Pan-cancer signaling landscape linked to endothelial and immune Sphingosine-1-phosphate receptor 1 (S1PR1) expression

Sphingosine-1-phosphate (S1P) promotes tumor growth and dissemination. Chronic positive feedback communication circuits between cancer and stromal cells involve S1P type-1-receptor (S1PR1) activating cell-type specific signaling networks. We hypothesized that such cell-type specific signaling components would be identifiable by rational, unbiased analysis of public oncogenomic and phosphoproteomic datasets. Guided by S1PR1 expression, we used data mining strategies applied to 32 cancer type datasets of the TCGA oncogenomics program, aiming to identify pan-cancer endothelial and immune S1PR1 signaling partners statistically correlated with patient survival. Gene ontology analysis and unbiased clustering of endothelial and immune S1PR1-signaling partners were used to reveal cell type-specific signaling components that individually and grouped, as transcriptional signatures, were statistically linked to patient survival. Furthermore, the breast cancer CPTAC dataset was analyzed focusing on the signaling phosphoproteome linked to S1PR1 expression. Oncogenic S1PR1 signaling companions included endothelial regulators of cell migration such as Ephexin5, a RhoGEF encoded by the ARHGEF15 gene, and RhoJ, a small Rho GTPase. The immune signaling repertoire linked to S1PR1 expression and patient survival included DOCK2, Vav1 and Rac2. Among the S1PR1 phospho-signaling partners, endothelial ARHGAP24, ARHGAP6, ARHGAP31, and TNS1, and immune ARHGAP25, known to be involved in cytoskeletal reorganization and cell mobilization, clustered as phosphoproteins within a subgroup of breast cancer patients. Given the pharmacological relevance of S1PR1 in endothelial and immune settings, revealing the identity of signaling molecules linked to S1PR1 expression provides useful information to further investigate therapeutic strategies targeting these pathways in the vascular and immune systems.