Search

A commercial antibody (clone 22) directed against the apoptosis-linked gene 2 (alg2, pdcd6) encoded protein has been used by several groups. Up-regulated expression of the antigen was observed in primary tumours and in metastatic tissue and also during rat brain ischemia. Furthermore, antigen down-regulation was found in human atherosclerotic plaques. Recently, we found that the clone 22 antibody does not recognise ALG-2. In the present study the antigen of the clone 22 antibody was identified as the heat shock protein 90 (HSP90) co-chaperone protein p23, identical to the cytosolic prostaglandin E2 synthase, by immunoprecipitation followed by tryptic in-gel digests and mass spectrometry of the purified peptides. Moreover, the heterogeneous ribonuclear protein A2/B1 was found to be a part of the p23 co-immunoprecipitated protein complex.

The role of the Ca(2+)-activated tyrosine kinase, Pyk2, in the pleiotropic coupling of nerve cell stimulation to the MAP kinase cascade still remains undefined. Using a panel of PC12 clones, one of which was defective in Pyk2, we demonstrate (1) that the MAP kinase response induced by a [Ca(2+)](i) rise (following application of the Ca(2+) ionophore, ionomycin) is inappreciable in the defective clone and is re-established after Pyk2 transfection; and (2) that the responses to both protein kinase C and P(2y2) receptor activation occur normally even in the defective cells. We conclude that Pyk2 is the key mediator in the pathway activated by Ca(2+) but has minor roles with the other types of stimulation.

Ubiquitously expressed focal adhesion kinase (FAK), a critical component in transducing signals from sites of cell contacts with extracellular matrix, was named after its typical localization in focal adhesions. A nuclear localization of FAK has been also reported and its scaffolding role in nucleus and requirement for p53 ubiquitination were only recently described. Whereas FAK nuclear localization signal (NLS) was found in F2 lobe of FERM domain, nuclear export signal (NES) sequences have not been yet determined. Here we demonstrate that FAK has two NES sequences, NES1 in F1 lobe of FERM domain and NES2 in kinase domain. Although, both NES1 and NES2 are evolutionary conserved, and present as well in FAK-related protein kinase Pyk2, only NES2 demonstrates full biological nuclear export activity.