Further evidence for increased macrophage migration inhibitory factor expression in prostate cancer

Katherine L Meyer-Siegler,Pedro L Vera,Kenneth A Iczkowski

doi:10.1186/1471-2407-5-73

Abstract

BackgroundMacrophage migration inhibitory factor (MIF) is a cytokine associated with prostate cancer, based on histologic evidence and circulating (serum) levels.Recent studies from another laboratory failed to document these results. This study's aims were to extend and confirm our previous data, as well as to define possible mechanisms for the discrepant results. Additional aims were to examine MIF expression, as well as the location of MIF's receptor, CD74, in human prostatic adenocarcinoma compared to matched benign prostate.MethodsMIF amounts were determined in random serum samples remaining following routine PSA screening by ELISA. Native, denaturing and reducing polyacrylamide gels and Western blot analyses determined the MIF form in serum. Prostate tissue arrays were processed for MIF in situ hybridization and immunohistochemistry for MIF and CD74. MIF released into culture medium from normal epithelial, LNCaP and PC-3 cells was detected by Western blot analysis.ResultsMedian serum MIF amounts were significantly elevated in prostate cancer patients (5.87 ± 3.91 ng/ml; ± interquartile range; n = 115) compared with patients with no documented diagnosis of prostate cancer (2.19 ± 2.65 ng/ml; n = 158). ELISA diluent reagents that included bovine serum albumin (BSA) significantly reduced MIF serum detection (p < 0.01). MIF mRNA was localized to prostatic epithelium in all samples, but cancer showed statistically greater MIF expression. MIF and its receptor (CD74) were localized to prostatic epithelium. Increased secreted MIF was detected in culture medium from prostate cancer cell lines (LNCaP and PC-3).ConclusionIncreased serum MIF was associated with prostate cancer. Diluent reagents that included BSA resulted in MIF serum immunoassay interference. In addition, significant amounts of complexed MIF (180 kDa under denaturing conditions by Western blot) found in the serum do not bind to the MIF capture antibody. Increased MIF mRNA expression was observed in prostatic adenocarcinoma compared to benign tissue from matched samples, supporting our earlier finding of increased MIF gene expression in prostate cancer.

Highlights

Macrophage migration inhibitory factor (MIF) is a cytokine associated with prostate cancer, based on histologic evidence and circulating levels.Recent studies from another laboratory failed to document these results
Increased MIF mRNA expression was observed in prostatic adenocarcinoma compared to benign tissue from matched samples, supporting our earlier finding of increased MIF gene expression in prostate cancer
The objectives of this study are: (1) to confirm and extend our previous serum findings by analyzing serum samples remaining following routine serum PSA analysis from both prostate cancer and non-prostate cancer patients; (2) to identify potential confounds within the ELISA protocol that may account for the contradictory findings reported [14]; (3) to localize, quantify, and compare MIF mRNA and protein amounts in matched cancer and benign biopsy samples using commercially available tissue arrays; (4) to localize the MIF receptor, CD74, within prostate tissue and (5) to compare MIF secretion by normal prostate epithelial cells and prostate cancer cells in vitro

Summary

Introduction

Macrophage migration inhibitory factor (MIF) is a cytokine associated with prostate cancer, based on histologic evidence and circulating (serum) levels. Recent studies from another laboratory failed to document these results. Macrophage migration inhibitory factor (MIF) is a cytokine initially isolated based upon its ability to halt the in vitro random migration of macrophages [1,2]. It was defined as a proinflammatory cytokine with a key regulatory role in inflammation and both specific and nonspecific immunity [3]. MIF is associated with cancer angiogenesis, progression, and metastasis, the exact mechanism of this cytokine's action is uncertain since a receptor for MIF has only recently been identified as the cell surface form of the invariant chain (CD74) [11]

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