Membrane-type Matrix Metalloproteinases in Pericellular Proteolysis and
Melanoma Cell Invasion
OLGA TATTI
Department of Pathology and Virology, Haartman Institute and Helsinki University Hospital, FI-00250, Finland.
E-mail: olga.tatti@helsinki.?
Olga Tatti defended her PhD thesis at the University of Helsinki, Finland, on May 31, 2013. The thesis was
supervised by Associate Professor Kaisa Lehti, Genome Scale Biology Research Program, University of Helsinki,
and Professor Jorma Keski-Oja, Departments of Pathology and Virology, Haartman Institute, Helsinki University
Hospital and Translational Cancer Biology Research Program, University of Helsinki, Helsinki, Finland. The
opponent was Professor Cornelia Mauch, Department of Dermatology and Venereology, University of Cologne,
Cologne, Germany. The thesis is available at: http://urn.?/URN:ISBN:978-952-10-8775-2.
Tumour microenvironment comprised of extracellular matrix
(ECM) and non-malignant cells has profound effects on cancer progression. Membrane-type matrix metalloproteinases
(MT-MMPs) expressed by both tumour and stroma cells are
involved in the modulation of tumour microenvironment
and thereby regulate tumour cell proliferation, invasion and
dissemination. MT1-MMP is a prototype of MT-MMP family,
which is overexpressed in many types of cancer, where it
promotes tumour cell invasion through collagen-rich tissues.
The biological functions of another member of the MT-MMP
family, MT3-MMP, have remained largely unknown. Unlike
MT1-MMP, MT3-MMP cannot cleave native collagen type I.
MT3-MMP is expressed in the adult brain, as well as various
cancer types such as brain tumours and nodular melanoma.
The purpose of this thesis was to elucidate the functions of
MT1-MMP and MT3-MMP in melanoma cell invasion. To
understand the pericellular growth regulation, we searched
for endogenous enzymes which could release latent TGF!
from endothelial cell extracellular matrix.
Neovessel formation (angiogenesis) is a prerequisite for tumour
growth. Pericellular modulation of the ECM by MT1-MMP releases matrix-associated growth factors and bioactive peptides,
which further affect angiogenesis and tumour cell biology. We
found that MT1-MMP mRNA expression and activity were
induced after morphological activation of endothelial cells,
which mimics the initial phases of angiogenesis. MT1-MMP
modulated subendothelial extracellular matrix, and cleaved
latent TGF
binding protein-1 (LTPB-1), with subsequent
release of latent TGF complexes from the ECM. TGF can
both promote and inhibit endothelial cell proliferation, and
the opposing effects of TGF- depend on its concentration.
Thus, MT1-MMP-mediated LTBP-1 cleavage provides a mechanism for the tightly controlled release of matrix-associated
TGF at the sites of neovessel formation.
To elucidate the functions of MT-MMPs in melanoma cell
invasion, we analysed the expression of MT1-MMP and MT3MMP from biopsies of normal human skin, benign naevi, and
melanoma metastases. MT3-MMP was upregulated in lymph
146
DISSERTATIONS
Olga Tatti defended her PhD thesis on membrane-type matrix metalloproteinases in Helsinki, Finland on 31st May, 2013. Left to right: Profe ssor
Jorma Keski-Oja, PhD Olga Tatti, Opponent, Professor Cornelia Mauch,
Associate Professor Kaisa Lehti.
node metastases of human melanoma, while MT1-MMP
expression was comparable in all biopsies. By culturing melanoma cells in 3D collagen and ?brin matrices, we found that
MT3-MMP was associated with expansive melanoma growth
in 3D collagen, but promoted their sprouting growth in 3D
?brin. In in vivo xenograft experiments, MT3-MMP expressing
melanoma xenografts grew slowly, while MT3-MMP silencing
enhanced tumour growth rate by over two fold. Interestingly, high MT3-MMP expression in murine xenografts and
a human melanoma tumour was associated with prominent
lymphatic vessel invasion but negligible blood vessel invasion
of melanoma cells. Silencing of MT3-MMP reduced lymphatic
invasion but facilitated blood vessel invasion of melanoma
cells > 10-fold. MT3-MMP reduced cell surface MT1-MMP in
vitro and in vivo, resulting in limited collagen invasion in vitro
and collagen accumulation in vivo. This suggested that low
collagenolytic ability of MT3-MMP-expressing melanoma
cells resulted in decreased blood vascular invasion. These
cells invaded instead into more permissive lymphatic vessels.
Since lymphatic vessel invasion is associated with metastatic
spread in melanoma, MT3-MMP expression may serve as a
new prognostic factor in this disease.
Forum for Nord Derm Ven 2013, Vol. 18, No. 4