CST7 and glioblastoma: Secreted cystatin F was internalized into the U-251 MG glioblastoma cell line, which does not express cystatin F. We have found that Asn115 is modified by M6P, which is in agreement with previous studies that showed that Asn115 glycosylation is important for the secretion and internalization of cystatin F [16, 28].