Direct interaction with a nuclear protein and regulation of gene silencing by a variant of the Ca2+-channel beta 4 subunit.
The beta subunits of voltage-gated Ca(2+) channels are known to be regulators of the channels' gating properties. Here we report a striking additional function of a beta subunit. Screening of chicken cochlear and brain cDNA libraries identified beta(4c), a short splice variant of the beta(4) subunit. Although beta(4c) occurs together with the longer isoforms beta(4a) or beta(4b) in the brain, eye, heart, and lung, the cochlea expresses exclusively beta(4c). The association of beta(4c) with the Ca(2+)-channel alpha(1) subunit has slight but significant effects on the kinetics of channel activation and inactivation. Yeast two-hybrid and biochemical assays revealed that beta(4c) interacts directly with the chromo shadow domain of chromobox protein 2heterochromatin protein 1gamma (CHCB2HP1gamma), a nuclear protein involved in gene silencing and transcriptional regulation. Coexpression of this protein specifically recruits beta(4c) to the nuclei of mammalian cells. Furthermore, beta(4c) but not beta(4a) dramatically attenuates the gene-silencing activity of chromobox protein 2heterochromatin protein 1gamma. The beta(4c) subunit is therefore a multifunctional protein that not only constitutes a portion of the Ca(2+) channel but also regulates gene transcription.
Hibino
H
H
The Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
Pironkova
R
R
Onwumere
O
O
Rousset
M
M
Charnet
P
P
Hudspeth
A J
AJ
Lesage
F
F
D017398:Alternative Splicing; D000818:Animals; D001921:Brain / Q000502:physiology*; D019556:COS Cells; D015220:Calcium Channels / Q000235:genetics* / Q000502:physiology; D002645:Chickens; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D003051:Cochlea / Q000502:physiology*; D017931:DNA Primers; D005260:Female; D015723:Gene Library; D020868:Gene Silencing; D014644:Genetic Variation; D006198:Hair Cells, Auditory / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D009687:Nuclear Proteins / Q000378:metabolism*; D009865:Oocytes / Q000502:physiology; D021122:Protein Subunits / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014982:Xenopus laevis
D015220:Calcium Channels; D017931:DNA Primers; D009687:Nuclear Proteins; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins