Expression and Roles of Lumican, a Small Leucine-rich Proteoglycan, in Gastrointestinal and Other Cancers

Lumican is a member of classⅡof the small leucine-richproteoglycan family, and it was first reported as a keratin sulfatecontainingproteoglycan in the cornea. Lumican plays an importantrole in collagen fibrillogenesis in cornea and other various humantissues. Recently, a number of reports have shown that lumicanis expressed in several types of malignant tumors includinggastrointestinal cancers; however, the roles of lumican in the tumorsare quite variable. In neuroendocrine tumors of the colon, forexample, lumican expression in the cytoplasm is negatively correlatedwith tumor malignancy grade. Increased expression of lumican inmalignant melanoma and osteosarcoma inhibits their aggressivegrowth. In contrast, the localization of lumican in the stromal tissuecorrelates with advanced cancer stage and retroperitoneal andduodenal invasion and residual tumor presence of pancreatic cancer,and increased secretion of lumican in the extracellular space inducesgrowth of the cancer. Lumican in colorectal cancer has tended tocorrelate with the spread of lymph node metastasis and the depth oftumor invasion. The reason for these opposing effects of lumican indifferent cancers is not well understood, but different glycosylationpatterns of lumican or receptors and in the cell signaling pathwaysinvolved may play pivotal roles in its cancer cell behaviors. Thisreview article summarizes the expression and roles of lumican inmalignant tumors, including gastrointestinal cancers, and discussesthe possibility of using lumican as a diagnostic marker and noveltherapeutic target for cancers.