Molecular chaperones in mammary cancer growth and breast tumor therapy

Heat shock protein (HSP) levels are elevated in breast cancer and are molecular targets for novel therapies. HSPs were first observed as proteins induced in massive amounts in normal cells exposed to stresses that lead to protein denaturation. Their expanded expression in mammary carcinoma appears to be largely due to the proliferation of malfolded mutant proteins and overexpressed oncoproteins that trigger transcription of HSP genes. HSPs play major roles in malignant transformation and progression mediated through their intrinsic molecular chaperone properties. These permit the emergence of new malignant traits through the facilitated accumulation of altered oncoproteins. The elevation of HSP concentrations in mammary carcinoma is at least partially dependent on heat shock transcription factor 1 (HSF1), a protein that responds to unfolded proteins and leads to HSP transcription. HSF1 activation has additional downstream activities, crucial for emergence of the breast cancer phenotype and these include activated cell signaling, HSP-mediated ability to evade apoptosis and senescence and an HSF1-dependent bias in transcriptional activity towards a metastatic phenotype. The HSPs are currently being targeted in breast cancer therapy and effective drugs for Hsp90 have been synthesized and evaluated in clinical trial. Mammary carcinoma cells also contain abundant quantities of HSP–tumor antigen complexes and these complexes are being used to develop effective tumor vaccine approaches that provide personalized therapy for each individual's cancer.