Endoplasmic reticulum targeted Bcl2 confers long term cell survival through phosphorylation of heat shock protein 27

Area of Science:

• Cell Biology
• Cancer Research
• Molecular Oncology

Background:

• Overexpression of anti-apoptotic Bcl2 family proteins contributes to cancer's resistance to apoptosis-inducing therapies.
• Bcl2 proteins associate with organelles, including mitochondria and the endoplasmic reticulum (ER), to inhibit programmed cell death.

Purpose of the Study:

• To investigate the long-term survival function of Bcl2 specifically targeted to the ER.
• To elucidate the molecular mechanisms underlying ER-Bcl2-mediated cancer cell survival, focusing on heat shock protein 27 (hsp27) and associated kinases.

Main Methods:

• Compared ER-targeted Bcl2 with wild-type Bcl2 in mammalian systems.
• Assessed hsp27 phosphorylation at specific serine sites (Ser15, 78, 82) and caspase-9 activity.
• Utilized inhibitors for p38 and MEK kinases to evaluate their role in ER-Bcl2 signaling.

Main Results:

• ER-targeted Bcl2 demonstrated a long-term survival function, distinct from wild-type Bcl2.
• This survival was mediated by enhanced phosphorylation of hsp27 and subsequent inhibition of caspase-9 activity.
• Inhibition of p38 and MEK kinases prevented hsp27 phosphorylation and reversed the survival advantage of ER-Bcl2 cells, identifying them as upstream regulators.

Conclusions:

• Bcl2 possesses an ER-associated, hsp27-dependent survival function that contributes to long-term cancer cell persistence.
• The spatial localization of Bcl2 family proteins, particularly at the ER, represents a critical regulatory level for cancer cell survival.
• The interplay between ER-Bcl2 and hsp27, often co-overexpressed in aggressive tumors, highlights a novel therapeutic target for overcoming cancer therapy resistance.