C. Fitzsimons

Histamine as an autocrine growth factor in experimental mammary carcinomas

In order to determine the role of endogenous histamine in the regulation of cell growth, thein vitro action of fluoromethyl-histidine (MFMH) was studied in experimental mammary carcinomas induced in rats. Tumor cells were cultured in soft agar using the clonogenic agar technique. The MFMH was added in different concentrations (0.01–100 μM). The effect observed was a 60% inhibition on colony formation with a maximal effect at concentrations over 10 μM. This action was completely reverted by the H2 agonists dimaprit and arpromidine with an IC50 value of 1 μM. The action of the H2 agonists when added alone was a significant increase in cell proliferation (135%), while the H1 agonist produced a dose-dependent inhibition on cell growth. In these experimental carcinomas endogenous histamine is critical for cell proliferation and one of its major effects may be the stimulation of cell growth by acting on specific H2 membrane receptors.

Inhibition of human primary melanoma cell proliferation by histamine is enhanced by interleukin-6.

Background Interleukin‐6 (IL‐6) is a bifunctional growth factor in malignant melanoma; its expression increases during the malignant progression of the disease. Histamine, detected in large amounts in normal and pathological proliferating tissues, is an important paracrine and autocrine regulator of normal and tumour cell proliferation as well.

Histamine deficiency induces tissue-specific down-regulation of histamine H2 receptor expression in histidine decarboxylase knockout mice

Histidine decarboxylase (HDC) is the single enzyme responsible for histamine synthesis. HDC‐deficient mice (HDC−/−) have no histamine in their tissues when kept on a histamine‐free diet. Therefore, the HDC−/− mice provide a suitable model to investigate the involvement of histamine in the regulation of histamine receptor expression. Gene expression of H1 and H2 histamine receptors was studied in several organs of HDC−/− mice and compared to standard (HDC+/+) mice. In many tissues, prolonged absence of histamine induced down‐regulation of the H2 receptor subtype. The expression of the H1 receptor was less sensitive to histamine deficiency. Exogenous histamine present in the diet abolished the differences observed in H2 receptor expression. These results suggest that the expression of mouse H2 receptor is under the control of histamine in a tissue‐specific manner.

HISTAMINE RECEPTORS SIGNALLING IN EPIDERMAL TUMOR CELL LINES WITH H-RAS GENE ALTERATIONS

A role for histamine in the carcinogenesis process has been widely postulated. In a previous study, we have described an atypical association of histamine receptors to signal transduction pathways [1], which could be an important feature for the action of histamine in multistage mouse skin carcinogenesis [2]. In this model, a crucial role for ras protooncogene activation has been proposed [3]. The aim of the present work was to study histamine receptors signalling in cultured cell lines derived from mouse keratinocytes harboring H-ras alterations.

Effect of histamine on growth and differentiation of the rat mammary gland

The presence of H1 and H2 histamine receptors and their associated second messenger systems were studied during the development of the rat mammary gland. In the tissue of the young female, histamine presented a double receptor site as previously described for experimental mammary tumors, namely a high affinity H2 site (Kd=10±2 nM,Bmax=1068±71 fm/mg prot.), which mediated its effect via the products of phosphoinositide hydrolysis and a low affinity H1 receptor (Kd1=5±2 nM,Bmax=188±33 fm/mg prot. andKd2=41±20 nM,Bmax=1980±790 fm/mg prot. when characterized with3H-mepyramine), coupled to adenylyl cyclase activation. On the other hand, the mammary gland of the adult rat presented these receptors coupled to the classical second messenger systems described for mammalian cells, that is, the H2 receptor produced an increase in intracellular cAMP levels and the H1 receptor increased the phosphoinositide turnover. We conclude that histamine plays a critical role during development and differentiation of the normal rat mammary gland.

Histamine as a potential autocrine regulator of melanoma.

Malignant tumor cells express autocrine and paracrine growth factors that can block immune effectiveness and facilitate the acquisition of partial or complete growth autonomy. Recently histamine (Hi) was proved to have an important role as a mediator in normal and malignant cell proliferation. We have reported that Hi behaves as an autocrine growth factor in an experimental mammary carcinoma and in pancreatic carcinoma cells [1, 2]. Human melanoma cells contain high HDC activity and mRNA expression [3, 4]. In this work, we thus investigated the possible role of Hi in the regulation of melanoma growth.

