The Role of COL6A3 in Tumorigenesis, Metastasis, Diagnosis, and Disease Management.

Collagens comprise a large, diverse family of proteins that are abundantly expressed throughout most tissues. As a main component of the extracellular matrix (ECM), it is becoming increasingly appreciated how vital collagens are to tumor development, progression, and metastasis. COL6A3, which encodes the alpha 3 chain of type VI collagen, is a unique member of the collagen family that encodes a C-terminal peptide with powerful signaling capabilities, named endotrophin (ETP). Expression of COL6A3 is required for the survival, migration, and invasion of many cancer cell lines, including breast, bladder, liver, and colorectal cancers. ETP, which was originally discovered to be enriched in the adipocytes of mammary tumors, is a powerful oncopeptide that can alter signaling of tumor and stromal cells. ETP has greater signaling potential than the parental COL6A3 as it can induce EMT and promote chemoresistance, metastasis, and stemness in an TGF-β-like manner. ETP can also function independently of TGF-β to recruit endothelial cells and macrophages. In this review, we examine the molecular implications of COL6A3 and ETP expression and their effects on tumor growth, metastasis, and therapeutic response. Finally, we speculate on the potential of serum ETP as a prognostic biomarker in both carcinomas and sarcomas. In summary, COL6A3 and ETP are powerful drivers of tumor growth that have potential as noninvasive diagnostic and prognostic tools for the clinical management of cancer.