Activity of glycogen synthase and phosphorylase and glucose 6-phosphate content in renal clear cell carcinomas

Kinetic modeling of glucose central metabolism in hepatocytes and hepatoma cells

BACKGROUND

Kinetic modeling and control analysis of a metabolic pathway may identify the steps with the highest control in tumor cells, and low control in normal cells, which can be proposed as the best therapeutic targets.

METHODS

Enzyme kinetic characterization, pathway kinetic modeling and control analysis of the glucose central metabolism were carried out in rat (hepatoma AS-30D) and human (cervix HeLa) cancer cells and normal rat hepatocytes.

RESULTS

The glycogen metabolism enzymes in AS-30D, HeLa cells and hepatocytes showed similar kinetic properties, except for higher AS-30D glycogen phosphorylase (GP) sensitivity to AMP. Pathway modeling indicated that fluxes of glycogen degradation and PPP were mainly controlled by GP and NADPH consumption, respectively, in both hepatocytes and cancer cells. Likewise, hexose-6-phosphate isomerase (HPI) and phosphoglucomutase (PGM) exerted significant control on glycolysis and glycogen synthesis fluxes in cancer cells but not in hepatocytes. Modeling also indicated that glycolytic and glycogen synthesis fluxes could be strongly decreased when HPI and PGM were simultaneously inhibited in AS-30D cells but not in hepatocytes. Experimental assessment of these predictions showed that both the glycolytic and glycogen synthesis fluxes of AS-30D cells, but not of hepatocytes, were inhibited by oxamate, by inducing increased Fru1,6BP levels, a competitive inhibitor of HPI and PGM.

CONCLUSION

HPI and PGM seem suitable targets for decreasing glycolytic and glycogen synthesis fluxes in AS-30D cells but not in hepatocytes.

GENERAL SIGNIFICANCE

The present study identified new therapeutic targets within glucose central metabolism in the analyzed cancer cells, with no effects on non-cancer cells.

Functional characterization of AMP-activated protein kinase signaling in tumorigenesis

AMP-activated protein kinase (AMPK) is a ubiquitously expressed metabolic sensor among various species. Specifically, cellular AMPK is phosphorylated and activated under certain stressful conditions, such as energy deprivation, in turn to activate diversified downstream substrates to modulate the adaptive changes and maintain metabolic homeostasis. Recently, emerging evidences have implicated the potential roles of AMPK signaling in tumor initiation and progression. Nevertheless, a comprehensive description on such topic is still in scarcity, especially in combination of its biochemical features with mouse modeling results to elucidate the physiological role of AMPK signaling in tumorigenesis. Hence, we performed this thorough review by summarizing the tumorigenic role of each component along the AMPK signaling, comprising of both its upstream and downstream effectors. Moreover, their functional interplay with the AMPK heterotrimer and exclusive efficacies in carcinogenesis were chiefly explained among genetically altered mice models. Importantly, the pharmaceutical investigations of AMPK relevant medications have also been highlighted. In summary, in this review, we not only elucidate the potential functions of AMPK signaling pathway in governing tumorigenesis, but also potentiate the future targeted strategy aiming for better treatment of aberrant metabolism-associated diseases, including cancer.

The effect of fixatives and temperature on the quality of glycogen demonstration

Glycogen is demonstrated in a number of lesions and is diagnostically significant, particularly in certain tumors. To stain glycogen accurately, it is essential to choose a suitable fixative, temperature and staining method. We used rabbit liver to assess these variables. Specimens were fixed in three fixatives at two temperatures: 10% formalin, neutral buffered formalin (NBF) and Bouin's solution at 37 and 4 degrees C. Seventy-two paraffin sections were prepared and stained with periodic acid-Schiff (PAS), hexamine (methenamine) silver and Best's carmine methods. Negative control sections using diastase digestion were used for all methods to confirm the presence of glycogen. For the PAS reaction, Bouin's fixative gave better results at both temperatures compared to the other fixatives. For hexamine (methenamine) silver, the quality of staining was improved for tissues fixed in both 10% formalin and NBF at 37 degrees C compared to Bouin's solution. Both 10% formalin and NBF at 4 degrees C gave better results than Bouin's solution. For Best's carmine, Bouin's solution gave the best results for tissues fixed at 4 degrees C. Fixation of tissues with NBF at 37 degrees C gave the best quality staining. We concluded that the quality of glycogen staining in paraffin sections is greatly affected by both the fixative and the temperature of fixation.

