Autocrine interleukin-1beta production in leukemia: evidence for the involvement of mutated RAS.

Interleukin (IL)-1beta is constitutively expressed in many leukemias and operates as an autocrine growth factor. To study the cellular basis for this aberrant production, we analyzed two cell lines, B1 (acute lymphoblastic leukemia) and W1 (juvenile chronic myelogenous leukemia), which express high levels of IL-1beta and have mutations in the K-RAS and N-RAS genes, respectively. Electromobility shift assays demonstrated transcription factor binding at multiple IL-1beta promoter elements [nuclear factor (NF)-IL6/CREB, NFB1, NFkappaB, and NF-IL6], consistent with the activation of an upstream signaling pathway. To determine whether activated Ras was involved, two structurally distinct classes of farnesyltransferase (FTase) inhibitors (the monoterpenes and a peptidomimetic) and an adenoviral vector expressing antisense targeted to K-RAS were used to specifically interfere with Ras function and/or expression. Treatment with the FTase inhibitors resulted in a concentration-dependent decrease in both NF-IL6/CREB binding to the IL-1beta promoter and IL-1beta protein levels, without a significant change in total cellular protein levels. Furthermore, exposure of the B1 cells to antisense against K-RAS resulted in an approximately 50% reduction in both p21Ras and IL-1beta protein levels. Growth suppression was observed after FTase inhibitor or antisense exposure, an effect that was partially reversible by the addition of recombinant IL-1beta to the cultures. Our observations suggest that mutated RAS genes may mediate autocrine IL-1beta production in some leukemias by stimulating signal transduction pathways that activate the IL-1beta promoter.

RAS and leukemia: from basic mechanisms to gene-directed therapy.

PURPOSE AND DESIGN: The purpose of this review is to provide an overview of the literature linking Ras signaling pathways and leukemia and to discuss the biologic and potential therapeutic implications of these observations. A search of MEDLINE from 1966 to October 1998 was performed. RESULTS: A wealth of data has been published on the role of Ras pathways in cancer. To be biologically active, Ras must move from the cytoplasm to the plasma membrane. Importantly, a posttranslational modification--addition of a farnesyl group to the Ras C-terminal cysteine--is a requisite for membrane localization of Ras. Farnesylation of Ras is catalyzed by an enzyme that is designated farnesyltransferase. Recently, several compounds have been developed that can inhibit farnesylation. Preclinical studies indicate that these molecules can suppress transformation and tumor growth in vitro and in animal models, with little toxicity to normal cells. CONCLUSION: An increasing body of data suggests that disruption of Ras signaling pathways, either directly through mutations or indirectly through other genetic aberrations, is important in the pathogenesis of a wide variety of cancers. Molecules such as farnesyl transferase inhibitors that interfere with the function of Ras may be exploitable in leukemia (as well as in solid tumors) as novel antitumor agents.

RAS inhibitors in hematologic cancers: biologic considerations and clinical applications.

As the molecular mechanisms responsible for the development and propagation of cancer are becoming elucidated, the nascent field of gene-directed therapy is emerging. Recently, several investigators have described inhibitors of the Ras protein. This molecule has been targeted because RAS is one of the most commonly mutated oncogenes in human neoplasia. In this review, we will discuss the role of Ras in the pathogenesis of hematologic neoplasms, and the biology behind the development of novel compounds which specifically suppress Ras function.