In contrast, there is no decline of serum retinol levels in Wt mice during the 6 weeks they are on this vitamin A deficient diet [26]. during carcinogen treatment (achieved in LRAT/) resulted in more proliferating cells in tongue epithelia from LRAT/mice and ultimately a greater probability of carcinogenesis. Keywords:stem cell, squamous cell carcinoma of the head and neck (SCCHN), retinol, cancer prevention, retinoic acid, nutrition == INTRODUCTION == Head and neck cancer is an important health threat worldwide [1,2]. According to the National Cancer Institute, over 22,000 new oral cancer cases are diagnosed annually in the United States (http://www.cancer.gov/cancertopics/types/oral/) and they account for approximately 3 to 5 5 percent of all cancers. Retinoids are structurally related compounds that are derived from vitamin A (retinol). Retinoids regulate cell proliferation and differentiation [3]. All-transretinoic acid (RA), the most biologically active metabolite of retinol, acts via binding and activating its nuclear receptors, which are transcription factors that directly regulate the transcription of certain target genes [4]. Two families of nuclear receptors mediate the effects of retinoids. All-transRA binds and activates the RA receptor family (RAR, and ), while 9-cisRA binds to both RARs and the retinoid X receptor family (RXR, and )[3-5]. Studies have shown that alterations in retinoid signaling occur during the malignant transformation of oral epithelia (S)-(-)-Citronellal [6-9]. Abnormal metabolism of retinoids and reduced expression ofRAR2have been observed in many types of malignant cells, as well as in the transition from pre-malignant lesions to aggressive carcinomas, including oral cancers [6,8-13]. RA treatment can up-regulateRAR2gene expression in normal epithelial cells, and can also partially restore the reducedRAR2expression in certain carcinoma cells [14,15]. For these reasons, retinoids and drugs that modulate the functions of RARs are useful therapeutic and cancer chemopreventive agents for many types of cancers [16-19]. Lecithin:retinol acyltransferase (LRAT) catalyzes the esterification of retinol and functions as one of the enzymes which regulates the levels of tissue retinoids. Retinyl esters are stored in a variety of tissues and can be hydrolyzed to retinol by retinyl ester hydrolases [20,21]. High LRAT activity is found in the liver [22-25], lung [26,27] and small intestine [28,29], but expression is also detected in eye [30-32], testis [33], skin [34,35], mammary gland [34,36], prostate epithelium [37] and oral cavity epithelial cells [34].LRATgene knockout mice do not store retinyl esters in the liver and other tissues and therefore they are more susceptible to retinol deficiency [26,38,39].LRATalso plays a role in the homeostasis of retinol in both mouse embryos and adult mice as the dietary retinol level fluctuates [40,41]. Since our previous research has shown that the expression ofLRATis much higher in normal cultured human oral epithelial cells than in oral carcinoma cell lines [34], we wanted to determine whether low or absent LRAT activity increased the incidence or severity of carcinogen induced oral carcinogenesis. We developed a mouse model of carcinogenesis in which the carcinogen 4-nitroquinoline 1-oxide (4-NQO) induces both tongue and, at a lower incidence, esophageal squamous cell carcinoma (S)-(-)-Citronellal (SCC) [42]. In this model the 4-NQO is added to the drinking water for several weeks. Then, the 4-NQO is removed and over the next several weeks hyperplasias, dysplasias, papillomas, and squamous cell carcinomas develop specifically on the tongue and at a lower frequency, in the esophagus [42]. This murine oral carcinogenesis model is based on the 4-NQO rat (S)-(-)-Citronellal model used previously by many researchers (eg. [43,44]). One advantage Rabbit Polyclonal to OR10J3 of the murine model over the rat model is that various transgenic and knockout animals can be tested in the murine model. In this study we investigated whether the carcinogen 4-NQO induced a higher incidence of oral cancer in mice in which theLRATgene is disrupted by homologous recombination [26]. == MATERIALS AND METHODS == == Animals == TheLRATgene knockout mice were produced as previously described [26] and bred into a C57BL/6 background. The genotypes were determined by polymerase chain reaction (PCR) from tail genomic DNA [26]. All studies were performed with the approval of the Research Animal Resource Center (RARC) of Weill Cornell Medical College. == 4-NQO treatment == The carcinogen 4-NQO (Sigma, St. Louis, MO) was used to induce oral carcinogenesis, as described by this laboratory previously [42]. Briefly, freshly prepared 4-NQO stock solution (5 mg/ml in propylene.