Dpy-19 like 3-mediated C-mannosylation and expression levels of RPE-spondin in human tumor cell lines.

C-mannosylation is a unique type of protein glycosylation with a mannose attached to the tryptophan residue via the C-C linkage. Our previous study revealed that dpy-19 like 3 (DPY19L3) acts as a C-mannosyltransferase in human cells. The present study hypothesized that RPE-spondin (RPESP) may be a substrate protein of DPY19L3-mediated C-mannosylation. RPESP has unknown biological functions and has two putative C-mannosylation sites at the W80 and W83 residues; however, to the best of our knowledge, C-mannosylation of RPESP has not previously been investigated. The present study suggested that RPESP is C-mannosylated at W80 and W83 in human cells, whereas gain-of-function experiments using S2 cells revealed that human DPY19L3 catalyzed the C-mannosylation of RPESP at W83 but not W80, which suggested substrate specificity. In addition, the present study detected mRNA expression levels of RPESP in various types of cancer cell lines and high expression levels of RPESP were revealed in certain colorectal cancer cell lines, suggesting that RPESP may have an association with the malignancy of colorectal cancers.