(62t) Investigation of the Jak-STAT and Erk-C/EBPβ Signaling Pathways in Response to Cytokine Stimulation in HepG2 Cells
Cytokines, such as interleukin-6 (IL-6) and interleukin-1 (IL-1), are important in the onset and sustenance of the acute phase inflammatory response of the liver upon injury or inflammation. Binding of IL-6 or IL-1 to its cell surface receptor (e.g., glycoprotein 130, gp130) leads to a series of intracellular molecular events that are collectively known as signal transduction. The end product of this signal transduction is the activation of transcription factors (TF). These events are instrumental in regulating the expression of target genes involved in the acute phase response. Two important signaling pathways?Jak-STAT3 and Erk-C/EBPβ-are mainly involved in IL-6 and IL-1 signal transduction. Examples of IL-6 regulated genes include plasma acute phase proteins (APPs) that are upregulated (e.g., C-reactive protein, haptoglobin, and serum amyloid A) as well as down-regulated (e.g., albumin and transferrin). Changes in the expression of these proteins are often used as indicators of the inflammatory response and its complications. Therefore, understanding the molecular mechanisms underlying the regulation of acute phase proteins could lead to novel approaches for the treatment of inflammatory diseases. We have developed a comprehensive signaling model for describing the activation of STAT3 and C/EBPβ upon IL-6 and IL-1 stimulation. In parallel, we have also developed enhanced green fluorescent protein (EGFP)-based HepG2 reporter cell lines for monitoring the activation of STAT3 and C/EBPβ. Our data show that the expression of EGFP (and hence, the activation of transcription factors) correlates with the amount and specificity of the cytokine used.