Enforced Expression of METCAM/MUC18 Increases Tumorigenesis of Human Prostate Cancer LNCaP Cells in Nude Mice

Purpose: Metastasis cell adhesion molecule/MUC18, a cell adhesion molecule in the Ig-like gene super family, is a key determinant in prostate cancer cell progression. However, the mechanisms by which human metastasis cell adhesion molecule/MUC18 stimulates progression are poorly understood. To investigate this and determine whether human metastasis cell adhesion molecule/MUC18 may act as a possible tumor progression gene, we studied the effect of its enforced expression on LNCaP cell tumorigenesis. Materials and Methods: We subcutaneously co-injected a metastasis cell adhesion molecule/MUC18 expressing LNCaP clone and control clones/cells with Matrigel T into nude mice, observed tumor formation of these cells and measured tumors at different times. To understand the mechanisms we also determined the expression of several downstream key effectors of metastasis cell adhesion molecule/MUC18 in subcutaneous tumors and compared them to those in previously obtained orthotopic (prostatic) tumors. Results: Tumors derived from human metastasis cell adhesion molecule/MUC18 expressing LNCaP clones/cells appeared about 18 days earlier than the empty vector transfected clone/cells. Enforced expression of human metastasis cell adhesion molecule/MUC18 also increased tumor take 2-fold, tumorigenicity 10 to 12-fold and final tumor weight 5-fold. Enforced expression appeared to render the cells with increased levels of the proliferation indexes Ki67 and proliferating cell nuclear antigen, the survival index phospho-AKT, and the angiogenesis indexes vascular endothelial growth factor, vascular endothelial growth factor receptor 2 and CD31. However, it did not significantly render the cells with altered levels of various apoptosis indexes. Conclusions: Enforced expression of human metastasis cell adhesion molecule/MUC18 increases prostate tumorigenesis in vivo and may affect the process by increasing proliferation, up-regulating the AKT survival pathway, and augmenting the angiogenic ability of prostate cancer cells.