Gene expression of activin, activin receptors, and follistatin in intestinal epithelial cells

Gene expression of activin, activin receptors, and follistatin was investigated in vivo and in vitro using semiquantitative RT-PCR in intestinal epithelial cells. Rat jejunum and the intestinal epithelial cell line IEC-6 expressed mRNA encoding the betaA-subunit of activin, alpha-subunit of inhibin, activin receptors IB and IIA, and follistatin. An epithelial cell isolation study focused along the crypt-villus axis in rat jejunum showed that betaA mRNA levels were eight- to tenfold higher in villus cells than in crypt cells. Immunohistochemistry revealed the expression of activin A in upper villus cells. The human intestinal cell line Caco-2 was used as a differentiation model of enterocytes. Four- to fivefold induction of betaA mRNA was observed in postconfluent Caco-2 cells grown on filter but not in those cells grown on plastic. In contrast, follistatin mRNA was seen to be reduced after reaching confluence. Exogenous activin A dose-dependently suppressed the proliferation and stimulated the expression of apolipoprotein A-IV gene, a differentiation marker, in IEC-6 cells. These results suggest that the activin system is involved in the regulation of such cellular functions as proliferation and differentiation in intestinal epithelial cells.     

Repression of integrin-linked kinase by antidiabetes drugs through cross-talk of PPARγ- and AMPKα-dependent signaling: Role of AP-2α and Sp1

Nasopharyngeal carcinoma (NPC) is one of the most common cancers of the head and neck, particularly in Southern China and Southeast Asia with high treatment failure due to the development of local recurrence and distant metastasis. The molecular mechanisms related to the progression of NPC have not been fully understood. In this study, we showed that antidiabetes drugs rosiglitazone and metformin inhibit NPC cell growth through reducing the expression of integrin-linked kinase (ILK). Blockade of PPARγ and AMPKα overcame the effects of rosiglitazone and metformin on ILK protein. Importantly, overexpression of ILK abrogated the effect of rosiglitazone and metformin on NPC cell growth. Furthermore, these agents reduced ILK promoter activity, which was not observed in AP-2α, but not Sp1 site mutation in ILK gene promoter. In addition, silencing of AP-2α or overexpression of Sp1 reversed the effect of these agents on ILK protein expression and cell growth. Chromatin immunoprecipitation (ChIP) assay showed that rosiglitazone induced AP-2α, while metformin reduced Sp1 protein binding to the DNA sequences in the ILK gene promoter. Intriguingly, overexpression of Sp1 abolished the effect of rosiglitazone on AP-2α protein expression. Collectively, we show that rosiglitazone and metformin inhibit ILK gene expression through PPARγ- and AMPKα-dependent signaling pathways that are involved in the regulation of AP-2α and Sp1 protein expressions. The effect of combination of rosiglitazone and metformin demonstrates greater extent than single agent alone. The cross-talk of PPARγ and AMPKα signaling enhances the synergistic effects of rosiglitazone and metformin. This study unveils novel mechanisms by which oral antidiabetes drugs inhibit the growth of human NPC cells.