Abstract
BackgroundThe L1 cell adhesion molecule (L1CAM) was originally identified as a neural adhesion molecule involved in axon guidance. In many human epithelial carcinomas L1CAM is overexpressed and thereby augments cell motility, invasion and metastasis formation. L1CAM positive carcinomas are associated with bad prognosis. Recent data point out that L1CAM is regulated in a fashion similar to epithelial-mesenchymal transition (EMT). Previous studies have implied the transcription factors Slug and/or Ī²-catenin in L1CAM transcriptional regulation. However, the regulation of human L1CAM expression at the transcriptional level is not well understood.ResultsTo better understand the molecular basis of L1CAM transcriptional regulation, we carried out a detailed characterization of the human L1CAM promoter. We identified two transcription start sites, the first in front of a non-translated exon 0 (promoter 1) and the other next to the first protein-coding exon 1 (promoter 2). Both sites could be verified in endometrial carcinoma (EC) cell lines and appear to be used in a cell-type specific manner. The two identified promoter regions showed activity in luciferase reporter assays. Chromatin-IP analyses confirmed the in silico predicted E-boxes, binding sites for transcription factors Snail and Slug, as well as Lef-1 sites, which are related to Ī²-catenin-mediated transcriptional regulation, in both promoters. Overexpression of Ī²-catenin exclusively augmented activity of promoter 1 whereas Slug enhanced promoter 1 and 2 activity suggesting that both promoters can be active. Overexpression of Ī²-catenin or Slug could upregulate L1CAM expression in a cell-type specific manner.ConclusionsOur results, for the first time, provide evidence that the L1CAM gene has two functionally active promoter sites that are used in a cell-type specific manner. Slug and Ī²-catenin are involved L1CAM transcriptional regulation. Nevertheless, Slug rather than Ī²-catenin levels are correlated with L1CAM expression in EC cell lines. Our findings suggest that the L1CAM transcriptional regulation is more complex than anticipated and this study provides the basis for a better understanding of L1CAM regulation in non-neuronal/tumor cells.
Highlights
The L1 cell adhesion molecule (L1CAM) was originally identified as a neural adhesion molecule involved in axon guidance
To confirm a role of these transcription factors in endometrial carcinoma (EC), we examined whether overexpression of Slug or a stabilised, constitutively active form of b-catenin (S33Y) in EC cell lines resulted in augmented L1CAM levels
Identification of in situ transcription start sites by 5ā²-RLMRACE we investigated the site of transcriptional initiation of the human L1CAM gene in endometrial carcinoma cell lines
Summary
The L1 cell adhesion molecule (L1CAM) was originally identified as a neural adhesion molecule involved in axon guidance. In many human epithelial carcinomas L1CAM is overexpressed and thereby augments cell motility, invasion and metastasis formation. Work from experimental systems showed that L1CAM augments tumour growth in NOD/SCID mice, enhances cell motility on extracellular matrix proteins and increases matrigel invasion [10,11,12,13]. Other studies reported L1CAMdependent gene expression signatures, metastasis formation [13,14,15] and an augmented resistance to apoptotic stimuli [16,17]. This raises the important question how L1CAM expression is regulated in human tumours
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