Regulation Of T-ALL Migration By PKCθ and Carma1

Acute lymphoblastic leukemia (ALL) is one of the most commonly seen childhood lymphomas, and can arise from the T or B cell lineage (T-ALL or B-ALL respectively). T-ALL patients have almost 80% cure rate, however relapse in central nervous system (CNS) remains a major therapeutic challenge. Recently it has been shown that a chemokine receptor CCR7 is an essential regulator of T-ALL cell infiltration into the CNS. CCR7 is a homeostatic chemokine receptor that controls the homing of cells to lymph nodes, including naïve T cells, dendritic cells, and lymphoma cells. The ligands for CCR7, CCL19 and CCL21, are expressed by stromal cells in the secondary lymphoid organs. CCL21 and CCL19 function as chemoattractants for T and B lymphocytes expressing CCR7. Defects in either CCR7 or its ligands impairs lymphocyte migration. Aberrant CCR7 expression has been associated with certain cancers such as gastric cancers, breast cancers and head and neck cancers and been linked to pro-survival and invasive pathways. While CCR7 controls the migration of naïve T cells and T-ALL leukemic cells, little is known about the signaling pathways downstream of CCR7. Numerous studies have demonstrated the importance of Protein Kinase C θ (PKCθ) in normal T cell function as well as T-ALL. PKCθ regulates NF-κB by interaction with a complex of proteins including CARMA1, BCL10, and MALT1, which all function together to activate NF-κB upon T cell receptor ligation. In addition to being crucial for normal T cell activation, PKCθ has also been shown to be important in T-ALL induction in a mouse model of T-ALL. While PKCθ is clearly important in multiple aspects of T cell function, nothing is known about the potential role of PKCθ in controlling migration of T cells, including leukemic cells.

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We have established xenograft model of T-ALL, where we could assess the engraftment of T-ALL tumors into the NOD/SCID/IL2Rγ2 immunodeficient mice. Using T-ALL cells that express luciferase, we can image tumor load using the IVIS imaging system. Here we show that animals receiving T-ALL cells lacking CARMA1 show a significant  delay in timing of leukemia development and longer overall survival compared to animals receiving Wild type T-ALL cells (n=25, P value < 0.0001). In contrast, we did not observe any difference in timing of leukemia development or overall survival of the mice injected with WT or T-ALL cells that lack PKCθ. We hypothesize that the longer survival of animals injected with CARMA1-knockdown T-ALL cells results from lower tumor burden in the brain. Currently we are analyzing different organs including brain using immunohistochemistry to determine whether the differences in the migration and tumor load account for the differences between WT and CARMA1-knockdown T-ALL cells. As an additional control, we will confirm the role of PKCθ and CARMA1 in T-ALL migration by inducing T-ALL with NOTCH-1 mutant in mice knocked out for CARMA1 and PKCθ. These results demonstrate for the first time that CARMA1 may play an important role in T-ALL induction and possibly migration to the CNS.