Determination of kinetic properties of G6PDH and PGDH and the expression of PCNA during liver carcinogenesis in coastal flounder

Abstract

Flounder sampled along a pollution gradient in the North Sea were investigated histochemically to determine in situ initial reaction velocities (Vini) and kinetic parameters (Vmax and Km values) of G6PDH and PGDH inside and outside hepatocellular foci and carcinomas. Reactions were monitored quantitatively in time using image analysis. PCNA was detected in serial sections as marker for cell proliferation by immuno-gold-silver labelling. Enzymic parameters were correlated with PCNA expression and histopathology. In all stages of carcinogenesis from early foci to well-organised adenomas and anaplastic carcinomas, higher Vini of G6PDH but not of PGDH and a higher PCNA labelling index (43–65%) than in surrounding liver tissue were found. PCNA expression in small satellites of carcinomas reflected their malignancy and were used to differentiate between early foci and invasively growing protrusions of carcinomas. Prolonged pollutant exposure partially inhibited or inactivated G6PDH (and not PGDH) in extrafocal liver tissue and this was compensated by a reduction in Km. In cancerous lesions, G6PDH levels were upregulated but the low Km values were kept to increase NADPH production in cancer cells that is required for biosynthesis during cell division and for xenobiotic biotransformation.