Abstract
Background
Membrane type 1 matrix metalloproteinase (MT1-MMP) plays a role in the progression of several common solid cancers. Given that osteosarcoma features extensive local invasion and haematogenous metastases, we hypothesised that osteosarcoma cells utilise MT1-MMP to drive these processes. Moreover, since hypoxia regulates MT1-MMP expression in breast cancer we investigated the effects of hypoxia on MT1-MMP expression in osteosarcoma cells.
Aims
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Examination of MT1-MMP expression in osteosarcoma biopsy tissue in relation to clinical outcome
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Assessment of MT1-MMP, together with hypoxia inducible factors HIF-1α and HIF-2α expression in a panel of osteosarcoma cell lines under normoxia and hypoxia
Methods
Immunohistochemistry: Formalin-fixed and paraffin embedded osteosarcoma biopsy samples from 71 patients were immunostained for MT1-MMP, HIF-1α and -2α and the data correlated with patient survival.
Confocal microscopy: following 24 hours culture in 20% versus 1% oxygen, a panel of osteosarcoma cell lines were analysed for the subcellular distribution of MT1-MMP, HIF-1α and -2α.
Subcellular fractionation: following 48 hours culture in 20% versus 1% oxygen, the U2OS cell line was fractionated and the compartmental lysates immunoblotted for MT1-MMP, HIF-1α and -2α.
Results
Immunohistochemistry showed MT1-MMP immunopositive cytoplasmic and nuclear staining. Biopsy samples with the highest MT1-MMP and HIF-2α intranuclear staining correlated with reduced patient survival: HR 16.10; (95% CI: 5.1–40.3); p< 0.0001.
In vitro studies confirmed the intranuclear MT1-MMP presence with an increased nuclear fraction in hypoxia and evidence of nuclear co-localisation with HIF-2α.
Conclusions
MT1-MMP expression in osteosarcoma tissue correlates with patient survival. The functional significance of the increased intranuclear presence in hypoxia warrants further investigation.
