A sensitive and high throughput method for the analysis of d-psicose by capillary electrophoresis.

d-Psicose/allulose is a rare sugar and it has high potential benefits for pharmaceutical and food industry. The existed analytical methods have its own limitations to quantify fructose and d-psicose mixtures. Hence there is a need for the development of an effective, efficient and sensitive analytical method for quantification of d-psicose in presence of other sugars. Quantification of sugars by capillary electrophoresis (CE) have been previously reported. However, the list does not include d-psicose. In this study, d-psicose is successfully quantified for the first time in the presence of d-fructose and glucose with a good resolution. Standard curves for all the sugars are established in a concentration range of 0.1 mM (0.0018% w/v) to 3.0 mM (0.0540% w/v) with a coefficient of determination of >0.99. The scope of this method can be extended to quantify d-psicose and their processed impurities in food products with minor modifications in sample preparation.

Regulation of protein tyrosine phosphatase 1B by sumoylation.

Protein-tyrosine phosphatase 1B (PTP1B) is an ubiquitously expressed enzyme that negatively regulates growth-factor signalling and cell proliferation by binding to and dephosphorylating key receptor tyrosine kinases, such as the insulin receptor. It is unclear how the activity of PTP1B is regulated. Using a yeast two-hybrid assay, a protein inhibitor of activated STAT1 (PIAS1) was isolated as a PTP1B-interacting protein. Here, we show that PIAS1, which functions as a small ubiquitin-like modifier (SUMO) E3 ligase, associates with PTP1B in mammalian fibroblasts and catalyses sumoylation of PTP1B. Sumoylation of PTP1B reduces its catalytic activity and inhibits the negative effect of PTP1B on insulin receptor signalling and on transformation by the oncogene v-crk. Insulin-stimulated sumoylation of endogenous PTP1B results in a transient downregulation of the enzyme; this event does not occur when the endogenous enzyme is replaced with a sumoylation-resistant mutant of PTP1B. These results suggest that sumoylation, which has been implicated primarily in processes in the nucleus and nuclear pore, also modulates a key enzyme-substrate signalling complex that regulates metabolism and cell proliferation.

Protein-tyrosine phosphatase 1B as a potential drug target for obesity.

Obesity is increasing at an alarming rate and is considered by the World Health Organization as one of the top 10 epidemics worldwide. Resistance to leptin and insulin are likely to play a central role in obesity; thus, blocking inhibitors of these signaling pathways could prove useful in treating this disorder. Several lines of evidence have converged on protein tyrosine-phosphatase 1B (PTP1B) as one of the most important negative regulators of leptin as well as insulin signaling. Therefore, PTP1B appears to be a promising therapeutic candidate for the treatment of obesity. In this review, we discuss the role of PTP1B in leptin and insulin signaling, as well as its potential as a drug target in the treatment of obesity.

Protein-tyrosine phosphatase 1B mediates the effects of insulin on the actin cytoskeleton in immortalized fibroblasts.

Insulin regulates diverse cellular responses including actin reorganization. The mechanism by which insulin induces formation of lamellipodia in cultured cells is not known but is likely to involve activation of Src family protein-tyrosine kinases. Here we show that protein-tyrosine phosphatase 1B (PTPIB) activates Src, thereby initiating the activation of a Rac-dependent pathway leading to cytoskeletal remodeling. Conversely, expression of a proline to alanine (P309,310A) PTP1B mutant, which cannot activate Src, fails to activate Rho GTPases or cause changes in actin organization. Rat fibroblasts lacking PTP1B expression do not activate Src or Rac in response to insulin and cannot reorganize actin. These results show that PTP1B, best known as a negative regulator of the metabolic effects of insulin, is required for the effects of insulin on actin organization in immortalized fibroblasts.

Interaction of protein tyrosine phosphatase (PTP) 1B with its substrates is influenced by two distinct binding domains.

We have shown previously that protein tyrosine phosphatase (PTP) 1B interacts with insulin receptor and negatively regulates insulin signalling by an N-terminal binding domain [Dadke, Kusari and Chernoff (2000) J. Biol. Chem. 275, 23642-23647] and it also negatively regulates integrin signalling through a proline-rich region present in the C-terminus [Liu, Hill and Chernoff (1996) J. Biol. Chem. 271, 31290-31295; Liu, Sells and Chernoff (1998) Curr. Biol. 8, 173-176]. Here we show that PTP1B mutants that are defective in Src homology 3 domain binding fully retain the ability to inhibit insulin signalling, whereas mutants defective in insulin-receptor binding fully retain the ability to inhibit integrin signalling. In contrast, both the C-terminal proline-rich region and the tandem tyrosine residues present in the N-terminal region are required for the activation of Src family kinases. These data show that PTP1B can independently regulate insulin and integrin signals, and that Src might represent a convergence point for regulating signal transduction by this phosphatase.