HSPB1 facilitates ERK-mediated phosphorylation and degradation of BIM to attenuate endoplasmic reticulum stress-induced apoptosis

Donna Kennedy,Sophie Janssens,Sanjeev Gupta,Karen Doyle,Vincent Timmerman,Michiel Krols,Svetlana Saveljeva,Afshin Samali,Adrienne M Gorman,Deepu Oommen,Leonardo Almeida-Souza,Katarzyna Mnich,Reka Chakravarthy

doi:10.1038/cddis.2017.408

Abstract

BIM, a pro-apoptotic BH3-only protein, is a key regulator of the intrinsic (or mitochondrial) apoptosis pathway. Here, we show that BIM induction by endoplasmic reticulum (ER) stress is suppressed in rat PC12 cells overexpressing heat shock protein B1 (HSPB1 or HSP27) and that this is due to enhanced proteasomal degradation of BIM. HSPB1 and BIM form a complex that immunoprecipitates with p-ERK1/2. We found that HSPB1-mediated proteasomal degradation of BIM is dependent on MEK-ERK signaling. Other studies have shown that several missense mutations in HSPB1 cause the peripheral neuropathy, Charcot-Marie-Tooth (CMT) disease, which is associated with nerve degeneration. Here we show that cells overexpressing CMT-related HSPB1 mutants exhibited increased susceptibility to ER stress-induced cell death and high levels of BIM. These findings identify a novel function for HSPB1 as a negative regulator of BIM protein stability leading to protection against ER stress-induced apoptosis, a function that is absent in CMT-associated HSPB1 mutants.

Highlights

Associated X protein (BAX) and BCL-2-antagonist/killer (BAK), causes mitochondrial outer membrane permeabilization (MOMP) and the release of pro-apoptotic factors such as cytochrome c into the cytosol.[1]
BCL-2 interacting mediator of cell death (BIM) can be phosphorylated by Jun N-terminal kinase (JNK) on Ser65.14,32 Here we show that endoplasmic reticulum (ER) stress induced JNK1/2 phosphorylation, which was attenuated at 48 h in HSPB1 cells (Figure 5c)
These data suggest a novel mechanism by which HSPB1 can inhibit the intrinsic apoptosis pathway, and demonstrates a novel way by which BIM is regulated by HSPB1 during cell stress (Figure 7)

Summary

Introduction

Associated X protein (BAX) and BCL-2-antagonist/killer (BAK), causes mitochondrial outer membrane permeabilization (MOMP) and the release of pro-apoptotic factors such as cytochrome c into the cytosol.[1]. Heat shock preconditioning protects cells from stresses that would ordinarily be toxic.[16,17] These effects are mediated by inducible heat shock proteins (HSPs), including HSPB1, which is a potent inhibitor of apoptosis signaling by diverse cellular stressors.[18,19,20,21,22] HSPB1 can indirectly inhibit BAX activation/oligomerization and MOMP induction to reduce cytochrome c release from the mitochondria.[20,23] Mutations in HSPB1 are associated with progressive degeneration of peripheral nerves in the inherited peripheral neuropathies. We show that overexpression of HSPB1 confers protection against apoptosis triggered by ER stress by enhancing the proteasomal degradation of BIM This effect was dependent on ERK1/2-mediated phosphorylation of BIM. In contrast to the wild-type HSPB1 protein, HSPB1 variants with

Methods

Results

Conclusion