Regulation of bradykinin B2 receptors by the ras oncogene: evidence for multiple mechanisms.

The objective of this study was to probe the molecular mechanisms underlying the increase in sensitivity of cells to bradykinin (BK) following expression of a transforming Ha-ras oncogene. We used native NIH3T3 fibroblast (3T3) cells and 3T3 cells transfected with a glucocorticoid sensitive oncogenic Ha-ras construct (DT cells). DT cells incubated in the presence of 1 microM dexamethasone (DEX) for 24 hr expressed a relatively high level of membrane-bound Ha-Ras protein, BK B2 receptor mRNA, and B2 receptor binding as determined by Western blotting with anti-Ha-Ras antibodies, reverse transcriptase-polymerase chain reaction using B2 receptor-specific primers, and specific [3H]BK binding, respectively. BK also stimulated a significant B2 receptor-mediated increase in [3H]thymidine incorporation in the cells both alone and in synergy with epidermal growth factor. In the absence of DEX, the DT cells expressed a considerably lower but yet clearly significant level of Ha-Ras. Under this condition, receptor mRNA and receptor binding remained maximally expressed. On the other hand, BK was unable to stimulate any increase in [3H]thymidine incorporation. In contrast to DT cells, no Ha-Ras, receptor mRNA, receptor binding, or BK-stimulated, B2 receptor-mediated [3H]thymidine incorporation was detected in 3T3 cells (+/- DEX). However, BK stimulated a transient increase in the level of intracellular free Ca2+ in the 3T3 cells indicating that these cells express a small number of functional B2 receptors. In all, these results show that oncogenic Ha-Ras regulates the sensitivity of 3T3 cells to BK through at least two different mechanisms. One mechanism occurs at a relatively low level of Ha-Ras and involves an increase in B2 receptor mRNA and expressed B2 receptor levels, and another mechanism occurs at a relatively high level of Ha-Ras and involves an increase in B2 receptor-mediated mitogenic signaling.