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Keywords:

  • knockout mice;
  • NMDA receptor;
  • proline-rich tyrosine kinase 2;
  • protein tyrosine phosphatase alpha;
  • src family kinases;
  • synaptosome

Abstract

Mice lacking protein tyrosine phosphatase alpha (PTPα) exhibited defects in NMDA receptor (NMDAR)-associated processes such as learning and memory, hippocampal neuron migration, and CA1 hippocampal long-term potentiation (LTP). In vivo molecular effectors linking PTPα and the NMDAR have not been reported. Thus the involvement of PTPα as an upstream regulator of NMDAR tyrosine phosphorylation was investigated in synaptosomes of wild-type and PTPα-null mice. Tyrosine phosphorylation of the NMDAR NR2A and NR2B subunits was reduced upon PTPα ablation, indicating a positive effect of this phosphatase on NMDAR phosphorylation via intermediate molecules. The NMDAR is a substrate of src family tyrosine kinases, and reduced activity of src, fyn, yes and lck, but not lyn, was apparent in the absence of PTPα. In addition, autophosphorylation of proline-rich tyrosine kinase 2 (Pyk2), a tyrosine kinase linked to NMDAR signaling, was also reduced in PTPα-deficient synaptosomes. Altered protein tyrosine phosphorylation was not accompanied by altered expression of the NMDAR or the above tyrosine kinases at any stage of PTPα-null mouse development examined. In a human embryonic kidney (HEK) 293 cell expression system, PTPα enhanced fyn-mediated NR2A and NR2B tyrosine phosphorylation by several-fold. Together, these findings provide evidence that aberrant NMDAR-associated functions in PTPα-null mice are due to impaired NMDAR tyrosine phosphorylation resulting from the reduced activity of probably more than one of the src family kinases src, fyn, yes and lck. Defective NMDAR activity in these mice may also be linked to the loss of PTPα as an upstream regulator of Pyk2.