Abstract 18460: Nuclear Translocation of Calmodulin, Which Dissociated From Cardiac Ryanodine Receptor, Promotes the Pathological Cardiac Hypertrophy
Calmodulin (CaM) is a ubiquitous Ca binding protein, and ~20% of cardiac myocyte CaM binds to and regulates cardiac ryanodine receptor (RyR2) channel function. CaM binding to RyR2 (CaM-RyR2) inhibits RyR2 opening at all [Ca]i and, as such, is a critical regulator of SR Ca release. Our recent studies indicated that CaM-RyR2 binding affinity is reduced in pathological conditions, such as heart failure and oxidative stress. However, the roles of CaM ‘released’ lost from RyR2, are unknown. Here, we tested whether RyR2-dissociated CaM play a pivotal role in pathological cardiac hypertrophy.
Methods and Results: First, we tested whether treatment with angiotensin II (AngII), which stimulates pathologic cardiac hypertrophy, reduced CaM-RyR2 binding and whether CaM moves to nucleus (using immunofluorescence). Since CaM lacks a nuclear localization signal (NLS) motif, CaM itself is not directed into the nucleus. Thus, we also tested whether GRK5, which has both CaM binding site and NLS, translocates like CaM. Treatment with AngII significantly reduced CaM-RyR2 binding, caused nuclear translocation of both CaM and GRK5 to the nucleus, and caused nuclear export of HDAC5 (which promotes hypertrophic transcription). Furthermore, we assessed whether dantrolene, which restore CaM binding to the RyR2, can prevent nuclear translocation of CaM from RyR2. Treatment with Dantrolene and AngII dramatically reduced nuclear CaM accumulation vs. AngII alone, indicating that the source of nucleus CaM is likely from CaM-RyR2. Next, we assessed the CaM-RyR2, GRK5 and HDAC5 nuclear translocation using an 8 wk pressure overload (TAC) model. After TAC (vs. sham), the binding affinity of CaM to RyR2 was lower, nuclear CaM and GRK5 were both elevated and there was enhanced nuclear export of HDAC5.
Conclusions: Under stress (acute AngII or 8 wk TAC) CaM dissociates from RyR2 and translocation to the nucleus together with GRK5. This may be an important step in driving pathological hypertrophic gene transcription, as indicated by parallel HDAC5 export from nucleus.
Author Disclosures: T. Oda: None. T. Yamamoto: None. T. Kato: None. S. Nishimura: None. G. Fukui: None. S. Okuda: None. S. Kobayashi: None. D. Bers: None. M. Yano: None.
- © 2016 by American Heart Association, Inc.