| Popis: |
Leptin communicates the status of body energy stores to the central nervous system, regulating appetite, metabolic rate, and neuroendocrine functions. These effects are mediated by leptin binding and activation of the cognate cell surface receptor, a member of type I cytokine receptor family, which lead to the activation of receptor-associated kinases of the Janus family. In this work, we demonstrate that leptin inhibits the l-alpha-lysophosphatidic acid (LPA)-induced intracellular calcium mobilization in a dose-dependent manner in HEK-293 cells stably expressing full-length leptin receptor (OB-Rb). This action appears to be selective, as it was not observed when other signaling families, such as VIP or EGF, were studied. Pretreatment with the phosphatidylinositol 3-kinase (PI3K) inhibitor, wortmannin, reversed the effect of leptin, pointing to PI3K as an intermediate molecule involved in this process. An unspecific protein kinase C (PKC) inhibitor, staurosporine, disrupted the inhibitory action of leptin. Furthermore, intracellular levels of phosphorylated PKCepsilon and PKCdelta rose to a maximum 5 min after leptin administration, suggesting that these atypical PKC isoforms are involved in the observed cross-desensitization. To define the regions of the OB-Rb intracellular domain required for the cross-desensitization, a series of C-terminal deletion mutants were transfected into HEK-293 cells. C-terminal truncation that removed the consensus Box 3 motif of OB-Rb prevented leptin action, indicating that heterologous desensitization over LPA was exerted at the level of this intracellular motif. Our date demonstrate that leptin plays a key role in the regulation of the earliest signaling pathways activated by growth factors, such as LPA, through a signaling pathway involving PKCdelta and PKCepsilon coupled to Box 3 motif of the OB-Rb through PI3K. |
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