Microenvironmental factors regulate Ly-6 A/E expression on PyV-transformed BALB/c 3T3 cells

LY6E: a conductor of malignant tumor growth through modulation of the PTEN/PI3K/Akt/HIF-1 axis

Lymphocyte antigen 6 complex, locus E (LY6E) has been implicated in the malignant progression of various types of cancers; however, the underlying mechanism remains unclear. Here, we identified LY6E as an activator of HIF-1 and revealed their mechanistic and functional links in malignant tumor growth. The aberrant overexpression of LY6E increased HIF-1α gene expression principally at the transcription level. This, in turn, led to the expression of the pro-angiogenic factors, VEGFA and PDGFB, through decreases in the expression levels of PTEN mRNA and subsequent activation of the PI3K/Akt pathway. The LY6E-HIF-1 axis functioned to increase tumor blood vessel density and promoted tumor growth in immunodeficient mice. LY6E expression levels were significantly higher in human breast cancers than in normal breast tissues, and were strongly associated with the poor prognoses of various cancer patients. Our results characterized LY6E as a novel conductor of tumor growth through its modulation of the PTEN/PI3K/Akt/HIF-1 axis and demonstrated the validity of targeting this pathway for cancer therapy.

Cloning and functional characterization of chicken stem cell antigen 2

Stem cell antigen 2 (SCA2) is a Ly6 family member whose function is largely unknown. To characterize biological properties and tissue distribution of chicken SCA2, SCA2 was expressed in E. coli, purified, and a polyclonal antibody developed. Utilizing the polyclonal antibody, SCA2 is a 13 kDa cell surface protein anchored by a glycosyl-phosphatidylinositol (GPI) moiety. SCA2 is expressed in connective tissues of thymus and bursa based on immunohistochemistry, immunoprecipitation, and western blots. In bursal follicles, SCA2 is specifically expressed on the cortical-medullary epithelial cells (CMEC) surrounded by MHC class II presenting cells. Expression profiles of bursal cells induced by contact with SCA2-expressing cells shows down-regulation of numerous genes including CD79B, B cell linker (BLNK), spleen tyrosine kinase (SYK), and gamma 2-phospholipase C (PLCG2) that are involved in the B cell receptor (BCR) and immune response signaling pathways. These results suggest chicken SCA2 plays a role in regulating B lymphocytes.

Receptors involved in microenvironment-driven molecular evolution of cancer cells

Cells, including cancer cells, communicate with their microenvironment via various types of membrane receptors. An important down-stream effect of such interactions is a change in the molecular phenotype of the cells. The microenvironment-driven molecular evolution of cancer cells may induce either growth arrest or death of the cells or alternatively, boost their malignancy phenotype. In this paper we summarize studies from our own laboratory on interactions of cancer cells with microenvironmental ligands via two types of receptors that are not commonly associated with tumour progression i.e. the receptor for the Fc portion of IgG, and Ly-6 proteins of mouse and human origin. We also review information on interactions of tumour-associated chemokines and chemokine receptors with the corresponding microenvironmental factors. We demonstrate how these interactions may drive the molecular evolution of tumour cells and discuss the possible impact of this evolution on tumour progression.

A monoclonal antibody against the 66-kDa protein expressed in mouse spleen and thymus inhibits Ly-6A.2-dependent cell-cell adhesion

The Ly-6 locus encodes several cell surface proteins of 10-12 kDa. Some members of this multigene family may function in cell signaling and/or cell adhesion processes. T lymphocytes overexpressing Ly-6A.2 (one member of the Ly-6 gene family) protein homotypically aggregate when cultured in vitro. Further analysis of this homotypic aggregation suggests that Ly-6A.2 participates in cell-cell adhesion. These observations indicated the presence of a Ly-6 ligand(s) on the surface of lymphoid cells. In this study we report generation of a hamster mAb, 9AB2, that blocks Ly-6A.2-dependent cell-cell adhesion. The 9AB2 Ab recognizes a 66-kDa glycoprotein with unique tissue expression. The 9AB2 mAb does not bind Ly-6A.2, but coimmunoprecipitates Ly-6A.2 molecule. Moreover, 9AB2 Ag-expressing thymocytes specifically bind to Chinese hamster ovary cells overexpressing Ly-6A.2 protein, and this binding is specifically blocked by 9AB2 and anti-Ly-6A.2 Abs. These results suggest that the 66-kDa protein recognized by 9AB2 mAb is the putative ligand for Ly-6A.2.

