Input from Ras is required for maximal PI(3)K signalling in Drosophila

Area of Science:

• Cellular signaling pathways
• Molecular biology
• Developmental biology

Background:

• Class I phosphoinositide 3-kinases (PI(3)Ks) are key signaling enzymes activated by receptor tyrosine kinases and G protein-coupled receptors.
• PI(3)Ks possess Ras-binding domains (RBDs) and can be activated by Ras GTPases, but the in vivo significance of this interaction is unclear.
• In Drosophila, the PI(3)K Dp110 is involved in insulin signaling, regulating growth, metabolism, and oogenesis.

Purpose of the Study:

• To investigate the in vivo importance of Ras-mediated activation of Class I PI(3)Ks.
• To determine if Ras binding to Dp110 is essential for normal PI(3)K function in Drosophila.

Main Methods:

• Generated a mutant Drosophila melanogaster line expressing a Dp110 protein lacking the Ras-binding domain (Dp110(RBD)).
• Assessed viability, egg production, imaginal disc growth, and overall fly size in Dp110(RBD) mutants.
• Analyzed PI(3)K signaling activation in response to insulin stimulation.

Main Results:

• Ras-mediated activation of Dp110 is dispensable for fly viability.
• Egg production is significantly reduced in Dp110(RBD) flies, indicating a role in growth-dependent processes.
• Dp110(RBD) flies exhibit reduced size and impaired maximal PI(3)K activation by insulin in imaginal discs.

Conclusions:

• Ras interaction with Dp110 is essential for achieving maximal PI(3)K signaling output in specific physiological contexts, particularly those requiring significant growth.
• Dp110 integrates signals from both phosphotyrosine-binding adaptors and Ras to modulate cellular functions.
• Ras-mediated activation contributes to the fine-tuning of PI(3)K signaling for processes like reproduction and overall organismal size.