PTEN M-CBR3, a versatile and selective regulator of inositol 1,3,4,5,6-pentakisphosphate (Ins(1,3,4,5,6)P5). Evidence for Ins(1,3,4,5,6)P5 as a proliferative signal.
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.
Orchiston
Elaine A
EA
Division of Cell Signalling, Faculty of Life Sciences, MSI/WTB Complex, Dow St., The University of Dundee, Dundee DD1 5EH, United Kingdom.
Bennett
Deborah
D
Leslie
Nick R
NR
Clarke
Rosemary G
RG
Winward
Lucinda
L
Downes
C Peter
CP
Safrany
Stephen T
ST
D000818:Animals; D015153:Blotting, Western; D002453:Cell Cycle; D002455:Cell Division; D002460:Cell Line; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D005434:Flow Cytometry; D015971:Gene Expression Regulation, Enzymologic; D006367:HeLa Cells; D006801:Humans; D007295:Inositol Phosphates / Q000096:biosynthesis* / Q000378:metabolism; D050356:Lipid Metabolism; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics*; D010766:Phosphorylation; D011233:Precipitin Tests; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics*
D007295:Inositol Phosphates; D025521:Tumor Suppressor Proteins; C451920:inositol-1,3,4,5,6-pentakisphosphate; D004815:Epidermal Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D010744:Phosphoric Monoester Hydrolases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human