Atypical association of H 1 and H 2 histamine receptors with signal transduction pathways during multistage mouse skin carcinogenesis C. Fitzsimons 1 , B. Molinari 2 , H. Duran 2 , M. Palmieri 3 , C. Davio 1 , G. Cricco 1 , R. Bergoc 1 and E. Rivera 1 1 Laboratorio de Radioiso ´topos, Facultad de Farmacia y Bioquı ´mica, Universidad de Buenos Aires, Junin 956, 1113 Buenos Aires, Argentina, Fax þ54 1 962 5341, e-mail: rivera@labrad.uba.ar 2 Departamento de Radiobiologı ´a, Comisio ´n Nacional de Energı ´a Ato ´mica, Laboratorio Tandar, Av. Gral Paz y Constituyentes, 1464 Pcia. de Buenos Aires, Argentina 3 Departamento de Biologı ´a, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, Argentina Received 18 November 1996; returned for revision 18 February 1997; accepted by W. Lorenz 13 May 1997 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-dimethyl- benz[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 produc- tion were measured after stimulation with H 1 or H 2 agonists in samples from all groups. Results: In non-treated skin, H 1 receptors were coupled to phosphatidylinositol hydrolysis and H 2 receptors mediated cAMP production. Conversely, in tumors H 2 receptors were associated with phosphatidylinositol hydrolysis and H 1 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. Key words: Histamine receptors – Inositol phosphates – cAMP – Mouse skin carcinogenesis Introduction The multistage model of skin carcinogenesis is a useful system to study the sequential changes that normal skin undergoes during its transformation into neoplastic tissue. In this model 12-O-tetradecanoylphorbol-13-acetate (TPA) induces tumor promotion in 7,12-dimethylbenz[a]anthracene (DMBA) initiated Sencar mice skin, resulting in the formation of benign papillomas, some of which progress to squamous cell carcinomas [1]. Substantial evidence supports the idea that histamine is involved in carcinogenesis. Several studies demonstrate the presence of histamine receptors in different cell lines derived from experimental and human neoplasias [2, 3], although their function is not yet clear. A possible role for histamine and its receptors in the multistage model of skin carcinogen- esis has been postulated in association with inflammatory response [4]. Pharmacological analyses have demonstrated that at least two different subclasses of histamine receptors are present and co-localized in skin and other normal tissues [5, 6]. Histamine H 1 receptors are known to be coupled to phosphatidylinositol hydrolysis pathway with histamine binding resulting in the mobilization of intracellular Ca 2þ , whereas H 2 receptors are coupled to adenylyl cyclase system, with histamine stimulating increases in adenosine 3 0 :5 0 -cyclic monophosphate (cAMP) production [7]. How- ever, several studies have shown that H 2 receptors can be simultaneously associated to different intracellular media- tors [8], i.e. in an experimental mammary carcinoma induced in rats with N-nitroso-N-methylurea (NMU), histamine exerts a regulatory function on cell growth by acting directly through H 1 and H 2 membrane receptors, which exhibit an atypical coupling to intracellular signaling systems [9]. In these tumors, the presence of a high affinity H 2 receptor coupled to the phosphatidylinositol breakdown pathway, supports the idea that histamine could stimulate cell proliferation acting as a growth factor [10]. It is already known that chronic TPA treatment of Sencar mice skin produces a remarkable increase in the number of mast cells [11]. Indeed, as a certain relationship between intradermal mast cell secretion and cutaneous mitogenesis has also been established [12], further evaluation of the role Inflamm. res. 46 (1997) 292–298  Birkha ¨user Verlag, Basel, 1997 1023-3830/97/080292-07 $ 1.50+0.20/0 Inflammation Research Correspondence to: E. Rivera 