Effect of MMP-13 degraded SPARC on type I collagen and its biomarker potential in colorectal cancer.

Abstract

717 Background: Increased collagen deposition and remodeling of the extracellular matrix has been shown to play a role in the pathology of gastrointestinal cancer (GC). The matricellular protein SPARC (secreted proteome acidic and rich in cysteine) binds collagens and hereby regulates collagen fibrillogenesis. Matrix metalloproteinase (MMP) mediated cleavage of SPARC, increases the affinity for collagens up to 20-fold. SPARC has been shown to be overexpressed in GC patients and associated with GC cell invasion and metastasis. Increased expression and cleavage of SPARC might therefore be implicated in GC pathology by increasing collagen deposition. Here, we present the development and validation of a competitive enzyme-linked immunosorbent assay (ELISA) quantifying a specific MMP-13 generated fragment of SPARC - a cleavage site involved in increased collagen affinity. The biomarker potential of this fragment was examined in serum from colorectal cancer (CRC) patients and healthy controls. Moreover, we evaluated the ability of cleaved SPARC to prevent type I collagen degradation in vitro. Methods: A monoclonal antibody was raised against a MMP-13-generated neo-epitope of SPARC and a competitive ELISA assay (SPARC-M) was developed and technically validated. Serum levels were assessed in CRC patients (n=50) and healthy controls (n=30). The ability of cleaved SPARC to prevent collagen degradation was investigated using an ELISA assay measuring type I collagen degradation by MMP-9. Results: SPARC-M was technically robust and specific for SPARC cleaved by MMP-13. The fragment was elevated in CRC patients when compared to healthy controls (p=0.0097). When MMP-13 degraded SPARC was incubated with type I collagen and MMP-9, type I collagen degradation was completely inhibited suggesting that SPARC increases collagen deposition by preventing collagen degradation. Conclusions: SPARC-M was significantly elevated in CRC patients compared to healthy controls suggesting biomarker potential. Biologically, cleaved SPARC may prevent type I collagen degradation hereby leading to a pro-tumorigenic environment. Larger clinical studies are needed to validate the clinical use of this biomarker in GC.