Discrimination between neuronal and glial cell tumours by pyruvate kinase electrophoresis

Comparison of pyruvate kinase variants from breast tumor and normal breast

BACKGROUND

Pyruvate kinase isozymes in human breast tumor tissue were compared in this study with normal human breast tissue. Two forms of pyruvate kinase present in normal and tumor human breast were purified by ammonium sulfate precipitation, dialysis, gel filtration, ion exchange, and affinity chromatography. Molecular weight of the native enzyme was determined.

METHODS

Presence of pyruvate kinase activity was examined in normal and tumor breast tissues. Pyruvate kinase was purified with Sephadex DEAE-50, Sepharyl S-200, and Blue Sepharose CL-6B chromatography. Spectrophotometric methods were used to determine activities of pyruvate kinase.

RESULTS

Molecular weights of fractions I and II as determined by gel filtration on Sepharyl S-200 were 135,000 Da, 260,000 Da in normal breast tissue, and 72,000 Da, 250,000 Da in tumor breast tissue, respectively. Fractions I and II of pyruvate kinase may be purified approximately 1,591-fold, 636.4-fold in normal breast tissue and 219-fold, 318-fold in tumor breast tissue, respectively. Pyruvate kinase activity in tumor tissue was found higher than in normal tissue. Only tumor fraction II showed tumor-specific sensitivity to L-cysteine. L-phenylalanine inhibited both fractions I and II of normal breast and fraction I of tumor breast, but not fraction II of pyruvate from tumor. ATP inhibited normal and tumor fraction I of pyruvate kinase. The influence of ATP on enzyme activity from normal and tumor fraction II depended upon its concentration.

CONCLUSIONS

It was thought that isozymes of pyruvate kinase from human breast tissue might be M1 and M2 isozymes when compared with those of other tissue pyruvate kinase isoenzymes. Fraction II from breast tumor represented different sensitivity to L-cysteine, L-phenylalanine, and specific activity in comparison with fraction II from normal breast. Different kinetic behavior of fractions in the human breast tumors may support the concept of an isozyme shift.

Purification and characterization of human meningioma M2-type pyruvate kinase

The M2-type pyruvate kinase was purified from human meningioma by ammonium sulfate precipitation, followed by ion exchange and affinity chromatography. The specific activity of the purified enzyme was 33.4 U/mg with a yield of 6.5%. The enzyme gave a single band with 63,000 +/- 2000 Da upon SDS polyacrylamide gel electrophoresis. On cellulose acetate electrophoresis zymograms, the purified enzyme (M2) showed a single band, while crude extracts gave two broad bands corresponding to pyruvate kinase isozymes. The pI value of purified enzyme was found to be 6.9. With phosphoenol pyruvate as substrate the purified enzyme showed sigmoidal kinetics, while in the presence of 0.6 mM fructose 1,6-diphosphate as modulator it gave a hyperbolic saturation curve with a Km value of 0.53 mM.

Cellular expression of K-type pyruvate kinase in normal and neoplastic human tissues

The cellular expression of K-type pyruvate kinase was studied immunohistochemically in several normal and neoplastic tissues of human origin. The authors used the monoclonal antibody, designated as ES1, which was raised against human K-type pyruvate kinase. In contrast to the normal counterparts, a strong immunoreactivity was found in a rhabdomyosarcoma (n = 1), in a carcinoma of the pancreas (n = 1), and in neurofibromas (n = 2). Furthermore, the staining in leiomyosarcomas (n = 2) was shown to be more intense when compared with both normal smooth muscle cells and leiomyomas (n = 2). These findings show that knowledge about the cellular expression of the K-type pyruvate kinase identifies cell types for which its expression serves as oncodevelopmental marker. In addition, these immunohistochemical studies give information whether shifts toward K-type containing isozymes of pyruvate kinase, which are determined by electrophoresis in whole cytosolic extracts of various tumors, are due to an altered gene expression or due to proliferation of cells which normally express already the K-type pyruvate kinase. The first possibility probably occurs in rhabdomyosarcomas. The latter possibility seems to be valid for astrocytomas because astrocytes express the K-type pyruvate kinase in normal brain.