Production of novel polyphosphoinositides in vivo is linked to cell transformation by polyomavirus middle T antigen.
Phosphatidylinositol 3-kinase associates with the polyomavirus middle T antigen (PyMTAg)-pp60c-src complex in polyomavirus-transformed cells. Here we show that anti-PyMTAg immunoprecipitates from PyMTAg-transformed NIH 3T3 cells have lipid kinase activities that phosphorylate phosphatidylinositol, phosphatidylinositol-4-bisphosphate, and phosphatidylinositol-4,5-bisphosphate at the D-3 position of the inositol ring to produce three new polyphosphoinositides: phosphatidylinositol-3-phosphate (PI-3-P), phosphatidylinositol-3,4-bisphosphate (PI-3,4-P2), and phosphatidylinositol trisphosphate (PIP3), respectively. PI-3-P was detected in intact parental and PyMTAg-transformed NIH 3T3 fibroblasts at both low and high cell densities. However, parental NIH 3T3 fibroblasts produced no detectable PI-3,4-P2 or PIP3 at high density. In contrast, growing, subconfluent cells and wild-type PyMTAg-transformed cells at high density had greatly enhanced incorporation of [3H]-inositol into these highly phosphorylated lipids. Cells transfected with a transformation-defective mutant of PyMTAg had undetectable levels of PI-3,4-P2 and PIP3 at high density. Thus, the synthesis of novel polyphosphoinositides by lipid kinase activity associated with PyMTAg correlates with cell growth and transformation.
Serunian
L A
LA
Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
Auger
K R
KR
Roberts
T M
TM
Cantley
L C
LC
D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics*; D002460:Cell Line; D002472:Cell Transformation, Viral; D007294:Inositol / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008815:Mice, Inbred Strains; D019869:Phosphatidylinositol 3-Kinases; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000096:biosynthesis* / Q000302:isolation & purification; D010770:Phosphotransferases / Q000378:metabolism; D011120:Polyomavirus / Q000235:genetics* / Q000276:immunology
D000952:Antigens, Polyomavirus Transforming; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D007294:Inositol; D010770:Phosphotransferases; D019869:Phosphatidylinositol 3-Kinases