Molecular insights into Profilin1-dependent regulation of cellular phosphatidylinositol-(4,5)-bisphosphate

Phosphatidylinositol (4,5)-bisphosphate (PIP₂), the most abundant form of cellular poly-phosphoinositide (PPI) class of phospholipid, is a central plasma membrane (PM)-associated signaling hub that controls a variety of cellular processes. In this study, we demonstrate that CRISPR-mediated deletion of the gene encoding actin-binding protein profilin1 (Pfn1) leads to downregulation of PM PIP₂ content in cells. This is also phenocopied when either Pfn1-actin interaction is genetically disrupted or F-actin is depolymerized implying that Pfn1-dependent PIP₂ alteration could be somehow related to its actin-regulatory function. We further show that phospholipase C activity is critical for Pfn1-deficient cells to exhibit the PIP₂-related phenotype. These findings, taken together with experimental evidence for select signatures of elevated PIP₂ hydrolysis in Pfn1-deficient cells, raise a possibility that altered PIP₂ hydrolysis may play a role in at least partly contributing to Pfn1-dependent regulation of PM PIP₂. Furthermore, our lipidomic studies unexpectedly found that Pfn1 loss leads to dramatic alterations in several other important forms of cellular lipids, revealing a previously unrecognized role of Pfn1 as a broad regulator of cellular lipid environment that extends beyond PPI control. In conclusion, the present study establishes Pfn1 as an important regulator of cellular lipid homeostasis.