A phosphatidylinositol 3,4,5-trisphosphate analogue with low serum protein-binding affinity.

Abstract Phosphatidylinositol 3,4,5-trisphosphate (PIP 3 ) plays an important role in the regulation of diverse physiological functions. Recent evidence indicates that PIP 3 is cell permeant, and can be added exogenously to modulate cellular responses. However, like many other phospholipids, PIP 3 binds serum proteins with high affinity, resulting in rapid deactivation of this lipid second messenger. Our study indicates that bovine serum albumin (BSA) at concentrations as low as 10 μg/mL abrogated the biological activity of dipalmitoyl-PIP 3 . This nonspecific interaction with serum proteins hampers the use of PIP 3 in biological studies where serum is needed. We report here an ether-linked PIP 3 analogue, 1- O -(1- O -hexadecyl-2- O -methyl- sn -glycero-3-phosphoryl)- myo -inositol 3,4,5-trisphosphate (C 16 Me-PIP 3 ), which displays low serum protein-binding affinity while retaining the biological function of PIP 3 . The affinity of C 16 Me-PIP 3 with BSA was two orders of magnitude lower than that of its dipalmitoyl-counterpart. Biochemical data indicate that C 16 Me-PIP 3 was able to stimulate Ca 2+ influx in T cells in the presence of moderate levels (up to 1 mg/mL) of BSA. Thus, C 16 Me-PIP 3 may provide a useful tool to study the physiological function of phosphoinositide (PI) 3-kinase in vivo.