The transforming growth factor-beta (TGF-ß) mediates acquisition of a mesenchymal stem cell-like phenotype in human liver cells.

ABSTRACT

Transforming growth factor-beta (TGF-ß) mediates several and sometime opposite effects in epithelial cells, inducing growth inhibition, and apoptosis but also promoting an epithelial to mesenchymal transition (EMT) process, which enhances cell migration and invasion. TGF-ß plays relevant roles in different liver pathologies; however, very few is known about its specific signaling and cellular effects in human primary hepatocytes. Here we show that TGF-ß inhibits proliferation and induces pro-apoptotic genes (such as BMF or BIM) in primary cultures of human fetal hepatocytes (HFH), but also up-regulates anti-apoptotic genes, such as BCL-XL and XIAP. Inhibition of the epidermal growth factor receptor (EGFR), using gefitinib, abrogates the increase in the expression of the anti-apoptotic genes and significantly enhances cell death. Simultaneously, TGF-ß is able to induce an EMT process in HFH, coincident with Snail up-regulation and a decrease in E-cadherin levels, cells showing mesenchymal proteins and reorganization of the actin cytoskeleton in stress fibers. Interestingly, these cells show loss of expression of specific hepatic genes and increased expression of stem cell markers. Chronic treatment with TGF-ß allows selection of a population of mesenchymal cells with a de-differentiated phenotype, reminiscent of progenitor-like cells. Process is reversible and the mesenchymal stem-like cells re-differentiate to hepatocytes under controlled experimental conditions. In summary, we show for the first time that human hepatocytes may respond to TGF-ß inducing different signals, some of them might contribute to tumor suppression (growth inhibition and apoptosis), but others should mediate liver tumor progression and invasion (EMT and acquisition of a stem-like phenotype).