The Short Isoform of the Ubiquitin Ligase NEDD4L Is a CREB Target Gene in Hepatocytes

<div><p>During cycles of fasting and feeding, liver function is regulated by both transcriptional and post-translational events. Regulated protein degradation has recently emerged as a key mechanism to control abundance of specific hepatic proteins under different nutritional conditions. As glucagon signaling through cAMP and PKA is central to glucose output during fasting, we hypothesized that this signaling pathway may also regulate ubiquitin ligases in the fasted state. Here we show that fasting stimuli promote expression of the short isoform of the E3 ubiquitin ligase <i>Nedd4l</i> in primary mouse hepatocytes. <i>Nedd4l-short</i> mRNA and NEDD4L (short isoform) protein accumulate in glucagon-treated primary mouse hepatocytes and in liver tissues during fasting. We identified a functional cAMP response element in the alternate <i>Nedd4l-short</i> promoter; mutation of this element blunts cAMP-induced expression of a <i>Nedd4l</i> reporter construct. CREB occupies the endogenous <i>Nedd4l</i> locus near this element. CREB and its co-activator CRTC2, both activated by fasting stimuli, contribute to glucagon-stimulated <i>Nedd4l-short</i> expression in primary hepatocytes. siRNA-mediated <i>Nedd4l</i> depletion in primary hepatocytes did not affect gluconeogenic gene expression, glucose output or glycogen synthesis. Our findings reveal a new mechanism of <i>Nedd4l</i> transcriptional regulation in liver cells. </p>