Regulation of phospholipase C activation by the number of H(2) receptors during Ca(2+)-induced differentiation of mouse keratinocytes

We have reported previously that the histamine H(2) receptor (H(2)R) can stimulate the phospholipase C (PLC) signaling pathway in mouse keratinocytes. In the present work, we examined the physiological mechanisms involved in this activation by studying histamine metabolism and H(2)R expression and coupling during mouse keratinocyte differentiation. Ca(2+)-induced differentiation decreased histidine decarboxylase (HDC) mRNA, the enzyme responsible for histamine synthesis, by 68.9+/-5.0%. Concomitantly, intracellular histamine content and its release into the extracellular medium were reduced significantly by 68.2+/-2.0 and 74.1+/-1.7%, respectively. Binding of [3H]tiotidine to H(2)Rs present on the surface of whole cells was also decreased by cellular differentiation [(18.17+/-2.1)x10(4) vs. (6.27+/-0.87)x10(4) sites/cell, undifferentiated and differentiated cells, respectively], without affecting H(2)R affinity. Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of the H(2)R mRNA showed that the expression was also down-regulated at the transcriptional level. Moreover, the inhibition of H(2)R expression strongly affected the ability of the receptor to induce PLC activation. Our findings suggest that H(2)R signaling through the PLC second messenger system is inhibited during keratinocyte differentiation by an autocrine loop involving down-regulation of H(2)R expression and inhibition of histamine metabolism.

Expression of histamine receptors in different cell lines derived from mammary gland and human breast carcinomas

Our group have previously reported the expression of H1 and H2 histamine receptors in human [1] and experimental m a m m a r y carcinomas [2]. In particular, in the NMUinduced m a m m a r y tumors in rats, histamine behaves as a growth factor [3] and modulates tumor cell growth in vivo and in vitro by acting th rough specific membrane receptors [4]. In the present work, we investigated the expression of histamine H1 and H2 receptors in different cell lines derived f rom h u m a n m a m m a r y carcinomas and epithelial m a m m a r y gland, in order to elucidate a possible role for histamine in the neoplastic t ransformat ion of the gland.

Atypical association of H1 and H2 histamine receptors with signal transduction pathways during multistage mouse skin carcinogenesis

Abstract.Objective: In the present work we studied the association of histamine receptors with second messengers during multistage carcinogenesis in Sencar mice skin.¶Methods: 96 Sencar female mouse, divided into six groups were used. Tumors appeared only in the 7,12-dimethylbenz[a]anthracene-initiated and 12-O-tetradecanoylphorbol-13-acetate-promoted group. Control groups received only TPA, or acetone or no treatment at all. Periodically during the promotion period, cAMP and inositol phosphate production were measured after stimulation with H1 or H2 agonists in samples from all groups.¶Results: In non-treated skin, H1 receptors were coupled to phosphatidylinositol hydrolysis and H2 receptors mediated cAMP production. Conversely, in tumors H2 receptors were associated with phosphatidylinositol hydrolysis and H1 mediated a rise in cAMP levels. The skin among tumors and the skin from all control groups maintained the same coupling as non-treated skin. An increase in mast cell number, with a homogeneous subepithelial distribution and marked phenotypic changes, was also observed in promoted skin.¶Conclusions: These findings indicate an atypical association of histamine receptors with second messengers that could be a critical feature for the postulated action of histamine in tumor growth.

An Experimental Model of Diabetes and Cancer in Rats

The aim of this study was to develop an experimental model for the study of cancer associated with diabetes. For diabetes induction, Sprague-Dawley rats were given streptozotocin (STZ, 90 mg/kg body weight (BW), by intraperitoneal injection on the second day of life. For mammary tumour induction, rats were injected with 50 mg/kg BW of N-nitroso-N-methylurea (NMU) at 50, 80 and 110 days old. The neoplastic process and the effect of tamoxifen treatment was examined in non-diabetic and diabetic rats. The latency period, NMU-induced tumour incidence and the number of tumours per rat in diabetic rats versus controls were 117 +/- 7 days versus 79 +/- 9 days (P < 0.001); 93% versus 95% (NS); and 5.2 +/- 1.6 versus 2.7 +/- 0.5 (P < 0.02). A more benign histological pattern for tumours in diabetic animals was observed. Mammary tumours in diabetic rats grew more slowly than in controls. Tamoxifen (1 mg/kg/day) treated diabetic rats showed tumour regression in 67% of NMU-induced mammary tumours versus 53% in controls (NS). Our results show that tumour progression seems to be affected by diabetes in this experimental model. We suggest this is the result of changes to insulin-like growth factors and their receptors, which occur in diabetics, and our future research will examine this hypothesis.