Chondroitin sulfate proteoglycan promotes APRIL‐induced tumor cell proliferation

A proliferation‐inducing ligand (APRIL), a member of the tumor necrosis factor superfamily, affects the survival and proliferation of tumor cells. Understanding the mechanism of action of APRIL in tumor cells, including intracellular signaling, is important for its potential use in diagnostics and prognosis. It has been shown that APRIL‐induced tumor proliferation requires heparan sulfate (HS) proteoglycans to mediate the binding of APRIL to tumor cells. Here, we show that chondroitin sulfate (CS) proteoglycan mainly contributes to the APRIL‐stimulated proliferation of triple‐negative breast cancer BT‐549 cells. Knockout of chondroitin 4‐O‐sulfotransferase‐1 (C4ST‐1), a key CS biosynthetic enzyme, suppressed APRIL‐induced tumor proliferation, whereas deficiency of exostosin 1 (EXT1), a key HS biosynthetic enzyme, had only weak effects. Molecular interaction analyses using Biacore revealed that although CS did not directly bind to tumor growth through Ca2+ modulator interactor (TACI), it enhanced the binding of APRIL to the APRIL receptor, TACI. The small leucine‐rich proteoglycan, biglycan, plays a pivotal role in tumor growth and progression. Biglycan knockdown inhibited BT‐549 cell proliferation. These results suggest that CS synthesized by C4ST‐1 participates in APRIL signaling and modulates pathological events in tumors.