Imbalance between Actin Isoforms Contributes to Tumour Progression in Taxol-Resistant Triple-Negative Breast Cancer Cells

The widespread occurrence of breast cancer and its propensity to develop drug resistance highlight the need for a comprehensive understanding of the molecular mechanisms involved. This study investigates the intricate pathways associated with secondary resistance to taxol in triple-negative breast cancer (TNBC) cells, with a particular focus on the changes observed in the cytoplasmic actin isoforms. By studying a taxol-resistant TNBC cell line, we revealed a shift between actin isoforms towards γ-actin predominance, accompanied by increased motility and invasive properties. This was associated with altered tubulin isotype expression and reorganisation of the microtubule system. In addition, we have shown that taxol-resistant TNBC cells underwent epithelial-to-mesenchymal transition (EMT), as evidenced by Twist1-mediated downregulation of E-cadherin expression and increased nuclear translocation of β-catenin. The RNA profiling analysis revealed that taxol-resistant cells exhibited significantly increased positive regulation of cell migration, hormone response, cell-substrate adhesion, and actin filament-based processes compared with naïve TNBC cells. Notably, taxol-resistant cells exhibited a reduced proliferation rate, which was associated with an increased invasiveness in vitro and in vivo, revealing a complex interplay between proliferative and metastatic potential. This study suggests that prolonged exposure to taxol and acquisition of taxol resistance may lead to pro-metastatic changes in the TNBC cell line.

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.

Physapubescin B inhibits tumorgenesis and circumvents taxol resistance of ovarian cancer cells through STAT3 signaling

Ovarian cancer is the most lethal gynaecological malignancy. Recurrence and subsequent resistance to chemotherapy have become major obstacles to treating these diseases. In the present study, we showed that a natural withanolide isolated from the plant Physalis pubescens L. (Solanaceae), Physapubescin B, exhibited potent anti-tumor activity against ovarian cancer cells. Physapubescin B promoted apoptosis, induced cell-cycle arrest and inhibited invasion of ES-2 and A2780 cells. Physapubescin B treatment also resulted in suppression of the transcriptional activity of STAT3, an oncogenic transcription factor activated in many human malignancies including ovarian cancer, through disturbing the dimerization of STAT3, and thereby inhibited the nuclear translocation of Tyr705/Ser727-phosphorylated STAT3. The IL-6-stimulated activation of STAT3 and its downstream genes Cyclin D1, survivin, and Bcl-xL was also repressed by Physapubescin B. Furthermore, Physapubescin B sensitizes A2780 cells to taxol-induced cell growth inhibition in vitro. These findings strongly suggest that Physapubescin B has potential antitumor activity and may circumvent taxol resistance in human ovarian cancer cells through inhibition of aberrant activation of STAT3.

Regulation of Oncoprotein 18/Stathmin Signaling by ERK Concerns the Resistance to Taxol in Nonsmall Cell Lung Cancer Cells

Taxol is a cytotoxic antiepithelioma chemotherapy drug widely used clinically, which results in appearing a broad range of taxol-resistant tumors. Oncoprotein 18 (Op18)/stathmin is a genetically highly conserved small-molecule cytosolic phosphoprotein and highly expressed in tumors. Extracellular signal-regulated kinase (ERK) is a main member of mitogen-activated protein kinases (MAPKs). The study demonstrated that combination of blockage of ERK signal by ERK inhibitor PD98059 and Taxol greatly promoted taxol-induced cellular apoptosis and growth inhibition, decreased the expression of Op18/stathmin and total levels of phosphor-Op18/stathmin, while weakened the cyclin-dependent kinase 2 (cdc2) activity and antiapoptotic protein Bcl-2 expression and inhibited IL-10 autocrine in taxol-resistant NCI-H1299 cells; Taxol-resistant NCI-H1299 cells expressed high levels of ERK and phosphor-ERK in contrast to taxol-sensitive CNE1 cells, and ERK mainly phosphorylated Op18/stathmin at Ser 25 site. These findings suggest that ERK-mediated Op18/stathmin is involved in taxol resistance of tumors; blockage of ERK signal improves the sensitivity of tumor cells to taxol, which provides new clues for treating taxol-resistant carcinomas.

Gene expression profiling of taxol-resistant nasopharyngeal carcinoma cells with siRNA-mediated FOLR1 downregulation

OBJECTIVES

Our previous study has shown that downregulation of FOLR1 by siRNA partially reversed taxol-resistant phenotype in taxol-resistant nasopharyngeal carcinoma cell lines. We aim to gain further insight into the molecular mechanisms of this process and identify the differentially expressed genes after FOLR1 downregulation.

METHOD

The global gene expression profile was identified and analyzed using the Affymetrix HG-U133 Plus 2.0 array.

RESULTS

There was a significant dysregulation in the global gene expression of the FOLR1-suppressed taxol-resistant nasopharyngeal carcinoma cell lines. There were 41 upregulated genes and 109 downregulated genes. QRT-PCR validation of the selected differentially expressed genes demonstrated there was a good correlation with the microarray analysis. There was a significant deregulation of expression in the apoptosis-related genes such as BIRC3, PRKX, TNFRSF10A and involved in Viral carcinogenesis, MAPK signaling pathways after FOLR1 was downregulated.

CONCLUSION

The suppression of FOLR1 by RNA interference altered gene expression profile of taxol-resistant nasopharyngeal carcinoma cell lines. The apoptosis-related genes and the gene alterations in viral carcinogenesis, MAPK signaling pathways might be important in FOLR1 siRNA-induced taxol-resistant reversal.