Serum/Glucocorticoid-Regulated Kinase 1 (SGK1) Is a Prominent Target Gene of the Transcriptional Response to Cytokines In Multiple Myeloma and Supports the Growth of Myeloma Cells

Abstract 1915

Multiple myeloma is a paradigm for a malignant disease that exploits external stimuli of the microenvironment for growth and survival. A thorough understanding of the complex interactions between malignant plasma cells and their surrounding requires a detailed analysis of the transcriptional response of myeloma cells to environmental signals. We hypothesized that the intracellular signals evoked by cytokines converge and regulate transcription of a set of genes that are common targets for several growth factors and therefore constitute pivotal mediators of the tumor-promoting effects of autocrine or paracrine stimuli. To identify such targets, we determined the changes in gene expression induced by IL-6, TNFalpha, IL-21 or co-culture with bone marrow stromal cells in myeloma cell lines. Among a limited set of genes that were consistently activated in response to growth factors, a prominent transcriptional target of cytokine-induced signaling in myeloma cells was the gene encoding the serine/threonine kinase SGK1, which is a down-stream effector of PI3-kinase and highly homologous to AKT. We could demonstrate a rapid, strong and sustained induction of SGK1 in the cell lines INA-6, ANBL-6, IH-1, OH-2 and MM.1S as well as in primary myeloma cells. Pharmacologic inhibition of the JAK/STAT pathway abolished STAT3 phosphorylation and SGK1 induction. In addition, shRNA-mediated knock-down of STAT3 reduced basal and induced SGK1 levels, demonstrating the involvement of the JAK/STAT3 signaling pathway in SGK1 induction. Furthermore, down-regulation of SGK1 by shRNAs resulted in decreased proliferation and viability of myeloma cell lines. Our results indicate that SGK1 is a highly cytokine-responsive gene in myeloma cells promoting their growth and survival and represents an attractive candidate for further evaluation as a therapeutic target.