Tumor-derived macrophage migration inhibitory factor promotes an autocrine loop that enhances renal cell carcinoma

Abstract

The macrophage migration inhibitory factor (MIF) is a hypoxia regulated gene that has a variety of tumorigenic functions. In clear cell renal carcinoma (CCRC), hypoxic signaling is constitutively active because of the frequent loss of function of the von Hippel-Lindau tumor suppressor protein. We therefore sought to assess the expression of MIF in CCRC and its biological functions. We stained tumor tissue microarrays comprising sections of 128 CCRC tumors and found MIF to be moderately or highly expressed in >98%. MIF expression was further found to be dramatically elevated in blood plasma of individuals with CCRC compared with healthy controls, suggesting that measurement of MIF levels in the blood may have utility as a diagnostic marker in CCRC. At a functional level, MIF has been reported to engage the CD74 and CD44 receptors and induce signal transduction. In CCRC cell lines, depletion of MIF, CD74 or CD44 by small hairpin RNA led to a significant reduction in growth rate, and clonogenic survival, coinciding with the degree of knockdown. Interruption of the MIF pathway also decreased tumorigenic potential. Biochemically, we found that in CCRC cells MIF signaling leads to activation of the mitogen-activated protein kinase pathway and to Src phosphorylation, which is critical for regulation of p27. Together, our studies establish MIF as a protumorigenic signaling molecule that functions in an autocrine fashion to promote renal cell carcinoma and may be useful as a minimally invasive marker of disease status.

Dysregulated D-dopachrome Tautomerase, a Hypoxia-inducible Factor-dependent Gene, Cooperates with Macrophage Migration Inhibitory Factor in Renal Tumorigenesis

“…6A). Interestingly, Akt phosphorylation was unaffected by single knockdown of either DDT or MIF, consistent with our previous findings (17). However, dual knockdown led to significant decreases in Akt phosphor-ylation.…”

“…However, our group has previously noted the absence of death in renal carcinoma cells upon MIF inhibition (17). Together, these data suggest that DDT promotes growth and clonogenic survival signaling of ccRCC cells.…”

“…Six fields of cell-free wounds for each cell type were recorded at ϫ100 magnification immediately after the scratch and at the indicated time points. To quantify the migration of cells, the images were analyzed by TScratch software (17). The presented images are representatives of triplicate experiments with a similar outcome.…”

“…When progrowth signaling was assessed, DDT-deficient cells showed decreased ERK phosphorylation and a concurrent increase in p27, the cell cycle-dependent kinase inhibitor (Fig. 4A), much like what we have found previously for MIF knockdown (17). We then assessed the growth characteristics of ccRCC cells that lack DDT expression by proliferation assays and by clonogenic survival assays.…”

“…MIF is directly associated with the growth of several types of carcinomas, and anti-MIF therapy with immunoglobulins and antisense oligonucleotides has been shown to have antitumorigenic effects (15,16). Prior studies from our laboratory demonstrated MIF to be a protumorigenic signaling molecule that functions in an autocrine fashion to promote ccRCC tumor growth (17). We observed the expression of MIF in the vast majority of ccRCC tumor samples and found MIF to be elevated in the blood plasma of patients with renal tumors compared with healthy controls.…”