Expression of RAS oncogene in cultured human cells alters the transcriptional and post transcriptional regulation of cytokine genes

Abstract

Autonomous production of cytokines such as the hematopoietic colony-stimulating factors (CSFs), IL-1, or IL-6 has been demonstrated in numerous human and murine neoplasms, and may be involved in the pathogenesis of several paraneoplastic syndromes such as leukocytosis, fever, and hypercalcemia. Because of the high frequency with which mutations in ras protooncogenes have been detected in human tumors, as well as evidence linking ras gene products to activation of certain cellular functions, we investigated whether ras mutations might influence the regulation of cytokine genes. Normal human fibroblasts transfected with a mutant val"2 H-ras oncogene expressed increased levels of mRNA transcripts encoding granulocyte-CSF (G-CSF), granulocyte-macrophage-CSF (GM-CSF), and IL-1, compared with controls. Human mesothelioma cells transfected with a mutant asp'2 N-ras oncogene exhibited similar alterations in cytokine gene expression. Estimates of transcriptional activity by nuclear run-on analysis revealed a selective increase in transcription only for the IL-1 gene. Analysis of mRNA half-life demonstrated a marked increase in the stability of numerous cytokine transcripts, including G-CSF, GM-CSF, IL-1, and IL-6. The addition of anti-IL-I neutralizing antibody to cultures of cells expressing ras mutants did not block the expression of any of the cytokines examined, suggesting that the baseline expression of GM-CSF, G-CSF, and IL-6 was not a secondary event due to the increased transcription of IL-1. These results indicate that mutations in ras genes may alter expression of several cytokine genes through both transcriptional and posttranscriptiona