Phosphoinositides participate in signaling events that control cytoskeletal dynamics, intracellular membrane trafficking, cell proliferation and many other cellular functions.
[3][4] PtdIns5P was first demonstrated by HPLC (high pressure liquid chromatography) in mouse fibroblasts as a substrate for PtdIns(4,5)P2 synthesis by type II PIP kinases (1-phosphatidylinositol-5-phosphate 4-kinase).
[5] In many cell types, however, PtdIns5P is not detected by HPLC due to technical limitations associated with its poor separation from the abundant PtdIns4P.
[6] Rather, PtdIns5P is measured by the "mass assay", where PtdIns5P (as a part of the extracted cellular lipids) is converted in vitro by purified PtdIns5P 4-kinase to PtdIns(4,5)P2 that is subsequently quantified.
[15] Such a role is reinforced by data in transgenic fibroblasts with one genetically disrupted PIKfyve allele, demonstrating equal reduction of steady-state levels of PtdIns5P and PtdIns(3,5)P2.
Insulin,[8][24] thrombin,[7] T-cell activation,[25] and cell transformation with nucleophosmin anaplastic lymphoma tyrosine kinase (NPM-ALK),[15] cause elevation of cellular PtdIns5P levels.
The proteins of this family associate with and modulate the activity of histone acetylases and deacetylases as well as induce apoptosis through p53 acetylation.
PtdIns5P is involved in regulation of both basic cellular functions and responses to a multitude of physiological and pathological stimuli by yet- to- be specified molecular mechanisms.