Progression of cancer to the metastatic state involves multiple cellular and genetic changes. Using somatic cell hybridization, we have demonstrated that acquisition of metastatic ability requires both the loss of metastasis suppressor functions and the activation of oncogenes. We have cloned a gene, termed KAI1, that can suppress the metastatic ability of a rat prostatic cancer cell line without affecting the growth rate of the primary tumor. We are investigating the ability of this gene to effect the metastasis of human prostate and breast cancer cell lines. KAI1 encodes a 267 amino acid protein with four hydrophobic transmembrane domains and a large extracellular domain with three potential N- glycosylation sites.We have found that KAI1 expression is high in normal prostate and breast cells, but is dramatically lower in cancer cell lines derived from metastatic tumors. We have also found reduced or altered protein expression in human bladder, endometrial, lung, ovarian, and melanoma cancer cell lines. We are developing new antibody reagents to allow study of KAI1 expression in archived tissue sections. We have collected matched pairs of normal prostate and tumors, as well as primary breast and lymph node metastases from breast cancer patients to investigate whether KAI1 expression can be used to predict metastatic ability of primary cancers. It does not appear that mutations in the KAI1 gene can account for the decreased expression that is observed; we are currently investigating other hypotheses that would cause KAI1 loss of function. These studies include alterations in and mechanisms leading to unstable mRNA and protein expression. We are also identifying KAI1 binding partners in order to determine how they may regulate KAI1 function. Finally, we are developing in vivo metastasis assays and are using various DNA expression vectors to test the ability of KAI1 to suppress metastasis in vivo; possibly KAI may be used in gene therapy protocols to prevent the spread of cancer.
