IDENTIFICATION OF PEANUT AGGLUTININ RECEPTORS RELATED TO THE STATE OF TUMORAL LIVER-CELL DIFFERENTIATION

The relationship between cell differentiation/tumorisation and plasma membrane glycoproteins was approached using peanut agglutinin (PNA) a lectin specific for the Gal-beta(1,3)GalNAc sequence and a homologous cell system consisted of normal rat hepatocytes (HyC) and a poorly differentiated hepatoma (ZHC). This work is focused on the molecular nature of PNA receptors. PNA bound strongly to ZHC, but bound very weakly, if at all to hepatocytes. After sialidase treatment this binding was slightly enhanced in ZHC and HyC. The total number of binding sites on ZHC was 9.6 x 10(6)/cell and 1.2 X 10(7)/cell before and after sialidase treatment respectively. In contrast, this number could not be calculated on HyC, even after sialidase treatment. The PNA receptors were isolated and identified from ZHC using affinity chromatography on immobilized PNA and lectin overlay. Two bands were revealed after SDS-PAGE of PNA receptors: a major one with a relative molecular mass of 160 kDa and a minor one of 110 kDa. The latter disappeared after sialidase treatment of ZHC suggesting the possibility that these two bands could be less and more sialylated forms of the PNA receptors, respectively. In contrast no PNA receptors could be detected on HyC. These PNA receptors could be considered O-linked glycoproteins containing the Gal-beta(1,3)GalNAc disaccharide because: i) PNA carbohydrate specificity toward this disaccharide found in this glycoprotein type; ii) their carbohydrate composition with Gal and GalNAc but not man residues; iii) their sensitivity to alkaline treatment; and iv) strong inhibition of PNA binding to ZHC with the Gal-beta(1,3)GalNAc structure. The absence of PNA receptors on HyC appeared to be related to the absence of this glycoprotein containing the disaccharide but not to the change or failure of glycosylation of the polypeptide chain of PNA receptors. The relationship between the presence of PNA receptors and differentiation/tumorisation phenomena as well as the mechanism that induced the expression of these receptors are discussed.