TNFalpha induces expression of transcription factors c-fos, Egr-1, and Ets-1 in vascular lesions through extracellular signal-regulated kinases 1/2.

ABSTRACT

Migration, proliferation and differentiation of vascular smooth muscle cells (VSMC) and macrophages are important pathological responses that contribute to the development and progression of vascular lesions. Cytokines such as TNFalpha are present at sites of vascular injury and regulate a variety of cellular functions of inflammatory cells and VSMC. Cell migration, proliferation and differentiation require de novo gene transcription resulting from extracellular signals being transduced to the nucleus, where multiple genes are regulated to participate in lesion formation. In VSMC and macrophages, TNFalpha induces activation of the extracellular signal-regulated kinases 1/2 (ERK 1/2), which transmit signals from the cytosol to the nucleus. Potential nuclear targets of TNFalpha-activated ERK 1/2 include the transcription factors Ets-1, Egr-1, and c-fos, which are known to regulate cellular growth, differentiation, and migration. The aim of this study was to investigate the expression of the transcription factors Ets-1, Egr-1 and c-fos in different types of vascular lesions, their regulation by TNFalpha and the role of ERK 1/2 in these signaling events. Atherosclerotic lesions from fructose-fed LDL-receptor deficient mice and neointimal lesions from rat aortae 2 weeks post balloon injury demonstrated the presence and colocalization of TNFalpha, phosphorylated and activated ERK 1/2, and transcription factors Ets-1, Egr-1 and c-fos. Neointimal lesions consisted primarily of VSMC, whereas atherosclerotic lesions predominantly contained macrophages. In cultured rat aortic VSMC, TNFalpha (100 U/ml) stimulated a rapid and transient expression of Ets-1, Egr-1 and c-fos with a maximal induction 1 h after stimulation. In cultured RAW 264.7 mouse macrophages, TNFalpha similarly induced the expression of Ets-1, Egr-1, and c-fos. Induction of these transcription factors was mediated via ERK 1/2 activation, since the ERK 1/2-pathway inhibitor PD98059 (10-30 microM) significantly inhibited their TNFalpha-induced expression. TNFalpha induced ERK 1/2 activation in both cell types. These findings underscore the importance of the ERK 1/2 pathway in the expression of TNFalpha-regulated transcription factors, which may participate in different forms of vascular lesion formation.