Regulation of the Human Leukemia Inhibitory Factor Gene by ets Transcription Factors

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Abstract
Objectives: Leukemia inhibitory factor (LIF) is a pleiotropic cytokine mainly produced by activated T lymphocytes. We previously demonstrated that human Jurkat T lymphoma cells represent a valid model of LIF gene expression. This study was designed to identify regions critical for LIF promoter activation in Jurkat cells. Methods: Luciferase constructs under the control of different portions of the human LIF promoter were transfected into Jurkat cells, and promoter activity was determined by luminometry. Similar experiments were performed with constructs bearing mutations in the putative ets binding regions in the LIF promoter. RT-PCR, Western blot and gelshift experiments were performed to study expression and DNA binding of ets factors in lymphoid cells. Results: With the exception of the shortest construct not including the putative ets binding sites, all wildtype LIF promoter constructs were strongly inducible by phorbol ester/ionomycin. In contrast, the mutant constructs were significantly less inducible. Cotransfection of the wild-type constructs with ets expression vectors resulted in significant enhancement of promoter activity. ets-1 and ets-2 mRNA and protein were shown to be expressed in Jurkat cells. Gelshift experiments revealed that proteins present in nuclear extracts from Jurkat cells specifically bind to both artificial ets consensus sites and ets binding sites present in the LIF promoter. Conclusions: We conclude that binding of ets transcription factors to the ets binding sites in the human LIF promoter is critical for its inducibility in response to T cell activators. ets transcription factors thus play an important functional role within the endocrine-immune network.

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