Expression of aryl hydrocarbon receptor gene battery in mammary and mast cell tumours of dogs

Introduction. In toxicological sciences an increasing importance is nowadays given to the definition of biomarkers (BM) useful for risk assessment and bio-monitoring [1]. In comparative oncology, the set up and validation of prognostic BM constitutes an objective of basic and applied research; in this respect, certain species (fishes and dogs) have been used as bio-indicators of human health exposure to potentially carcinogenic environmental chemicals [2-4]. The aim of this study was to evaluate, in canine mammary tumours (MT) and mastocytomas (MCT), the expression of known contaminants-responsive genes such as the aryl hydrocarbon receptor (AhR), its nuclear translocator (ARNT) as well as CYP1A1, CYP1A2 and CYP1B1 (coding for enzymes involved in pollutants biotransformation). Materials and Methods. Forty biopsies of canine tumours (15 MT and 25 MTC), classified according to WHO guidelines, were obtained from veterinary clinics of Venezia-Mestre and Torino (Italy). Control samples from Beagle or euthanized dogs were also collected. Total RNA was isolated and checked for its purity and concentration. Primers for canine CYP1A1, CYP1A2, CYP1B1, AHR, ARNT and 3 housekeeping genes were set up and validated for quantitative Real Time RT-PCR by using UPL probes. Finally, gene expression profiles of aforementioned genes were measured in control and tumour biopsies. Results. As a whole, an up-regulation phenomenon, with –fold changes higher than the cut-off of 2, was noticed in tumour samples if compared with respective control tissues; however, some differences were observed in target gene responses. CYP1A1 and CYP1A2 were usually poorly expressed, but increasing mRNA levels were found in 1 MT from Venezia and in 4 MTC from Torino (CYP1A2 only). ARNT mRNA was increased in 3 MTC from Torino. On the contrary, CYP1B1 was over-expressed in 15 of 25 available MCT, while AHR in 23 MTC and in 3 MT (2 out of 3 from Venezia). Discussion and Conclusion. Several CYP enzymes concur to metabolize a variety of carcinogens, producing active derivatives leading to the tumour initiation [5]. In particular CYP1 gene family, which plays a crucial role in contaminants bioactivation, is under the positive regulatory control of AhR [6]. In this study, an induction of CYP1B1 gene expression, coupled (in few cases) with an increase of CYP1A1 and CYP1A2 mRNAs was observed in MT and MTC, confirming previous results obtained in different human tumours [5-7]. Moreover, a general increasing expression of AHR gene (over the cut-off of 2-fold change) was pointed out in a wide number of tumours, as already observed in human lymphomas [8]. Thus, CYP1B1 and AHR seem to be sensitive contaminants-responsive genes and might be proposed as possible BM of effect in dog cancer.