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Rybak A.P.,McMaster University | Rybak A.P.,Father Sean OSullivan Research Institute | Rybak A.P.,The Hamilton Center for Kidney Research | Tang D.,McMaster University | And 2 more authors.
Cellular Signalling | Year: 2013

SOX2 is an essential transcription factor for stem cells and plays a role in tumorigenesis, however its role in prostate cancer stem cells (PCSCs) remains unclear. We report here a significant upregulation of SOX2 at both mRNA and protein levels in DU145 PCSCs propagated as suspension spheres in vitro. The expression of SOX2 in DU145 PCSCs is positively regulated by epidermal growth factor receptor (EGFR) signaling. Activation of EGFR signaling, following the addition of epidermal growth factor (EGF) or ectopic expression of a constitutively-active EGFR mutant (EGFRvIII), increased SOX2 expression and the self-renewal of DU145 PCSCs. Conversely, a small molecule EGFR inhibitor (AG1478) blocked EGFR activation, reduced SOX2 expression and inhibited PCSC self-renewal activity, implicating SOX2 in mediating EGFR-dependent self-renewal of PCSCs. In line with this notion, ectopic SOX2 expression enhanced EGF-induced self-renewal of DU145 PCSCs, while SOX2 knockdown reduced PCSC self-renewal with EGF treatment no longer capable of enhancing their propagation. Furthermore, SOX2 knockdown reduced the capacity of DU145 PCSCs to grow under anchorage-independent conditions. Finally, DU145 PCSCs generated xenograft tumors more aggressively with elevated levels of SOX2 expression compared to xenograft tumors derived from non-PCSCs. Collectively, we provide evidence that SOX2 plays a critical role in EGFR-mediated self-renewal of DU145 PCSCs. © 2013 Elsevier Inc.


Yan J.,McMaster University | Yan J.,Father Sean OSullivan Research Institute | Yan J.,The Hamilton Center for Kidney Research | Tang D.,McMaster University | And 2 more authors.
Experimental Cell Research | Year: 2014

Despite the development of chemoresistance as a major concern in prostate cancer therapy, the underlying mechanisms remain elusive. In this report, we demonstrate that DU145-derived prostate cancer stem cells (PCSCs) progress slowly with more cells accumulating in the G1 phase in comparison to DU145 non-PCSCs. Consistent with the important role of the AKT pathway in promoting G1 progression, DU145 PCSCs were less sensitive to growth factor-induced activation of AKT in comparison to non-PCSCs. In response to etoposide (one of the most commonly used chemotherapeutic drugs), DU145 PCSCs survived significantly better than non-PCSCs. In addition to etoposide, PCSCs demonstrated increased resistance to docetaxel, a taxane drug that is commonly used to treat castration-resistant prostate cancer. Etoposide produced elevated levels of γH2AX and triggered a robust G2/M arrest along with a coordinated reduction of the G1 population in PCSCs compared to non-PCSCs, suggesting that elevated γH2AX plays a role in the resistance of PCSCs to etoposide-induced cytotoxicity. We have generated xenograft tumors from DU145 PCSCs and non-PCSCs. Consistent with the knowledge that PCSCs produce xenograft tumors with more advanced features, we were able to demonstrate that PCSC-derived xenograft tumors displayed higher levels of γH2AX and p-CHK1 compared to non-PCSC-produced xenograft tumors. Collectively, our research suggests that the elevation of DNA damage response contributes to PCSC-associated resistance to genotoxic reagents. © 2014 Elsevier Inc.


Rybak A.P.,McMaster University | Rybak A.P.,Father Sean OSullivan Research Institute | Rybak A.P.,The Hamilton Center for Kidney Research | Ingram A.J.,McMaster University | And 5 more authors.
PLoS ONE | Year: 2013

