Abstract
The PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumor suppressor is a phosphatidylinositol 3,4,5-trisphosphate (PtdInsP3) 3-phosphatase that plays a crucial role in regulating many cellular processes by antagonizing the phosphoinositide 3-kinase signaling pathway. Although able to metabolize soluble inositol phosphates in vitro, the question of their significance as physiological substrates is unresolved. We show that inositol phosphates are not regulated by wild type PTEN, but that a synthetic mutant, PTEN M-CBR3, previously thought to be inactive toward inositides, can selectively regulate inositol 1,3,4,5,6-pentakisphosphate (Ins(1,3,4,5,6)P5). Transfection of U87-MG cells with PTEN M-CBR3 lowered Ins(1,3,4,5,6)P5 levels by 60% without detectable effect on PtdInsP3. Although PTEN M-CBR3 is a 3-phosphatase, levels of myo-inositol 1,4,5,6-tetrakisphosphate were not increased, whereas myo-inositol 1,3,4,6-tetrakisphospate levels increased by 80%. We have used PTEN M-CBR3 to study the physiological function of Ins(1,3,4,5,6)P5 and have found that Ins(1,3,4,5,6)P5 does not modulate PKB phosphorylation, nor does it regulate clathrin-mediated epidermal growth factor receptor internalization. By contrast, PTEN M-CBR3 expression, and the subsequent lowering of Ins(1,3,4,5,6)P5, are associated with reduced anchorage-independent colony formation and anchorage-dependent proliferation in U87-MG cells. Our results, together with previously published data, suggest that Ins(1,3,4,5,6)P5 has a role in proliferation.
Highlights
PTEN1 is a dual specificity phosphatase that is mutated
Functional interference with this C2 domain, exemplified by the artificially modified PTEN M-CBR3 protein first described by Lee et al (10), causes a reduction in the ability to interact with lipid membranes but marginally increases phosphatase activity toward inositol phosphate substrates (4, 10)
A comparison with extracts obtained from cells with normal PTEN status showed that levels of expression of GFP-PTEN were comparable with the range of PTEN expression found in a variety of cell types (Fig. 2)
Summary
PTEN (phosphatase and tensin homologue deleted on chromosome 10)1 is a dual specificity phosphatase that is mutated. Functional interference with this C2 domain, exemplified by the artificially modified PTEN M-CBR3 protein first described by Lee et al (10), causes a reduction in the ability to interact with lipid membranes but marginally increases phosphatase activity toward inositol phosphate substrates (4, 10). In this study we have clarified the effects of PTEN expression on inositol lipid and inositol phosphate levels in cells.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
