H1.0 induces paclitaxel-resistance genes expression in ovarian cancer cells by recruiting GCN5 and androgen receptor.

More than 90% of ovarian cancer deaths are due to relapse following development of chemoresistance. Our main objective is to better understand the molecular mechanism underlying paclitaxel resistance (taxol resistance, Txr) in ovarian cancer. Here, we observed that the linker histone H1.0 is upregulated in paclitaxel-resistant ovarian cancer cells. Knockdown of H1.0 significantly downregulates the androgen receptor (AR) and sensitizes paclitaxel-resistant SKOV3/Txr and 2774/Txr cell lines to paclitaxel. Conversely, ectopic expression of H1.0 upregulates AR and increases Txr in parental SKOV3 and MDAH2774 cells. Notably, H1.0 upregulation is associated with disease recurrence and poor survival in a subset of ovarian cancer subjects. Inhibition of PI3K significantly reduces H1.0 mRNA and protein levels in paclitaxel-resistant cells, suggesting the involvement of the PI3K/AKT signaling pathway. Knockdown of H1.0 and AR also downregulates the Txr genes ABCB1 and ABCG2 in paclitaxel-resistant cells. Our data show that H1.0 induces GCN5 expression and histone acetylation, thereby enhancing Txr gene transactivation. These findings suggest that Txr in ovarian cancer involves the PI3K/AKT pathway and leads to upregulation of histone H1.0, recruitment of GCN5 and AR, followed by upregulation of a subgroup of Txr genes that include ABCB1 and ABCG2. This study is the first report describing the relationship between histone H1.0 and GCN5 that cooperate to induce AR-dependent Txr in ovarian cancer cells.

Androgen receptor transcriptional activity and chromatin modifications on the ABCB1/MDR gene are critical for taxol resistance in ovarian cancer cells.

We report here that the androgen receptor (AR) and ABCB1 are upregulated in a model of acquired taxol resistance (txr) in ovarian carcinoma cells. AR silencing sensitizes txr cells to taxol threefold, whereas ectopic AR expression in AR-null HEK293 cells induces resistance to taxol by 1.7-fold. AR activation using the agonist dihydrotestosterone (DHT) or sublethal taxol treatment upregulates ABCB1 expression in both txr cells and AR-expressing HEK293 cells. In contrast, AR inactivation using the antagonist bicalutamide downregulates ABCB1 expression and enhances cytotoxicity to taxol. A functional ABCB1 promoter containing five predicted androgen-response elements (AREs) is cloned. Deletion assays reveal a taxol-responsive promoter segment which harbors ARE4. Notably, DHT- or taxol-activated AR potentiates binding of the AR to ARE4 as revealed by the chromatin immunoprecipitation. On the other hand, txr cells display an increase in chromatin remodeling. AR/H3K9ac and AR/H3K14ac complexes bind specifically to ARE4 in response to taxol. Furthermore, acetyltransferase protein levels (p300 and GCN5) are upregulated in txr cells. Silencing of p300 or GCN5 reduces chromatin modification and enhances cytotoxicity in both parental and txr SKOV3 cells. While the phosphatidylinositol 3-kinase (PI3K)/serine/threonine protein kinase (AKT) pathway is significantly activated by taxol, taxol-induced ABCB1 expression, histone posttranslational modifications, and p300 binding to ARE4 are suppressed following inhibition of the PI3K/AKT cellular pathway. These results demonstrate that the AKT/p300/AR axis can be activated to target ABCB1 gene expression in response to taxol, thus revealing a new treatment target to counter taxol resistance.