Cross talk between progesterone receptors and retinoic acid receptors in regulation of cytokeratin 5-positive breast cancer cells

Abstract

Half of estrogen receptor-positive breast cancers contain a subpopulation of cytokeratin 5 (CK5)-expressing cells that are therapy resistant and exhibit increased cancer stem cell (CSC) properties. We and others have demonstrated that progesterone (P4) increases CK5+ breast cancer cells. We previously discovered that retinoids block P4 induction of CK5+ cells. Here we investigated the mechanisms by which progesterone receptors (PR) and retinoic acid receptors (RAR) regulate CK5 expression and breast CSC activity. After P4 treatment, sorted CK5+ compared to CK5 − cells were more tumorigenic in vivo. In vitro, P4-treated breast cancer cells formed larger mammospheres and silencing of CK5 using small hairpin RNA abolished this P4-dependent increase in mammosphere size. Retinoic acid (RA) treatment blocked the P4 increase in CK5+ cells and prevented the P4 increase in mammosphere size. Dual small interfering RNA (siRNA) silencing of RARα and RARγ reversed RA blockade of P4-induced CK5. Using promoter deletion analysis, we identified a region 1.1 kb upstream of the CK5 transcriptional start site that is necessary for P4 activation and contains a putative progesterone response element (PRE). We confirmed by chromatin immunoprecipitation that P4 recruits PR to the CK5 promoter near the − 1.1 kb essential PRE, and also to a proximal region near − 130 bp that contains PRE half-sites and a RA response element (RARE). RA induced loss of PR binding only at the proximal site. Interestingly, RARα was recruited to the − 1.1 kb PRE and the − 130 bp PRE/RARE regions with P4, but not RA alone or RA plus P4. Treatment of breast cancer xenografts in vivo with the retinoid fenretinide reduced the accumulation of CK5+ cells during estrogen depletion. This reduction, together with the inhibition of CK5+ cell expansion through RAR/PR cross talk, may explain the efficacy of retinoids in prevention of some breast cancer recurrences.

Breast Cancer Suppression by Progesterone Receptors Is Mediated by Their Modulation of Estrogen Receptors and RNA Polymerase III

“…RARα is a common and necessary co-factor at many ER transcribed genes in breast cancer cells (43). Furthermore, we have observed co-recruitment of PR and RARα at sequences resembling PREs and RAREs in breast cancer cells (44). Our results also imply that PR has a general impact on Pol III transcription and could possibly affect ribosome function since 5S rRNA abundance was depressed by P4 and MPA (Fig.…”

CTCs Expression Profiling for Advanced Breast Cancer Monitoring

“…Analyzing clinical data in a comprehensible manner, we found an association between higher tumor grade at diagnosis and overexpression of KRT5 in CTCs at V1, which is the gene that encodes CK5. CK5-positive BC cells have enhanced mammosphere forming potential and are endocrine and chemotherapy-resistant in MBC [38]. However, KTR5 expression has not been reported yet on CTCs.…”

Isobavachalcone sensitizes cells to E2‐induced paclitaxel resistance by down‐regulating CD44 expression in ER+ breast cancer cells

“…Paclitaxel blocks the G2/M phase of cell cycle and induces cancer cell apoptosis. 33 As shown in Figure 5B Figure 5D). Real-time PCR showed that compared with that in cells transfected with control plasmids, the expression of CD44 mRNA was down-regulated in paclitaxel-resistant cells transfected with ERa-shRNA ( Figure 5E).…”

“…Indeed, compared with that in control cells, the expression of ERα and CD44 protein was down‐regulated in paclitaxel‐resistant cells treated with IBC (Figure A). Paclitaxel blocks the G2/M phase of cell cycle and induces cancer cell apoptosis . As shown in Figure B and C, IBC could increase the proportion of cells in G2/M phase as determined by flow cytometry in MCF‐7/R cells treated with paclitaxel.…”