Tumor suppressor function of Rab25 in triple-negative breast cancer Ji-Ming Cheng 1 , Lisa Volk 2 , Deepak Kumar Mummidavarapu Janaki 3 , Sudhir Vyakaranam 4 , Sophia Ran 2 and Krishna A. Rao 1,2 1 Division of Hematology and Oncology, Department of Internal Medicine, Southern Illinois University School of Medicine and SimmonsCooper Cancer Institute at SIU, Springfield, IL 2 Department of Medical Microbiology, Immunology and Cell Biology, Southern Illinois University School of Medicine and SimmonsCooper Cancer Institute at SIU, Springfield, IL 3 Department of Internal Medicine, University of Illinois College of Medicine at Peoria, Peoria, IL 4 Division of Nephrology, University of Cincinnati, Cincinnati, OH Rab proteins are a group of ubiquitously expressed proteins that are responsible for intracellular transport of vesicles. Recent evidence has shown that certain Rab proteins are involved in the pathogenesis of cancer. We have recently shown that Rab25 is lost in a large fraction of breast cancer samples, particularly those derived from hormonally insensitive tumors. We have further investigated the role of Rab25 by re-expressing Rab25 in tumorigenic cell lines and measuring the impact on tumor formation as well as on various molecular pathways through PCR array analysis. In vivo tumor growth of cell lines with re-expressed Rab25 was markedly suppressed. Our data suggest that Rab25 acts through multiple pathways to enhance apoptosis and to suppress angiogenesis and invasion by modulating VEGF-A and VEGFR-1 expression. These findings suggest that Rab25 represents a novel class of cellular modulators that can influence both tumor initiation and the progression of the established tumors, thus ultimately affecting the biology of the malignant disease. The rab (RAS-related in brain) proteins 1 are intracellular transport proteins that belong to the ras superfamily of small GTPases responsible for a variety of vesicle trafficking func- tions. 2 Greater than 60 rab proteins have been described to date in mammals. 3,4 The large number of rab proteins in eukaryotes reflects the complexity of transport within these cells. This notion is supported by the fact that certain rabs are expressed only in certain cell types and aid in specific transport functions. 5 Prominent expression of Rab25 has been observed throughout the gastrointestinal mucosa with the highest expression seen in the ileum and colon. High lev- els of expression are also present in the lung and kidney. 6 The loss of expression or overexpression of Rab proteins in malignancy is a relatively novel field of study and suggests that in addition to many of the characteristics enumerated by Hanahan and Weinberg, 7 disordered or reordered intracellu- lar communication is also a feature of the transformation process. Cheng et al. 8 have recently described the overexpres- sion of Rab25 in ovarian and breast cancer and have studied the impact of Rab25 overexpression and loss in cell lines. They reported elevated expression of Rab25 in 47% of breast cancers. Their data suggest that Rab25 enhances the aggres- sive behavior of ovarian and breast cancers, although they did not specify whether this behavior is specifically associated with expression of hormone receptors (HRs). 8 Our group previously reported the presence of Rab25 in normal mam- mary epithelium, immortalized human mammary epithelial cells and majority (92%) of HR-positive breast cancer tissues. We also reported absence of detectable Rab25 in a significant number of HR breast cancer lines and in a majority (83%) of HR-negative breast tumor specimens. 9 We observed signifi- cant effects of re-expressed Rab25 on behavior of HR-nega- tive breast carcinoma lines that included a dramatic reduc- tion in cell growth in vitro, significant reduction of tumorigenic growth in vivo, altered cell morphology in vivo, increased apoptosis and disruption of the angiogenic path- ways. These data suggest that Rab25 may affect angiogenic pathways within the tumor cells, thus influencing tumori- genic potential. The vascular endothelial growth factor (VEGF-A) family represents a group of multifunctional cytokines that regulate both physiologic and pathologic angiogenesis. 10,11 The main members of this family include VEGF-A, VEGF-B, VEGF-C and VEGF-D, 12,13 VEGF-A exerts its effects through 2 tyro- sine kinase receptors, VEGFR-1 and VEGFR-2. 14,15 VEGF-A Key words: mammary neoplasia, Rab25, p21 RAS, tumorigenesis, apoptosis Additional Supporting Information may be found in the online version of this article Grant sponsors: Ilinois Department of Public Health Penny Severns, McElroy Charitable Fund DOI: 10.1002/ijc.24900 History: Received 12 Sep 2008; Accepted 11 Aug 2009; Online 30 Sep 2009 Correspondence to: Krishna A. Rao, Assistant Professor of Clinical Medicine, Division of Hematology and Oncology, Department of Internal Medicine, Southern Illinois University School of Medicine, Post Office Box 19678, Springfield, IL 62794-9678, USA, Fax: þ217-545-7021, E-mail: krao@siumed.edu Cancer Cell Biology Int. J. Cancer: 126, 2799–2812 (2010) V C 2009 UICC International Journal of Cancer IJC