title: Cytosolic galectin-7 impairs p53 functions and induces chemoresistance in breast cancer cells.
abstract: BACKGROUND
  Resistance to apoptosis induced by anti-cancer drugs is a major obstacle for the treatment of aggressive forms of breast cancer. Galectin-7 (gal-7) was recently shown to be specifically expressed in basal-like but not in luminal subtypes of human breast cancer.
  
  
  METHODS
  We generated a mutant form of gal-7 (R74S). Arginine 74 is the structural equivalent of arginine 186 found in human galectin-3. Mutation R186S was previously shown to abolish the biological function of galectin-3.
  
  
  RESULTS
  Mutation of arginine 74 induced only limited and local changes to the gal-7 fold. Recombinant forms of R74S and wtgal-7 were also equally effective at forming dimers in solution. Analysis of the thermodynamic parameters by isothermal titration calorimetry (ITC) indicated, however, that binding of lactose to gal-7 was inhibited by the R74S mutation. Using confocal microscopy and electron microscopy, we confirmed the expression of gal-7 in the cytosolic and nuclear compartments of breast cancer cells and the ability of gal-7 to translocate to mitochondria. The mutation at position 74, however, greatly reduced the expression of gal-7 in the nuclear and mitochondrial compartments. Interestingly, cells expressing mutated gal-7 were equally if not even more resistant to drug-induced apoptosis when compared to cells expressing wtgal-7. We also found that both wtgal-7 and R74S inhibited dox-induced PARP-1 cleavage and p53 protein expression. The inhibition of p53 correlated with a decrease in p21 protein expression and CDKN1A mRNA. Furthermore, analysis of nuclear and cytoplasmic fractions showed that both wild type and R74S mutant gal-7 inhibited p53 nuclear translocation, possibly by increasing degradation of cytosolic p53.
  
  
  CONCLUSIONS
  These findings pose a challenge to the paradigm that has guided the design of galectin-specific inhibitors for the treatment of cancer. This study suggests that targeting CRD-independent cytosolic gal-7 in breast cancer cells may be a valuable strategy for the treatment of this disease. Our study will thus complement efforts towards improving selectivity of targeted anticancer agents.
authors.forename: Andrée-Anne
authors.initials: AA
authors.lastname: Grosset
authors.forename: Marilyne
authors.initials: M
authors.lastname: Labrie
authors.forename: Donald
authors.initials: D
authors.lastname: Gagné
authors.forename: Maria-Claudia
authors.initials: MC
authors.lastname: Vladoiu
authors.forename: Louis
authors.initials: L
authors.lastname: Gaboury
authors.forename: Nicolas
authors.initials: N
authors.lastname: Doucet
authors.affiliation: INRS-Institut Armand-Frappier, 531 Blv, des Prairies, Laval, Quebec H7V 1B7, Canada. yves.st-pierre@iaf.inrs.ca.
authors.forename: Yves
authors.initials: Y
authors.lastname: St-Pierre
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000648:ultrastructure; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005260:Female; D037161:Galectins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D021381:Protein Transport; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D037161:Galectins; C092525:LGALS7 protein, human; D016159:Tumor Suppressor Protein p53; D016283:Proto-Oncogene Proteins p21(ras)