We are interested in study the molecular mechanism of MUC18 (CD146)-mediated prostate cancer and melanoma metastasis. MUC18 is a cell adhesion molecule in the immunoglobulin gene super family. We were the first group to fin that huMUC18 expressed only in metastatic prostate cancer cells, but not in non-metastatic cancer cells. The level of MUC18 expression appeared to correlate with the increasing pathological grade of human prostate cancer. From this result, we concluded that huMUC18 might be a diagnostic marker for the early detection of the malignant potential of human prostate cancer. We have proposed a hypothesis that MUC18 may also mediate the metastasis of prostate cancers. To test this hypothesis, we have found that ectopic expression of MUC18 increases tumor-take as well as mediate metastasis of human prostate cancer cells to the seminal vesicles, the peri-aortic lymph nodes, ureter, and kidney. This shows that MUC18 plays an important role in causing human prostate cancer cells to metastasize to other organs, if they are injected orthotopically, but not subcutaneously. To further test our hypothesis above, we have been collaborating with Norman Greenberg on his TRAMP model and found that increased MUC18 expression in the TRAMP mice correlated with the malignant progression of prostate cancer in this transgenic mouse model. Currently we are in the process of defining the functional domains and the ligands and cofactors of huMUC18. We are also collaborating with Leland Chung¹s group on a bone metastasis xenograft model, and with Chris Gregory and Thomas Pretlow on their CWR22 xenographft model. We will also collaborate with Jeff Gordon on his neuroendocrine cells-derived prostate carcinoma transgenic mouse model. We have also cloned the genomic copy of the huMUC18 gene that contains the 5'-flanking transcription regulatory sequences for studying transcription factors and signal transduction mediators that regulate their expression in normal versus cancer cells. Methods used for the research include recombinant DNA methods, cell cloning, DNA sequencing, PCR, immunoblotting, Northern and Southern blotting, immunohistochemistry, differential gene expression, proteomics, protein-DNA interactions, tissue culture, and mouse models.

We also studied the role of moMUC18 in mediating the metastasis of melanoma cells in syngeneic mouse model. From molecular biological and immunological studies, we found that moMUC18 expression correlates with the metastatic ability of nine mouse melanoma cell lines. To further study the role of moMUC18 in mediating melanoma metastasis, we have transfected an expressible moMUC18 cDNA gene into a non-tumorigenic and non-metastatic melanoma cell line, K1735-clone 10, and two tumorigenic and low-metastatic melanoma cell lines, K1735-clones 3 and 9, and obtained G418-resistant clones that express high levels of MUC18. We inject the cells from the MUC18-high-expression clone derived from K1735-10 into syngeneic mice via i.v. and s.c. routes to study their pulmonary metastasis in vivo. We have found that moMUC18 expression definitely promotes melanoma cells to have pulmonary metastasis, but the effect is dependent upon the intrinsic properties of the melanoma cells. MoMUC18 expression may have a negative effect on melanoma growth in vivo. We conclude that moMUC18 expression may mediate later steps of, but not early steps of melanoma pulmonary metastasis that required cofactors. Currently we are in the process of defining the functional domains and the ligands and cofactors of moMUC18.

[wu@microbio.emory.edu ]