Leukemia inhibitory factor (LIF) is a cytokine that plays an important role during mouse embryogenesis. We showed that adenovirus E1A represses the interleukin-6 signal transduction pathway that uses the same JAK tyrosine kinase and STAT (signal transducer and activator of transcription) transcription factor as LIF. Here, we report that the LIF-JAK-STAT signal transduction pathway is blocked in cellular E1A-expressing undifferentiated F9 cells, and that the block is overcome by retinoic

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... uced differentiation. LIF failed to stimulate the expression of the acute phase response element (APRE)driven luciferase gene in undifferentiated F9 cells, whereas the luciferase activity was remarkably increased by LIF treatment in dif- Plasmids The 4ϫAPRE-luciferase gene containing four repeats of APRE (IL-6 response element of the rat ␣ 2 -macroglobulin promoter), was constructed by subcloning two repeats of the oligonucleotides (5Ј-TCG-ACATCCTTCTGGGAATTCTGATCCTTCTGGGAATTCTGGGTAC-3Ј) (19) in front of the minimal junB promoter-luciferase gene as previously