Decorin is internalized and inhibits myeloma cell growth through up-regulation of p21WAF and induction of apoptosis. (A) Myeloma cells were exposed to decorin (30 μg/mL) for 30 minutes, washed, and then subjected to Western blotting for detection of decorin at the indicated times. The level of decorin was high after 30 minutes and then rapidly diminished by 120 minutes. Recombinant decorin (rDec) was used as a positive control. (B) Primary myeloma cells (patient 5) were cultured alone in the absence or presence of increasing doses of decorin (1-20 μg/mL) for approximately 36 hours. (C) Annexin V–PI flow cytometry of myeloma cells from 3 patients cultured in the absence or presence of decorin for 36 hours showed an increased percentage of apoptotic annexin V–positive myeloma cells after decorin treatment. (D) The level of phosphorylated p21WAF in myeloma cells was increased after 24-hour incubation with decorin (10 μg/mL).
