Mice deficient in MIM expression are predisposed to lymphomagenesis

Missing in metastasis (MIM) is a member of newly emerged inverse Bin-Amphiphysin-Rvs (BAR) domain protein family and a putative metastasis suppressor. Although reduced MIM expression has been associated with bladder, breast and gastric cancers, evidence for the role of MIM in tumor progression remains scarce and controversial. Herein we characterized a MIM knockout mouse strain and observed that MIM-deficient mice often developed enlarged spleens. Autopsy and histological analysis revealed that nearly 78% of MIM(-/-) mice developed tumors with features similar to diffuse large B lymphoma during a period from 1 to 2 years. MIM(-/-) mice also exhibited abnormal distribution of B cells in lymphoid organs with decrease in the spleen but increase in the bone marrow and the peripheral blood. Furthermore, the bone marrow of MIM(-/-) mice contained a higher percentage of pre-B2 cells but fewer immature B-cells than wild-type mice. In response to CXCL13, a B-cell chemokine released from splenic stromal cells, MIM-deficient B-cells did not undergo chemotaxis or morphological changes in response to the chemokine and also did not internalize CXCR5, the receptor of CXCL13. Microarray analyses demonstrated that MIM is the only member of the I-BAR domain family that was highly expressed in human B cells. However, low or absent MIM expression was common in either primary B-cell malignancies or established B-cell acute lymphocytic leukemia or lymphomas. Thus, our data demonstrate for the first time an important role for MIM in B-cell development and suggest that predisposition of MIM-null mice to lymphomagenesis may involve aberrant interactions between B lineage cells and the lymphoid microenvironment.