| Summary: | MTBP is implicated in cell cycle progression, DNA replication, and cancer metastasis. However, the function of MTBP remains enigmatic and is dependent on cellular contexts and its cellular localization. To understand the in vivo physiological role of MTBP, it is important to generate <i>Mtbp</i> knockout mice. However, complete deletion of the <i>Mtbp</i> gene in mice results in early embryonic lethality, while its heterozygous deletion shows modest biological phenotypes, including enhanced cancer metastasis. To overcome this and better characterize the in vivo physiological function of MTBP, we, for the first time, generated mice that carry an <i>Mtbp</i> hypomorphic allele (<i>Mtbp<sup>H</sup></i>) in which Mtbp protein is expressed at approximately 30% of that in the wild-type allele. We treated wild-type, <i>Mtbp<sup>+/−</sup></i>, and <i>Mtbp<sup>H/−</sup></i> mice with a liver carcinogen, diethylnitrosamine (DEN), and found that the <i>Mtbp<sup>H/−</sup></i> mice showed worse overall survival when compared to the wild-type mice. Consistent with previous reports using human liver cancer cells, mouse embryonic fibroblasts (MEFs) from the <i>Mtbp<sup>H/−</sup></i> mice showed an increase in the nuclear localization of p-Erk1/2 and migratory potential. Thus, <i>Mtbp<sup>H/−</sup></i> mice and cells from <i>Mtbp<sup>H/−</sup></i> mice are valuable to understand the in vivo physiological role of Mtbp and validate the diverse functions of MTBP that have been observed in human cells.
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