Heat shock protein 27 (Hsp27) is a chaperone of the small heat shock protein group, that is expressed constitutively at low levels in all cells under physiological conditions. Their expression is induced rapidly in response to elevated temperatures and other stresses, with the prominent members of this group involved in the folding and unfolding of other proteins.
Reduced expression of Hsp27 protein is associated with a less aggressive phenotype and improved survival in breast cancer1,2. High levels of Hsp27 are associated with increased angiogenesis and more rapid tumour growth3. Whilst these findings highlight the role of Hsp27 in controlling the angiogenic switch to regulate the growth of primary tumours, the role of Hsp27 in the mechanisms underlying breast cancer metastasis, such as endothelial-to-mesenchymal plasticity (EMP), still remain unclear.
In this study, we present a novel orthotopic ‘competition’ assay to determine the role of Hsp27 and other potential EMP regulating genes in breast cancer metastasis. In this assay two metastatic human breast tumour cell lines MDA-MB-468 and MDA-MB-231-HM with stable Hsp27 knock-down and TurboGFP expression, are co-inoculated into the mammary fat pad of NOD SCID gamma (NSG) mice with TagRFP expressing control cells, at a varying ratios. Palpable primary mammary tumours are resected, and mice are subsequently culled upon showing signs of sickness. The ratio of TurboGFP-to-TagRFP expressing cells in the primary tumour and in organs such as the lung is assessed via a combination of fluorescence imaging and flow cytometry, or by gDNA qPCR.
Initial results have indicated that suppression of Hsp27 in these human breast cancer cells reduces proliferation in the primary tumour and subsequent metastasis to lung. Subsequent experiments utilising an increased ratio of Hsp27 knock-down cells to control cells in the primary tumour, and experimental metastasis to lung, are underway to focus specifically on the involvement of Hsp27 in metastasis.