The Evaluation of Estrogen Receptor β as a Potential Prognosis Factor in Melanoma

CRISTINA BEIU, MARIUS-NICOLAE POPESCU*, MIHAI CRISTIAN DUMITRASCU*, AIDA PETCA, CLAUDIA MEHEDINȚU, PATRICIA DELIA FARCASANU, RĂZVAN-COSMIN PETCA, CĂLIN CHIBELEAN, FLORICA ȘANDRU “Carol Davila” University of Medicine and Pharmacy, Eroii Sanitari Bvd., no. 8, 050474 Bucharest, Romania; Elias University Emergency Hospital, Bvd. Marasti no. 17, 011461 Bucharest, Romania University Emergency Hospital, Splaiul Independenței no.169, 050098 Bucharest, Romania Malaxa Clinical Hospital, 12 Vergului Str., 022441, Bucharest, Romania „Prof. Th. Burghele” Clinical Hospital, 20 Panduri Str., 050653, Bucharest, Romania „George Emil Palade” University of Medicine, Pharmacy, Science and Technology of Târgu Mureș, 38 Gheorghe Marinescu Str., 540139, Târgu Mureș, Romania

Sex disparities have also been noticed in a study in xiphophorus fish which expressed up-regulation of androgen levels after UVB exposure. The female vs. male melanoma incidence for UVB-exposed Xiphophorus is consistent with that seen in the human population, suggesting a sex-specific molecular genetic response [7]. Another study performed on Xiphophorus maculatus showed differences in the genetic perception of UVB in males and females, consistent with a twofold higher incidence of melanoma in males vs. females [11].
In line with this observation, various studies support a role for sex in contributing to the better survival rates among women (Table 1). RSrelative survival (estimate of DSS). a) Relative risk of women compared with men; presented as harzard ratio unless otherwise specified. b) Presented as relative excess risk. c) Value reported here is the inverse of the original risk estimate, because men were compared with women in the cited publication. d) For patients who underwent surgery.
Table adapted from review article [12] discussing cutaneous melanoma in women co-written by article authors

Hormones and melanoma
It has been discussed that sex hormones deserve a spot in the multifactorial gender-related disparities in melanoma. Furthermore, hormone-related therapeutic possibilities have been taken into account and their antimelanoma effect is yet a controversy. While melanoma is classically considered a non-hormone -related cancer, mounting evidence suggest a direct correlation between estrogen levels and melanoma outcome [13][14][15].
The biological effects of estrogens are mediated through two ER subtypes, ERα and ERβ, members of the nuclear steroid hormone receptor superfamily [16]. The balance between this two subtypes expression is essential in the estrogen signaling. These receptors bind to 17-β-estradiol and control certain genes expression through specific DNA sequences [17][18][19].
It has been showed that both benign and malignant melanocytic lesions are positive for ERβ, but not for ERα, which seems to be very rarely expressed in the skin [20][21]. In line with this observation, various studies support a role for ERβ in contributing to the better survival rates among women [22,23].
It is well known that ERα and ERβ have different biological functions, according to their tissue-specific action [24][25][26][27][28]. Increasing evidence show a promotion of cancer progression through perturbed estrogen signaling. The differential expression of ERα and ERβ in cancer cells supports the concept that the two ER subtypes have contrasting functions in the essential fundamentals of cancer biology [29].
ERα promotes carcinogenesis due to its pro-proliferation properties, while ERβ has a protective role against skin tumor growth. In such a way, that both natural and non-natural synthetic ERβ ligands may inhibit tumorigenesis either by activating ERβ or by suppressing the tumor activity of ERα through heterodimers formations which is highly increased by the presence of the ligands [24][25][26] -Figure 2.

Correlations between ERβ expression in the tumoral microenvironment and melanoma progression De Georgi et al. showed that ERβ expression in melanoma cells is reduced compared with perilesional healthy skin [30].
Furthermore, supporting the role for ERs in melanoma outcome, the loss of of ERβ protein levels was found to be directly proportional to Breslow thicknessits most important prognostic factor -and this reduction in ERβ resulted in more aggressive melanoma. ERβ expression levels were lower in metastatic melanomas than in non-metastatic lesions. Also, consistent with gender differences in melanoma prognosis, men showed lower levels of ERβ than woman in both tumoral and healthy tissues [31].
Kanda and Watanabe [32] reported that following incubation of the 17-beta-isomer of estradiol, metastatic melanoma cells growth was inhibited in vitro, by inhibiting the production of interleukin-8. This effect was neutralized by exogenously added IL-8 and was only observed in ER-positive human melanoma cells, indicating a receptor-dependent manner of inhibiting melanoma cell growth.
As a possible mechanism for the female survival benefit, Richardson et al. [33] and Roy et al. [34] noted that the main estrogenic hormone, 17 beta-estradiol, repressed human melanoma cells invasiveness, but the antitumoral effect was inconsistent after syngeneic B16 tumors transplantation in C57BL/6 mice.
Cho et al. [35] used a mouse melanoma skin cancer model to assess the protective role of ERβ against tumor growth. They showed that implanted B16 murine melanoma cells grew faster in mice lacking ERβ (suppression of ERβ signaling via ERβ knockout) in comparison to congenic C56BL/6 mice with unharmed ERβ.
In a more recent paper, ERβ expression has also been shown to be down-regulated in invasive melanomas, with sentinel lymph node metastasis, suggesting its potential efficacy as an immunohistochemical marker for metastatic potential and poor outcome in malignant melanomas [36].
Contradictory results come from Tellez et. al who recently performed retrospective analysis of 420 women under the age of 50 and reported the following: an increased risk of mortality, recurrence, and metastasis in pregnancy-associated melanoma and lower survival rates associated with higher incidence of sentinel lymph node metastasis in woman aged 40 to 49 years old. One of the author's several explanations for this results was the adverse effects of high serum estrogen levels [37]. In response to this emerging evidence, Gori. et al tried to find a surrogate etiopathogenetic explanation, stating that the loss of ERβ expression with age and pregnancy may explain a more poor outcome in melanoma [38].
It was also recently demonstrated that ERβ, and not ERα, is the predominant subtype expressed in a group of various melanoma cell lines harboring distinct genetic mutations (A375, BLM, WM115, and WM1552) [39]. Expression pattern of the ERβ isoforms was comparable in BLM (harboring the NRAS, but not the BRAF mutation) and WM115 (BRAF V600Dmutant) melanoma cells: decreased expressions of ERβ1 and ERβ5 were found to be at similar levels whereas ERβ2 exhibited an increased level of expression. Contrarily, both ERβ2 and ERβ5 were expressed at higher levels than ERβ1 in A375 (BRAF V600E-mutant) cells [39].
Taken together, these studies indicate that there is indeed a potential role of ERβ as a prognostic marker of melanoma and the loss of its expression may promote tumor growth.

Conclusions
Overall, the correlation between estrogen receptors and the prognosis of cutaneous melanoma is still intriguing and controversial. In line with the better outcome of women compared to men and with clinical data demonstrating a hormonallydependent melanoma course, we hypothesize that the female advantage is associated with biological characteristics of the host, independently of the other key prognostic factors. Large-scale studies will ultimately be required to elucidate the potential role of ERβ expression as a prognostic marker of melanoma and detecting ERβ expression could become a useful tool for the clinicians in monitoring melanoma patients. Further understanding of the estrogen-dependent regulation of melanoma cells through stimulation of ERβ receptors could even serve as a starting point in unraveling new ways to trigger anti-tumor hormonal responses in melanoma patients.