Dominant negative retinoic acid receptor initiates tumor formation in mice.
BACKGROUND
Retinoic acid suppresses cell growth and promotes cell differentiation, and pharmacological retinoic acid receptor (RAR) activation is anti-tumorigenic. This begs the question of whether chronic physiological RAR activation by endogenous retinoids is likewise anti-tumorigenic.


RESULTS
To address this question, we generated transgenic mice in which expression of a ligand binding defective dominant negative RARalpha (RARalphaG303E) was under the control of the mouse mammary tumor virus (MMTV) promoter. The transgene was expressed in the lymphoid compartment and in the mammary epithelium. Observation of aging mice revealed that transgenic mice, unlike their wild type littermates, developed B cell lymphomas at high penetrance, with a median latency of 40 weeks. MMTV-RARalphaG303E lymphomas were high grade Pax-5+, surface H+L Ig negative, CD69+ and BCL6- and cytologically and phenotypically resembled human adult high grade (Burkitt's or lymphoblastic) lymphomas. We postulated that mammary tumors might arise after a long latency period as seen in other transgenic models of breast cancer. We tested this idea by transplanting transgenic epithelium into the cleared fat pads of wild type hosts, thus bypassing lymphomagenesis. At 17 months post-transplantation, a metastatic mammary adenocarcinoma developed in one of four transplanted glands whereas no tumors developed in sixteen of sixteen endogenous glands with wild type epithelium.


CONCLUSIONS
These findings suggest that physiological RAR activity may normally suppress B lymphocyte and mammary epithelial cell growth and that global RAR inactivation is sufficient to initiate a stochastic process of tumor development requiring multiple transforming events. Our work makes available to the research community a new animal resource that should prove useful as an experimental model of aggressive sporadic lymphoma in immunologically uncompromised hosts. We anticipate that it may also prove useful as a model of breast cancer.
Kupumbati
Tara S
TS
Department of Medicine, Mount Sinai School of Medicine, New York, NY 10029, USA. tara.s.kupumbati@medtronic.com
Cattoretti
Giorgio
G
Marzan
Christine
C
Farias
Eduardo F
EF
Taneja
Reshma
R
Mira-y-Lopez
Rafael
R
D000818:Animals; D001943:Breast Neoplasms / Q000098:blood supply / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000473:pathology; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000378:metabolism / Q000637:transplantation; D005799:Genes, Dominant / Q000235:genetics*; D005998:Glycine / Q000235:genetics / Q000378:metabolism; D008221:Lymphoid Tissue / Q000166:cytology / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D009368:Neoplasm Transplantation; D018168:Receptors, Retinoic Acid / Q000235:genetics* / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D015996:Survival Rate
C000607071:RARA protein, human; C000607072:Rara protein, mouse; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D005998:Glycine