Septins tune lipid kinase activity and PI(4,5)P₂ turnover during G-protein–coupled PLC signalling in vivo

Abstract

Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] hydrolysis by phospholipase C (PLC) is a conserved mechanism of signalling. Given the low abundance of PI(4,5)P2, its hydrolysis needs to be coupled to resynthesis to ensure continued PLC activity; however, the mechanism by which depletion is coupled to resynthesis remains unknown. PI(4,5)P2 synthesis is catalyzed by the phosphorylation of phosphatidylinositol 4 phosphate (PI4P) by phosphatidylinositol 4 phosphate 5 kinase (PIP5K). In Drosophila photoreceptors, photon absorption is transduced into PLC activity and during this process, PI(4,5)P2 is resynthesized by a PIP5K. However, the mechanism by which PIP5K activity is coupled to PI(4,5)P2 hydrolysis is unknown. In this study, we identify a unique isoform dPIP5KL, that is both necessary and sufficient to mediate PI(4,5)P2 synthesis during phototransduction. Depletion of PNUT, a non-redundant subunit of the septin family, enhances dPIP5KL activity in vitro and PI(4,5)P2 resynthesis in vivo; co-depletion of dPIP5KL reverses the enhanced rate of PI(4,5)P2 resynthesis in vivo. Thus, our work defines a septin-mediated mechanism through which PIP5K activity is coupled to PLC-mediated PI(4,5)P2 hydrolysis.

A novel homeostatic mechanism tunes PI(4,5)P2-dependent signaling at the plasma membrane

“…Since this paper was initially submitted for publication, another study has reported a similar homeostatic feedback loop in Drosophila photoreceptors, utilizing the fly homologue of septin 7 as the receptor and control center ( Kumari et al, 2022 ). This conclusion is based on the observation that cells with reduced septin 7 levels have enhanced PIP5K activity in lysates, and exhibit more rapid PI(4,5)P 2 resynthesis after PLC activation.…”

“…Given that there is no mammalian homolog of Opy1, this homeostatic mechanism appears to have appeared at least twice through convergent evolution. Combined with hints of a role for septins in maintaining PI(4,5)P 2 levels ( Kumari et al, 2022 ), the possibility arises that there might yet be more feedback controls of PI(4,5)P 2 levels to be discovered.…”

Septins as membrane influencers: direct play or in association with other cytoskeleton partners

“…In addition, it was shown that phosphoinositides containing very-long-chain fatty acids could organize septins at the membrane of the M. oryzae fungus to mediate appressoriumdependent infection of rice cells (He et al, 2020). Reciprocally, septins may control the content in phosphoinositides, since the Drosophila Peanut/SEPT7 decreases the PIP5 kinase activity and the resulting PI(4,5)P2 resynthesis (Kumari et al, 2022).…”