Expression of Ly-6, a marker for highly malignant murine tumor cells, is regulated by growth conditions and stress

Ly-6E.1 is highly expressed in murine tumor cells with a high malignancy phenotype and may serve as a marker for such a phenotype. In this study, we examined the effects of various growth conditions and stress on the expression levels of Ly-6E.1 by tumor cells. Previous preliminary results have shown that murine DA3 mammary tumor cells expressing high levels of Ly-6E.1 (Ly-6(hi)) are more highly tumorigenic than the same tumor cells expressing low levels of this membrane protein (Ly-6(lo)). In this study, we demonstrate that mice bearing Ly-6(hi) DA3 tumors have a significantly higher burden of spontaneous pulmonary metastasis than mice bearing Ly-6(lo) DA3 tumors. Furthermore, the survival time of the former mice was significantly shorter than that of the latter ones. We further show that certain other members of the Ly-6 gene family such as Ly-6C.1 and Ly-6G.1 are coregulated with Ly-6E.1. This was shown to occur with respect to both DA3 cells as well as A3 tumor cells which are of fibroblast origin. However, these 2 cells differ with respect to regulation of Sca-2 (TSA1, another member of the Ly-6 family) expression on these cells. Levels of Sca-2 on A3 cells appear to be coregulated with Ly-6E.1 (i.e., Ly-6(hi) A3 cells express high levels of Sca-2 and Ly-6(lo) A3 cells express low levels of Sca-2). These 2 Ly-6 proteins were, however, not coregulated on DA3 cells. Both Ly-6(hi) as well as Ly-6(lo) DA3 cells express equal levels of Sca-2. Levels of Thy-1, another glycosylphosphatidylinositol (GPI)-anchored protein expressed by A3 tumor cells, were equally expressed by both Ly-6(hi) and Ly-6(lo) A3 tumor cells. Levels of Ly-6 (but not those of CD44) on A3 tumor cells were upregulated on cells from dense cultures but were not influenced by the position of the cells in the cell cycle. Stress conditions such as serum starvation or heat shock upregulated the expression of Ly-6 by the 2 types of tumor cells but did not induce apoptosis in these cells. The kinetics of the stress-dependent upregulation of Ly-6 expression differed, however, between the epithelial and fibroblastic tumor cells.

TNFalpha and anti-Fas antibodies regulate Ly-6E.1 expression by tumor cells: a possible link between angiogenesis and Ly-6E.1

Angiogenic and poorly angiogenic tumor variants were obtained by an intraperitoneal inoculation of cells from clones of polyoma-virus transformed BALB/c 3T3 cells into syngeneic mice. The angiogenic tumor cells expressed a higher tumorigenicity phenotype and a higher capacity to produce artificial pulmonary metastases than cells from the poorly angiogenic tumors. The former cells expressed also significantly higher levels of the lymphocyte activation protein Ly-6E.1 than the former cells. The two types of cells did not differ in expression levels of CD44 and of a polyoma-virus specific membrane antigen. These results raise the possibility that the angiogenic phenotype is coregulated with Ly-6. The effect on Ly-6 expression of signal transduction through TNF receptors, functioning as pivotal regulators of angiogenesis was therefore studied. It was found that TNFalpha and more so antibodies against Fas down-regulate expression levels of Ly-6. This down-regulation seemed to be selective as expression levels of CD44 were not affected by this treatment.