Leptin-induced signaling pathways in cancer cell migration and invasion

This review is dedicated to E-cadherin, a calcium-dependent cell-cell adhesion molecule with pivotal roles in epithelial cell behavior, tissue formation, and suppression of cancer. As founder member of the cadherin superfamily, it has been extensively investigated. We summarize the structure and regulation of the E-cadherin gene and transcript. Models for E-cadherin-catenin complexes and cell junctions are presented. The structure of the E-cadherin protein is discussed in view of the diverse functions of this remarkable protein. Homophilic and heterophilic adhesion are compared, including the role of E-cadherin as a receptor for pathogens. The complex post-translational processing of E-cadherin is reviewed, as well as the many signaling activities. The role of E-cadherin in embryonic development and morphogenesis is discussed for several animal models. Finally, we review the multiple mechanisms that disrupt E-cadherin function in cancer: inactivating somatic and germline mutations, epigenetic silencing by DNA methylation and epithelial to mesenchymal transition-inducing transcription factors, and dysregulated protein processing.

Cadherin cell-adhesion proteins mediate many facets of tissue morphogenesis. The dynamic regulation of cadherins in response to various extracellular signals controls cell sorting, cell rearrangements and cell movements. Cadherins are regulated at the cell surface by an inside-out signalling mechanism that is analogous to the integrins in platelets and leukocytes. Signal-transduction pathways impinge on the catenins (cytoplasmic cadherin-associated proteins), which transduce changes across the membrane to alter the state of the cadherin adhesive bond.

The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway plays critical roles in orchestrating of immune system, especially cytokine receptors and they can modulate the polarization of T helper cells. This pathway is regulated by an array of regulator proteins, including Suppressors of Cytokine Signaling (SOCS), Protein Inhibitors of Activated STATs (PIAS) and Protein Tyrosine Phosphatases (PTPs) determining the initiation, duration and termination of the signaling cascades. Dysregulation of the JAK-STAT pathway in T helper cells may result in various immune disorders. In this review, we represent how the JAK-STAT pathway is generally regulated and then in Th cell subsets in more detail. Finally, we introduce novel targeted strategies as promising therapeutic approaches in the treatment of immune disorders. Studies are ongoing for identifying the other regulators of the JAK-STAT pathway and designing innovative therapeutic strategies. Therefore, further investigation is needed.