Induction of histidine decarboxylase activity in the spleen of mice treated with staphylococcal enterotoxin A and demonstration of its non-mast cell origin

Expression of Histidine Decarboxylase and Its Roles in Inflammation

Histamine is a well-known mediator of inflammation that is released from mast cells and basophils. To date, many studies using histamine receptor antagonists have shown that histamine acts through four types of receptors: H1, H2, H3, and H4. Thus, histamine plays more roles in various diseases than had been predicted. However, our knowledge about histamine-producing cells and the molecular mechanisms underlying histamine production at inflammatory sites is still incomplete. The histamine producing enzyme, histidine decarboxylase (HDC), is commonly induced at inflammatory sites during the late and chronic phases of both allergic and non-allergic inflammation. Thus, histamine levels in tissues are maintained at effective concentrations for hours, enabling the regulation of various functions through the production of cytokines/chemokines/growth factors. Understanding the regulation of histamine production will allow the development of a new strategy of using histamine antagonists to treat inflammatory diseases.

Inductions of histidine decarboxylase in mouse tissues following systemic antigen challenge: contributions made by mast cells, non-mast cells and IL-1

BACKGROUND

Previous findings suggest that antigen challenge (AC) may induce histidine decarboxylase (HDC) in cells other than mast cells (MCs) via MC-derived IL-1. We examined this hypothesis.

METHODS

Mice were sensitized to ovalbumin. After the sensitization, an AC was delivered intravenously.

RESULTS

In control mice, AC markedly induced HDC at a postanaphylactic time in the liver, lung, spleen, and ears. In MC-deficient W/W(v) mice, AC also induced HDC, although the effect was weaker than in control mice. AC increased IL-1 in the tissues, the pattern being similar in W/W(v) and control mice. AC induced HDC similarly in IL-1-deficient and control mice. In control mice, AC decreased histamine in the tissues (except the liver) for several hours.

CONCLUSION

(1) AC induces HDC in both MC-dependent and MC-independent ways. (2) AC induces IL-1 mostly in non-MCs, but this IL-1 is not a prerequisite for the induction of HDC by AC. (3) HDC induction may contribute to the replenishment of the reduced pool of MC histamine in the anaphylactic period. (4) In the case of MC-dependent HDC induction, AC may stimulate MCs in such a way as to induce HDC within the MCs themselves, and/or AC-stimulated MCs may stimulate HDC induction in other cells, which will need to be directly identified in future studies.

Histamine-cytokine connection in immunity and hematopoiesis

A number of recent studies have led to a reappraisal of the functional capacities of histamine in immunity and hematopoiesis. This change of perspective was provided by the following findings: (1) the evidence for multiple cellular sources of histamine, differing from mature basophils and mast cells by their ability to newly synthesize and liberate the mediator without prior storage, (2) the discovery of a novel histamine receptor (H4R), preferentially expressed on hematopoietic and immunocompetent cells, (3) the potential intracellular activity of histamine through cytochrome P450 and (4) the demonstration of a histamine-cytokine cross-talk. Indeed, cytokines not only modulate the degranulation process of histamine but also control its neosynthesis by the histamine-forming enzyme, histidine decarboxylase (HDC), at transcriptional and post-transcriptional levels. In turn, histamine intervenes in the intricate cytokine network, regulating cytokine production by immune cells through distinct receptors signaling distinct biological effects. This type of regulation is particularly relevant in the context of TH1/TH2 differentiation, autoimmunity and tumor immunotherapy.

