Role of CD164 in Skeletal Myogenesis

描述(由申请人提供)：骨骼肌谱系的确定和分化由肌源性转录因子MyoD家族控制。这些因子与MEF-2转录因子家族一起，自动激活和交叉激活彼此的表达，从而形成一个自我调节的正反馈网络，维持肌源性表型。这一谱系中细胞的确定和分化也需要肌肉前体之间的细胞-细胞接触。然而，参与这一现象的细胞表面蛋白的身份，以及它们在肌肉发生中的具体作用，还没有被很好地理解。唾液粘蛋白是以粘蛋白结构域为特征的细胞表面蛋白，它是富含脯氨酸、丝氨酸和苏氨酸的区域，其上高比例的丝氨酸和苏氨酸残基是O-糖基化的。这些O-连接的多糖是唾液粘蛋白功能的中心，因为特定的唾液粘蛋白被认为是选择素的高亲和力配体；选择素是跨膜受体，在白细胞运输过程中识别这些唾液粘蛋白上的唾液酸化的碳水化合物结构。唾液粘蛋白在白细胞转运之外的生物学作用还知之甚少。我们已经确定CD164是一个在C2C12成肌细胞增殖过程中表达的基因，在分化过程中特异性上调。CD164编码一种广泛表达的细胞表面唾液粘蛋白，参与调节细胞的增殖、分化和造血前体的黏附。CD164稳定过表达可促进成肌细胞分化。用唾液酸酶或O-唾液酸糖蛋白酶处理C2C12细胞，这两种酶会破坏CD164上的功能表位，也会抑制分化。综上所述，我们假设CD164可能是肌肉发生过程中细胞-细胞接触需求的效应者，基于碳水化合物的细胞识别可能参与了这一过程。其具体目的是：1)鉴定CD164促肌原活性的结构决定因素；2)鉴定CD164的拮抗受体；3)研究CD164在体内肌发生中的作用。这些实验将为从分子和遗传学上理解CD164‘S在肌发生中的作用提供重要信息。因此，这项研究应该有助于揭示骨骼肌发育的基本过程。

DESCRIPTION (provided by applicant): Determination and differentiation of the skeletal muscle lineage is controlled by the MyoD family of myogenic transcription factors. These factors, along with the MEF-2 family of transcription factors, auto-activate and cross-activate the expression of each other, resulting in an autoregulatory, positive feedback network that maintains the myogenic phenotype. Determination and differentiation of cells in this lineage also require cell-cell contact between muscle precursors. However, the identities of the cell surface proteins involved in this phenomenon, and their specific roles in myogenesis, are not well understood. Sialomucins are cell surface proteins characterized by mucin domains, which are proline-, serine-, and threonine-rich regions on which a high percentage of the serine and threonine residues are O-glycosylated. These O-linked glycans are central to sialomucin function, as specific sialomucins are known to serve as high affinity ligands for selectins; selectins are transmembrane receptors that recognize sialylated carbohydrate structures on these sialomucins during leukocyte trafficking. The biological roles of sialomucins outside of leukocyte trafficking are poorly understood. We have identified Cd164 as a gene expressed in proliferating C2C12 myoblasts that is specifically upregulated during differentiation. Cd164 encodes a widely expressed cell surface sialomucin that has been implicated in regulation of cell proliferation, differentiation and adhesion of hematopoietic precursors. Stable overexpression of Cd164 enhances myoblast differentiation. Treatment of C2C12 cells with sialidase or O-sialoglycoprotease, two enzymes which destroy functional epitopes on CD164, also inhibits differentiation. Taken together, we hypothesize that CD164 is a likely effector of the need of cell-cell contact in myogenesis and that carbohydrate-based cell recognition may be involved in this process. The Specific Aims are: 1) to identify structural determinants of the pro-myogenic activity of CD164; 2) to identify counter-receptors for CD164; and 3) to investigate the role of CD164 in myogenesis in vivo. These experiments will provide information critical to molecular and genetic understanding of CD164's role in myogenesis. This research should therefore shed light on fundamental processes by which skeletal muscles develop.