SummaryMADS-box transcription factors are key regulators of plant developmental processes. While the function of MIKC (type II) MADS-box genes has been intensively studied, only limited data are available for the other more recently identified classes of MADS-box genes, despite these latter comprising more than 60% of the Arabidopsis MADS-box gene family. Here we describe the function of AGL23, an Arabidopsis type I MADS-box gene belonging to the Ma subfamily. We show that AGL23 plays an important role during development of the female gametophyte and embryo. The agl23-1 mutant forms a functional megaspore. However, at this stage female gametophyte development is arrested and the megaspore persists during subsequent phases of ovule development. Despite the incomplete penetrance of the female gametophyte defect, plants homozygous for the agl23-1 mutation were never identified. Analysis of developing seeds showed that embryos homozygous for the agl23-1 allele are albino and unable to give rise to viable plants. Electron microscopy analysis revealed that this phenotype is due to the absence of chloroplasts, strongly suggesting that AGL23 is involved in controlling the biogenesis of organelles during embryo development.

Synthetic progesterone used in contraception drugs (progestins) can promote breast cancer growth, but the mechanisms involved are unknown. Moreover, it remains unclear whether cytoplasmic interactions between the progesterone receptor (PR) and estrogen receptor alpha (ERa) are required for PR activation. In this study, we used a murine progestin-dependent tumor to investigate the role of ERa in progestin-induced tumor cell proliferation. We found that treatment with the progestin medroxyprogesterone acetate (MPA) induced the expression and activation of ERa, as well as rapid nuclear colocalization of activated ERa with PR. Treatment with the pure antiestrogen fulvestrant to block ERa disrupted the interaction of ERa and PR in vitro and induced the regression of MPA-dependent tumor growth in vivo. ERa blockade also prevented an MPA-induced increase in CYCLIN D1 (CCND1) and MYC expression. Chromatin immunoprecipitation studies showed that MPA triggered binding of ERa and PR to the CCND1 and MYC promoters. Interestingly, blockade or RNAi-mediated silencing of ERa inhibited ERa, but not PR binding to both regulatory sequences, indicating that an interaction between ERa and PR at these sites is necessary for MPA-induced gene expression and cell proliferation. We confirmed that nuclear colocalization of both receptors also occurred in human breast cancer samples. Together, our findings argued that ERa-PR association on target gene promoters is essential for progestin-induced cell proliferation. Cancer Res; 72(9); 2416-27. Ó2012 AACR.

Fibroblast growth factor (FGF) receptor 2 (FGFR-2) polymorphisms have been associated with an increase in estrogen receptor and progesterone receptor (PR)-positive breast cancer risk; however, a clear mechanistic association between FGFR-2 and steroid hormone receptors remains elusive. In previous works, we have shown a cross talk between FGF2 and progestins in mouse mammary carcinomas. To investigate the mechanisms underlying these interactions and to validate our findings in a human setting, we have used T47D human breast cancer cells and human cancer tissue samples. We showed that medroxyprogesterone acetate (MPA) and FGF2 induced cell proliferation and activation of ERK, AKT, and STAT5 in T47D and in murine C4-HI cells. Nuclear interaction between PR, FGFR-2, and STAT5 after MPA and FGF2 treatment was also showed by confocal microscopy and immunoprecipitation. This effect was associated with increased transcription of PRE and/or GAS reporter genes, and of PR/STAT5-regulated genes and proteins. Two antiprogestins and the FGFR inhibitor PD173074, specifically blocked the effects induced by FGF2 or MPA respectively. The presence of PR/FGFR-2/ STAT5 complexes bound to the PRE probe was corroborated by using NoShift transcription and chromatin immunoprecipitation of the MYC promoter. Additionally, we showed that T47D cells stably transfected with constitutively active FGFR-2 gave rise to invasive carcinomas when transplanted into NOD/SCID mice. Nuclear colocalization between PR and FGFR-2/STAT5 was also observed in human breast cancer tissues. This study represents the first demonstration of a nuclear interaction between FGFR-2 and STAT5, as PR coactivators at the DNA progesterone responsive elements, suggesting that FGFRs are valid therapeutic targets for human breast cancer treatment. Cancer Res; 71(10); 3720-31. Ó2011 AACR.