Objectives: RCAS1 is becoming a clinically relevant molecule in cancer biology. Its expression has been shown to correlate with overall survival in 15 types of cancer. RCAS1 expression also correlates with several clinicopathological parameters which reflect aggressive tumor characteristics. The concentration of RCAS1 in serum or pleural effusions is significantly higher in patients with cancer as compared to normal controls. Concerning the biological activity, RCAS1 induces apoptosis in peripheral lymphocytes and NK cells. The number of cells expressing vimentin significantly decreases in relation to the RCAS1 expression level in tumor stromal tissue. In addition, enhanced RCAS1 expression significantly promotes in vivo tumor growth via increased expression of VEGF. These findings suggest that RCAS1 may contribute to tumor progression by the escape from immune surveillance and connective tissue remodeling. We previously showed that RCAS1 is secreted by ectodomain shedding. Ectodomain shedding is an important regulatory step and affects the biological activity of membrane proteins. We here studied regarding (1) a key protease involved in RCAS1 shedding and (2) an influence of ectodomain shedding on RCAS1 function. Materials and Methods: (1) The key protease involved in RCAS1 shedding was investigated using three cell lines: cervical adenocarcinoma cell line SiSo, breast adenocarcinoma cell line MCF-7, and kidney fibroblast-like cell line COS-7. Both SiSo and MCF-7 express RCAS1, but RCAS1 secretion is undetectable in MCF-7. COS-7 does not express RCAS1. The protease expression was evaluated by microarray analysis and immnocytochemistry. The expression and secretion of RCAS1 were measured by using flow cytometry and ELISA after knockdown or introduction of protease expression. (2) The inhibition of growth in erythroleukemia cell line K562 and fibroblast cell line L cell, which express a putative RCAS1 receptor, was investigated. These cells were co-cultured with SiSo, MCF-7, or soluble RCAS1 to follow RCAS1 secretion in apoptosis initiation. Vimentin expression in L cells was assessed by Western blot after stimulation with RCAS1. Results: (1) Microarray analysis revealed that SiSo expressed MMP-28, ADAM9, and ADAM21 at significantly higher levels than did MCF-7. The association of RCAS1 and ADAM9 was detected by immunocytochemistry. Manipulation of ADAM9 expression revealed it to be a key protease for RCAS1 secretion. (2) Growth inhibition and apoptosis were induced by secreted but not membrane-anchored RCAS1. Vimentin expression diminished with its degradation after RCAS1 stimulation. Conclusions: Further exploration regarding the regulatory mechanisms involved in the conversion of membrane-anchored RCAS1 into its soluble form should aid the development of novel therapeutic strategies against human malignancies by targeting RCAS1.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2288.