Purification of a Tumoral Marker Recognized by Monoclonal Antibody Po66 and Associated with Human Lung Squamous Cell Carcinoma

Immunohistochemical expression of the intracellular component of galectin-8 in squamous cell metaplasia of the bronchial epithelium in neoplastic and benign processes

Specified galectins are known to play a role in regulating cell proliferation, differentiation, adhesion and migration. Po66, a mouse IgG1 monoclonal antibody produced by immunization against squamous cell cancer, reacts against a carbohydrate-binding protein (Po66-CBP), recently shown to be a member of the galectin family with a strong homology with galectin-8 (PCTA-1), identified as a human tumor-associated antigen. We studied Po66 in squamous metaplasia of the bronchi in order to determine whether it could be specifically involved in neoplastic conditions and if so, if it would be helpful in distinguishing metaplasia at risk of cancer. Twenty-eight formalin-fixed, paraffin-embedded archival tissues of 17 metaplasias with SCC, 3 metaplasia with distant neoplastic disease and 8 metaplasias with an inflammatory process, were immunostained using a streptavidin biotin peroxydase method. The squamous metaplasias were positively stained in non-neoplastic disease as well as in neoplastic processes. Expression was also observed in stromal and normal cells. Po66-CBP was not associated with a pre-neoplastic character. We discussed the expression of this intra-cellular component of galectin-8 according to the functions of galectins in cellular differentiation, host reaction against tumor, and inflammation.

Two messenger RNAs and five isoforms for Po66-CBP, a galectin-8 homolog in a human lung carcinoma cell line

Galectins are animal proteins which specifically bind beta-D-galactoside residues and their specific cellular function is not yet clearly established. However, these proteins seem to play a role in neoplastic transformations. Po66 is a murine monoclonal antibody directed against a protein from human lung carcinoma, Po66 Carbohydrate-Binding-Protein (Po66-CBP), which belongs to the galectin-8 family. Our results show that the Po66-CBP gene generates five transcripts by alternative splicing, which could give rise to five proteins: two proteins belong to the tandemly repeated galectin family and three belong to the single carbohydrate recognition domain galectins. All these proteins are encoded by a unique gene located in 1q42. Experiments carried out by reverse transcriptase-polymerase chain reaction show that the levels of expression of these five galectin-8 isoforms are variable during the culture time in SK-MES-1, a human lung squamous carcinoma cell line. Cancer Genome Anatomy Project database analysis confirms the presence of Po66-CBP in lung cancer and its absence in healthy lung.