Alterations in specific protein-tyrosine phosphatases accompany insulin resistance of streptozotocin diabetes

To test whether protein tyrosine phosphatases (PTPases) may play a role in the insulin resistance of insulinopenic diabetes, we assessed PTPase activity as well as the protein and mRNA abundance of three major candidate PTPases in subcellular fractions of liver and skeletal muscle of streptozotocin-diabetic rats before and after insulin treatment. PTPase activity against the insulin receptor in liver and muscle cytosol increased to 120-125% of control in the diabetic animals and by an additional 5-10% after insulin treatment. In the particulate fraction, PTPase activity decreased to 65-70% of control in diabetic liver and muscle and increased to 115-120% of control after insulin treatment. Protein for the leukocyte common antigen-related PTPase paralleled the changes in the PTPase activity in the particulate fraction. SH-PTP2/syp and PTPase 1B were both significantly increased in diabetes. SH-PTP2/syp also exhibited an increased ratio of particulate to cytosol distribution in diabetic tissues (1.8-1.9) that was reversed after insulin treatment (0.79-0.95). Northern analysis suggested that the PTPases were regulated at a pretranslational level. These changes in the abundance and distribution of specific PTPases may be involved in the pathogenesis of insulin resistance in insulinopenic diabetes.

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Crystal structures and inhibitor identification for PTPN5, PTPRR and PTPN7: a family of human MAPK-specific protein tyrosine phosphatases

Biochemical Journal ◽

10.1042/bj20051931 ◽

2006 ◽

Vol 395 (3) ◽

pp. 483-491 ◽

Cited By ~ 35

Author(s):

Jeyanthy Eswaran ◽

Jens Peter von Kries ◽

Brian Marsden ◽

Emma Longman ◽

Judit É. Debreczeni ◽

...

Keyword(s):

Therapeutic Potential ◽

Phosphorylation Site ◽

Protein Tyrosine Phosphatases ◽

Salt Bridge ◽

Specific Protein ◽

Tyrosine Phosphatases ◽

Selective Inhibitors ◽

Crystal Forms ◽

Protein Tyrosine ◽

Mitogen Activated Protein

Protein tyrosine phosphatases PTPN5, PTPRR and PTPN7 comprise a family of phosphatases that specifically inactivate MAPKs (mitogen-activated protein kinases). We have determined high-resolution structures of all of the human family members, screened them against a library of 24000 compounds and identified two classes of inhibitors, cyclopenta[c]quinolinecarboxylic acids and 2,5-dimethylpyrrolyl benzoic acids. Comparative structural analysis revealed significant differences within this conserved family that could be explored for the design of selective inhibitors. PTPN5 crystallized, in two distinct crystal forms, with a sulphate ion in close proximity to the active site and the WPD (Trp-Pro-Asp) loop in a unique conformation, not seen in other PTPs, ending in a 310-helix. In the PTPN7 structure, the WPD loop was in the closed conformation and part of the KIM (kinase-interaction motif) was visible, which forms an N-terminal aliphatic helix with the phosphorylation site Thr66 in an accessible position. The WPD loop of PTPRR was open; however, in contrast with the structure of its mouse homologue, PTPSL, a salt bridge between the conserved lysine and aspartate residues, which has been postulated to confer a more rigid loop structure, thereby modulating activity in PTPSL, does not form in PTPRR. One of the identified inhibitor scaffolds, cyclopenta[c]quinoline, was docked successfully into PTPRR, suggesting several possibilities for hit expansion. The determined structures together with the established SAR (structure–activity relationship) propose new avenues for the development of selective inhibitors that may have therapeutic potential for treating neurodegenerative diseases in the case of PTPRR or acute myeloblastic leukaemia targeting PTPN7.

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