Retinoic acid (RA), from dietary sources of Vitamin A, is a potent inhibitor of cell and tumor growth. As such, RA has been considered for chemoprevention and therapy of epithelial cancer. However, contradictory responses to RA and its precursors in both preclinical models and chemoprevention/therapeutic clinical trials imply that RA can have a dual face: in some contexts it can act as a tumor inhibitor, in others as a tumor promoter. Literature data and our preliminary work indicate that an impaired RA signal through the RA receptor alpha (RARA) in both untransformed and transformed breast cancer cells leads to variegated and paradoxical effects implicating one, or more, prosurvival and prometastatic signaling pathway such as the TGFB and Sphingosine 1 Phosphate (S1P) pathways, and pathways governed by non-RAR targets capable of interacting directly with RA, such as the Protein Kinase C alpha (PKCA) and PPAR beta/delta (PPARD) pathways. We hypothesize that: Loss/impairment of RA-RARA- mediated epigenetic regulation due to upstream intrinsic/extrinsic factors makes RA activate, via non-RAR-targets, one, or more, tumor-promoting signaling pathways. To expand on this hypothesis we propose to combine in vitro and in vivo breast cancer cell models and mechanistic approaches to: identify candidate factors that can lead to loss/impairment of RA-RAR-mediated epigenetic regulation thus causing breast cancer tumor progression (Aim 1);understand whether TGFBR2 epigenetic silencing, consequent to impaired RA-RAR signaling, contributes to RA-induced tumor progression (Aim 2);further test whether the S1P signaling contributes to RA-induced survival in vivo, and test for drugs that can counteract this effect (Aim 3);mechanistically test whether, in the absence of RARA, and its downstream RAR targets, RA exerts its tumor promoting action through non-RAR targets such as PKCA and PPARD (Aim 4). The outcome of these studies is expected to impact prevention and treatment of breast cancer, at early, as well as late stages.
Retinoic acid (RA), from dietary sources of Vitamin A, is a potent inhibitor of cell and tumor growth. As such, RA has been considered for chemoprevention and therapy of epithelial cancer. However, contradictory responses to RA and its precursors in both preclinical models and chemoprevention/therapeutic clinical trials imply that RA can have a dual face: in some contexts it can act as a tumor inhibitor, in others as a tumor promoter. We found in our preliminary studies that impairment of RA-signal through canonical RA receptors (RARs) on one hand abrogates epigenetic regulation of RAR- targets and on the other hand activates via as yet unidentified non-RARs one, or more, tumor-promoting signaling pathways. To expand on this hypothesis we propose four specific aims to combine in vitro and in vivo breast cancer cell models and mechanistic approaches to identify candidate factors that can lead to loss/impairment of RA-RAR- mediated epigenetic regulation thus causing breast cancer tumor progression. The outcome of these studies is expected to impact prevention and treatment of breast cancer, at early, as well as late stages.
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