Archives

  • 2018-07
  • 2018-10
  • 2018-11
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-07
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • Despite many studies having demonstrated the importance

    2020-11-24

    Despite many studies having demonstrated the importance of connexin43 (Cx43), the most abundant connexin in bone cells, for bone development and turnover during the last decade [27], little is currently known about GJIC and Cx43 in primary bone tumors. In this report, we analyzed the specific role of Cx43-driven GJIC in ES tumor growth. Using a combination of in vitro and in vivo experimental approaches, we demonstrated: i) a lack of Cx43 gene expression in ES cells, ii) that the expression level of Cx43 is associated with that of EWS–FLI1, iii) that Cx43 inhibits ES tumor growth via modulation of cell proliferation, and iv) Cx43 reduces tumor cell-driven osteoclast activity.
    Materials and methods
    Results
    Discussion Observations indicating a role of connexin in tumorigenesis are supported by many in vitro analyses demonstrating the down-regulation or loss of connexin expression in a wide range of neoplastic SMIP004 and primary tumors [35], [36], [37]. Here, we demonstrated a loss of SMIP004 Cx43 gene expression in ES cell lines. Early works using the NIH3T3 cell model have demonstrated that EWS–FLI1 acts as a transcriptional activator that allows oncogenic transformation [38], [39]. Current opinion holds that EWS–FLI1 functions as an aberrant transcription factor supported by works which demonstrated that EWS–FLI1 localizes to the nucleus, binds DNA in a site-specific manner and possesses a powerful transcriptional activator that is more potent than the native FLI1 [7]. Gene expression studies have further demonstrated that EWS–FLI1 is able to enhance the expression of many genes implicated in transformation and/or tumor progression, including MYC [40], ID2 [41], CCND1 [42] and PDGFC [43]. Other studies have revealed that EWS–FLI1 is able to decrease the expression of many genes including those encoding p21 [44], p57kip [45], TGFβRII [46] and IGFBP3 [47]. Among these, only the TGFβRII and IGFBP3 genes, which are down-regulated by EWS–FLI1, have been identified as direct EWS–FLI1 targets [48]. Here, using a EWS–FLI1 knock-down approach, we demonstrated that EWS–FLI1 affects the Cx43 gene expression, suggesting that Cx43 is a EWS–FLI1 target gene. However, we cannot exclude that Cx43 induction in response to EWS–FLI1 silencing is a consequence of modified cell differentiation for example. The exact mechanisms underlying the down-regulation of Cx43 gene by EWS–FLI1 remain to be elucidated. Through a molecular gain-of-function approach, we demonstrated that Cx43 overexpression inhibits in vivo ES tumor growth, providing the first experimental evidence indicating that the decrease of Cx43 gene expression is one mechanism through which ES cells can acquire high tumor growth potential. Since the main function of connexins is the formation of intercellular channels, the mechanisms by which connexins modulate cell proliferation and thus tumor growth were firstly proposed to depend on the ability of these channels to promote exchange of molecules that regulate the cell cycle [49]. Over the past 40years, numerous studies have demonstrated a loss or at least a decrease of GJIC between cancer cells or between cancer cells and their surrounding normal cells, supporting the link between gap junction defects and tumor growth [20]. In agreement with this dogma, numerous studies reported that many tumor promoters were indeed inhibitors of GJIC [50] supporting the idea that the inhibition of GJIC during the tumor promoting stage may favor the clonal expansion of initiated cells [20], [51]. It was thus proposed that the recovery of GJIC between cancer cells could inhibit their proliferation and by consequence in vivo tumor growth. In this context, over-expression of connexins in different tumor cells was shown to restore GJIC and therefore inhibit cell proliferation [20], [21], [35]. Although we showed that Cx43 overexpression in ES cells restores GJIC, we cannot exclude that the effect of Cx43 overexpression on cell proliferation and in vivo tumor growth was not associated with the restoration of GJIC. Indeed, numerous studies have provided evidence for a dissociation of GJIC and the ability of connexins to inhibit cell proliferation and tumor growth [21]. Mechanistic studies demonstrated that Cx43 overexpression may inhibit cell proliferation via the inhibition of the expression of S phase kinase associated protein 2 (skp2), the protein that promotes the ubiquitination of cyclin-dependent kinase inhibitor p27kip [49]. With regard to primary bone tumors, a down-regulation of cyclin D1 associated with a blockade of the cell cycle in G0/G1 phase was observed in osteosarcoma after Cx43 overexpression [52]. Supporting this observation, we demonstrated that Cx43 overexpression in ES cells increases p27 levels with an associated marked decrease of Rb phosphorylation, consistent with the observed blockade of the cell cycle in G0/G1 phase.