Abstract The development of cancer prevention strategies depends on the elucidation of molecular pathways underlying oncogenesis. In a previous pro- teomic study of matched normal breast ducts and Ductal Carcinoma in Situ (DCIS), we identified over- expression of Rab11a in DCIS. Rab11a is not well studied in cancer, but is known to regulate the recy- cling of internalized cell surface proteins and receptors from the early endosome through the trans-Golgi network. Using immunohistochemistry, we confirmed our observation, noting increased Rab11a expression in 19 of 22 (86%) DCIS cases compared to matched normal breast epithelium. To study the function of Rab11a, immortal, nontumorigenic MCF10A breast cells were stimulated with ligands to the EGF receptor (EGFR) after transfection with empty vector (control), Rab11a, or a S25N dominant-negative (DN) Rab11a. Using an iodinated ligand:receptor recycling assay, transfection of Rab11a accelerated, while DN-Rab11a postponed EGFR recycling in vitro. The signaling and in vitro phenotypic consequences of Rab11a expression and function were studied. Transfection of DN-Rab11a increased Erk1/2 activation downstream of EGF, but exerted no effect on the Akt pathway. Expression of DN-Rab11a inhibited MCF10A proliferation by 50– 60%, and also inhibited anchorage-dependent coloni- zation. Notably, DN-Rab11a transfection increased motility toward EGFR ligands. The data provide a first demonstration that Rab11a modulates EGFR recy- cling, and promotes the proliferation but inhibits the motility of an immortal breast line, consistent with the DCIS phenotype. Keywords Breast Æ DCIS Æ Rab11 Æ EGF receptor Introduction The development of rational approaches to the pre- vention of breast cancer will require an understanding of the signaling pathways that initiate this disease. Tamoxifen reduced the development of estrogen receptor-positive breast cancers in high risk women, and prophylactic surgery reduced the development of hereditary breast cancers; more effective, tolerable prevention strategies for these subtypes and strategies for the remaining estrogen receptor-negative cancers are needed (rev. in [1–4]). We have focused on the identification of molecular events identified in human biopsy and surgical tissues, comparing normal ducts with premalignant lesions and/or ductal carcinoma in situ (DCIS) [5–7]. If such molecular pathways are Electronic Supplementary Material Supplementary material is available for this article at http://dx.doi.org/10.1007/s10549-006- 9244-6 and is accessible for authorized users. D. Palmieri Æ A. Bouadis Æ P. S. Steeg Women’s Cancers Section, Laboratory of Molecular Pharmacology, Center for Cancer Research, NCI, NIH, Bethesda, MD 20892, USA R. Ronchetti Æ M. J. Merino Surgical Pathology Section, Laboratory of Pathology, Center for Cancer Research, NCI, NIH, Bethesda, MD 20892, USA D. Palmieri (&) Women’s Cancers Section, Laboratory of Molecular Pharmacology, Center for Cancer Research, NCI, NIH, 37 Convent Drive, Building 37, Rm. 1222, Bethesda, MD 20892, USA e-mail: palmierd@mail.nih.gov Breast Cancer Res Treat (2006) 100:127–137 DOI 10.1007/s10549-006-9244-6 123 PRECLINICAL STUDY Rab11a differentially modulates Epidermal Growth Factor-induced proliferation and motility in immortal breast cells Diane Palmieri Æ Amina Bouadis Æ Ruban Ronchetti Æ Maria J. Merino Æ Patricia S. Steeg Received: 28 March 2006 / Accepted: 3 April 2006 / Published online: 22 June 2006 Ó Springer Science+Business Media B.V. 2006