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Deleted in malignant brain tumors 1 (DMBT1) is a secreted glycoprotein displaying a broad bacterial-binding spectrum. Recent functional and genetic studies linked DMBT1 to the suppression of LPS-induced TLR4-mediated NF-jB activation and to the pathogenesis of Crohn's disease. Here, we aimed at unraveling the molecular basis of its function in mucosal protection and of its broad pathogen-binding specificity. We report that DMBT1 directly interacts with dextran sulfate sodium (DSS) and carrageenan, a structurally similar sulfated polysaccharide, which is used as a texturizer and thickener in human dietary products. However, binding of DMBT1 does not reduce the cytotoxic effects of these agents to intestinal epithelial cells in vitro. DSS and carrageenan compete for DMBT1-mediated bacterial aggregation via interaction with its bacterial-recognition motif. Competition and ELISA studies identify poly-sulfated and poly-phosphorylated structures as ligands for this recognition motif, such as heparansulfate, LPS, and lipoteichoic acid. Dose-response studies in Dmbt1 À/À and Dmbt1 1/1 mice utilizing the DSS-induced colitis model demonstrate a differential response only to low but not to high DSS doses. We propose that DMBT1 functions as pattern-recognition molecule for poly-sulfated and polyphosphorylated ligands providing a molecular basis for its broad bacterial-binding specificity and its inhibitory effects on LPS-induced TLR4-mediated NF-jB activation. IntroductionCrohn's disease (CD) is one of the major subtypes of inflammatory bowel disease (IBD) and is thought to emerge through the complex interplay of various environmental and genetic factors. Nutritional compounds, bacterial pathogens, and the endogenous bacterial microflora have been considered as environmental factors contributing to the etiology of CD [1,2]. The putative involvement of bacteria is also reflected at the level of susceptibility genes for CD, of which some appear to exert important functions in innate mucosal immunity [1,3,4]. Genetic variants of the gene nucleotide-binding oligomerization domain 2/Caspase recruitment domain 15 (NOD2/CARD15) at the IBD1 locus, for example, have been shown to be associated with an increased risk for CD [5][6][7]. NOD2 encodes an intracellular pattern-recognition receptor with specificity for muramyldipeptide, and is thought to function in the sensing of intracellular bacteria [8]. Dysfunction of NOD2 may result in altered NF-kB signaling and attenuated expression of secreted anti-bacterial factors such as a-defensin-2 [9-11]. In addition, decreased copy numbers of the b-defensin-4 gene DEFB4 (HBD-2) at chromosome 8p23.1 have been reported to result in reduced DEFB4 expression levels and to confer an increased risk for CD [4].Recent studies demonstrated that deleted in malignant brain tumors 1 (DMBT1) is up-regulated in the inflamed mucosa of CD patients with normal NOD2 but not in those with the frequent CD-associated L1007fsinsC mutation in NOD2 [12,13]. The DMBT1 gene locates at human chromosome 10q26.13 and ...

Deleted in malignant brain tumors 1 (DMBT1) has been proposed as a candidate tumor suppressor for brain and epithelial cancer. Initial studies suggested loss of expression rather than mutation as the predominant mode of DMBT1 inactivation. However, in situ studies in lung cancer demonstrated highly sophisticated changes of DMBT1 expression and localization, pointing to a chronological order of events. Here we report on the investigation of DMBT1 in breast cancer in order to test whether these principles might also be attributable to other tumor types. Comprehensive mutational analyses did not uncover unambiguous inactivating DMBT1 mutations in breast cancer. Expression analyses in the human and mouse mammary glands pointed to the necessity of DMBT1 induction. While age-dependent and hormonal effects could be ruled out, 9 of 10 mice showed induction of Dmbt1 expression after administration of the carcinogen 7,12-dimethybenz(alpha)anthracene prior to the onset of tumorigenesis or other histopathological changes. DMBT1 displayed significant up-regulation in human tumor-flanking tissues compared to in normal breast tissues (P < 0.05). However, the breast tumor cells displayed a switch from lumenal secretion to secretion to the extracellular matrix and a significant down-regulation compared to that in matched normal flanking tissues (P < 0.01). We concluded that loss of expression also is the predominant mode of DMBT1 inactivation in breast cancer. The dynamic behavior of DMBT1 in lung carcinoma is fully reflected in breast cancer, which suggests that this behavior might be common to tumor types arising from monolayered epithelia.