Abstract
purpose. Immunohistochemistry was used to investigate whether uveal malignant
melanoma expresses ezrin, a protein involved in cell migration and cell
recognition by acting as a linker between the plasma membrane and actin
cytoskeleton. Also investigated was whether ezrin immunoreactivity
correlates with survival prognosis.
methods. A monoclonal antibody, 3C12, that reacts with the carboxyl-terminal
part of ezrin was used in retrospective analysis of a population-based
cohort of 167 consecutive choroidal and ciliary body melanomas in eyes
enucleated from 1972 through 1981, with a median follow-up of 22 years.
results. Ezrin immunoreactivity in tumor cells was graded negative in 47 (36%)
melanomas, positive in 74 (57%), and strongly positive in 9 (7%). The
immunoreactivity tended to be homogenous throughout the tumor, with
focal concentrations along the cell surface. Positive reaction was
significantly associated with high microvascular density
(P < 0.001) and presence of macrophages
(P < 0.001), but not with tumor size, cell type,
or microvascular loops and networks. The 10-year melanoma-specific
survival was significantly associated with ezrin immunoreactivity
(P = 0.018). After adjustment by Cox regression for
tumor size, cell type, microvascular loops and networks, and
microvascular density, a clinically meaningful 0.15 difference in
10-year melanoma-specific survival persisted.
conclusions. The presence of ezrin immunoreactivity in uveal malignant melanoma is
associated with higher mortality and with two independent high-risk
characteristics: microvascular density and number of infiltrating
macrophages. Further experimental studies on the interrelationship of
these three factors may shed light on the progression of uveal melanoma
and perhaps that of other cancers.
Ezrin, radixin, and moesin form the ERM protein family,
which mediates interaction between actin microfilaments and cell
membranes.
1 2 3 Ezrin is a phylogenetically conserved
80-kDa phosphoprotein isolated from microvilli and previously also
called cytovillin.
4 It tethers actin filaments to the
plasma membrane on one hand and anchors membrane proteins at specific
sites on the other, thus enabling cells to maintain specialized
functions in defined surface environments.
5 6 Blocking the
function of ezrin and other ERM proteins prevents formation of
microvilli and other membrane protrusions.
7 8 9 Ezrin is
regulated by growth-factor–induced phosphorylation.
10 11 12 It is widely expressed by epithelial cells, but also by several
nonepithelial cell types.
1
Because ezrin is a protein that participates in cell migration and cell
recognition by the immune system, it may have an impact on tumor
progression and development of metastasis.
9 13 14 15 In cell
culture, transformation of fibroblasts is associated with increased
expression, hyperphosphorylation, and redistribution of
ezrin.
8 In surgical specimens epithelial tumors, renal
cell adenocarcinoma, and stromal cells of capillary hemangioblastoma
express ezrin detectable in immunohistochemistry.
16 17 The
expression of ezrin in cell lines of endometrial, pancreatic, and
colorectal carcinoma has suggested that it has a role as a modulator of
tumor cell morphology, migration, and invasion.
9 14 15 A
closely related protein, merlin, is a tumor suppressor protein
inactivated in schwannomas and meningiomas.
18
When charting the presence of ezrin in the human retinal pigment
epithelium
19 we observed that a subset of uveal malignant
melanomas were immunoreactive with monoclonal antibody (mAb) 3C12 to
ezrin. Given the potential pathogenic role of ezrin in malignant cells,
we undertook a study to investigate in a larger, population-based data
set whether uveal melanomas express ezrin, whether ezrin
immunoreactivity is correlated with prognosis, and which tumor
characteristics are associated with the presence of ezrin
immunoreactivity. To our knowledge, the present report is the first
clinicopathologic study that links ezrin to tumor-specific survival.