Control of fructose 2,6-bisphosphate levels in rat macrophages by glucose and phorbol ester

Tumor-associated macrophages (TAMs) form an interconnected cellular supportive network in anaplastic thyroid carcinoma

BACKGROUND

A relationship between the increased density of tumor-associated macrophages (TAMs) and decreased survival was recently reported in thyroid cancer patients. Among these tumors, anaplastic thyroid cancer (ATC) is one of the most aggressive solid tumors in humans. TAMs (type M2) have been recognized as promoting tumor growth. The purpose of our study was to analyze with immunohistochemistry the presence of TAMs in a series of 27 ATC.

METHODOLOGY/PRINCIPAL FINDINGS

Several macrophages markers such as NADPH oxidase complex NOX2-p22phox, CD163 and CD 68 were used. Immunostainings showed that TAMs represent more than 50% of nucleated cells in all ATCs. Moreover, these markers allowed the identification of elongated thin ramified cytoplasmic extensions, bestowing a "microglia-like" appearance on these cells which we termed "Ramified TAMs" (RTAMs). In contrast, cancer cells were totally negative. Cellular stroma was highly simplified since apart from cancer cells and blood vessels, RTAMs were the only other cellular component. RTAMs were evenly distributed and intermingled with cancer cells, and were in direct contact with other RTAMs via their ramifications. Moreover, RTAMs displayed strong immunostaining for connexin Cx43. Long chains of interconnected RTAMs arose from perivascular clusters and were dispersed within the tumor parenchyma. When expressed, the glucose transporter Glut1 was found in RTAMs and blood vessels, but rarely in cancer cells.

CONCLUSION

ATCs display a very dense network of interconnected RTAMs in direct contact with intermingled cancer cells. To our knowledge this is the first time that such a network is described in a malignant tumor. This network was found in all our studied cases and appeared specific to ATC, since it was not found in differentiated thyroid cancers specimens. Taken together, these results suggest that RTAMs network is directly related to the aggressiveness of the disease via metabolic and trophic functions which remain to be determined.

Streptozotocin-induced diabetes increases fructose 2,6-biphosphate levels and glucose metabolism in thymus lymphocytes

Acute effect of streptozotocin-induced diabetes on several parameters of glucose metabolism was investigated in thymus lymphocytes (thymocytes). The cells from diabetics rats accumulated in vitro about 2-fold more fructose 2,6-bisphosphate (Fru-2, 6-P2) in the presence of increasing glucose concentration than cells from normal rats. An increased production of lactate was also observed. Phosphofructokinase-1 (PFK-1) and phosphofructokinase-2 (PFK-2) activities were enhanced in cells from diabetic rats compared with those from normal rats. [U-14C]glucose incorporation into glycogen was also increased in cells from diabetic rats and the 14CO2 liberation was lesser than in cells from normal animals. From these data it may be concluded that the response of thymocytes to streptozotocin-induced diabetes is similar to that observed in other extrahepatic tissues.

Cyclosporin A antagonizes phenylephrine, oxytocin and angiotensin effects on glucose metabolism in rat thymus lymphocytes

Effects of phenylephrine, oxytocin and angiotensin on fructose 2,6-bisphosphate (Fru 2,6-P2) content and glycolytic parameters were studied in incubated thymus lymphocytes. These hormones modified Fru 2,6-P2 content dependent upon the energetic status of the cells. In non-preincubated thymus lymphocytes (with relatively high levels of glycogen and ATP), phenylephrine, oxytocin and angiotensin depressed Fru 2,6-P2 content in a dose-dependent manner. The opposite was found when the cells were preincubated for 2 h without substrates (low levels of ATP and glycogen). Changes in lactate release were less evident, but significant. Phenylephrine did not modify the maximal activities of phosphofructokinase (PFK)-1 or PFK-2. However, both submaximal PFK-1 and PFK-2 activities were inhibited by phenylephrine, and the response to exogenous Fru 2,6-P2 on PFK-1 was also altered. The activities of Fru 1,6-P2 and pyruvate kinase were not modified by phenylephrine or A23187 treatment. Simultaneous presence of Cyclosporin A (CsA), an immunosuppressive drug, antagonizes the alpha-adrenergic effect on Fru 2,6-P2 content. CsA alone did not alter basal levels of ATP, hexose phosphate or Fru 2,6-P2, and its opposing effect to alpha-agonist was dose-dependent. CsA cannot change the positive action of PMA or the negative action of A23187 on Fru 2,6-P2 content. The present data suggest that CsA acts prior to calcium liberation and protein kinase C activation. Different possible molecular models are discussed.

