Induction of the estrogen-regulated "24K" protein by heat shock.

We have previously demonstrated an estrogen-regulated protein, termed 24K, in human breast cancer cell lines and human tumor biopsies. The presence of the protein correlates well with the presence of steroid hormone receptors. We have cloned a partial complementary DNA to 24K and show that the nucleotide and deduced amino acid sequence contains a striking homology to the low molecular weight heat shock proteins of Drosophila and the mammalian alpha-crystallins. Our complementary DNA is identical to that reported for the 3' region of human heat shock protein 27/28 with the mRNAs for the gene significantly induced by both heat shock and estradiol treatment in MCF-7 breast cancer cells. A variant polymorphism of the gene was detected in two estrogen-unresponsive cell lines, but not in other human breast cancer cell lines or human placenta; the polymorphism did not affect heat shock induction of the gene. The heat shock protein 27/28 model system in MCF-7 cells will afford a valuable tool to analyze the molecular events underlying the hormonal regulation of gene expression; heat shock may offer an approach to manipulate the hormonal regulation of the heat shock protein 27/28 gene.