Mouse mammary tumor virus (MMTV) is a retrovirus, activating Wnt genes (Wnt1/int-1, Wnt3/int-4, Wnt10b), Fgf genes (Fgf3/int-2, Fgf4, Fgf8) and other genes (Notch4/int-3, Eif3s6/int-6) due to proviral integration. Among 19 WNT genes, WNT3 and WNT14B genes are clustered in human chromosome 17q21, WNT3A and WNT14 in human chromosome 1q42, WNT10A and WNT6 in human chromosome 2q35, and WNT10B and WNT1 in human chromosome 12q13. Among 22 FGF genes, FGF19, FGF4 and FGF3 genes are clustered in human chromosome 11q13, while FGF23 and FGF6 in human chromosome 12p13. WNT and FGF gene clusters are conserved between the human genome and the mouse genome. Activation of mouse Wnt or Fgf genes due to proviral integration of MMTV occurs in 5 out of 13 clustered genes, and in 1 out of 28 solitary genes (p=0.0033), which clearly indicates that mouse Wnt or Fgf gene clusters are recombination hot spots associated with carcinogenesis. Recombination results in retroviral integration as well as in chromosomal translocation, gene amplification and deletion during carcinogenesis. The CCND1-FGF19-FGF4-FGF3 gene cluster in human chromosome 11q13 is amplified in breast cancer, squamous cell carcinoma of head and neck, and bladder tumors, and is also translocated in parathyroid tumors and B-cell lymphoma. WNT gene clusters on human chromosome 1q42, 2q35, 12q13, and 17q21 as well as FGF gene cluster on human chromosome 12p13 might be amplified or translocated in human cancer just like FGF gene cluster on human chromosome 11q13.

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