TGF β Supports, Platelet‐activating Factor (PAF) Inhibits Intestinal Epithelial Cell (IEC) Migration In Vitro via Effects on Phoshatidylinositol 3 Kinase (PI3K)

We aimed to identify mechanisms involved in the regulation of IEC migration by growth factors that are known to be beneficial to prevent mucosal injury and by (PAF), a mediator implicated in inflammatory bowel diseases. In 5% FBS, IEC6 migrate, on fibronectin, for two hours at an average linear rate of V=0.38±0.04 ìm/min, while PIP3 concentration oscillates in the leading edge of lamellipodia at 83mHz, as assessed by live cell imaging and using AKT‐PH domain‐GFP fusion protein as a PIP3 sensor. FBS withdrawal aborts PIP3 oscillations and migration in the second hour (V=0.03±0.02 ìm/min), correlating with steady state dephosphorylation of AKT on S473. Activation of the PAF receptor by 20ìM carbamyl‐PAF or inhibition of PI3K using 10 ìM LY294002 in the presence of FBS leads to the same outcome. TGFâ (1ng/ml) partly restores migration (V=0.22±0.04 ìm/min) and steady state AKT phosphorylation in the absence of FBS. AKT phosphorylation, but not migration, is restored by either EGF and/or IGF (10ng/ml each). Though all three growth factors compensate for the loss of steady state Akt phosphorylation upon FBS withdrawal, only TGFâ is able to restore migration. Further studies are aimed to determine whether divergent effects by TGFβ and EGF/IGF on PIP3 oscillations and/or focal adhesions explain the discrepancy between effects by these growth factors on steady state Akt phosphorylation and migration. Supported by DK062960