Resting Distribution and Stimulated Translocation of Protein Kinase C Isoforms Alpha, Epsilon and Zeta in Response to Bradykinin and TNF in Human Endothelial Cells

Protein kinase C (PKC) has been linked to functional and morphological changes in endothelial cells involved in increased microvessel permeability. Bradykinin and TNF are potent inflammatory mediators which translocate PKC from the cytosol to the membrane of various cell types, including endothelial cells. The PKC isoforms α, ε and ζ have been demonstrated as the most prominent in human umbilical vein endothelial cells (HUVEC). We propose that bradykinin and TNF cause increased microvascular permeability via a PKC-dependent endothelial cell signalling pathway. HUVEC were incubated at 37°C and 5% CO2 for 1 min, 15 min and 3 h with either bradykinin (1 μM) or TNF (100 U/ml). PMA incubation served as a positive control (100 nM, 15 min). Cytosolic and membrane-bound extracts were obtained by incubation in digitonin (0.5%) and Triton X100 (1%). PKC isoforms were assayed by Western blot and membrane fractions calculated. These experiments revealed that: HUVEC clearly displayed a non-uniform basal membrane fraction distribution of PKC isoforms, with ζ (35.4%) greater than ε (30.6%) and both much greater than α (8.6%); Bradykinin caused significant translocation of PKC α with 15 min and 3 h of treatment but not 1 min; TNF caused dramatic translocation of PKC α at 1 min treatment which subsided at 15 min and 3 h but remained significantly elevated; and PMA caused dramatic translocation of α and ε but not ζ. Treatments of bradykinin and TNF that translocated PKC also showed cytoskeletal rearrangement of rhodamine-phalloidin stained actin, causing it to become more prevalent near cell membranes and concentrated at focal points between cells. These results suggest that PKC α may contribute to long term low grade increases in microvessel permeability in response to bradykinin, and that PKC α could be involved in both transient and sustained microvessel permeability changes induced by TNF. Also, cytoskeletal actin organization appears to be a downstream pathway in the activation process, possibly leading to alteration in endothelial cell shape and contact points