A cytoplasmic protein, bystin, interacts with trophinin, tastin, and cytokeratin and may be involved in trophinin-mediated cell adhesion between trophoblast and endometrial epithelial cells

Abstract

Trophinin and tastin form a cell adhesion molecule complex that potentially mediates an initial attachment of the blastocyst to uterine epithelial cells at the time of implantation. Trophinin and tastin, however, do not directly bind to each other, suggesting the presence of an intermediary protein. The present study identifies a cytoplasmic protein, named bystin, that directly binds trophinin and tastin. Bystin consists of 306 amino acid residues and is predicted to contain tyrosine, serine, and threonine residues in contexts conforming to motifs for phosphorylation by protein kinases. Database searches revealed a 53% identity of the predicted peptide sequence with the Drosophila bys (mrr) gene. Direct proteinprotein interactions of trophinin, tastin, and bystin analyzed by yeast two-hybrid assays and by in vitro protein binding assays indicated that binding between bystin and trophinin and between bystin and tastin is enhanced when cytokeratin 8 and 18 are present as the third molecule. Immunocytochemistry of bystin showed that bystin colocalizes with trophinin, tastin, and cytokeratins in a human trophoblastic teratocarcinoma cell, HT-H. It is therefore possible that these molecules form a complex and thus are involved in the process of embryo implantation.Embryo implantation is a process that depends on the coordinated development of the embryo and differentiation of the uterus to the receptive state (1-4). A two-way interaction between the blastocyst and uterus is essential for successful implantation and subsequent decidualization (5). In the mouse, the first conspicuous sign of the implantation is an increased endometrial vascular permeability at the site of blastocyst apposition, and this coincides with the initial attachment reaction (3, 6). This attachment is followed by adherence and penetration by trophoblasts cells through the underlying basement membrane and results in proliferation and differentiation of stromal cells into decidual cells. Numerous factors including growth factors (7), cytokines (8), homeotic genes (9), and prostaglandin (10, 11) have been implicated in implantation process. Among these, null mutations of leukemia inhibitory factor and Hoxa-10 genes result in defective implantation (8, 9), and a prostaglandin regulating cyclooxigenase 2 gene knock-out results in multiple failures of female reproductive processes including implantation (10, 11).To understand the molecular mechanisms underlying embryo implantation, identification and characterization of specific molecules responsible for the initial attachment of the embryo and subsequent invasion of the trophoblasts to the uterus are essential. However, such analysis has been difficult because of the absence of appropriate in vitro models for implantation. In this regard two human cell lines, a trophoblastic teratocarcinoma, HT-H (12), and an endometrial adenocarcinoma, SNG-M (13), are noteworthy, because the interaction between these two cell types appears to mimic that of trophoblasts and endometrial epithelial cells parti...

Bystin-like protein is upregulated in hepatocellular carcinoma and required for nucleologenesis in cancer cell proliferation

“…This observation agrees with the previous studies reporting BYSL in nuclei of yeast and mouse ES cells, while only small amounts of BYSL/ ENP1 were cytoplasmic in HeLa cells and yeast [17,18]. Interestingly, BYSL promotes cell adhesion of trophoblasts by forming a complex with trophinin and tastin [39,45], thus mediating embryo implantation which is Hanzhi Wang et al 1161 npg accompanied by rapid cellular invasion and proliferation [39,46,47]. It is likely that cytoplasmic activity of BYSL is important in cancer cell metastasis.…”

“…Overall, these observations suggest that BYSL upregulation may be a general feature of human cancers and crucial for tumor formation. BYSL is not a widely expressed gene in adult human tissue through both northern blot and immunohistology analysis in various human tissues [39]. The lack of BYSL protein leads to G2/M arrest and cell death at the end of mitosis in cancer cells, indicating that BYSL is more required in continual cell division.…”

Genome‐wide examination of myoblast cell cycle withdrawal during differentiation

“…The expression of two other cell adhesion proteins, bystin and neuronal cell adhesion molecule (N-CAM) L1, also were decreased at the onset of C2C12 differentiation (Table 4). Bystin is a cytoplasmic protein known to interact with trophinin and tastin, forming a cell adhesion complex that mediates initial attachment of the blastocyst to uterine epithelial cells at the time of implantation (Suzuki et al, 1998). N-CAM L1 belongs to the immunoglobulin super family, consisting of six immunoglobulin-like domains and five fibronectin-type III repeats, followed by a transmembrane region and a highly conserved cytoplasmic tail (Hortsch, 2000).…”

Global gene expression analysis identifies molecular pathways distinguishing blastocyst dormancy and activation

“…This is consistent with our observation of up-regulation of Ocln, Zyx, Lgals4, and Bysl in activated blastocysts (Tables 2 and 4). Ocln encoding occludin is important for the formation and maintenance of the blastocoel cavity (36), and Bysl that encodes bystin is involved in trophininmediated cell adhesion between trophoblast and uterine epithelial cells via interaction with trophinin, tastin, and cytokeratin (37). Although mice lacking zyxin function normally (38), and mice carrying galectin1͞3 double mutations (39) are viable and compatible with implantation, the function of Lgals4 (galectin4) is not known.…”