Single-cell transcriptomics and functional analyses identified SPIN.DOC as a regulator for Wnt signaling and cancer stemness in colorectal cancer.

The role of SPIN.DOC in tumorigenesis remains unclear. In this study, we utilized single-cell RNA sequencing (scRNA-seq) data to investigate SPIN.DOC expression in a cohort of normal, primary human colorectal cancer (CRC) and metastatic tissues from CRC patients. Our findings revealed differential expressions of SPIN.DOC across multiple cell clusters in different conditions and with the highest expression observed in tumor samples, suggesting its potential role in CRC progression. Further analysis showed that SPIN.DOC positive cell-cluster showed upregulation of β-catenin and cancer stem cell (CSC) marker genes, indicating its role in activating Wnt signaling for cell proliferation. Additionally, these cells also showed downregulation of genes associated with cell-cell junctions, promoting epithelial-mesenchymal transition (EMT) and cancer progression in colon tumors. To validate these findings experimentally, we analyzed the expression of SPIN.DOC in normal colorectal and three colorectal cancer cell lines by immunofluorescence and western blotting. SPIN.DOC was expressed at low level in human normal colon epithelial cells but was highly expressed in all the three colorectal cancer cell lines tested. Consistent with the scRNA data, overexpression of SPIN.DOC in CRC cell line, enhanced cell proliferation, cell migration, invasion, colony-forming capability and Wnt signaling. Moreover, these cells upregulate EMT-associated genes and cancer stem cell markers, as determined by qRT-PCR and immunoblotting. Enhanced spheroid formation in SPIN.DOC overexpressing cells further indicated increased stemness of the cells. Conversely, the knockdown of SPIN.DOC diminished the aforesaid phenotypes. Overall, these data suggest that SPIN.DOC promotes cancer cell proliferation, metastasis and regulates pluripotency and self-renewal of colorectal CSCs. Overall, our study highlights SPIN.DOC as a key essence of CRC by regulating cancer stemness and provides an opportunity of using SPIN.DOC, as a diagnostic and prognostic biomarker of colorectal cancer.