Involvement of Retinoic Acid Receptors RARb and RARg in growth, self-renewal and differentiation on mammary cancer stem cells

BERARDI DE; FLUMIAN C; DIAZ BESSONE MI; CIRIGLIANO SM; BAL DE KIER JOFFE ED; URTREGER AJ; TODARO LB

Congreso; 106th Annual Meeting of the American Association for Cancer Research (AACR); 2015

Retinoids exert different effects on cell differentiation and malignant phenotype reversion through the modulation of Retinoid Acid Receptors (RAR).In this work we have analyzed the involvement of retinoid system induction on proliferation, self-renewal and differentiation of cancer stem cells (CSC) using the triple negative mammary cell line LM38-LP.In order to obtain a CSC enriched culture, cells where cultured under mammosphere conditions. The treatment with All-trans retinoid acid (ATRA1µM for 96 h) reduced CSC growth rate evaluated as mammosphere diameter (Control: 176±8 µm vs. ATRA: 129±10 µm). Surprisingly, ATRA pre-treatment for 96 h increased CSC self-renewal evaluated as the number of secondary mammospheres (Control: 313±19; ATRA: 495±21) and as the clonogenic capacity of LM38-LP CSC (Control: 6±0.5; ATRA: 11±1.2). Concomitant with these biological effects, the same treatment showed, by RT-PCR, an increase in RARb and RARg levels in LM38-LP- CSC.Through the use of specific RAR antagonists, we found that RARg inhibition impaired ATRA effects over self-renewal but RARb inhibition increased the number of secondary mammospheres. (Control: 382±27; ATRA: 735±11; ATRA/RARγ antagonist: 352±17; ATRA/RARb Antagonist: 1260±177). Similar result was observed in clonogenic capacity only when RARg was blockedFinally, we performed a matrigel 3D culture with cells from LM38-LP mammospheres. Colonies formed in this condition generated large irregular structures while under ATRA treatment led to formation of differentiated colonies with evidence of lumen.Our findings suggest that RARg down modulation and RARb induction could lead to CSC self-renewal inhibition and differentiation in triple negative mammary cancers.