Insuline-Like Growth Factor-2 (IGF2) and Hepatocyte Growth Factor (HGF) Promote Lymphomagenesis in p53-null Mice in Tissue-specific and Estrogen-signaling Dependent Manners.

mice are prone to develop lymphomas at old ages. Factors promoting this tumorigenesis are unknown. Here, we showed human ovulatory follicular fluid (FF) largely promotes lymphomagenesis in mice at earlier ages. Meanwhile, we clarified that IGF2 and HGF are important cell transforming factors within FF. To induce tumor formation, 5% FFs, 100 ng/ml IGF2, 20 ng/ml HGF, or both IGF2 and HGF in a volume of 200 µl PBS, was injected into 8-wk-old female mice at the mammary fat pad. The injection was repeated weekly for up to 7 weeks or extending to 13 weeks to observe the accumulative incidence of lymphomagenesis. Immunohistochemistry staining and gene rearrangement analysis were used to identify the tumor type. By injecting FF into the mammary fat pad weekly, lymphomas developed in 8/16 (50%) of mice by seven weeks. We identified IGF2 and HGF in FF is largely responsible for this activity. The same weekly injection of IGF2, HGF, and their combination induced lymphomas in 4/11 (36%), 3/8 (38%), and 6/9 (67%) mice, respectively. Interestingly, tumorigenesis was induced only when those were injected into the adipose tissues in the mammary gland, but not when injected into non-adipose sites. We also found this tumor-promoting activity is estradiol (E2)-dependent and relies on estrogen receptor (ER) α expression in the adipose stroma. No tumor or only tiny tumor was yielded when the ovaries were resected or when ER is antagonized. Finally, an extension of the weekly FF-injection to 13 weeks did not further increase the lymphomagenesis rate, suggesting an effect on pre-initiated cancer cells. Taken together, the study disclosed a robust tumor-promoting effect of IGF2 and HGF in the p53 loss-initiated lymphomagenesis depending on an adipose microenvironment in the presence of E2. In light of the clarity of this spontaneous tumor promotion model, we provide a new tool for studying p53-mediated lymphomagenesis and suggest that, as a chemoprevention test, this is a practical model to perform.