C1Q‐TNF‐related peptide 8 (CTRP8) in human prostate cancer

Abstract

Introduction C1Q Tumor Necrosis Factor related Peptide 8 (CTRP8) is the one of the least characterized members of the C1Q/TNF family of proteins which is engaged in diverse functions ranging from metabolism to immunity and is one of only two CTRP family members absent in the mouse genome. CTRP8 was identified in our lab as a novel ligand of the RXFP1 receptor and was found to promote invasiveness and chemoresistance to temozolomide in glioblastoma (GB)(Glogowska et al., 2013; Thanasupawat et al., 2018). We have generated high‐affinity rabbit antisera to human CTRP8 to identify a selective mast cell subpopulation in human prostate cancer tissues (Hempel Sullivan et al., 2020). Mast cells are innate immune cells which are primarily known for their role in the mediation of allergic responses. They have been detected within prostate cancer tissues and serve as potential prognostic marker in prostate cancer (Johansson et al., 2010; Hempel Sullivan et al., 2020). Methods Affinity‐purified rabbit polyclonal antisera directed against an epitope unique to human CTRP8 were characterized by Western blot, immunofluorescence, and immunohistochemistry in prostate cancer tissue sections and human prostate cancer tissue microarrays (TMAs). Results Of several Flag‐tagged human and mouse CTRP family members transiently expressed in HEK293T cells, the CTRP8 antisera exclusively detected human CTRP8 as assessed by Western blot, demonstrating the specificity of the antisera. We studied the expression of CTRP8 in human prostate tissues. CTRP8 was expressed in a subpopulation of human mast cells distributed in prostate cancer tissues, as demonstrated by co‐localization of CTRP8 immunoreactivity and toluidine blue positive mast cells in prostate cancer tissues. This was further validated by dual immunofluorescence of CTRP8 with Tryptase, a marker for mature mast cells. Initial analysis of prostate cancer tissue microarrays (TMAs) (n= 360) revealed a comparative increase in the proportion of Tryptase+/ CTRP8+ cells versus total number of mast cells (Tryptase+/ CTRP8+ and Tryptase+/ CTRP8‐ cells) in the extra‐tumoral compartment as compared to intra‐tumoral regions for Gleason grades 6 and 7 prostate cancer samples. Weak staining of CTRP8 was detected in prostate epithelial cells. The RXFP1+ human prostate cancer cell line PC3 responded to CTRP8 treatment with increased protein kinase C delta signaling and enhanced motility as determined by real‐time migration assays. Conclusions Here we have identified the expression of adipokine family member CTRP8 in prostate epithelial cells and in a subpopulation of mature mast cells in patient prostate cancer tissues, thus, identifying CTRP8 as a novel player in prostate cancer and associated mast cell compartment. References Glogowska, A., et al. J. Pathol., 231, 466–479, 2013 Thanasupawat, T., et al. Mol. Oncol. 12, 1464–1479, 2018 Johansson, A., Am. J. Pathol, 177, 1031–1041, 2010 Hempel Sullivan H, et al. J. Pathol., 2020 Hempel Sullivan H, et al. Cancer Epidemiol Biomarkers Prev., 2020