Differentiation-dependent glycosylation of cells in squamous cell epithelia detected by a mammalian lectin

The squamous stratified epithelia contain a proliferative
(harboring mitotic activity) and a differentiating compartment. Due
to the potential of protein-carbohyd rate interactions to regulate
cellular activities we introduced a mammalian lectin to cyto- and
histochemical analysis. We answer the questions of whether and to
what extent this new probe can pinpoint differentiation-dependent
glycosylation changes in sections and in culture of keratinocytes.
Material and Methods: Purification and labeling enabled monitoring
of galectin-3 reactivity in frozen sections of human and pig
epidermis and basal cell carcinomas as well as in culture of
keratinocytes. The staining pattern of the lectin was correlated
with the staining profile of other cell markers including
desmosomal proteins, beta(1) integrin, and the proliferation marker
Ki-67. The Dolichos biflorus agglutinin (DBA) sharing binding
reactivity of galectin-3 to the A type histoblood group epitope was
used for comparison. Results: Both lectins exhibit suprabasal
binding. However, their profiles were not identical, substantiated
by lack of coinhibition. Strong DBA reactivity was also observed in
a limited number of basal layer cells, namely in cells without the
expression of the proliferation marker Ki-67. Cultured mitotic
epidermal cells have no reactivity for DBA. Presence of ligands for
this plant lectin was connected with decreased positivity of nuclei
for Ki-67 and the occurrence of ring-shaped nucleoli, micronucleoli
or absence of nucleoli. Considering colocalization the pattern of
galectin-3-binding sites coincided with the presence of desmosomal
proteins such as desmoplakin-1 and desmoglein but not beta(1)
integrin, a potential ligand. Interestingly, studied basal cell
carcinomas expressed no binding sites for galectin-3, while a
limited number of cells were DBA-reactive. Conclusion: The
expression of galectin-3-binding sites and also DBA-reactive
glycoligands correlates with an increased level of differentiation
and/or cessation of proliferation in the examined squamous
stratified epithelia. Further application of tissue lectins for
characterizing ligand expression and its modulation is an important
step to reveal functional relevance.