J. Tsuchida1, M. Nagahashi1, K. Moro1, A. Otani1, M. Endo1, M. Ikarashi1, M. Nakajima1, Y. Koyama1, J. Sakata1, T. Kobayashi1, H. Kameyama1, Q. Qi3, L. Yan3, K. Takabe2,4, T. Wakai1 1Niigata University Graduate School Of Medical And Dental Sciences,Division Of Digestive And General Surgery,Niigata, NIIGATA, Japan 2Roswell Park Cancer Institute,Breast Surgery,Buffalo, NEW YORK, USA 3Roswell Park Cancer Institute,Department Of Biostatistics And Bioinformatics,Buffalo, NEW YORK, USA 4University At Buffalo Jacobs School Of Medicine And Biomedical Sciences, The State University Of New York,Department Of Surgery,Buffalo, NEW YORK, USA
Introduction: It is known that immune cells such as certain T cells and macrophages assist cancer progression. Those tumor-associated immune cells (TAICs) are considered to be one of the key players in the mechanisms how cancer invades and metastasizes. Sphingosine-1-phosphate (S1P), a pleiotropic bioactive lipid mediator, has emerged as a new player in cancer progression. S1P is produced by sphingosine kinases (SPHKs) inside cells and exported out of the cells. Extracellular S1P exerts its functions by binding to S1P specific receptors on the cell surface, and regulates various cellular functions such as cell proliferation, migration, and angiogenesis. Although previous in vivo studies indicated that S1P regulates immune function in many pathological conditions, the role of S1P in tumor-associated immune function has not been fully investigated in patients. Here, we test our hypothesis that S1P signaling affects TAICs in human breast cancer.
Methods: The expression level of each enzyme-encoding gene involved in S1P production was evaluated by retrieving RNA sequencing and gene expression quantification data using the Genomics Data Commons (GDC) data portal of the The Cancer Genome Atlas cohort. Gene expression levels were derived using normalization methods provided in the DESeq2 package. We compared the difference in expression levels of S1P related genes between HER2-negative and sphingosine kinase 1 (SPHK1)-high breast tissue (n = 263), and HER2-negative and SPHK1-low breast tissue (n = 277). We also compared the expression level of TAIC-related genes in between the same groups of the patients.
Results: The expression of some of the S1P-related genes; S1PR1, S1PR2, S1PR4, S1PR5, and SPNS2, were significantly increased in patients with high SPHK1 compared to those with low SPHK1. In contrast, expression of some of the S1P-related genes; S1PR3, ABCG2, SGPL1 and ORMDL3 were significantly decreased in patients with high SPHK1 compared to those with low SPHK1. Importantly, we found a significant increase in the expression of the TAIC-related genes, including CD4, CD8A, CD8B, PTPRC as T cell markers in SPHK1-high HER2-negative breast cancer tissues than in SPHK1-low. Macrophage markers including CCL2, CD163, CD68, CXCL8, IL-10, MSR-1, TGFB1, VEGFA, but not PLIN1, are increased in SPHK1-high HER2-negative breast cancer tissues. Moreover, adepocyte-related genes, such as HOXC9, LEP, SERPINE1, TNF, and TNFRSF9, but not UCP1, AGT, and ADIPOQ, were also increased in SPHK1-high HER2-negative breast cancer tissue. Taken together, these data revealed that SPHK1 is associated with increased expression of most of the TAIC-related genes in HER2-negative breast cancer.
Conclusion: Our results suggest that S1P affects TAICs in HER2-negative breast cancer patients, indicating the important roles of S1P in the complicated immune system related to tumor progression. Further investigations are needed to understand the underlying mechanisms.