FOXM1: An emerging master regulator of DNA damage response and genotoxic agent resistance.

AbstractFOXM1 is a transcription factor required for a wide spectrum of essential biological functions, including DNA damage repair, cell proliferation, cell cycle progression, cell renewal, cell differentiation and tissue homeostasis. Recent evidence suggests that FOXM1 also has a role in many aspects of the DNA damage response. Accordingly, FOXM1 drives the transcription of genes for DNA damage sensors, mediators, signal transducers and effectors. As a result of these functions, it plays an integral part in maintaining the integrity of the genome and so is key to the propagation of accurate genetic information to the next generation. Preserving the genetic code is a vital means of suppressing cancer and other genetic diseases. Conversely, FOXM1 is also a potent oncogenic factor that is essential for cancer initiation, progression and drug resistance. An enhanced FOXM1 DNA damage repair gene expression network can confer resistance to genotoxic agents. Developing a thorough understanding of the regulation and function of FOXM1 in DNA damage response will improve the diagnosis and treatment of diseases including cancer, neurodegenerative conditions and immunodeficiency disorders. It will also benefit cancer patients with acquired genotoxic agent resistance

SUMOylation modulates FOXK2-mediated paclitaxel sensitivity in breast cancer cells

The forkhead transcription factor FOXK2 plays a critical role in suppressing tumorigenesis and mediating cytotoxic drug action in breast cancer. However, the mechanism by which the biological function of FOXK2 is regulated remains poorly understood. Here, we investigated the role of SUMOylation in modulating FOXK2-mediated drug sensitivity. We identified SUMOylation consensus motifs within the FOXK2 sequence and constructed two SUMOylation-defective double mutants by converting lysine 527 and 633 to arginines and glutamic acid 529 and 635 to alanines, respectively. We found that both the FOXK2 SUMOylation-deficient (K527/633 R) and (E529/635 A) mutants were ineffective in mediating the cytotoxic function of paclitaxel when compared to the wild-type (WT) FOXK2. When overexpressed, unlike the wild-type (WT) FOXK2, the K527/633 R mutant had little effect on the sensitivity of MCF-7 and MDA-MB-231 cells to paclitaxel, as examined by cell viability and clonogenic assays. Our results also showed that MCF-7 cells overexpressing the K527/633 R mutant form of FOXK2 or the empty expression vector have lower protein and mRNA levels of its tumour suppressive transcriptional target FOXO3 compared to the wild-type FOXK2. Consistently, ChIP assays revealed that unlike wild-type FOXK2, the SUMOylation-defective (K527/633 R) mutant is unable to bind to the FOXO3 promoter, despite expressing comparable levels of protein and having the same subcellular localization as the wild-type FOXK2 in MCF-7 cells. Interestingly, expression of neither the wild-type nor the K527/633 R mutant FOXK2 had any effect on the proliferation and paclitaxel sensitivity of the MCF-7 TaxR paclitaxel-resistant cells. In agreement, both the wild-type and the (K527/633 R) mutant FOXK2 failed to bind to the endogenous FOXO3 promoter in these cells. Collectively, our results suggest that SUMOylation positively regulates FOXK2 transcriptional activity and has a role in mediating the cytotoxic response to paclitaxel through the tumour suppressor FOXO3

SUMOylation modulates FOXK2-mediated paclitaxel sensitivity in breast cancer cells

