Fig. 5. Osmotic stress and DIF-1 treatment decrease cellular PTP3 activity. Cells at 4 hours of development in suspension and expressing myc:PTP3 were left untreated or exposed to DIF-1 (100 nM), sorbitol (200 mM) or pervanadate (1 mM H₂O₂ and 2 mM Na₃VO₄) for 5 and 15 minutes. They were lysed in a non-ionic detergent and immunoprecipitated using a myc antibody. The precipitates were dissolved and assayed for tyrosine phosphatase activity using the general substrate pNPP. As controls, parental Ax2 cell extracts or cells transformed with myc:PTP3CS were immunoprecipitated with myc antibody. Neither precipitation yielded significant activity (data not shown). For purposes of comparison, the western blot at the bottom shows the level of the STATc phosphorylation in parental Ax2 cells after the treatments described above.