Page 105 - Read Online

Page 4 of 15 Spencer et al. J Cancer Metastasis Treat 2022;8:2 https://dx.doi.org/10.20517/2394-4722.2021.174

[18]
A study by Engelholm et al. examined OS patient samples to identify novel bone degradation pathways.
Of the 10 samples that were tested, by immunohistochemical analysis, for MT1-MMP protein expression,
all were positive to varying degrees; scattered expression was observed in 2 samples, moderate expression
(< 50%) in 4 samples and high (> 50%) expression in 4 samples. This study also demonstrated the
differential expression of MMPs in primary OS tumours and tumours resulting from carcinomas. OS
tumour samples showed high expression of MT1-MMP and other endocytic collagen receptors, whereas, in
tumours originating from breast carcinoma, there was little to no expression of these proteins.

[19]
Also utilising immunostaining techniques, Biswas et al. , demonstrated that in biopsies collected from
patients that had undergone standard MAP chemotherapy - that involves administering high dose
methotrexate (M), doxorubicin (A - adriamycin) and cisplatin (P) - more than 90% of samples evaluated
expressed the MT1-MMP protein. A reduction in overall survival was associated with an increase in the
localisation of MT1-MMP to the cytoplasm (P = 0.0002) and to the nucleus (P < 0.0001). In addition to this,
a reduction in the EFS was observed in patients with localisation of MT1-MMP to the nucleus, but not to
the cytoplasm. Therefore MT1-MMP localisation could prove to be crucial in predicting patient prognosis
and in determining the patients’ response chemotherapy.

In experimental models of OS
MMP expression in OS has garnered a lot of attention, but studies primarily focus on the expression of the
widely-studied MMP-2 [11,20] or MMP-9 [21,22] rather than MT1-MMP (MMP-14). The vast majority of
literature regarding gene expression of MMP-14 in human OS cell lines has been reported in U2OS, Saos-2
and MG-63 cells, but there is some evidence of expression in OHS, HOS (HOS-MNNG and HOS-143B)
[23]
and the newly derived HMOS cell lines (HMOS-A and HMOS-P) . The phenotypical and functional
characteristics of multiple osteosarcoma cell lines, both in vitro and in vivo, have been well documented. Of
the cell lines examined, HOS cell lines, with the exception of HOS-MNNG, are highly tumorigenic and
frequently form metastases (primarily in the lung), while U2OS, Soas-2 and MG-63 cells are less
tumorigenic and non-metastatic [24,25] .

[26]
Giambernardi et al. reported the differential gene expression of MMPs in cell lines; a strong expression of
MMP-14 was observed in HOS, MG-63 and Saos-2. It has been shown that the transformation of the HOS-
Te85 parental cell line to its 143B derivative, brought about an increase in MT1-MMP protein expression,
which has been associated with a more metastatic phenotype, whereas a reduction in MT1-MMP expression
in the transformed HOS-MNNG cell line played a role in reducing its metastatic capacity .
[27]

Hypoxia, resulting from oxygen deprivation, is common in many solid tumours with an associated increase
in hypoxia-related markers, such as hypoxia-inducible factors-1α or -2α (HIF-1α/-2α), which often
correlates with poorer prognoses. Many genes, including those of MMPs, are transcriptionally regulated by
these HIFs . Chan et al. determined, by way of Western blot, that the degree of MT1-MMP protein
[28]
[29]
expression in U2OS cells was equal to that of the positive control cell line HT1080, which exhibits a high-
level expression of the majority of MMPs. Further to this, immunohistochemical staining revealed that, in
normoxia, MT1-MMP is primarily located in the cell cytoplasm and was shown to interact with HIF-1α -
this interaction was not observed following a reduction in O levels. Hypoxia-induced alterations in the
2
subcellular location of MT1-MMP, with a higher expression of MT1-MMP observed within the nucleus. In
normoxia, a proximity ligation assay showed that there is minimal interaction between HIF-2α and MT1-
MMP, but when cells were cultured under hypoxic conditions, there was a marked increase in the
interaction signals within the nucleus. This interaction was shown to be specific to U2OS cells when
compared to bone marrow mesenchymal stem cells.