Leukemia inhibitory factor (LIF) is a pleiotrophic cytokine, which plays an important role in inducing cancer cachexia. We have previously reported that LIF promotes cell proliferation in some human carcinoma cells through c-fos, jun-B and cyclin-E expression. In the present study, we analyzed the regulation of LIF and its receptor (LIFR) expression in pancreatic carcinoma cells. Seven pancreatic carcinoma cells expressed constitutively LIF and its heterodimer receptor (LIFR and gp130) mRNA in RPMI-1640 medium without FBS. The amount of LIF immunoreactive protein was 132.5+/-52 pg/10(6) cells in culture supernatants without FBS. Pro-inflammatory cytokines, such as TNF-alpha, IL-1beta, IL-6, IL-8, or LIF, enhanced the expression of LIF mRNA in Hs-700T and Hs-766T cells. Addition of LIF significantly induced cell proliferation of Hs700T in 13 days LIF dose-dependently. However, anti-LIF IgG failed to suppress cell proliferation in Hs-700T cells. LIF acted as a paracrine growth factor in Hs-700T cells, which expressed low amount of LIF without stimuli. Cellular signal transductions by LIF was down-regulated by inhibitors of protein kinase C (PKC), protein tyrosine kinase (PTK), and Ca/Calmodulin. LIF induced phosphorylation of STAT3. Moreover, exogenous LIF upregulated the expression of LIFR mRNA. Antisense LIFR oligonucleotide significantly suppressed cell growth in the presence of LIF in Hs-700T cells. These results suggest that cytokine network might alter the expression and responsiveness to LIF in tumor microenvironment.