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

Phosphatidylinositol 3,4,5-trisphosphate (PIP3) plays an important role in the regulation of diverse physiological functions. Recent evidence indicate s that PIP3 is cell permeant, and can be added exogenously to modulate cell ular responses. However, like many other phospholipids, PIP3 binds serum pr oteins with high affinity, resulting in rapid deactivation of this lipid se cond messenger. Our study indicates that bovine serum albumin (BSA) at conc entrations as low as 10 mug/mL abrogated the biological activity of dipalmi toyl-PIP3. This nonspecific interaction with serum proteins hampers the use of PIP; in biological studies where serum is needed. We report here an eth er-linked PIP3 analogue, 1-O-(1-O-hexadecyl-2-O-methyl-sn-glycero-3-phospho ryl)-myo-inositol 3,4,5-trisphosphate (C16Me-PIP3), which displays low seru m protein-binding affinity while retaining the biological function of PIP3. The affinity of C16Me-PIP3 with BSA was two orders of magnitude lower th a n that of its dipalmitoyl-counterpart. Bio-chemical data indicate that C16M e-PIP3 was able to stimulate Ca2+ influx in T cells in the presence of mode rate levels (up to 1 mg/mL) of BSA. Thus, C16Me-PIP3 may provide a useful t ool to study the physiological function of phosphoinositide (PI) 3-kinase i n vivo. (C) 2000 Elsevier Science Ltd. All rights reserved.