Structure
MUC4 is an O-glycoprotein that can reach up to 2 microns outside the cell. MUC4 mucins consist of a large extracellular alpha subunit that is heavily glycosylated and a beta subunit that is anchored in the cell membrane and extends into the cytosol. This beta subunit is considered an oncogene, whose role in cancer is increasingly being recognized particularly due to its involvement in signalling pathways, particularly with ErbB2 (Her2). This subunit serves as a ligand for ErbB2, which is suggested to cause the repression of apoptosis found in many cancer cells
The large alpha subunit that is glycosylated likely confers the anti-adhesive properties to the cell, allowing for cell-cell and cell-matrix detachment in normal as well as cancerous cells. The heavy glycosylation may also serve as a reservoir for growth factors, which may become released upon degradation.
The two subunits of Muc4 are transcribed from a single gene Over 24 splice variants have been found for MUC4, in normal as well as abnormal tissue. Some forms are soluble, while others are membrane bound Many polymorphisms are observed in the tandem repeat region of the alpha subunit, which has a variable number of repeats
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