Identification of an Upstream Enhancer in the Mouse Lamininα1 Gene Defining Its High Level of Expression in Parietal Endoderm Cells

Laminin-1 is the major component of the embryonic basement membrane and consists of α1, β1, and γ1 chains. The expression of laminin-1 is induced in mouse F9 embryonal carcinoma cells upon differentiation into parietal endoderm through transcriptional up-regulation of the genes encoding these subunits. Here, we identified a 435-bp enhancer in the 5′-flanking region of the mouse laminin α1 (LAMA1) gene that activated its transcription in a differentiation-dependent manner. This enhancer was also active in PYS-2 parietal yolk sac-derived cells but not in NIH/3T3 fibroblasts, indicating that it was a parietal endoderm-specific enhancer. This enhancer was also active in Engelbreth-Holm-Swarm (EHS) tumor-derived cells characterized by excessive production of laminin-1 and other basement membrane components, suggesting that EHS tumors have a transcriptional control mechanism similar to that of parietal endoderm cells. Electrophoretic mobility shift analyses revealed four protein binding sites (PBS1-PBS4) in the 435-bp region. However, these DNA-binding proteins were detected not only in parietal endoderm cells (i.e. differentiated F9 cells, PYS-2 cells, and EHS tumor-derived cells) but also in undifferentiated F9 cells and NIH/3T3 cells. Mutational analyses revealed that three of these binding sites (PBS2, PBS3, and PBS4) function synergistically to confer the parietal endoderm-specific enhancer activity. The proteins binding to PBS2 and PBS4 were identified as the Sp1/Sp3 family of transcription factors and YY1, respectively.This research was originally published in the Journal of Biological Chemistry. Tomoaki Niimi, Yoshitaka Hayashi and Kiyotoshi Sekiguchi. Identification of an Upstream Enhancer in the Mouse Lamininα1 Gene Defining Its High Level of Expression in Parietal Endoderm Cells. J. Biol. Chem. 2003; 278: 9332–9338 © the American Society for Biochemistry and Molecular Biolog