JNK-mediated BIM phosphorylation potentiates BAX-dependent apoptosis

Area of Science:

• Cellular Biology
• Molecular Biology
• Biochemistry

Background:

• Trophic factor deprivation (TFD) triggers apoptosis through the c-Jun N-terminal kinase (JNK) pathway.
• The JNK pathway leads to the activation of AP1 transcription factors, inducing proapoptotic proteins like BIM(EL) and HRK.
• These proteins are crucial for BAX-dependent release of cytochrome c and subsequent caspase activation.

Purpose of the Study:

• To investigate the role of JNKs in regulating the proapoptotic protein BIM(EL) during TFD.
• To determine if JNKs directly phosphorylate BIM(EL) and how this affects its function.
• To elucidate the dual transcriptional and posttranslational regulation of BIM(EL) by JNKs in apoptosis.

Main Methods:

• Utilizing cell culture models subjected to trophic factor deprivation.
• Employing Western blotting and phospho-specific antibodies to detect BIM(EL) expression and phosphorylation.
• Using kinase inhibitors and activators to manipulate JNK pathway activity.
• Assessing apoptosis through cytochrome c release and caspase activation assays.

Main Results:

• TFD induced both the expression and phosphorylation of BIM(EL).
• Mitochondrially localized JNKs, but not upstream kinases (MLKs, MKKs), specifically phosphorylated BIM(EL) at Ser65.
• This phosphorylation potentiated BIM(EL)'s proapoptotic activity.
• Inhibition of JNK attenuated BIM(EL) expression and phosphorylation, blocking TFD-induced apoptosis.
• JNK pathway activation promoted BIM(EL) expression and phosphorylation, leading to BIM- and BAX-dependent cell death.

Conclusions:

• JNKs play a critical role in regulating the proapoptotic function of BIM(EL) during trophic factor deprivation.
• JNKs control BIM(EL) activity through both transcriptional induction and direct posttranslational phosphorylation at Ser65.
• This dual regulation by JNKs enhances BIM(EL)'s ability to promote apoptosis.