Heat Shock Protein-27 (Hsp-27) in Breast Cancers: Regulation of Expression and Function.

The small heat shock protein, Hsp27, is elevated in a significant proportion of breast cancers. Over-expression of Hsp27 in breast cancer cells increases anchorage-independent growth, invasiveness and resistance to chemotherapeutic drugs and is associated with poor prognosis and shorter disease free survival in a proportion of cancer patients. Hsp27 acts in a complex manner to elicit diverse effects e.g. increasing survival in response to many stresses by acting either as a molecular chaperone, by association with components of the apoptotic machinery and/or by increasing cellular glutathione to regulate the redox state of the cells. Hsp27 also regulates cytoskeleton organization and stability. Therefore, factors that increase the expression and/or alter the functions of Hsp27 in breast cancer cells can affect disease progression and outcome following treatment. Although Hsp27 expression can be mediated via the classical Heat Shock response following stress, its elevation in breast cancer cells is associated with independent positive regulators which include the estrogen receptor (ER) and transcription factors such as Brn-3b and Sp1. HET/SAF-B negatively regulates Hsp27 in these cells. The effects of Hsp27 are also regulated post-translationally by phosphorylation at specific residues, which alter the oligomerization state of the protein and thus its effects in the cells. The expression, effects and mechanisms by which Hsp27 acts in breast cancer cells are described in this chapter [ABSTRACT FROM AUTHOR]