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Activated leukocyte cell adhesion molecule (ALCAM/CD166) is a progression marker of a variety of cancers, including melanoma, and is a marker for mesenchymal stem cells. ALCAM expression triggers matrix metalloproteinase activity and correlates with the transition between superficial melanoma growth and deep dermal invasion in vivo. We previously showed that manipulating ALCAM functionality could both decrease and increase melanoma invasion, depending on the manner by which ALCAM function was altered. How ALCAM exerts these opposing invasive phenotypes remained elusive. In the present study, we analyzed differences in melanoma cell gene expression in two- and three-dimensional cultures as function of ALCAM-mediated adhesion. We identified a cluster of genes highly responsive to ALCAM functionality and relevant for melanoma invasion. This cluster is characterized by known invasion-related genes similar to L1 neuronal cell adhesion molecule and showed a remarkable induction of several innate immune genes. Unexpectedly, we identified major variations in the expression of genes related to an immunological response when modulating ALCAM function, including complement factors C1r and C1s. The expression and function of these proteinases were confirmed in protein assays and in vivo. Together, our results demonstrate a link between ALCAM functionality and the immune transcriptome, and support the assumption that ALCAM-ALCAM interactions could function as a cell signaling complex to promote melanoma tumor invasion.

Progression of human cutaneous primary melanoma is, among others, accompanied by de novo expression of activated leukocyte cell adhesion molecule (ALCAM/CD166) and enhanced activity of proteolytic cascades in the invasive, vertical growth phase (VGP) of lesions. The homophilic cell adhesion function of wild-type ALCAM mediates homotypic clustering of melanoma cells and would, thus, antagonize cell release from the primary tumor, an early prerequisite for metastasis. Stable transfection of a transmembrane, amino-terminally truncated ALCAM (DeltaN-ALCAM) into metastatic cells diminished cell clustering mediated by wild-type ALCAM. We have addressed the biological effects of DeltaN-ALCAM on tumorigenicity and found that the relief of cell clustering constraints promoted motility in vitro and the transition from expansive tumor growth to tissue invasion in reconstructed skin in culture. In a transplant tumor model, the changes were reflected in reduced subcutaneous tumor growth and in accelerated, spontaneous lung metastasis. These data indicate that the intact cell adhesion function of ALCAM may both favor primary tumor growth and represent a rate-limiting step for tissue invasion from VGP melanoma. ALCAM induction could, thus, provide an attractive target for proteolysis as a part of a more complex cellular program that couples growth and migration and facilitates dissemination.