Abstract
Angiotensin II (Ang II) induces, through AT1, intracellular Ca^2+^ increase in both normal and cancerous breast cells in primary culture (Greco et al., 2002 Cell Calcium 2:1–10). We here show that Ang II stimulated, in a dose‐dependent manner, the 24 h‐proliferation of breast cancer cells in primary culture, induced translocation of protein kinase C (PKC)‐α, ‐β1/2, and δ (but not ‐ε, ‐η, ‐θ, ‐ζ, and ‐ι), and phosphorylated extracellular‐regulated kinases 1 and 2 (ERK1/2). The proliferative effects of Ang II were blocked by the AT1 antagonist, losartan. Also epidermal growth factor (EGF) had mitogenic effects on serum‐starved breast cancer cells since induced cell proliferation after 24 h and phosphorylation of ERK1/2. The Ang II‐induced proliferation of breast cancer cells was reduced by (a) Gö6976, an inhibitor of conventional PKC‐α and ‐β1, (b) AG1478, an inhibitor of the tyrosine kinase of the EGF receptor (EGFR), and (c) downregulation of 1,2‐diacylglycerol‐sensitive PKCs achieved by phorbol 12‐myristate 13‐acetate (PMA). A complete inhibition of the Ang II‐induced cell proliferation was achieved using the inhibitor of the mitogen activated protein kinase kinase (MAPKK or MEK), PD098059, or using Gö6976 together with AG1478. These results indicate that in human primary cultured breast cancer cells AT1 regulates mitogenic signaling pathways by two simultaneous mechanisms, one involving conventional PKCs and the other EGFR transactivation. J. Cell. Physiol. 196: 370–377, 2003. © 2003 Wiley‐Liss, Inc.