RESUMEN
HOM/C homeobox (Hox) and forkhead box (Fox) factors are reported to be expressed in the foregut endoderm and are subsequently detected in a spatio-temporal pattern during lung development. Some of these factors were reported to influence the expression of lung marker proteins or to modulate lung development. To clarify the molecular mechanisms for generating functional lung cells from progenitor cell populations, we introduced the forkhead box factors, FoxA1 and FoxA2, and the homeobox factor, HoxB3, into the differentiation process in a multipotent hamster lung epithelial M3E3/C3 cell line. Ectopic expression of FoxA2 promoted differentiation to Clara-like cells with up-regulation of the expression of the lung marker proteins, Clara cell-specific 10-kDa protein and surfactant protein-B. In contrast, FoxA1 repressed the differentiation. HoxB3 transfection induced FoxA2 expression transiently at the pre-differentiation stage. The endogenous HoxB3 expression level decreased at later stages of Clara-like cell differentiation, and the attenuation was enhanced by FoxA2 transfection. HoxB3 is a putative upstream regulator that enhances FoxA2 expression at the pre-differentiation stage. In addition, we found that the expression of HoxA4, HoxA5, and HoxC9 increased differentially during Clara-like cell differentiation. These results suggest that HoxB3 may be a putative positive regulator of FoxA2 expression at the pre-differentiation stage, and those interactions of Fox factors and Hox factors could participate in Clara cell differentiation.
Asunto(s)
Diferenciación Celular/fisiología , Proteínas de Unión al ADN/metabolismo , Células Epiteliales/metabolismo , Proteínas de Homeodominio/metabolismo , Pulmón/metabolismo , Proteínas Nucleares/metabolismo , Factores de Transcripción/metabolismo , Animales , Diferenciación Celular/genética , Línea Celular , Cricetinae , Proteínas de Unión al ADN/genética , Factor Nuclear 3-alfa del Hepatocito , Factor Nuclear 3-beta del Hepatocito , Proteínas de Homeodominio/genética , Humanos , Pulmón/citología , Pulmón/embriología , Proteínas Nucleares/genética , Factores de Transcripción/genética , TransfecciónRESUMEN
Homeobox (Hox)-containing factors have been shown to play regulatory roles on lung development. Although HoxB3 gene expression is detected in the prenatal lung during development, its function has not been clarified precisely. We constructed an expression vector of a hamster HoxB3 coding region, which was cloned from hamster fetal lung cell line M3E3/C3. Sixteen-base deletion was found in the hamster HoxB3 coding sequence when compared with the mouse sequence. Under conditions of differentiation, cells transfected transiently with HoxB3 augmented the retinol-induced gene expression of Clara cell-specific secretory protein, whereas the cells showed reduced expression of surfactant-associated protein C. These alterations were attenuated by the transfection with HoxB3 antisense nucleotide. The results show that the cells with overexpressed HoxB3 were reinforced to have characteristics of Clara cells but did not have the characteristics of alveolar type II cells, and that HoxB3 played a stimulatory role on Clara cell differentiation in M3E3/C3 cells. In addition, the expression of Clara cell-specific secretory protein and surfactant-associated protein C genes was enhanced upon transfer of cells to collagen substrate, suggesting that collagen substrate has some regulatory functions on lung cell differentiation through cell adhesion.