Mxi1 regulates cell proliferation through insulin-like growth factor binding protein-3

Highlights: ► Mxi1 regulates cell proliferation. ► Expression of IGFBP-3 is regulated by Mxi1. ► Inactivation of Mxi1 reduces IGFBP-3 expression in vitro and in vivo. -- Abstract: Mxi1, a member of the Myc–Max–Mad network, is an antagonist of the c-Myc oncogene and is associated with excessive cell proliferation. Abnormal cell proliferation and tumorigenesis are observed in organs of Mxi1−/− mice. However, the Mxi1-reltaed mechanism of proliferation is unclear. The present study utilized microarray analysis using Mxi1 mouse embryonic fibroblasts (MEFs) to identify genes associated with cell proliferation. Among these genes, insulin-like growth factor binding protein-3 (IGFBP-3) was selected as a candidate gene for real-time PCR to ascertain whether IGFBP-3 expression is regulated by Mxi1. Expression of IGFBP-3 was decreased in Mxi1−/− MEFs and Mxi1−/− mice, and the gene was regulated by Mxi1 in Mxi1 MEFs. Furthermore, proliferation pathways related to IGFBP-3 were regulated in Mxi1−/− mice compared to Mxi1+/+ mice. To determine the effect of Mxi1 inactivation on the induction of cell proliferation, a proliferation assay is performed in both Mxi1 MEFs and Mxi1 mice. Cell viability was regulated by Mxi1 in Mxi1 MEFs and number of PCNA-positive cells was increased in Mxi1−/− mice compared to Mxi1+/+ mice. Moreover, the IGFBP-3 level was decreased in proliferation defect regions in Mxi1−/− mice. The results support the suggestion that inactivation of Mxi1 has a positive effect on cell proliferation by down-regulating IGFBP-3.