The autophagic response to nutrient deprivation in the hl-1 cardiac myocyte is modulated by Bcl-2 and sarco/endoplasmic reticulum calcium stores

Nathan R. Brady, Anne Hamacher-Brady, Hua Yuan, Roberta A. Gottlieb

Research output: Contribution to journalArticlepeer-review

Abstract

Macroautophagy is a vital process in the cardiac myocyte: it plays a protective role in the response to ischemic injury, and chronic perturbation is causative in heart disease. Recent findings evidence a link between the apoptotic and autophagic pathways through the interaction of the antiapoptotic proteins Bcl-2 and Bcl-XL with Beclin 1. However, the nature of the interaction, either in promoting or blocking autophagy, remains unclear. Here, using a highly sensitive, macroautophagy-specific flux assay allowing for the distinction between enhanced autophagosome production and suppressed autophagosome degradation, we investigated the control of Beclin 1 and Bcl-2 on nutrient deprivation-activated macroautophagy. We found that in HL-1 cardiac myocytes the relationship between Beclin 1 and Bcl-2 is subtle: Beclin 1 mutant lacking the Bcl-2-binding domain significantly reduced autophagic activity, indicating that Beclin 1-mediated autophagy required an interaction with Bcl-2. Overexpression of Bcl-2 had no effect on the autophagic response to nutrient deprivation; however, targeting Bcl-2 to the sarco/endoplasmic reticulum (S/ER) significantly suppressed autophagy. The suppressive effect of S/ER-targeted Bcl-2 was in part due to the depletion of S/ER calcium stores. Intracellular scavenging of calcium by BAPTA-AM significantly blocked autophagy, and thapsigargin, an inhibitor of sarco/endoplasmic reticulum calcium ATPase, reduced autophagic activity by ∼ 50%. In cells expressing Bcl-2-ER, thapsigargin maximally reduced autophagic flux. Thus, our results demonstrate that Bcl-2 negatively regulated the autophagic response at the level of S/ER calcium content rather than via direct interaction with Beclin 1. Moreover, we identify calcium homeostasis as an essential component of the autophagic response to nutrient deprivation.

Original languageEnglish (US)
Pages (from-to)3184-3197
Number of pages14
JournalFEBS Journal
Volume274
Issue number12
DOIs
StatePublished - Jun 2007
Externally publishedYes

Keywords

  • Autophagy
  • Bcl-2
  • Beclin 1
  • GFP-LC3
  • HL-1 cardiac myocyte

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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