Mutating RBF can enhance its pro-apoptotic activity and uncovers a new role in tissue homeostasis

Area of Science:

• Molecular Biology
• Developmental Biology
• Cancer Research

Background:

• The tumor suppressor retinoblastoma protein (pRb) is crucial for cell cycle regulation and is frequently inactivated in cancers.
• The role of pRb in apoptosis and its regulation by caspase-mediated cleavage remains incompletely understood.
• Shorter forms of pRb, generated by caspase cleavage, can modulate apoptotic functions.

Purpose of the Study:

• To investigate the role of a specific caspase cleavage site (TELD) in the Drosophila homolog of pRb (RBF) in apoptosis and tissue homeostasis.
• To characterize the in vivo functions of a mutated RBF protein lacking the TELD cleavage site.

Main Methods:

• Bioinformatic analysis to identify conserved caspase cleavage sites in RBF.
• Site-directed mutagenesis to create a punctual mutant RBF (RBFD253A) at the TELD site.
• Analysis of RBFD253A's effects on apoptosis, proliferation, and tissue development in Drosophila adult wings and imaginal discs.

Main Results:

• A conserved TELD caspase cleavage site was identified in Drosophila RBF.
• The RBFD253A mutant retained JNK-dependent pro-apoptotic properties but induced overgrowth phenotypes in adult wings.
• This overgrowth resulted from abnormal proliferation in wing imaginal discs, dependent on JNK pathway activation.

Conclusions:

• The TELD cleavage site in RBF is important for regulating its function in vivo.
• RBF's apoptotic and proliferative functions are linked and influenced by caspase-mediated cleavage.
• These findings shed light on RBF's role in maintaining tissue homeostasis.