Increased gap junctional intercellular communication is directly related to the anti-tumor effect of all-trans-retinoic acid plus tamoxifen in a human mammary cancer cell line

Claudia G. Sáez, L. Velásquez, M. Montoya, Eliseo Eugenin, M. G. Alvarez

Research output: Contribution to journalArticle

26 Scopus citations

Abstract

Additive effects against tumor cells might be achieved by combining anti-neoplastic agents directed against one or more altered mechanisms in cancer. We investigated the participation of gap junctional intercellular communication (GJIC), which is commonly dysfunctional in tumor cells as a possible mediating mechanism of the effect of all-trans-retinoic acid (RA) and tamoxifen (Tx) in MCF-7 human breast cancer cell lines. The combination of RA + Tx stimulated GJIC in approximately 53 ± 3% of MCF-7 cells as early as after 6 h of treatment remaining communicated through 144 h of culture. The GJIC enhancement occurred along with immunolocalization of Cx26 and 43 at the membrane of contacting cells and correlated with higher protein levels. Cx40 immunoreactive plaques were detected at cell-to-cell contacts during 48 h of RA + TX treatment that did not involve higher protein expression, to the contrary, a downregulation occurred after 72 h of treatment. Cell proliferation inhibition upon RA + Tx exposure was observed with optimal effects at 96-120 h of culture with an accumulation of cells primarily in G2/M and G0/G1 cell cycle boundaries. An enhancement of the pre-existing E-cadherin levels was observed after drug exposure along with a downregulation of Bcl-2 and C-myc protein levels and a reduction of telomerase activity, suggesting partial tumor phenotype reversion. Blockage of the RA + Tx-induced GJIC with 18-β-glycyrrhetinic acid (β-Gly) prevented in 34% the inhibition of MCF-7 proliferation and the E-cadherin increment in 30% at 96 h of culture. GJIC blockage did not alter the downregulation of Bcl-2, c-Myc, or telomerase activity induced by RA + Tx. Our results showed the participation of GJIC as a mediator mechanism of the combined action of RA and Tx in MCF-7 cells. The chemopreventive modulation of GJIC might represent an approachable alternative for the improvement of cancer therapy.

Original languageEnglish (US)
Pages (from-to)450-461
Number of pages12
JournalJournal of Cellular Biochemistry
Volume89
Issue number3
DOIs
StatePublished - Jun 1 2003
Externally publishedYes

Keywords

  • Anti-tumor
  • Chemoprevention
  • Gap junctional intercellular communication
  • Human breast cancer cells

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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