Aberrant activation of ERK/FOXM1 signaling cascade triggers the cell migration/invasion in ovarian cancer cells

Forkhead box M1 (FOXM1) is a proliferation-associated transcription factor essential for cell cycle progression. Numerous studies have documented that FOXM1 has multiple functions in tumorigenesis and its elevated levels are frequently associated with cancer progression. Here, we characterized the role of ERK/FOXM1 signaling in mediating the metastatic potential of ovarian cancer cells. Immunohistochemical (IHC), immunoblotting and semi-quantitative RT-PCR analyses found that both phospho-ERK and FOXM1 were frequently upregulated in ovarian cancers. Intriguingly, the overexpressed phospho-ERK (p<0.001) and FOXM1 (p<0.001) were significantly correlated to high-grade ovarian tumors with aggressive behavior such as metastasized lymph node (5 out of 6). Moreover, the expressions of phospho-ERK and FOXM1 had significantly positive correlation (p<0.001). Functionally, ectopic expression of FOXM1B remarkably enhanced cell migration/invasion, while FOXM1C not only increased cell proliferation but also promoted cell migration/invasion. Conversely, inhibition of FOXM1 expression by either thiostrepton or U0126 could significantly impair FOXM1 mediated oncogenic capacities. However, the down-regulation of FOXM1 by either thiostrepton or U0126 required the presence of p53 in ovarian cancer cells. Collectively, our data suggest that over-expression of FOXM1 might stem from the constitutively active ERK which confers the metastatic capabilities to ovarian cancer cells. The impairment of metastatic potential of cancer cells by FOXM1 inhibitors underscores its therapeutic value in advanced ovarian tumors. © 2011 Lok et al.published_or_final_versio

Differential regulation of RNF8-mediated Lys48- and Lys63-based poly-ubiquitylation

Pairing of a given E3 ubiquitin ligase with different E2s allows synthesis of ubiquitin conjugates of different topologies. While this phenomenon contributes to functional diversity, it remains largely unknown how a single E3 ubiquitin ligase recognizes multiple E2s, and whether identical structural requirements determine their respective interactions. The E3 ubiquitin ligase RNF8 that plays a critically important role in transducing DNA damage signals, interacts with E2s UBCH8 and UBC13, and catalyzes both K48- and K63-linked ubiquitin chains. Interestingly, we report here that a single-point mutation (I405A) on the RNF8 polypeptide uncouples its ability in catalyzing K48- and K63-linked ubiquitin chain formation. Accordingly, while RNF8 interacted with E2s UBCH8 and UBC13, its I405A mutation selectively disrupted its functional interaction with UBCH8, and impaired K48-based poly-ubiquitylation reactions. In contrast, RNF8 I405A preserved its interaction with UBC13, synthesized K63-linked ubiquitin chains, and assembled BRCA1 and 53BP1 at sites of DNA breaks. Together, our data suggest that RNF8 regulates K48- and K63-linked poly-ubiquitylation via differential RING-dependent interactions with its E2s UBCH8 and UBC13, respectively.published_or_final_versio

Over-expression of FOXM1 is associated with cell migration/invasion of ovarian cancer cells

Poster Session: abstract no. 4078FOXM1 is a typical transcription factor regulating the S- and M-phase progression in cell cycle. It is frequently over-expressed and is associated with tumor stages in numerous human cancers. The influence of FOXM1 expression on cell proliferation has been well studied, yet its impact on other tumor characteristics in ovarian cancer, like cell migration/invasion remains unclear. In the present study, we demonstrated that FOXM1 was significantly up-regulated in ovarian cancer cell lines at both RNA and protein level by semi-quantitative RT- PCR and Western blot analyses. Immunohistochemical analysis showed that FOXM1 was highly correlated with the high-grade ovarian cancer. To examine the effect of FOXM1 on ovarian cancer cell motility, the FOXM1 specific inhibitor, thiostrepton, was used to reduce FOXM1 expression in OVCA433 cells. The FOXM1 reduced OVCA433 cells, as a result, showed a significant decrease in cell migration using wound healing assay. By using MEK specific inhibitor, U0126, we demonstrated that the inhibition of ERK activity caused a reduction of FOXM1 level in a time dependent manner and significant reduction of cell migration rate in the wound healing assay in OVCA433. In sum, FOXM1 is over-expressed and regulated by constitutive activated ERK activity in ovarian cancer cells. Our data also suggested that the ERK /FOXM1 signaling axis is crucial in regulating migration/invasion of ovarian cancer cells. Further studies on the molecular mechanism of FOXM1 in the regulation of ovarian cancer cell migration/invasion are warranted.The 101st Annual Meeting of the American Association For Cancer Research (AACR), Washington, D.C., 17-21 April 2010