Research Article Malignancy Associated MicroRNA Expression Changes in Canine Mammary Cancer of Different Malignancies Marie-Charlotte von Deetzen, 1 Bernd T. Schmeck, 2 Achim D. Gruber, 1 and Robert Klopfleisch 1 1 Institute of Veterinary Pathology, Freie Universit¨ at Berlin, Robert-von-Ostertag-Straße 15, 14163 Berlin, Germany 2 Molecular Pulmonology, German Center for Lung Research, Philipps Universit¨ at Marburg, Hans-Meerwein-Straße 2, 35043 Marburg, Germany Correspondence should be addressed to Robert Klopleisch; robert.klopleisch@fu-berlin.de Received 11 February 2014; Accepted 18 March 2014; Published 2 April 2014 Academic Editors: M. H. Kogut and A. Shamay Copyright © 2014 Marie-Charlotte von Deetzen et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. MicroRNA has been suspected to be generally involved in carcinogenesis since their irst description. A irst study supported this assumption for canine mammary tumors when miRNA expression was compared to normal gland. he present study extends these results by comparing the expression of 16 microRNA (miRNA) and 4 small nucleolar RNA (snoRNA) in tumors of diferent malignancy, for example, adenomas, nonmetastasizing and metastasizing carcinomas as well as lymph node metastases, with each other and with normal mammary gland. All neoplastic tissues difered in their miR-210 expression levels from normal gland. While metastatic cells difered in their expression of mir-29b, miR-101, mir-125a, miR-143, and miR-145 from primary tumors, the comparison of miRNA expression in primary tumors of diferent malignancy failed to reveal signiicant diferences except for a signiicant downregulation of mir-125a in metastasizing carcinomas when compared to adenomas. 1. Introduction MicroRNA (miRNA) is an evolutionarily conserved, non- coding, but regulatory RNA species of approximately 22 nucleotides in length. It plays a crucial role in various physiological and pathological processes by regulating gene expression posttranscriptionally. miRNA binds to messenger RNA (mRNA) and thereby induces a sequence-depending mRNA degradation or translational repression [1–3]. A deregulation of miRNA is associated with a wide variety of pathologic states including carcinogenesis [4]. Nevertheless, in many cases the speciic function of individual miRNA species is still unknown. For instance, miR-10b has been identiied as a tumor suppressor which prevents human breast cancer development but also as an oncogene which initiates breast cancer invasion and metastasis [5]. Several miRNA species have been identiied to be involved in human breast cancer development including miR-21, miR-145, and miR-210 [6–8]. In veterinary medicine, only a single study is available on miRNA expression in canine mammary tumors. Boggs et al. [7] compared the expression levels of ten miRNA species in malignant mammary tumors and normal canine mammary gland and found a signiicant deregulation of miR- 21, miR-29b, let-7f, miR-15a, and miR-16 in the tumors. In the present study, we expand these recent indings on the impact of miRNA deregulation on canine mammary tumors by asking for diferences in expression levels of four small nucleolar RNA (snoRNA) and 16 canine miRNA with known relevance for human and canine mammary tumor development in tissue samples of normal mammary gland, adenomas, metastasizing, and nonmetastasizing canine mammary carcinomas as well as lymph node metastases. 2. Materials and Methods Mammary gland tissues including regional lymph nodes from 30 dogs submitted to the Department of Veterinary Pathology of the Freie Universit¨ at Berlin were included in the study. Clinical data of the dogs included breed, age, and Hindawi Publishing Corporation ISRN Veterinary Science Volume 2014, Article ID 148597, 5 pages http://dx.doi.org/10.1155/2014/148597