The cyclin-dependent kinase (CDK) inhibitor flavopiridol inhibits glycogen phosphorylase

Flavopiridol has been shown to induce cell cycle arrest and apoptosis in various tumor cells in vitro and in vivo. Using immobilized flavopiridol, we identified glycogen phosphorylases (GP) from liver and brain as flavopiridol binding proteins from HeLa cell extract. Purified rabbit muscle GP also bound to the flavopiridol affinity column. GP is the rate-limiting enzyme in intracellular glycogen breakdown. Flavopiridol significantly inhibited the AMP-activated GP-b form of the purified rabbit muscle isoenzyme (IC50 of 1 microM at 0.8 mM AMP), but was less inhibitory to the active phosphorylated form of GP, GP-a (IC50 of 2.5 microM). The AMP-bound GP-a form was poorly inhibited by flavopiridol (40% at 10 microM). Increasing concentrations of the allosteric effector AMP resulted in a linear decrease in the GP-inhibitory activity of flavopiridol suggesting interference between flavopiridol and AMP. In contrast the GP inhibitor caffeine had no effect on the relative GP inhibition by flavopiridol, suggesting an additive effect of caffeine. Flavopiridol also inhibited the phosphorylase kinase-catalyzed phosphorylation of GP-b by inhibiting the kinase in vitro. Flavopiridol thus is able to interfere with both activating modifications of GP-b, AMP activation and phosphorylation. In A549 NSCLC cells flavopiridol treatment caused glycogen accumulation despite of an increase in GP activity, suggesting direct GP inhibition in vivo rather than inhibition of GP activation by phosphorylase kinase. These results suggest that the cyclin-dependent kinase inhibitor flavopiridol interferes with glycogen degradation, which may be responsible for flavopiridol's cytotoxicity and explain its resistance in some cell lines.

Chromophilic renal cell carcinoma: cytomorphological and cytogenetic characterisation of four permanent cell lines

Chromophilic renal cell carcinoma is a distinct type of human renal cancer, only recently recognised and defined by its characteristic histomorphological aspect and cytogenetic aberrations. We are the first to report on the establishment and cytogenetic characterisation of a panel of four permanent cell lines, i.e. chromphi-1, -2, -3 and -4, derived from strictly defined renal cell carcinomas (RCCs) of the chromophilic type and kept in continuous culture for up to 5 years. Immunohistochemistry revealed coexpression of vimentin and cytokeratins in all cell lines the cytokeratin polypeptide patterns, however, varying between the different cell lines. By light and transmission electron microscopy, various amounts of cytoplasmatic glycogen deposition were observed, being most pronounced in chromphi-3 and -4. The mean population doubling time ranged from 24 h (chromphi-1) to 51 h (chromphi-4). Chromphi-1 tumour cells produced slowly growing tumours in nude mice using the subrenal capsule assay. In all cell lines, cytogenetic analysis revealed numerical chromosomal aberrations known to be characteristic for chromophilic RCCs, i.e. loss of the Y chromosome, tri- or tetrasomy of chromosomes 7 and 17 as well as various combinations of additional structural and numerical chromosomal aberrations. Karyological aberrations were least pronounced in chromphi-2 and most complex in chromphi-1. Chromosomal aberrations typically affecting the short arm of chromosome 3 in clear cell RCCs were not observed in any of our cell lines.

Preneoplastic lesions in rodent kidney induced spontaneously or by non-genotoxic agents: predictive nature and comparison to lesions induced by genotoxic carcinogens

The current literature on non-genotoxic renal carcinogens and the associated neoplastic and preneoplastic lesions has been reviewed in order to determine their occurrence and predictive nature with regard to tumor formation. In addition the mechanisms involved in the genesis of renal tumors are discussed. A more generalized classification of preneoplastic and neoplastic renal lesions was introduced, based on studies conducted with genotoxic and non-genotoxic renal carcinogens. Reports on preneoplastic lesions were found in the literature for control animals as well as animals treated with non-genotoxic carcinogens. Due to the paucity of data regarding preneoplastic lesions in control animals and animals treated with non-genotoxic carcinogens, new data were also generated by rereading kidney slides of control animals of a randomly selected NTP study and kidney slides of male rats treated with the highest dose of ochratoxin A, one of the most potent non-genotoxic renal carcinogens known. The control slides and the slides from the ochratoxin A study indicated that the cytologic and morphologic types of preneoplastic lesions characteristically observed in bioassays using genotoxic carcinogens are also present in control animals and animals treated with non-genotoxic carcinogens. The incidence of preneoplastic lesions was low in control animals and higher in animals treated with non-genotoxic carcinogens. The diverse classifications used in the literature did not allow a direct comparison of lesions and corresponding incidences with those of the newly generated data. However, three major tendencies were observed: (a) whenever a high incidence of preneoplastic lesions was reported, renal neoplasms were also found, (b) the larger the size and the further a lesion had progressed, the higher was the probability of tumor formation, and (c) not all preneoplastic lesions are irreversible, but reversibility seemed to decrease with increasing lesion size and progression. It must be emphasized that the data available for these conclusions are limited. This is not due to the lack of adequate numbers of bioassays with non-genotoxic carcinogens, but rather to the lack of consistent reporting of data. A generalized and more widely used classification which incorporates early lesions would certainly improve the current data base on renal lesions and provide future improvements in the predictive nature of these lesions.

[Classification of renal cell carcinoma/tumors and their relationship to the nephron-collecting tubules system]

After a controversial phase of nomenclature (including--among others--the terms "hypernephroma" and "hypernephroid carcinoma") a cytomorphologically defined subtyping of renal cell tumours (adenomas, carcinomas, oncocytomas) is offered, based on new electron microscopical and histochemical observations. These data are in part supported by cytogenetical findings reported in the literature. Phenotypical/histogenetical relations to different parts or cell types, respectively, of the nephron-collecting duct system could be demonstrated. Chromophobe cell carcinoma and oncocytoma exhibit features of the intercalated cells.