The bone morphogenetic protein antagonist Gremlin is overexpressed in human malignant mesothelioma

Gremlin is a member of the bone morphogenetic protein (BMP) antagonist family and its antagonistic effect is likely through direct binding to BMP proteins. As an antagonist of BMP, Gremlin plays a role in regulating organogenesis, body patterning and tissue differentiation. Recent studies have shown a deregulation of Gremlin in several types of human cancers. However, the role of Gremlin in human malignant mesothelioma (MM) is still unknown. In this study, we investigated the expression of Gremlin in human MM. We found that Gremlin mRNA and protein were both overexpressed in the majority of primary MM tissue samples that we examined. We also observed high level expression of the Gremlin gene in 4 of the 6 MM cell lines. Consistently, we found that the Gremlin promoter activity was significantly elevated in those MM cell lines expressing the Gremlin gene. On the other hand, no activity of the Gremlin promoter was detected in the two MM cell lines lacking Gremlin expression. Moreover, to examine the functional significance of the Gremlin overexpression in MM, we used shRNA to knock down Gremlin expression in MM cell lines expressing Gremlin and found that inhibition of Gremlin expression significantly suppressed proliferation of those MM cells. Taken together, our results suggest that the BMP antagonist Gremlin is overexpressed in MM and that aberrant activation of Gremlin may play a critical role in the tumorigenesis of human MM.