Interpretation of these observations is complicated by the fact that a uniform protein structure that defines biologically active CCN2 has not yet been resolved.
Here, using DG44 CHO cells engineered to produce and secrete FL-CCN2 and cell signaling and cell physiological activity assays, we demonstrate that FL-CCN2 is itself an inactive precursor and that a proteolytic fragment comprising domains III (thrombospondin type 1 repeat) and IV (cystine knot) appears to convey all biologically relevant activities of CCN2. In congruence with these findings, purified FL-CCN2 could be cleaved and activated following incubation with matrix metalloproteinase activities. Furthermore, the C-terminal fragment of CCN2 (domains III and IV) also formed homodimers that were ∼20-fold more potent than the monomeric form in activating intracellular phosphokinase cascades.
The homodimer elicited activation of fibroblast migration, stimulated assembly of focal adhesion complexes, enhanced RANKL-induced osteoclast differentiation of RAW264.7 cells, and promoted mammosphere formation of MCF-7 mammary cancer cells. In conclusion, CCN2 is synthesized and secreted as a preproprotein that is autoinhibited by its two N-terminal domains and requires proteolytic processing and homodimerization to become fully biologically active. Connective tissue growth factor (CCN2) is a matricellular preproprotein controlled by proteolytic activation
J Biol Chem.
2018 Nov 16;293(46):17953-17970.
Kaasbøll, Ashish K Gadicherla, Jian-Hua Wang, Vivi Talstad
Monsen, Else Marie Valbjørn Hagelin, Meng-Qiu Dong, Håvard