Tumor and Stem Cell Biology Production of Gastrointestinal Tumors inMice byModulating Latent TGF-b1 Activation

TGF-b and its signaling pathways are importantmediators in the suppression of cancers of the gastrointestinal tract. TGF-b is released from cells in a latent complex consisting of TGF-b, the TGF-b propeptide [latency associated protein (LAP)], and a latent TGF-b binding protein (LTBP).We previously generatedmice in which the LTBP-binding cysteine residues in LAP TGF-b1 were mutated to serine precluding covalent interactions with LTBP. These Tgfb1 mice develop multiorgan inflammation and tumors consistent with reduced TGF-b1 activity. To test whether further reduction in active TGF-b levels would yield additional tumors and a phenotype more similar to Tgfb1 / mice, we generated mice that express TGF-b1 and are deficient in either integrin b8 or TSP-1, known activators of latent TGF-b1. In addition, we generated mice that have one mutant allele and one null allele at the Tgfb1 locus, reasoning that these mice should synthesize half the total amount of TGF-b1 as Tgfb1 mice, and the amount of active TGF-b1 would be correspondingly decreased compared with Tgfb1 mice. These compound-mutant mice displayed more severe inflammation and higher tumor numbers than the parental Tgfb1 animals. The level of active TGF-b1 in compound mutant mice seemed to be decreased compared with Tgfb1 mice as determined from analyses of surrogate markers of active TGF-b, such as P-Smad2, C-Myc, KI-67, and markers of cell-cycle traverse. We conclude that these mutant mice provide a useful system for modulating TGF-b levels in a manner that determines tumor number and inflammation within the gastrointestinal tract. Cancer Res; 73(1); 459–68. 2012 AACR.