pERK 1/2 inhibit Caspase-8 induced apoptosis in cancer cells by phosphorylating it in a cell cycle specific manner

Area of Science:

• Molecular Biology
• Cancer Research
• Cell Signaling

Background:

• ERK 1/2 are frequently hyperactive in various cancers.
• Active ERK 1/2 (pERK 1/2) are implicated in protecting cancer cells from apoptosis, but the precise mechanisms remain unclear.

Purpose of the Study:

• To elucidate the mechanism by which active ERK 1/2 (pERK 1/2) protect cancer cells from apoptosis.
• To investigate the role of pERK 1/2 in regulating Caspase-8 activity and TRAIL-induced apoptosis.

Main Methods:

• In vitro kinase assays and mass spectrometry were employed to identify phosphorylation targets of pERK 1/2.
• RNA interference (RNAi) was used to knock down endogenous pro-Caspase-8 and introduce a non-phosphorylatable mutant (S387A).
• Apoptosis assays were conducted in EGFR-overexpressing ovarian and breast cancer cell lines treated with TRAIL, with or without ERK 1/2 inhibition.

Main Results:

• Demonstrated that pERK 1/2 directly phosphorylates pro-Caspase-8 at serine 387 (S387).
• Showed that pERK 1/2 inhibits TRAIL-induced apoptosis, particularly during the G1/S phase, in cancer cell lines.
• Found that replacing wild-type pro-Caspase-8 with a non-phosphorylatable S387A mutant significantly increased Caspase-8 activity upon TRAIL stimulation, even with active ERK 1/2 present.

Conclusions:

• Propose a novel mechanism where pERK 1/2-mediated phosphorylation of pro-Caspase-8 at S387 contributes to resistance against TRAIL-induced apoptosis.
• Suggest that combining TRAIL therapy with ERK 1/2 inhibitors could be a promising strategy to overcome resistance in cancers with hyperactive ERK 1/2.