Leukemia inhibitory factor (LIF) is a member of the interleukin-6 family of cytokines, which induces a wide range of responses in a variety of cells. The aim of this study was to investigate whether LIF induces cardiomyocyte hypertrophy and transmits signals through the JAK/STAT (indicating just another kinase/signal transducer and activator of transcription) pathway in primary cultured neonatal rat cardiomyocytes. LIF increased protein content and [3H]phenylalanine uptake in cardiomyocytes in a dose-dependent manner. LIF (103 U/mL) induced rapid tyrosine phosphorylation of gp130, JAK1, JAK2, STAT1, and STAT3 but not Tyk2 or STAT2. LIF also induced autokinase activity of JAK1 in a time-dependent manner. Gel shift assays for interferon gamma activation site/interferon-stimulated responsive element and sis-inducible element (SIE) revealed that LIF induced dimerization of STAT1 and STAT3 and formation of sis-inducing factor complexes, which subsequently interacted with SIE in the promoter. Preincubation with anti-STAT1 and anti-STAT3 antibodies inhibited the binding of SIF complexes. In conclusion, LIF induces cardiac hypertrophy and directly stimulates the JAK/STAT pathway in cardiomyocytes.
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