Chemical Inhibition of Palmitoyl Protein Thioesterase I (PPTI) in Normal Human Schwann Cells: Ras Activation and Expression of the Neurofibromatosis Type 1 (NF1) Phenotype
Palmitoyl protein thioesterase I (PPTI) is an enzyme that is essential in cleaving from proteins palmitoyl groups that were added during post-translational modification. The protein Ras requires depalmitoylation by PPTI in order to be released from the plasma membrane and become inactive. A palmitoyl protein thioesterase I synthetic inhibitor, AcG-palmitoyl diaminoproprionate-VKlKK (DAPI) (100 uM), was used in an attempt to keep Ras constituitively active in normal human Schwann cells (NHSC). Hyperactivated Ras is a characteristic of Neurofibromatosis type I (NFl) derived Schwann cells, and DAPI inhibition ofPPTI acts to mimic this characteristic in NHSC. We show that DAPI does inhibit PPTI (27%) in culture, and treatment ofNHSC with this inhibitor leads to elevated Ras-GTP levels. An increase in MAP kinase activation, a downstream target of Ras, is also detected. Furthermore, we report a morphological change in the treated cells themselves, and expression of the receptor for stem cell factor, kit, not normally present on NHSC, but expressed in NFl derived Schwann cell lines. Thus, DAPI treatment ofNHSC produces phenotypic characteristics of NFl derived Schwann cells, and this model may be useful in identifying the role hyperactivated Ras plays in generating the NFl phenotype.