Membrane-bound
mucins belong to an ever-increasing family of O-
glycoproteins that share a structure conserved throughout evolution. Typically, membrane-bound
mucins contain a long extracellular domain, a hydrophobic transmembrane domain, and a short cytoplasmic tail. They are modular
proteins and have a structural organization containing Pro/ Thr/Ser-rich O-glycosylated domains and
EGF-like domains. The
biological roles of
mucins arise from their structures. MUC1 and MUC4 modulate
biological properties of the cell, alter its behavior and modulate cell signaling pathways associated with
tumorigenesis. Altered expression and post-translational modifications confer an important role to MUC1 and MUC4 in
tumor progression,
metastasis, and
cancer cell chimioresistance. Moreover, increasing knowledge about their animal counterparts has made possible a greater understanding of their pathophysiological role in vivo. Most
biological functions attributed to MUC4 are based on the structural homology with its rat homologue. From these results, the development of new
biological tools targeting
mucins has been increasing and the recent attention given to these complex molecules may bring hope for improved
cancer treatments in the future. This review discusses the structure/function of MUC1 and MUC4 membrane-bound
mucins in relation to
cancer cell behavior and cell signaling pathways associated with
tumorigenesis, as well as their potential as
biological tools for gene therapy and
immunotherapy approaches.