Myosin XVA in Digestive Endocrine Tumors 29 Clinical Research 29 Department of Pathology (SLR), Ospedale di Circolo, Varese, Italy; Department of Clinical and Biological Sciences (CC), University of Insubria, Varese, Italy; and Department of Laboratory Medicine and Pathology (RVL), Mayo Clinic, Rochester, MN. Address for correspondence to Dr. Stefano La Rosa, Servizio di Anatomia Patologica, Ospedale di Circolo, Viale Borri, 57, I-2100 Varese, Italy. E-mail: anapat@ospedale.varese.it Endocrine Pathology, vol. 13, no. 1, 29–37, Spring 2002 © Copyright 2002 by Humana Press Inc. All rights of any nature whatsoever reserved. 1046–3976/02/13:29–37/ $12.25 Localization of Myosin XVA in Endocrine Tumors of Gut and Pancreas Stefano La Rosa, MD, Carlo Capella, MD, and Ricardo V. Lloyd, MD, PHD Abstract The myosin superfamily includes conventional and unconventional myosin proteins. Among unconventional myosins, myosin XVA has recently been characterized, and it has been suggested that it may be involved in cytoplasmic organelle movement, including secretory granules in pituitary cells and pituitary adenomas. In this study, we investigated the expression of myosin XVA protein and mRNA in normal endocrine cells and in a series of 53 endocrine tumors of the gut and pancreas. Myosin XVA was expressed in rare nor- mal endocrine cells of the gut and in almost all pancreatic islet cells. In addition, myosin XVA was detected in several cells of all endocrine tumors investigated, and its expression was not related to malignancy, type, site, or functional status of tumors. These results indicate that myosin XVA protein and mRNA are widely distributed in endocrine cells of the gut and pancreas. Although the role of this protein in endocrine cells is unknown, previous studies suggest that it may have a role in secretory granule movement and/or hormone secretion. Key Words: Myosin XVA; endocrine tumor; gut; pancreas; immunohistochemistry; in situ hybridization. motif ), and a tail domain that varies in length and sequence among various myo- sin family classes [1,2,6,7]. Unconventional myosins are widely distributed; they con- stitute 4 of 5 myosin genes in Saccharo- myces cerevisiae, 11 of 13 myosin genes in Drosophila, and about two thirds of myo- sin genes in humans [2]. Moreover, recent findings have indicated that typical nonmuscle cells appear to express only 1 or 2 conventional myosin genes, but upward of 10 or more unconventional myosin genes [8–10]. Among various unconventional myosin proteins, myosin XVA is a large protein of 395 kDa, consisting of a unique 1200 amino acid N-terminal domain, which pre- cedes the motor and 1631 amino acids in Introduction Myosins are actin-based motors playing fundamental biologic roles including cell motility, maintenance of cell shape, and organelle/particle trafficking [1,2]. They are also important in some biologic pro- cesses such as signal transduction [3], establishment of cell polarity [4], and rDNA transcription in the nucleoli [5]. The myosin superfamily includes conven- tional (or class II myosins) and at least 16 classes of unconventional myosins [1,2]. Members of the myosin family share simi- lar structural organization consisting of a common domain that has been shown to interact with actin in an adenosine triph- osphate–sensitive manner, a neck region with myosin light chain binding sites (IQ