title: Inhibition of receptor tyrosine kinase signalling by small molecule agonist of T-cell protein tyrosine phosphatase.
abstract: BACKGROUND
  T-cell protein tyrosine phosphatase (TCPTP/TC45) is a ubiquitously expressed intra-cellular non-receptor protein tyrosine phosphatase involved in the negative regulation of several cancer relevant cellular signalling pathways. We have previously shown that interaction between the alpha-cytoplasmic tail of alpha1beta1 integrin and TCPTP activates TCPTP by disrupting an inhibitory intra-molecular bond in TCPTP. Thus, inhibition of the regulatory interaction in TCPTP is a desirable strategy for TCPTP activation and attenuation of oncogenic RTK signalling. However, this is challenging with low molecular weight compounds.
  
  
  METHODS
  We developed a high-throughput compatible assay to analyse activity of recombinant TCPTP in vitro. Using this assay we have screened 64280 small molecules to identify novel agonists for TCPTP. Dose-dependent response to TCPTP agonist was performed using the in vitro assay. Inhibition effects and specificity of TCPTP agonists were evaluated using TCPTP expressing and null mouse embryonic fibroblasts. Western blot analysis was used to evaluate attenuation of PDGFRbeta and EGFR phosphorylation. Inhibition of VEGF signalling was analysed with VEGF-induced endothelial cell sprouting assays.
  
  
  RESULTS
  From the screen we identified six TCPTP agonists. Two compounds competed with alpha1-cytoplasmic domain for binding to TCPTP, suggesting that they activate TCPTP similar to alpha1-cyt by disrupting the intra-molecular bond in TCPTP. Importantly, one of the compounds (spermidine) displayed specificity towards TCPTP in cells, since TCPTP -/- cells were 43-fold more resistant to the compound than TCPTP expressing cells. This compound attenuates PDGFRbeta and VEGFR2 signalling in cells in a TCPTP-dependent manner and functions as a negative regulator of EGFR phosphorylation in cancer cells.
  
  
  CONCLUSIONS
  In this study we showed that small molecules mimicking TCPTP-alpha1 interaction can be used as TCPTP agonists. These data provide the first proof-of-concept description of the use of high-throughput screening to identify small molecule PTP activators that could function as RTK antagonists in cells.
authors.affiliation: VTT Technical Research Centre of Finland, Medical Biotechnology, Itainen Pitkakatu 4B, FIN-20520 Turku, Finland.
authors.forename: Elina
authors.initials: E
authors.lastname: Mattila
authors.forename: Heidi
authors.initials: H
authors.lastname: Marttila
authors.forename: Niko
authors.initials: N
authors.lastname: Sahlberg
authors.forename: Pekka
authors.initials: P
authors.lastname: Kohonen
authors.forename: Siri
authors.initials: S
authors.lastname: Tähtinen
authors.forename: Pasi
authors.initials: P
authors.lastname: Halonen
authors.forename: Merja
authors.initials: M
authors.lastname: Perälä
authors.forename: Johanna
authors.initials: J
authors.lastname: Ivaska
mesh_terms: D000818:Animals; D004730:Endothelium, Vascular / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D039222:Integrin alpha1beta1 / Q000378:metabolism; D051379:Mice; D008942:Mitoxantrone / Q000494:pharmacology; D009389:Neovascularization, Pathologic; D010766:Phosphorylation; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2 / Q000737:chemistry*; D034741:RNA, Small Interfering / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D011994:Recombinant Proteins / Q000737:chemistry; D015398:Signal Transduction; D013095:Spermidine / Q000494:pharmacology; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism
chemical_list: D039222:Integrin alpha1beta1; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D008942:Mitoxantrone; D066246:ErbB Receptors; D020794:Receptor Protein-Tyrosine Kinases; D040301:Vascular Endothelial Growth Factor Receptor-2; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2; D013095:Spermidine