6- but not that of TRPV5-expressing HEK293 cells. By combining pull-down assays and co-immunoprecipitations, we demonstrated that CaM binds to both TRPV5 and TRPV6 in a Ca(2+)-dependent fashion. The binding of CaM to TRPV6 was localized to the transmembrane domain (TRPV6(327-577)) and consensus CaM-binding motifs located in the N (1-5-10 motif, TRPV6(88-97)) and C termini (1-8-14 motif, TRPV6(643-656)), suggesting a mechanism of regulation involving multiple interaction sites. Subsequently, chimeric TRPV6/TRPV5 proteins, in which the N and/or C termini of TRPV6 were substituted by that of TRPV5, were co-expressed with CaM(34) in HEK293 cells. Exchanging, the N and/or the C termini of TRPV6 by that of TRPV5 did not affect the CaM(34)-induced reduction of the Ca(2+) and Na(+) currents. These results suggest that CaM positively affects TRPV6 activity upon Ca(2+) binding to EF-hands 3 and 4, located in the high Ca(2+) affinity CaM C terminus, which involves the N and C termini and the transmembrane domain of TRPV6.