Abstract 1756 Stabilin-1 Cellular Signaling in Immunosuppressive Monocytes and Macrophages

Stabilin-1 is a multifunctional scavenger receptor expressed in sinusoidal endothelial cells, immunosuppressive (M2) macrophages and monocytes, and tumor associated macrophages (TAMs).TAMs have been known to participate in the formation of the tumor microenvironment through phagocytosis of tumor modulators and as well as progress metastasis.Expression of Stabilin-1 increases during this maturation phase by unknown mechanisms, though IL-4 increases expression in in vitro experiments.The literature is very limited with regards to the signaling activity mediated by Stabilin-1.A structurally similar protein, Stabilin-2, is activated by receptor mediated endocytosis of multiple ligands including heparin, hyaluronic acid and initiates a MAP kinase signaling response (Kyosseva, et al., J. Biol.Chem.2008).Our research goals focus on 1.) characterizing the Stabilin-1 promoter region and 2.) elucidating downstream signaling effects via kinase phosphorylation.We used transcription factor (TF) promoter binding screening array to give us candidate TFs that may bind the promoter, and we will confirm the TFs using an EMSA as well as chromatin immunoprecipitation.To determine which specific kinase are activated by Stabilin-1, we will use a Proteome Profiler Human Phospho-kinase array kit.If we know the kinases that are activated, we can then make inferences as to which signaling pathway Stabilin-1 mediates.We will also be investigating whether Stabilin-1, itself, is phosphorylated upon ligand binding.Here, we will incubate our recombinant human Stabiln-1 cell line with multiple known ligands of Stabilin-1, like human placental lactogen, and confirm phosphorylation with immunoprecipitation and gel staining.A more robust biochemical characterization of Stabilin-1 which includes promoter induction and signal transduction will outline strategies for targeting the tumor microenvironment for the prevention of metastasis.