Fructose 2,6-bisphosphate and the control of glycolysis by growth factors, tumor promoters and oncogenes

Tumor and proliferating cells maintain a high glycolytic rate even under aerobic conditions. The discovery of fructose 2,6-bisphosphate, a potent stimulator of glycolysis, has prompted a re-investigation of this phenomenon. Rat hepatoma cells and fibroblasts stimulated by mitogens or transformed by the Rous sarcoma virus carrying the v-src oncogene were used as models. The results indicate that in established lines of hepatoma cells the biochemical properties of the bifunctional enzyme, PFK-2/FBPase-2, involved in the synthesis and degradation of fructose 2,6-bisphosphate, differ from those of the enzyme from normal liver. In addition, the stimulation of glycolysis induced by phorbol esters and pp60v-src can be explained by an increase in the concentration of fructose 2,6-bisphosphate and an activation of PFK-2. The mechanism of stimulation involves the transcription of a gene whose product activates PFK-2 or is a distinct PFK-2 isozyme. Finally, mercaptopurines were found to block fructose 2,6-bisphosphate synthesis in vitro and in lymphocytes and lymphoblastic cells. In these cells, this resulted in an inhibition of glycolysis.

Stimulation of glycolysis as an activation signal in rat peritoneal macrophages. Effect of glucocorticoids on this process

1. Peritoneal macrophages were prepared from control, Escherichia coli-treated and triamcinolone acetonide-treated rats. Control and E. coli-treated rats produced resident and activated macrophages respectively. Glycolysis in these cells was studied by the fructose 2,6-bisphosphate (Fru-2,6-P2) content, lactate release and 6-phosphofructo-1-kinase (PFK-1) and 6-phosphofructo-2-kinase (PFK-2) activities. 2. In activated macrophages, lactate release and Fru-2,6-P2 content were increased several-fold compared with those in resident cells. Moreover, the response of these parameters to phorbol 12-myristate 13-acetate in activated macrophages was greater than for resident cells. 3. PFK-2 activity was moderately increased (about 3-fold), but PFK-1 activity was increased 5-fold in activated macrophages compared with resident cells. Partially purified preparations of PFK-1 were sensitive to Fru-2,6-P2, with K0.5 about 0.25 microM in both control and activated cells. However, the Vmax. of PFK-1 from activated cells was increased. In addition, AMP stimulated PFK-1, but the kinetic pattern was different from that described for Fru-2,6-P2. Moreover there was no difference in the stimulation by AMP of PFK-1 from resident and activated cells. 4. Fru-2,6-P2 content and lactate release in macrophages from triamcinolone acetonide-treated rats were decreased in both resident and activated cells. Also, the glucocorticoid inhibited PFK-1 and PFK-2 activities in both resident and activated macrophages. PFK-1 from triamcinolone acetonide-treated rats was not stimulated by Fru-2,6-P2, whereas the effect of AMP was unchanged. The effects of glucocorticoid seem to be specific for phagocytic cells, since the glucocorticoid treatment increased PFK-1 and PFK-2 activities in liver.

Cyclosporin A inhibits phorbol ester-induced activation of superoxide production in resident mouse peritoneal macrophages

Peritoneal resident macrophages from mice are sensitive to inhibition by cyclosporin A (CsA) of phorbol 12-myristate 13-acetate (PMA)-stimulated oxidative burst. Inhibition was assessed in terms of superoxide anion (O2.-) and H2O2 production. Key findings were as follows. (a) CsA inhibited in a dose-dependent manner the production of O2.- when cells were stimulated with PMA. CsA did not alter the respiratory burst induced by other stimuli (zymosan, concanavalin A and fMet-Leu-Phe). It was verified that CsA itself had no scavenger effect. (b) A concomitant decrease in H2O2 liberation following CsA exposure was found. This inhibition was observed both in the initial rate of synthesis and in the accumulation after 15 min of incubation. (c) NADPH oxidase activity in the crude supernatant was unaffected by the previous incubation of macrophages with CsA. CsA does not inhibit glucose transport measured as 14CO2 production. (d) The production of O2.- was strongly dependent on the glucose concentration. Sodium oleate also stimulated O2.- production in resident macrophages. These data might be correlated with the inhibitory effect of CsA upon other functions of macrophages.