L-histidine decarboxylase as a probe in studies on histamine

Because the Falck-Hillarp formaldehyde fluorescence method, which was superbly applied to identify catecholaminergic and serotonergic neurons, is not applicable to histamine, the first author (T.W.) developed an antibody to L-histidine decarboxylase (HDC) for identification of the histaminergic neuron system in the brain. The anti-HDC antibody was of great use for mapping the location and distribution of this histaminergic neuron system. (S)-alpha-fluoromethylhistidine, a specific and potent irreversible inhibitor of HDC, was also very useful in studies on functions of the neuron system. The activity of HDC is increased by various agents, treatments, and physiological conditions. We found new compounds that increased HDC activity (i.e., tetradecanoylphobol acetate (TPA), other tumor promoters, and staphylococcal enterotoxin A); and using mast cell-deficient mutant (W/W(v)) mice, we obtained evidence that this increase occurred in macrophages. To further characterize the mechanism of increases in HDC activity, the second author (H.O.) cloned human HDC cDNA and a human HDC gene. In studies on the regulation mechanism of the HDC gene, which is expressed only in limited types of cells such as mast cells, enterochromaffin-like cells in the stomach, cells in the tuberomammillary nucleus of the brain, and macrophages, CpG islands in the promoter region of the HDC gene were found to be demethylated in cells expressing the gene, whereas they are methylated in other cells that do not express the HDC gene. In collaboration with many other researchers, we developed HDC knockout mice. The resulting research is producing a lot of interesting findings in our laboratory as well as in others. In summary, HDC has been and will be useful in studies on functions of histamine.

Histamine production by cultured microglial cells of the mouse

We previously reported that cells other than mast cells or neurons could synthesize histamine in response to lipopolysaccharide (LPS) or interleukin 1beta in the rat brain. To identify the responsible cells, we examined histidine decarboxylase (HDC) activity and the expression of HDC mRNA in GMI 6-3 mouse microglial cells. Both the activity and mRNA for HDC in GMI 6-3 cells were induced by LPS treatment, and the induction was sensitive to calmodulin-dependent kinase II inhibitor, KN62. These findings indicate that microglia is a third cell type producing histamine in the brain.

Interleukin-1 beta induces histamine release in the rat hypothalamus in vivo

We have previously demonstrated the increase of histidine decarboxylase activity and histamine content in the murine hypothalamus after intracerebroventricular injection of lipopolysaccharide possibly due to inducible interleukin-1 beta (IL-1 beta). Therefore, we investigated the effects of IL-1 beta on brain histamine dynamics by directly injecting it into the tuberomammillary nucleus of the rat hypothalamus (TM) using an in vivo microdialysis method. Injection of artificial cerebrospinal fluid or recombinant murine IL-1 beta at 0.1 ng into the TM did not evoke a significant change in core temperature, however, a significant monophasic febrile response was observed following injection of IL-beta at more than 1 ng per animal. Histamine release in the anterior hypothalamic area in vivo was significantly augmented from 140 min to 360 min following injection of IL-1 beta at 10 ng dose. These results suggest the possibility that interrelationship between histamine and IL-1 beta may modulate the acute phase reaction in the central nervous system.

Synergistic effects of 12-O-tetradecanoylphorbol-13-acetate and dexamethasone on de novo synthesis of histidine decarboxylase in mouse mastocytoma P-815 cells

12-O-Tetradecanoylphorbol-13-acetate (TPA) markedly enhanced the increase in L-histidine decarboxylase (HDC) activity induced by dexamethasone in mouse mastocytoma P-815 cells, even with a concentration of the latter that had the maximal effect, whereas it induced a rapid and transient increase in HDC activity, which peaked after 3 h in the absence of dexamethasone. The synergistic effect of TPA on HDC activity induced by dexamethasone was detected after 4 h, a plateau level being reached by 6 h, which was similar to the time course with dexamethasone alone. TPA enhanced the induction of HDC activity by various glucocorticoids, but had no effect on the induction by dibutyryl cAMP, prostaglandin E2 or sodium butyrate. Both 1-oleoyl-2-acetylglycerol, a protein kinase C activator, and okadaic acid, a protein phosphatase inhibitor, enhanced the increase in HDC activity induced by dexamethasone, but 4 alpha-phorbol-12,13-didecanoate, an inactive derivative of TPA, did not. Protein kinase C inhibitors, such as staurosporin, H-7 and K255a, suppressed the increase in HDC activity induced by TPA with or without dexamethasone. The enhancement of HDC activity by dexamethasone was completely suppressed by cycloheximide or actinomycin D. Furthermore, TPA markedly enhanced the accumulation of HDC mRNA due to dexamethasone (5 to 10-fold, from 6 to 12 h after). TPA did not cause a significant increase in the level of either [3H]dexamethasone binding capacity or preformed HDC activity in cells. These results taken together suggest that dexamethasone-induced de novo synthesis of HDC in mastocytoma P-815 cells is up-regulated by TPA-activated protein kinase C through the mechanism involving an increased rate of transcription.

