MNX1 Promotes Invasive Progression Of Breast Ductal Carcinoma In Situ By Regulating MMP-1

With the wide application of mammography screening,the diagnostic rate of ductal carcinoma in situ(DCIS)is obviously increased.About 25%–50% of DCIS lesions would progress to invasive breast cancer(IBC)if left it untreated.This means that,in theory,some patients with DCIS need prompt surgical treatment,while others can be observed for a long time,but we still cannot identify which DCIS lesions will develop into IBC lesions.The transformation mechanism of DCIS into IBC is still not clear,so it is very important to explore the transformation mechanism and find the key targets in the transformation process.We previously made a bioinformatics analysis of the GEO database and found that the motor neuron and pancreas homeobox 1(MNX1)expression was increased gradually from normal mammary gland to DCIS then IBC.This study aims to clarify the biological significance of MNX1 in the transformation from DCIS to IBC.In this study,we confirmed that MNX1 expression level gradually increased from normal breast tissue to DCIS tissue,and then from DCIS tissue to IBC tissue by using immunohistochemistry assay.From cell level,we found that the expression level of MNX1 also increased gradually from normal breast epithelial MCF-10 A cells to ductal carcinoma in situ SUM225 cells,and from SUM225 cells to invasive breast cancer MCF-7 and ZR-75-1 cells.This suggests that MNX1 may be involved in the transition process from DCIS to IBC.Subsequently,we transfected MNX1-sh RNA and MNX1-overexpressed plasmids into SUM225 cells and invasive breast cancer MCF-7 and ZR-75-1 cells using lentivirus infection.The 3D organoid culture assay showed that MNX1 knockdown inhibited breast cancer cell line MCF-7,SUM225 and ZR-75-1 cells spheroid invasion in vitro.In contrast,MNX1 overexpression promoted SUM225 and ZR-75-1 cells spheroid invasion.Furthermore,in the Mouse Intraductal Xenografts model(MIND),upregulation of MNX1 can promote the formation of DCIS and the transition from DCIS to IBC.Therefore,we hypothesize that MNX1 can promote the invasive progression of DCIS.Moreover,we found that when MNX1 was knockdown,the m RNA and protein expression levels of MMP1 were decreased in SUM225 and ZR-75-1 cells,while overexpression of MNX1 increased the expression level of MMP1 in these cells.To further verify,we transfected MMP1-sh RNA into SUM225 cells to block the up-regulation of MMP1 caused by overexpression of MNX1.The 3D organoid culture assay and MIND assay were used to detect the invasion ability of transfected SUM225 cells.The results showed that the ability to promote the formation of DCIS and the conversion of DCIS to IBC induced by up-regulation of MNX1 was partially eliminated by down-regulation of MMP1.This suggests that MNX1 may promote the conversion of DCIS to IBC by upregulating MMP1,but the specific mechanism of how it regulates MMP1 still needs to be further studied.In conclusion,our data suggest that MNX1 can promote the invasion ability of DCIS cells in vivo and in vitro,and it participates in the process of invasive progression of DCIS to IBC by regulating MMP1.Taken together,our results indicate that MNX1 is a potential biomolecular marker for the identification of invasive progression of DCIS to IBC.