Abstract 3619: Specificity of the human autoantibody response against the stress oncoprotein LEDGF/p75

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Overexpression of self-antigens in malignant tissues may lead to the elicitation of autoantibodies (AAbs) that could serve as tools for the characterization of novel tumor-associated antigens (TAA). We and others have demonstrated that the stress survival protein LEDGF/p75 (lens epithelium derived growth factor p75, also known as DFS70, dense fine speckled nuclear antigen of 70 kD) is targeted by IgG AAbs in some patients with prostate cancer (PCa), leukemia, non-rheumatic inflammatory conditions, and even in healthy individuals. These AAbs are thought to be sensors of events associated with malignancy or inflammation, or protective antibodies that influence host immunosurveillance against LEDGF/p75-overexpressing tumors. LEDGF/p75 is overexpressed in cancer cells and tumors of the prostate, colon, and thyroid, and promotes chemoresistance. A better understanding of the significance of the autoantibody response to LEDGF/p75 requires establishing its specificity. Our objective is to determine whether this response, particularly in healthy individuals, is a component of the host immunosurveillance of LEDGF/p75-overexpressing tumors. Recent studies by our group showed that LEDGFp75 interacts with MeCP2 (methyl CpG binding protein 2) in PCa cells to influence transcriptional activation of Hsp27. Interestingly, non-human antibodies against MeCP2 produce an identical molecular weight and dense fine speckled (DFS) nuclear distribution as AAbs to LEDGF/p75, as assessed by immunoblotting and indirect immunofluorescence (IIF) microscopy, respectively, in cancer cells. These observations led us to determine if human AAbs producing the DFS-IIF pattern, considered specific for LEDGF/p75, are exclusive to this protein or may also target MeCP2. We screened in immunoblots of PC3 cell lysates over 90 human sera producing the LEDGF/p75-associated DFS-IIF pattern to determine if they possess dual reactivity against the two antigens, or are specific for one or the other. Initial results showed that the sera exhibited different reactivity strengths against a 75 kD protein. A group of 20 strongly reacting sera was selected for subsequent studies. Immunoblots of lysates from PC3 cells with LEDGF/p75 knockdown showed that the selected sera did not recognize the 75 kD band, indicating their specificity for LEDGF/p75. We also confirmed the specificity of these sera by demonstrating that they recognized the signature caspase-mediated cleavage pattern of LEDGF/p75 in PC3 cells treated with the apoptosis inducing drug TRAIL. These findings suggest that human AAbs producing the DFS-IIF pattern are specific for LEDGF/p75 and are not reactive with its interacting partner MeCP2. These results enhance our understanding of the specificity of the autoantibody response to this TAA, and have implications for the future development of LEDGF/p75-based vaccines to induce immunity to LEDGF/p75-overexpressing tumors. Citation Format: Anamika Basu, Greisha L. Ortiz-Hernandez, Carlos A. Casiano. Specificity of the human autoantibody response against the stress oncoprotein LEDGF/p75. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3619. doi:10.1158/1538-7445.AM2014-3619