The Biological Effects and Mechanisms of Interleukin-34 in the U937 Human Leukemic Cell Model.

Abstract 2155

Interleukin-34 (IL-34) is a cytokine consisting of a 39kD homodimer employing the Macrophage Colony Stimulating Factor (MCSF/CSF-1) receptor; recently identified through functional proteomics experiments. Among its physiological activities, IL-34 has been shown to promote monocyte viability and proliferation; promote the differentiation of bone marrow cells into macrophage progenitors and induce pro-inflammatory cytokines: IL-1β, IL-6, TNF-α, and GM-CSF in human whole blood. All of the published work on IL-34 involves its effects on hematopoietic and osteoclast progenitors; however, it is not known whether IL-34 has the ability to induce any of these physiological responses in cancer cells. The purpose of this study is to evaluate the biological effects of IL-34 in the U937 leukemia cell line while deducing the signaling mechanisms associated with these effects. Thus far, we have evaluated IL-34 on U937 cells for cell growth and proliferation, induction of cytokines, migration, differentiation and apoptosis. Congruently, we are also exploring the JAK/STAT and PI3K/Akt signaling pathways for activation. In U937 cells, we have noted that while IL-34 does not induce cell growth or proliferation, there is a reduction in cells in the S phase of the cell cycle at 48hours, post treatment. Additionally, we note a differential induction of a number of Th1/Th2/Th17 and pro-inflammatory cytokines, namely IL-1α, IL-1b, IL-6, IL-8 and G-CSF. Our results also show that IL-34 influences the migration of monocytes by the possible induction of chemoattractant cytokines in media. Furthermore, we report that IL-34 is able to differentiate the human leukemic cellular model, U937, from monoblastic precursor cells towards monocyte- and macrophage-like cells. Accompanying this differentiation appears to be a selective induction of apoptosis in undifferentiated U937 cells, supported by the induction of cleaved Caspase-3. To our knowledge, this is the first report that IL-34 induces differentiation in human leukemic cellular model, let alone any cancer model. Exploration of the JAK/STAT signaling pathway has identified TYK2 and JAK 1 as mediators of the IL-34 signal through in U937 cells, while identification of its associated STAT proteins is currently ongoing. Interestingly, the evaluation of the PI3K/Akt pathway has demonstrated a reduction of phosphorylated Akt, suggesting an influence of PTEN, which is currently being evaluated. This research may provide insight into the influence of IL-34 in the cancer microenvironment as compared to the normal cell microenvironment, resulting in potential therapies targeting its mechanistic actions.