Grande S M, Katz E, Crowley J E, Bernardini M S, Ross S R, Monroe J G
Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Oncogene. 2006 May 4;25(19):2748-57. doi: 10.1038/sj.onc.1209296.
Immunoreceptor tyrosine-based activation motifs (ITAMs) are involved in the transduction of signals necessary for activation, differentiation, and survival in hematopoietic cells. Several viruses have been shown to encode ITAM-containing transmembrane proteins. Although expression of these viral proteins has in some cases been shown to transform nonhematopoietic cells, a causal role for a functional ITAM in this process has not been elucidated. To examine the potential transforming properties of ITAM-containing proteins, a recombinant protein consisting of ITAM-containing cytoplasmic regions of the B-cell antigen receptor was expressed in immortalized murine mammary epithelial and fibroblast cells. Mammary epithelial cells expressing this construct exhibited depolarized morphology in three-dimensional cultures. This transformed phenotype was characterized by a loss of anchorage dependence and hallmarks of epithelial to mesenchymal transition. Fibroblasts expressing this ITAM construct also lost contact inhibition and anchorage dependence. The transformed phenotype seen in both cell types was abrogated upon tyrosine to phenylalanine substitutions of the ITAMs. Inhibition of Syk tyrosine kinase, which associates with the ITAM, also prevented cell transformation. Our results indicate that expression of a nonviral ITAM-containing protein is sufficient for cell transformation. Despite lacking intrinsic enzymatic activity, ITAM-containing proteins can function as potent oncoproteins by scaffolding downstream mediators.
基于免疫受体酪氨酸的激活基序（ITAM）参与造血细胞激活、分化和存活所需信号的转导。已有几种病毒被证明可编码含ITAM的跨膜蛋白。尽管在某些情况下，这些病毒蛋白的表达已被证明可转化非造血细胞，但在此过程中功能性ITAM的因果作用尚未阐明。为了研究含ITAM蛋白的潜在转化特性，在永生化的小鼠乳腺上皮细胞和成纤维细胞中表达了一种由B细胞抗原受体含ITAM的胞质区域组成的重组蛋白。表达该构建体的乳腺上皮细胞在三维培养中呈现去极化形态。这种转化表型的特征是失去锚定依赖性以及上皮-间质转化的特征。表达这种ITAM构建体的成纤维细胞也失去了接触抑制和锚定依赖性。当ITAM的酪氨酸被苯丙氨酸取代时，两种细胞类型中出现的转化表型均被消除。与ITAM相关的Syk酪氨酸激酶的抑制也可阻止细胞转化。我们的结果表明，表达一种非病毒含ITAM蛋白足以实现细胞转化。尽管缺乏内在酶活性，但含ITAM蛋白可通过搭建下游介质发挥强效癌蛋白的作用。
