title: Protein-tyrosine phosphatase PTPL1/FAP-1 triggers apoptosis in human breast cancer cells.
abstract: Studies in Jurkat leukemia cells have suggested that protein-tyrosine phosphatase PTPL1/FAP-1 rescues Fas-induced cell death. However, we have previously shown that this enzyme triggers 4-hydroxytamoxifen-induced growth inhibition in human breast cancer cells. The present study addresses the role of PTPL1/FAP-1 in antiestrogen-regulated apoptotic effect and insulin-like growth factor-I survival action in MCF7 cells and further identifies the impacted signaling pathway. By terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling and cytoplasmic nucleosome enzyme-linked immunosorbent assay, we demonstrated that 4-hydroxytamoxifen-induced apoptosis was totally lost in PTPL1/FAP-1 antisense transfectants in which enzyme expression was abrogated, revealing the crucial role of this phosphatase in the apoptotic process in human breast cancer cells. Time-dependent expression of PTPL1/FAP-1 in MCF7 cells completely abolished the survival action of insulin-like growth factor-I. This effect occurred through a highly significant reduction in phosphatidylinositol 3-kinase/Akt pathway activation (80% reduction in phosphatidylinositol 3-kinase activity, 55% inhibition of Akt activation) accompanied by a 65% decrease in insulin receptor substrate-1 growth factor-induced tyrosine phosphorylation. These results provide the first evidence that PTPL1/FAP-1 has a key role in the apoptotic process in human breast cancer cells independent of Fas but associated with an early inhibition of the insulin receptor substrate-1/phosphatidylinositol 3-kinase pathway. Our data therefore suggest new therapeutic routes and strengthen the importance of identifying endogenous regulators and substrates of this phosphatase in breast tumors.
mesh_terms: D017209:Apoptosis; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism* / Q000502:physiology*; D002470:Cell Survival; D053938:DNA Fragmentation; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D020287:In Situ Nick-End Labeling; D055504:Insulin Receptor Substrate Proteins; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D054595:Protein Tyrosine Phosphatase, Non-Receptor Type 13; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism* / Q000502:physiology*; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D016376:Oligonucleotides, Antisense; D010750:Phosphoproteins; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; C516742:PTPN13 protein, human; D054595:Protein Tyrosine Phosphatase, Non-Receptor Type 13; D017027:Protein Tyrosine Phosphatases