ll line led to an increase in -catenin and N-cadherin staining along the length of cell junctions, which colocalized precisely with ALCAM. Despite this, cell morphology remained fairly similar to MUM-2C’s spindle shape, and no increase in total N-cadherin or -catenin levels was observed. In parental MUM-2C cells, only,15% of cells had catenin-positive junctions; in contrast, over 75% of 2C-ALC cells did. Together with our analysis of sh5 silenced cells, these data suggest that ALCAM expression is both necessary and sufficient to promote the recruitment of N-cadherin and -catenin to form adherens junctions in uveal melanoma cells. Cadherin-based Junctions are Disorganized in ALCAMsilenced Cells Another way in which ALCAM could influence tumor cell behavior is through the regulation of other adhesion molecules, particularly those that have been implicated in metastasis, such as classical cadherins. Several previous lines of evidence support such a hypothesis. First, a report by Tomita and colleagues described the coordinate recruitment of epithelial -cadherin and ALCAM to cell contacts upon transfection of alpha-catenin into prostate cancer cell lines that have lost this protein. Second, ALCAM has been shown to colocalize with both alpha-catenin and filamentous actin in MV3Tiam1 cells. Finally, ALCAM could be co-immunoprecipitated with VE-cadherin and N-cadherin in PVMEC cells, and has been reported to be present in the same lipid microdomain compartments as cadherins. We began by assessing the expression of cadherins in uveal melanoma cell lines. Both MUM-2B and MUM-2C expressed N-cadherin as well as -catenin; neither had detectable levels of E-cadherin. To determine whether ALCAM silencing affects adherens junctions, we compared N-cadherin and -catenin staining in sh5, sh6, and sh5rxd cells. In parental MUM-2B cells or in sh6 control cells, strong -catenin and N-cadherin staining was localized to cell-cell contacts that were also ALCAM-positive, and cells had a flattened, epithelioid shape. In contrast, sh5 silenced cells had disorganized -catenin and N-cadherin junctions, a more spindle-like shape, and often grew on top of each other. This phenotype was significantly rescued by reexpression of ALCAM in the sh5rxd cell line. Quantification showed that the percentage of cells with contiguous, strong -catenin-positive adherens junctions was AG-1478 reduced from nearly 75% in control lines 
to,25% in sh5. Neither silencing of ALCAM in sh5 nor its re-expression in sh5rxd appeared to affect levels of -catenin or N-cadherin expression. This phenomenon was not restricted to uveal melanoma cells. Transient transfection of HEK293 cells with an shRNA construct confirmed to silence ALCAM also resulted in reduced catenin localization to cell-cell contacts, and a lack of strong Discussion ALCAM has demonstrated functions PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/22205151 in many critical developmental processes such as hematopoiesis, neurite outgrowth, retinal ganglion cell targeting, and Tcell activation. ALCAM has also been implicated in pathological states, such as cancer metastasis, but its role remains somewhat confusing. ALCAM has been identified as a marker of metastasis in many tumor cell types, and yet in other cases it has been associated with inhibition of metastasis. Reports from the literature thus present a paradox regarding ALCAM’s relationship to tumor cell motility and invasiveness. For example, initial studies described a positive correlation between ALCAM expression and metastatic capacity