Functional evaluation of members of the LIV-1 family of proteins and their role in breast cancer

C51

Abstract
 All nine members of the LIV-1 family of proteins (LZT subfamily) have similarity to members of the ZIP superfamily, especially in the region associated with zinc transport. Computer analysis of the nine sequences suggests that they are all members of this superfamily, however, in phylogenetic tree some members group separately, suggesting differences in function. LZT-Hs7, LZT-Hs8 and LZT-Hs9 were cloned into a vector suitable for expression of recombinant proteins in mammalian cells. This demonstrated, similar to LIV-1, a plasma membrane location for LZT-Hs7 and LZT-Hs8 for the first time and an intracellular location for LZT-Hs9, similar to that observed previously for LZT-Hs1. Zinc transport capability was also investigated. Affymetrix Human Genome U133A GeneChips^® analysis of LZT-Hs1, LIV-1, LZT-Hs4, LZT-Hs5 and pS2 confirmed that LZT-Hs1, LIV-1 and LZT-Hs4 were regulated by estradiol. This study was extended to investigate the expression of all nine family members in breast cancer cells treated with oestradiol, anti-oestrogens and additionally in our tamoxifen and faslodex resistant cells using semi-quantitative PCR. Differential expression of these family members was seen with some members constitutively expressed whilst others either elevated or reduced in the different conditions. This analysis demonstrated that LZT-Hs1 was considerably elevated in tamoxifen resistance. In an effort to investigate a possible role for LZT-Hs1 in tamoxifen resistant cells, it was reduced by siRNA. Interestingly, in the presence of siRNA for LZT-Hs1, it was not possible to demonstrate the activation of EGFR or Src as previously observed in the tamoxifen resistant phenotype using Western blotting analysis. This is an exciting result, which suggests a role for LZT-Hs1 in driving the growth of tamoxifen resistant breast cancer cells.