Histidine decarboxylase in human basophilic leukemia (KU-812-F) cells. Characterization and induction by phorbol myristate acetate

The human leukemic cell line KU-812-F is known to differentiate into mature basophil-like cells under serum-free culture conditions. In the present study, the activity of histidine decarboxylase (HDC), a histamine-forming enzyme, in KU-812-F cells was found to be high, ranging from 10 to 57 pmol/min/mg protein. The great variation in HDC activity appeared to be due to different percentages and degrees of maturity of basophil-like cells during differentiation of this cell line. The enzyme was inhibited by alpha-fluoromethylhistidine but not by carbidopa, was unable to form dopamine from L-3,4-dihydroxyphenylalanine, and had a Km value for histidine of 0.27 mM, indicating that it was HDC and not aromatic amino acid decarboxylase. The HDC activity increased 1.8-fold when the cells were stimulated by phorbol myristate acetate, which is known to activate protein kinase C, and this increase was blocked by staurosporine, a potent inhibitor of protein kinase C.

Increase of histidine decarboxylase activity in murine myelomonocytic leukemia cells (WEHI-3B) in parallel to their differentiation into macrophages

When cells of mouse myelomonocytic leukemia cell line, WEHI-3B, were cultured in the presence of actinomycin D plus the serum which was obtained from mice injected with bacterial endotoxin, i.e., lipopolysaccharide, their histidine decarboxylase (L-histidine carboxy-lyase, EC 4.1.1.22) (HDC) activity increased about 100-fold with a peak at 48 h. According to the increase in HDC activity, the expression of surface antigens associated with macrophages, such as Mac II, Mac III and Iad, increased markedly on WEHI-3B cells as well as their morphological changes to macrophages. Histamine levels in the culture medium increased concomitantly with the increase in the HDC activity in WEHI-3B cells, whereas the histamine contents inside the cells did not increase remarkably. Furthermore, the addition of lipopolysaccharide to the culture medium caused an additional 2-fold increase in the HDC activity of WEHI-3B cells. These results indicate that the increase in HDC activity in WEHI-3B cells may represent an event in the process of the differentiation to macrophages.

Induction of histidine decarboxylase of rat basophilic leukemia (2H3) cells stimulated by higher oligomeric IgE or phorbol myristate acetate

When rat basophilic leukemia (2H3) cells were stimulated by higher oligomer, the chemically cross-linked oligomers of IgE, in the presence of calcium the activity of histidine decarboxylase (HDC, L-histidine carboxylase, E.C.4.1.1.22), a histamine-forming enzyme, was increased by 1 hr, reaching maximum activity by 2 hr, and returning to the original level by 8 hr. A similar increase in enzyme activity was observed in cells treated with phorbol myristate acetate (PMA) or oleoyl-acetylglycerol (OAG), which are known activators of protein kinase C. Removal of calcium from medium abolished the increase in HDC activity in response to higher oligomer but not that induced by PMA or OAG, suggesting that the increase in HDC activity may be mediated by protein kinase C. The increase in the HDC activity probably required induction of enzyme synthesis, because it was prevented by cycloheximide.