Plasma fibronectin (FN1) is degraded by cathepsin G (CTSG) into a characteristic pattern of gelatin-binding peptides of M, = 64000, 40000, and 30000 (Vartio et al. 1981, Vartio 1982). CTSG is activated by UV exposure and can activate matrix metalloproteinases MMP1 and MMP2, but increased levels of MMP activity did not correlate with increased FN degradation in normal human fibroblasts (NHFs) following exposure to UVB (50 mJ/cm2) irradiation, while addtion of CTSG inhibitor decreased FN degradation, suggesting that CTSG is directly responsible for FN1 degradation (Son et al. 2009).