|Ph.D Student||Derdikman Yael|
|Subject||Regulation of CXCR1/2 Receptor Signaling in Tumor|
Infiltrating T Cells by Lnk Adaptor Protein
|Department||Department of Medicine||Supervisors||Dr. Yishai Ofran|
|Dr. Igal Louria-Hayon|
|Full Thesis text|
Lnk (SH2B3) is a non-enzymatic signal-transduction modulator protein. As a member of the SH2B family of adaptor proteins, Lnk has common binding domains such as dimerization domain, pleckstrin homology and Src Homology 2 domain (SH2), which binds phosphorylated tyrosine residues on target proteins.
Lnk is an important regulator of different cytokine signaling pathways in a wide variety of cells throughout the hematopoietic and immune systems. Through its SH2 domain, Lnk binds phosphorylated tyrosine residues on intracellular protein targets and inhibits their downstream signaling. This enables regulation of the cellular response to cytokine stimulation.
In human, an increasing number of Lnk mutations have been demonstrated in myeloproliferative neoplasm (MPN) patients. Defected Lnk regulation lead to an increased hematopoietic stem cell (HSC) proliferation, probably due to high activity of the Jak-STAT pathway. Similarly, Lnk-deficient (Lnk‑/-) mice mainly exhibit MPN-like phenotype with enlarged spleen and abnormal blood counts. Lnk-/- mice also present immune-mediated intestinal inflammation with marked proportion of activated CD8 T-cells. This study investigates whether the regulation of Lnk adaptor protein in immune cells effects their antitumor activities.
Chemokines are chemotactic cytokines expressed at the tumor microenvironment. Together with their cognate receptors, chemokines form a complex signaling network that modulates both tumor progression and leukocyte infiltration into the tumor, including trafficking and infiltration of T-cells. Thus far, chemokines of the IL-8 superfamily and their cognate receptors CXCR1/2 were mostly shown to mediate the recruitment of innate immunosuppressive immune cells into the tumor site, and to mediate the initiation and development melanoma.
In this work we used Lnk-/- mice and murine melanoma cancer cells as a model to examine the role of Lnk regulation in the response of tumor infiltrating immune cells to tumor secreted chemokines. Our initial aim in this study was to demonstrate that Lnk deficiency in immune cells at the tumor microenvironment affects tumor growth. We identified a dominant tumor-secreted cytokine at the tumor microenvironment and detected an Lnk-deficient cellular immune population responsive to that cytokine. Specifically, we focused on the invasion capacity of Lnk-deficient CD8 T-cells in response to environmental cues of the IL-8 superfamily and activation of the CXCR1/2 receptors.
We show here that Lnk-/- mice present smaller melanoma tumors with increased tumor infiltration of CD8 T-cells. Furthermore, Lnk-/- CD8 T-cells demonstrated enhanced invasion in response to environmental IL-8 and melanoma secreted chemokines, that is CXCR1/2 dependent. Moreover, the hypersensitivity of Lnk-/- CD8 T-cells to IL-8 stimulation is mediated downstream to the CXCR1/2 receptors, with enhanced activation of Erk1/2 and STAT3. Finally, we show that Lnk-/- CD8 T-Cells also present enhanced induced activation.
Altogether, our findings revealed that Lnk is a novel regulator of the response of tumor infiltrating CD8 T-cells to IL-8 signals. Loss of Lnk in these cells leads to their enhanced invasion and infiltration into melanoma tumors. This may potentially turn Lnk to a potent target for enhancement of T-cell trafficking in adoptive cellular transfer immunotherapies.