PubMed · 10697403
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Z M Rupniewska, M Dmoszyńska, J Roliński. 1999. [CD5 and CD6 molecules--similarities and differences].. https://pubmed.ncbi.nlm.nih.gov/10697403/
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CD6 is a cell surface receptor primarily expressed on immature thymocytes and mature T and B1a lymphocytes. Through its binding to activated leukocyte cell adhesion molecule (ALCAM/CD166), CD6 is considered to play an important role in lymphocyte development and activation. Accordingly, CD6 associates with the TCR/CD3 complex and colocalizes with it at the center of the mature immunological synapse on T lymphocytes. Moreover, the CD6-ALCAM interaction has been shown to be critical for proper immunological synapse maturation and T cell proliferative responses. However, the precise biological effects of CD6 ligation and its signaling pathway are still not well understood. The present study shows that CD6 ligation with three different specific mAbs (161.8, SPV-L14.2, and MAE1-C10) induces time- and dose-dependent activation of ERK1/2 on normal and leukemic human T cells. This effect was also observed upon CD6 ligation with a chimerical ALCAM protein (ALCAM-Fc). The C-terminal cytoplasmic region of CD6, as well as Src tyrosine kinases, was critical for CD6-induced ERK1/2 activation. Synergistic effects were observed upon coligation of the TCR/CD3 complex with CD6. The ligation of CD6 induced the transcriptional activation of reporter genes under the control of the c-Fos serum responsive element and AP-1. Accordingly, CD6-mediated activation of p38 and JNK was also observed. These findings indicate that the CD6-ALCAM interaction results in activation of the three MAPK cascades, likely influencing the dynamic balance that determines whether resting or activated lymphocytes survive or undergo apoptosis.
BACKGROUND: Activated leukocyte cell adhesion molecule (ALCAM/CD166) is a 105-kDa transmembrane glycoprotein linked with cell migration and development and with cancer progression (malignant melanoma, prostate cancer and, very recently, breast cancer). This report is the first evaluation of ALCAM/CD166 in an estrogen-dependent (MCF-7) and a metastatic (MDA-MB-231) breast cancer cell line and a reference breast cell line (HBL-100). The effects of estrogen and anti-estrogen treatment, bcl-2 overexpression, and ALCAM gene silencing on ALCAM/CD166 protein concentration and cell survival were investigated. MATERIAL/METHODS: Laser scanning cytometry, confocal microscopy, and Western blotting were used for the determination of ALCAM/CD166 protein and biochemical markers of apoptosis and autophagy. RESULTS: 17-beta-estradiol increased and tamoxifen inhibited ALCAM/CD166 expression and survival of MCF-7 cells. Overexpression of the bcl2 gene in MCF-7 bcl2/neo, MDA-MB-231 bcl2/neo, and HBL-100 bcl2/neo cells significantly increased ALCAM/CD166 expression and was accompanied by decreasing MMP-2 concentrations. Appearance of the ALCAM/CD166 protein was noted in HBL-100 bcl2/neo in contrast to an almost undetectable level in HBL-100 cells. ALCAM gene silencing in MCF-7 cells decreased the concentration of BCL-2 and increased levels of apoptosis (89-kDa PARP, active caspase7) and autophagy (MAP1LC3, Beclin1) markers. CONCLUSIONS: The above results indicate that ALCAM-ALCAM interactions are crucial to the survival and primary site maintenance of breast cancer cells. Impaired expression of ALCAM/CD166 is associated with the induction of two types of programmed cell death, apoptosis and autophagy, in breast cancer cells. This adhesion molecule can therefore be regarded as a potential novel breast cancer indicator and therapeutic target.
Transendothelial leukocyte migration is a major aspect of the innate immune response. It is essential in repair and regeneration of damaged tissues and is regulated by multiple cell adhesion molecules (CAMs) including members of the immunoglobulin (Ig) superfamily. Activated leukocyte cell adhesion molecule (ALCAM/CD166) is an Ig CAM expressed by activated monocytes and endothelial cells. Hitherto, the functional relevance of ALCAM expression by endothelial cells and activated monocytes remained unknown. In this report, we demonstrate soluble recombinant human ALCAM significantly inhibited the rate of transendothelial migration of monocyte cell lines. Direct involvement of ALCAM in transendothelial migration was evident from the robust inhibition of this process by ALCAM blocking antibodies. However, soluble recombinant ALCAM had no impact on monocyte migration or adhesion to endothelium. Localization of ALCAM specifically at cell-cell junctions in endothelial cells supported its role in transendothelial migration. This study is the first to localize ALCAM to endothelial cell junctions and demonstrate a functional relevance for co-expression of ALCAM by activated monocytes and endothelial cells.