Abstract The forkhead transcription factor FOXK2 plays a critical role in suppressing tumorigenesis and mediating cytotoxic drug action in breast cancer. However, the mechanism by which the biological function of FOXK2 is regulated remains poorly understood. Here, we investigated the role of SUMOylation in modulating FOXK2-mediated drug sensitivity. We identified SUMOylation consensus motifs within the FOXK2 sequence and constructed two SUMOylation-defective double mutants by converting lysine 527 and 633 to arginines and glutamic acid 529 and 635 to alanines, respectively. We found that both the FOXK2 SUMOylation-deficient (K527/633 R) and (E529/635 A) mutants were ineffective in mediating the cytotoxic function of paclitaxel when compared to the wild-type (WT) FOXK2. When overexpressed, unlike the wild-type (WT) FOXK2, the K527/633 R mutant had little effect on the sensitivity of MCF-7 and MDA-MB-231 cells to paclitaxel, as examined by cell viability and clonogenic assays. Our results also showed that MCF-7 cells overexpressing the K527/633 R mutant form of FOXK2 or the empty expression vector have lower protein and mRNA levels of its tumour suppressive transcriptional target FOXO3 compared to the wild-type FOXK2. Consistently, ChIP assays revealed that unlike wild-type FOXK2, the SUMOylation-defective (K527/633 R) mutant is unable to bind to the FOXO3 promoter, despite expressing comparable levels of protein and having the same subcellular localization as the wild-type FOXK2 in MCF-7 cells. Interestingly, expression of neither the wild-type nor the K527/633 R mutant FOXK2 had any effect on the proliferation and paclitaxel sensitivity of the MCF-7 TaxR paclitaxel-resistant cells. In agreement, both the wild-type and the (K527/633 R) mutant FOXK2 failed to bind to the endogenous FOXO3 promoter in these cells. Collectively, our results suggest that SUMOylation positively regulates FOXK2 transcriptional activity and has a role in mediating the cytotoxic response to paclitaxel through the tumour suppressor FOXO3

11a-N-Tosyl-5-deoxi-pterocarpan, LQB-223, a novel compound with potent antineoplastic activity toward breast cancer cells with different phenotypes.

Multidrug resistance is the major obstacle for successful treatment of breast cancer, prompting the investigation of novel anticancer compounds. PURPOSE: In this study, we tested whether LQB-223, an 11a-N-Tosyl-5-deoxi-pterocarpan newly synthesized compound, could be effective toward breast cancer cells. METHODS: Human breast cell lines MCF-7, MDA-MB-231, HB4a and MCF-7 Dox(R) were used as models for this study. Cell culture, MTT and clonogenic assay, flow cytometry and Western blotting were performed. RESULTS: The LQB-223 decreased cell viability, inhibited colony formation and induced an expressive G2/M arrest in breast cancer cells. There was an induction in p53 and p21(Cip1) protein levels following treatment of wild-type p53 MCF-7 cells, which was not observed in the mutant p53 MDA-MB-231 cell line, providing evidence that the compound might act to modulate the cell cycle regardless of p53 status. In addition, LQB-223 resulted in decreased procaspase levels and increased annexin V staining, suggesting that the apoptotic cascade is also triggered. Importantly, LQB-223 treatment was shown to be less cytotoxic to non-neoplastic breast cells than docetaxel and doxorubicin. Strikingly, exposure of doxorubicin-resistant MCF-7-Dox(R) cells to LQB-223 resulted in suppression of cell viability and proliferation in levels comparable to MCF-7. Of note, MCF-7-Dox(R) cells have an elevated expression of the P-glycoprotein efflux pump when compared to MCF-7. CONCLUSION: Together, these results show that LQB-223 mediates cytotoxic effects in sensitive and resistant breast cancer cells, while presenting low toxicity to non-neoplastic cells. The new compound might represent a potential strategy to induce toxicity in breast cancer cells, especially chemoresistant cells

[Corrigendum] The pterocarpanquinone LQB-118 induces apoptosis in acute myeloid leukemia cells of distinct molecular subtypes and targets FoxO3a and FoxM1 transcription factors.

Subsequent to the publication of the above article, the authors have realized that there were errors associated with Figs. 1c and 2b. In Fig. 1c, the authors noted that the same data were incorrectly presented for the 'Untreated cells" and 'DMSO' dot‑blot experiments. After having re‑examined their source data, the authors were able to confirm that the data correctly shown for the 'Untreated cells' experiment had inadvertently been included in the Figure as the data for the 'DMSO' experiment. Additionally, in Fig. 2b, the authors noticed that the percentage of untreated cells with active caspase‑3 was missing (the label for the 'No antibody' experiment). Corrected versions of Figs. 1 (including the correct data for the 'DMSO' dot blot) and 2 (with the label now incorporated) are shown opposite. Note that these changes do not affect the results or the conclusions reported in this paper, and all the authors agree to this correction. The authors apologize to the Editor and to the readership of the Journal for any inconvenience caused. [the original article was published in International Journal of Oncology 45: 1949‑1958, 2014; DOI: 10.3892/ijo.2014.2615]