An increasing number of studies have shown that the
disaccharide GalNAcβ1→4GlcNAc (
LacdiNAc) group bound to N- and O-
glycans in
glycoproteins is expressed in a variety of mammalian cells. Biosynthesis of the
LacdiNAc group was well studied, and two β4-N-acetylgalactosaminyltransferases, β4GalNAcT3 and β4GalNAcT4, have been shown to transfer N-
acetylgalactosamine (GalNAc) to
N-acetylglucosamine (GlcNAc) of N- and O-
glycans in a β-1,4-linkage. The
LacdiNAc group is often sialylated, sulfated, and/or fucosylated, and the
LacdiNAc group, with or without these modifications, is recognized by receptors and
lectins and is thus involved in the regulation of several biological phenomena, such as cell differentiation. The occurrences of the
LacdiNAc group and the β4GalNAcTs appear to be tissue specific and are closely associated with the
tumor progression or regression, indicating that they will be potent diagnostic markers of particular
cancers, such as
prostate cancer. It has been demonstrated that the expression of the
LacdiNAc group on N-
glycans of
cell surface glycoproteins including β1-integrin is involved in the modulation of their
protein functions, thus affecting cellular invasion and other malignant properties of
cancer cells. The
biological roles of the
LacdiNAc group in
cancer cells have not been fully understood. However, the re-expression of the
LacdiNAc group on N-
glycans, which is lost in
breast cancer cells by transfection of the β4GalNAcT4 gene, brings about the partial restoration of normal properties and subsequent suppression of malignant phenotypes of the cells. Therefore, elucidation of the
biological roles of the
LacdiNAc group in
glycoproteins will lead to the suppression of breast
cancers.