DISRUPTION OF DICTYOSTELIUM P13K GENES REDUCES [P-32] PHOSPHATIDYLINOSITOL 3,4-BISPHOSPHATE AND [P-32] PHOSPHATIDYLINOSITOL TRISPHOSPHATE LEVELS, ALTERS F-ACTIN DISTRIBUTION AND IMPAIRS PINOCYTOSIS

To understand how phosphatidylinositol 3-kinase (PI3K) modulates cell structure and function, we examined the molecular and cellular defects of a Dictyostelium mutant strain (pik1 Delta 2 Delta) missing two (Dd PIK1 and 2) of three PI3K genes, which are homologues of the mammalian p110 subunit, Levels of [P-32]phosphatidylinositol 3,4 bisphosphate ( PI(3,4)P-2) and [P-32]phosphatidylinositol trisphosphate (PIP3) were r educed in pik1 Delta 2 Delta, which had major defects in morphological and functional correlates of macropinocytosis. This was accompanied b y dramatic deficits in a subset of F-actin-enriched structures such as circular ruffles, actin crowns and pseudopodia. Although pik1 Delta 2 Delta were mobile, they failed to aggregate into streams, Therefore w e conclude that PIK1 and 2, possibly through modulation of the levels of PIP3 and PI(3,4)P-2, regulate the organization of actin filaments n ecessary for circular ruffling during macropinocytosis, the extension of pseudopodia and the aggregation of cells into streams, but not the regulation of cell motility.