Leptin is a multifunctional cytokine and hormone that primarily acts in the hypothalamus and plays a key role in the regulation of food intake and energy expenditure. In addition, it has direct effects on many cell types on the periphery. Leptin acts through its receptor, the product of the db gene, which has six isoforms. Only one of them (OB-Rb) has full signalling capabilities and is able to activate the Jak/STAT pathway, the major pathway used by leptin to exert its effects. However, some signalling events can be initiated by the short isoforms. Besides Jak/STAT, other pathways, such as MAPK and the 5'-AMP-activated protein kinase (AMPK) pathway, are also involved in leptin signalling. Leptin also interacts with insulin signalling. In this paper, we give an overview of the signal transduction mechanisms that are related to the actions of leptin.

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Interleukin-6 (IL-6) belongs to a family of cytokines that use receptors consisting of a common signal-transducing chain (gp130). Baf/3 cells transfected with the human IL-6 receptor (IL-6R) and gp130 (Baf/3-gp130/IL-6R) can only grow in medium containing IL-6. We attempted to interrupt the signal transducing pathway of IL-6 with the help of antisense oligonucleotides (ASOs) designed against the IL-6R. We used 18 different kinds of antisense oligonucleotides of overlapping sequences around the translational start codon of the human IL-6R. Sense ASOs were used as a control. The proliferation of cells was analysed by H-thymidine incorporation. Cell surface expression of the IL-6R was assessed by FACS analysis. We identified three ASOs which strongly inhibited the proliferation of IL-6 dependent transfected Baf/3 cells. Flow cytometric studies on the suppression of surface expression of IL-6R by ASOs showed a similar pattern. These results should help to clarify the structural requirements of functionally effective ASOs in the inhibition of IL-6R.