The modulation of protein kinase A and heat shock protein 70 is involved in the reversible increase of blood-brain tumor barrier permeability induced by papaverine

Intra-arterial administration of papaverine has been revealed to cause an increase in the blood-brain tumor barrier (BTB) permeability. The exact mechanism of papaverine opening the BTB in chemotherapy of malignant cerebral tumors, however, has not been well described. We used a rat brain glioma (C6) model for studying how papaverine modulates the permeability of BTB by monitoring the activities of the tight junction (TJ)-associated protein occludin, claudin-5 and cytoskeletal protein filamentous actin (F-actin) and whether protein kinase A (PKA) and heat shock protein 70 (HSP70) were involved in the regulation of this biological process. The levels of occludin, claudin-5 and F-actin protein in the tumor tissues were down-regulated by papaverine via immunohistochemistry, immunofluorescence assays and Western blot, corresponding to the time-dependent change of the BTB permeability. The most obvious attenuation of occludin, claudin-5 and F-actin protein was observed at 1 h after papaverine perfusion, companied by a significant decrease in expression levels of PKA protein. The expression level of HSP70 in the tumor tissues was also progressively increased after papaverine perfusion and reached the maximum at 3 h. The results demonstrate that the reversible openning of BTB mediated by papaverine may be associated with the functional combination between PKA and HSP70. That is, BTB opening may be attributable to the down-regulation of occludin, claudin-5 and F-actin, and cAMP/PKA signaling pathway might be involved in this process. HSP70 is likely responsible for the BTB closing, which helping the repairment of injured TJ protein and the rebuilding of the BTB.