Related Experiment Videos
Different in vitro and in vivo activity of low Mr phosphotyrosine protein phosphatase on epidermal growth factor
S Rigacci1, R Marzocchini, M Bucciantini
1Department of Biochemical Sciences, University of Firenze, Viale Morgagni 50, Firenze, 50134, Italy.
Abstract:
Low Mr phosphotyrosine protein phosphatase is a cytosolic enzyme which dephosphorylates platelet-derived growth factor and insulin receptor in vivo, thus reducing cellular mitogenic response to such growth factors. Following cell stimulation with platelet-derived growth factor the phosphatase undergoes a redistribution from the citosol to the Triton X-100-insoluble fraction where its activity upon the growth factor receptor is intense. Previous research uncovered evidence that low Mr phosphotyrosine protein phosphatase dephosphorylates the epidermal growth factor receptor in vitro. Here we demonstrate that in vivo the enzyme is not active on the phosphorylated epidermal growth factor receptor and it does not influence the mitogenic response of cells. Since the enzyme distribution is not affected by epidermal growth factor stimulation, involvement of a recruitment mechanism in the definition of low Mr phosphotyrosine protein phosphatase substrate specificity is hypothesized.
Insights
Low molecular weight phosphotyrosine protein phosphatase dephosphorylates growth factor receptors, but not epidermal growth factor receptor in vivo. Its substrate specificity is likely determined by recruitment mechanisms.
Area of Science:
- Cellular biology
- Molecular signaling
- Enzymology
Background:
- Low molecular weight phosphotyrosine protein phosphatase (LMW-PTP) is a cytosolic enzyme.
- LMW-PTP dephosphorylates platelet-derived growth factor (PDGF) and insulin receptors in vivo.
- LMW-PTP reduces cellular mitogenic response to growth factors.
Purpose of the Study:
- To investigate the in vivo activity of LMW-PTP on epidermal growth factor receptor (EGFR).
- To determine if LMW-PTP influences the mitogenic response to epidermal growth factor (EGF).
- To explore the mechanisms defining LMW-PTP substrate specificity.
Main Methods:
- In vivo enzymatic activity assays.
- Cellular redistribution studies following growth factor stimulation.
- Assessment of mitogenic response.
Main Results:
- LMW-PTP does not dephosphorylate phosphorylated EGFR in vivo.
- LMW-PTP does not affect cellular mitogenic response to EGF.
- EGFR stimulation does not alter LMW-PTP distribution.
Conclusions:
- LMW-PTP's in vivo activity is specific and does not extend to EGFR.
- Recruitment mechanisms may define LMW-PTP substrate specificity.
- LMW-PTP's role in EGF signaling is distinct from its role in PDGF and insulin signaling.