RESUMO
A previous study in the bovine mammary epithelial cell line BME-UV1 demonstrated that suppression of the phosphatidylinositol-4,5-biphosphate 3 kinase (PI3K)/AKT (somatotropic) signaling pathway was required for transforming growth factor ß1 (TGFß1)-induced programmed cell death (PCD). To investigate whether this is a universal mechanism for TGFß1 to induce PCD in bovine mammary epithelium, we compared TGFß1 modulation of PI3K/AKT and its role in PCD in 2 bovine mammary epithelial cell lines: MAC-T and BME-UV1. In MAC-T cells, TGFß1 promoted cell survival, and this paralleled a reduction in PI3K/AKT activity, rather than an increase. In BME-UV1 cells, TGFß1 induced PCD, and this was accompanied by a time-dependent effect on PI3K/AKT activity, including an initial significant increase in the phosphorylation of AKT at 3 h, followed by a reduction between 12 and 24 h, and then an increase at 48 h. Inhibition of AKT activity enhanced TGFß1-induced PCD in BME-UV1 cells but had no effect on MAC-T cells, suggesting that TGFß1 mediates PCD in BME-UV1 cells through suppression of AKT activity. Inhibition of TGFß receptor type I (TßRI) kinase activity completely abrogated TGFß1-induced PCD in BME-UV1 cells but had no effect on TGFß1-induced suppression of PCD in MAC-T cells, demonstrating that TGFß1-induced PCD in BME-UV1 cells is dependent on TßRI/SMAD signaling. These and previous observations suggest that the different effects of TGFß1 on PCD in these cell lines might involve noncanonical signaling pathways other than PI3K/AKT, and may reflect their different lineages. Future studies should address this finding, taking into consideration the effect that different culture conditions might have on cell phenotype.