Prostate cancer stem-like cells (PCSCs) are being intensely investigated largely owing to their contributions towards prostate tumorigenesis, however, our understanding of PCSC biology, including their critical pathways, remains incompletely understood. While epidermal growth factor (EGF) is widely used in maintaining PCSC cells in vitro, the importance of EGF-dependent signaling and its downstream pathways in PCSC self-renewal are not well characterized. By investigating DU145 sphere cells, a population of prostate cancer cells with stem-like properties, we report here that epidermal growth factor receptor (EGFR) signaling plays a critical role in the propagation of DU145 PCSCs. Activation of EGFR signaling via addition of EGF and ectopic expression of a constitutively-active EGFR mutant (EGFRvIII) increased sphere formation. Conversely, inhibition of EGFR signaling by using EGFR inhibitors (AG1478 and PD168393) and knockdown of EGFR significantly inhibited PCSC self-renewal. Consistent with the MEK-ERK pathway being a major target of EGFR signaling, activation of the MEK-ERK pathway contributed to EGFR-facilitated PCSC propagation. Modulation of EGFR signaling affected extracellular signal-related kinase (ERK) activation. Inhibition of ERK activation through multiple approaches, including treatment with the MEK inhibitor U0126, ectopic expression of dominant-negative MEK1(K97M), and knockdown of either ERK1 or ERK2 resulted in a robust reduction in PCSC propagation. Collectively, the present study provides evidence that EGFR signaling promotes PCSC self-renewal, in part, by activating the MEK-ERK pathway. © 2013 Rybak et al.


Wei F.,McMaster University | Wei F.,Father Sean OSullivan Research Institute | Wei F.,The Hamilton Center for Kidney Research | Wei F.,Guangdong Pharmaceutical University | And 8 more authors.
Cellular Signalling | Year: 2010

The MEK-ERK pathway plays a role in DNA damage response (DDR). This has been thoroughly studied by modulating MEK activation. However, much less has been done to directly examine the contributions of ERK1 and ERK2 kinases to DDR. Etoposide induces G2/M arrest in a variety of cell lines, including MCF7 cells. DNA damage-induced G2/M arrest depends on the activation of the protein kinase ataxia-telangiectasia mutated (ATM). ATM subsequently activates CHK2 by phosphorylating CHK2 threonine 68 (T68) and CHK2 inactivates CDC25C via phosphorylation of its serine 216 (S216), resulting in G2/M arrest. To determine the contribution of ERK1 and ERK2 to etoposide-induced G2/M arrest, we individually knocked-down ERK1 and ERK2 in MCF7 cells using specific small interfering RNA (siRNA). Knockdown of either kinases significantly reduced ATM activation in response to etoposide treatment, and thereby attenuated phosphorylation of the ATM substrates, including the S139 of H2AX (γH2AX), p53 S15, and CHK2 T68. Consistent with these observations, knockdown of either ERK1 or ERK2 reduced etoposide-induced CDC25C S216 phosphorylation and significantly compromised etoposide-induced G2/M arrest in MCF7 cells. Taken together, we demonstrated that both ERK1 and ERK2 kinases play a role in etoposide-induced G2/M arrest by facilitating activation of the ATM pathway. These observations suggest that a cellular threshold level of ERK kinase activity is required for the proper checkpoint activation in MCF7 cells. © 2010 Elsevier Inc.


Wei F.,McMaster University | Wei F.,Father Sean OSullivan Research Institute | Wei F.,The Hamilton Center for Kidney Research | Wei F.,Guangdong Pharmaceutical University | And 11 more authors.
Cellular Signalling | Year: 2011

Modulation of MEK has been demonstrated to affect hydroxyurea (HU) induced-DNA damage response (DDR), implying the involvement of ERK1 and ERK2 in the process. To directly examine how the ERK kinases function in HU-initiated DDR, we knocked-down either ERK1 or ERK2 in MCF7 cells. This resulted in reduction of HU-induced phosphorylation of CHK1 S345 (serine 345), p53 S15, and H2AX S139. While HU potently induced CDC2 Y15 (tyrosine 15) phosphorylation, an event causing CDC2 inactivation, inhibition of ERK kinases using U0126 (a MEK inhibitor), MEK1K97M (a dominant negative MEK1), and knockdown of either ERK1 or ERK2 significantly attenuated HU-induced CDC2 Y15 phosphorylation. As CDC2 kinase activity is required for mitosis, our observations reveal that ERK1 and ERK2 kinases play important roles in preventing mitotic entry in response to HU. Consistent with ATR being the apical kinase to initiate HU-induced DDR, knockdown of ERK1 or ERK2 significantly inhibited HU-induced ATR recruitment to the stalled replication forks (ATR foci), an event required for ATR activation. Mechanistically, knockdown of ERK1 or ERK2 resulted in relocation of ATR from the nucleoplasm to the nucleolus in response to HU, therefore making ATR unavailable to the sites of DNA damage. Taken together, we demonstrate that ERK kinases sit upstream of ATR to facilitate its activation. © 2010 Elsevier Inc.

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