Human BCL–2 Activates Erk Signaling Pathway to Regulate Gene Expression in Lens Epithelial Cells

Abstract

Abstract: : Purpose: Our previous studies have demonstrated that human Bcl–2 can down–regulate expression of alphaB–crystallin in rabbit lens epithelial cells (Mao et al., 2001. J. Biol. Chem. 276:43435–43445). Here, we present evidence to show that Bcl–2 activates the RAF/MEK/ERK signaling pathway, which modulates the phosphorylation (functional) status of numerous transcriptional factors, leading to positive or negative regulations of the down–stream genes. Methods: The gel mobility shifting was used to assay the DNA binding activities of transcriptional factors. The CAT reporter gene activity assay was used to detect the transactivity of the transcriptional factors. And Western blot analysis was used to analyze MAP kinase activities. Results: Human Bcl–2 positively regulates expression of the proto–oncogenes, c–jun and c–fos. Moreover, it enhances the DNA binding activity and transactivity of the activating protein–1. Furthermore, Bcl–2 also activates ERK1/2 MAP kinases and the upstream activating kinases. Inhibition of the activities of the ERK kinases or the upstream activating kinases by pharmacological inhibitors or dominant negative mutants abolishes the Bcl–2–mediated regulation of the transcription factors and their downstream genes. Conclusions: Through activation of the ERK kinase signaling pathway, Bcl–2 regulates the transcriptional activities of multiple transcription factors, and hence modulates the expression of their downstream genes. These results provide a novel mechanism to explain how Bcl–2 regulates expression of other genes.

Keywords: gene/expression • apoptosis/cell death • cell death/apoptosis