Modulation of gap junctional intercellular communication by EGF in human kidney epithelial cells

Abstract

Modulation of gap junctional intercellular communication (GJIC) was studied in a multistep model of human renal epithelial carcinogenesis. We report that the majority of primary human kidney epithelial cells (NHKE) grown from fetal kidney explants did not communicate through gap junctions. Communication could, however, be observed within a subpopulation of the cells. Ni(II)-immortalized cells (IHKE) showed GJIC at a level of 10-20 communicating cells, but with heterogeneous regions on the dish, with regard to both communication and distribution of connexin43. The heterogeneity was less pronounced in a ras-transfected tumourigenic cell line (THKE), which also showed communication of ~10-20 dye-coupled cells. Communication within the IHKE sub-clone K7 decreased from 55 dye-coupled cells communicating on day 1 after seeding to ~13 in cells grown for 4 days. Daily change of growth medium reduced the decrease in GJIC. EGF enhanced communication following a lag period which depended on days in culture. The largest increase in GJIC was observed in 2-day-old cultures, where the number of communicating cells in some experiments increased from ~45 to 130 dye-coupled cells 4 h following change to medium with EGF. The induction was concentration dependent and communication was enhanced gradually between 2 and 7 h after exposure to EGF. A 15 min pulse of EGF was sufficient to induce the GJIC increase if the total incubation period was unchanged. Cycloheximide completely blocked the EGF-induced enhancement of communication, while actinomycin D had no effect. EGF exposure resulted in an increase in the cellular level of connexin43 protein in parallel with the enhancement in communication. Together, these results indicate that the EGF-induced enhancement of GJIC in human kidney epithelial cells was mediated through translational control of connexin43 expression.