Protein tyrosine phosphorylation and dephosphorylation are important in the regulation of cell proliferation and signaling cascade. In order to examine whether phosphatase activity of CPTP1 and HPTP1B, typical nontransmembrane protein tyrosine phosphatase, could be controlled by phosphorylation, affinity-purified PTPs were phosphorylated by CKII and p56lck in vitro. Phosphoamino acid analysis revealed that CPTP1 was phosphorylated on both serine and threonine residues by CKII, and tyrosine residue by p56lck. Phosphatase activity of CPTP1 was gradually increased by three-fold concomitant with phosporylation by CKII. Phosphorylation of HPTP1B by CKII resulted in quick two-fold enhancement of its phosphatase activity within 5 min of incubation and remained in that state. In the presence of CKII inhibitor, heparin or poly(Glu.Tyr), both phosphorylation and enhancement of phosphatase activity of CPTP1 and HPTP1B were mostly blocked. p56lck catalyzed tyrosine phosphorylation of CPTP1 and HPTP1B was only observed by inhibiting the intrinsic tyrosine phosphatase activity. Taken together, these results indicate that CPTP1 or HPTP1B possesses a capability to regulate its phosphatase activity through phosphorylation processes and may participate in the cellular signal cascades.
Adenosine Triphosphate/metabolism ; Animal ; Chickens ; Dose-Response Relationship, Drug ; Heparin/pharmacology ; Human ; Hydrogen Peroxide/pharmacology ; Lymphocyte Specific Protein Tyrosine Kinase p56(lck)/metabolism* ; Peptides/pharmacology ; Phosphorus Radioisotopes/diagnostic use ; Phosphorylation/drug effects ; Protein-Serine-Threonine Kinases/metabolism* ; Protein-Tyrosine-Phosphatase/metabolism* ; Tyrosine/metabolism ; Vanadates/pharmacology

OBJECTIVE: To evaluate the clinical feasibility and obtain useful parameters of 31P magnetic resonance spectroscopy (MRS) study for making the differential diagnosis of brain tumors. MATERIALS AND METHODS: Twenty-eight patients with brain tumorous lesions (22 cases of brain tumor and 6 cases of abscess) and 11 normal volunteers were included. The patients were classified into the astrocytoma group, lymphoma group, metastasis group and the abscess group. We obtained the intracellular pH and the metabolite ratios of phosphomonoesters/phosophodiesters (PME/PDE), PME/inorganic phosphate (Pi), PDE/Pi, PME/adenosine triphosphate (ATP), PDE/ATP, PME/phosphocreatine (PCr), PDE/PCr, PCr/ATP, PCr/Pi, and ATP/Pi, and evaluated the statistical significances. RESULTS: The brain tumors had a tendency of alkalization (pH = 7.28 +/- 0.27, p = 0.090), especially the pH of the lymphoma was significantly increased (pH = 7.45 +/- 0.32, p = 0.013). The brain tumor group showed increased PME/PDE ratio compared with that in the normal control group (p = 0.012). The ratios of PME/PDE, PDE/Pi, PME/PCr and PDE/PCr showed statistically significant differences between each brain lesion groups (p < 0.05). The astrocytoma showed an increased PME/PDE and PME/PCr ratio. The ratios of PDE/Pi, PME/PCr, and PDE/PCr in lymphoma group were lower than those in the control group and astrocytoma group. The metastasis group showed an increased PME/PDE ratio, compared with that in the normal control group. CONCLUSION: We have obtained the clinically applicable 31P MRS, and the pH, PME/PDE, PDE/Pi, PME/PCr, and PDE/PCr ratios are helpful for differentiating among the different types of brain tumors.
Adolescent ; Adult ; Aged ; Aged, 80 and over ; Astrocytoma/diagnosis/*metabolism ; Brain Abscess/diagnosis/*metabolism ; *Brain Chemistry ; Brain Neoplasms/diagnosis/*metabolism/secondary ; Case-Control Studies ; Diagnosis, Differential ; Feasibility Studies ; Female ; Humans ; Hydrogen-Ion Concentration ; Lymphoma/diagnosis/*metabolism ; Magnetic Resonance Imaging ; Magnetic Resonance Spectroscopy/*methods ; Male ; Middle Aged ; Phosphorus/diagnostic use ; Prospective Studies ; Young Adult