1. ¹Universität Halle-Wittenberg, Universitätsklinik und Poliklinik für Gynäkologie, Ernst-Grube-Str. 40, 06097 Halle (Saale), Germany
2. ²Abteilung Innere Medizin I, Med. Klinik, Eberhard-Karls-Universität, Otfried-Müller-Str. 10, 72076 Tübingen, Germany

Correspondence: J Dittmer, E-mail: juergen.dittmer@medizin.uni-halle.de

³These authors contributed equally to this work.

⁴Current address: Gene Regulation Laboratory, Cancer Immunology Division, The Peter MacCallum Cancer Institute, Smorgon Family Building, St Andrews Place, East Melbourne 3002, Victoria, Australia

Received 9 July 2004; Revised 23 September 2004; Accepted 29 September 2004; Published online 8 November 2004.

Abstract

PKC and Ets1 are both associated with breast cancer progression. Our previous studies suggested that these proteins are likely to functionally interact with one another. Here, we show that attenuation of endogenous PKC expression (siP) by RNA interference leads to reduced Ets1 protein expression in a variety of cancer cells. Pulse-chase experiments and treatment with proteasome inhibitor MG-132 revealed that siP interferes with both Ets1 protein synthesis and stability. The effect of siP on Ets1 expression could be partially prevented by KN-93, suggesting that calcium/calmodulin-dependent kinase II (CaMKII), a modulator of Ets1 activity, may play a role in PKC-dependent Ets1 regulation. In contrast, Ets1-regulating kinases ERK1/2 were not found to be involved in this process. To assess the importance of the PKC/Ets1 interaction, we compared the biological responses of MDA-MB-231 cells to PKC- and Ets1-specific siRNAs (siE1). While only siP induced changes in cellular morphology and anchorage-independent growth, both siRNAs similarly affected cellular responses to the antitumor drug mithramycin A and to UV light. Microarray analyses further showed that the expression of a certain set of genes was equally affected by siP and siE1. The data suggest that Ets1 serves as an effector for PKC to fulfil certain functions in cancer cells.