Role of novel gene LIX1L in epithelial-mesenchymal transition

Division Of Basic Sciences - Nci

Investigators

Abstract

In a recent study of gene expression correlations in the NCI-60 human cancer cell lines, we discovered that a novel gene of unknown function, LIX1L, was the most highly expression correlated gene for genes that promote the epithelial-mesenchymal transition (EMT) (Kohn et al 2014 PLOS ONE). We therefore initiated laboratory investigations of the functions of this gene, especially in relationship to the EMT. As a result of experiments summarized below, we came to the surprising conclusion that LIX1L, although expression correlated with EMT-promoting genes, behaves as if it inhibits the EMT! First we verified in the database of the Cancer Cell Line Encyclopedia (CCLE, Broad Institute) and the human cancer tissue database of The Cancer Genome Anatomy project (TCGA) that LIX1L expression was indeed highly correlated with the expression of known EMT-promoting genes, such as ZEB1, SNAI2/slug, and VIM. After failing to suppress LIX1L expression adequately by means of siRNA, we generated LIX1L knockouts of mesenchymal-like human cancer cell lines using the CRISPR method. In cell migration and invasion assays we were surprised to find that, rather than the expected inhibition, LIX1L knockout actually enhanced cell migration and invasion. Moreover, rather than inhibiting the expression of ZEB1 and VIM, the knockout lines showed increased expression of these EMT-promoting genes. We were forced to strongly suspect that LIX1L, despite its expression correlation with known EMT-promoting genes, functions to suppress the EMT. Our current hypothesis is that LIX1L functions as an EMT regulator that assures existence of a valid signal before cells are committed to an EMT. Examining the gene structure of LIX1L disclosed a double strand RNA binding domain and features suggestive of a histone lysine methyltransferase. We are testing whether LIX1L binds to or affects the degradation of RNAs, such as VIM mRNA.