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Retinoic acid receptor α and retinoid
X receptor α: Do they have a role in
prognostication of prostate cancer?
Anju Bansal, Harsh Hora
Website:
www.oncotargets.com
DOI:
10.4103/2395-4469.182979
Abstract:
Background: Androgens acting through the androgen receptor (AR) are essential for prostate development
and normal prostate function. The evolving role of retinoids in cancer treatment and prevention is being
extensively studied in many malignancies including prostate cancer. Effects of retinoids are mediated by retinoic
acid receptors (RARs) and retinoid X receptors (RXRs). Materials and Methods: Sixty cases of prospective
prostate cancer over 3 years were evaluated to study the immunohistochemical expression of AR, RARα, and
retinoic X receptor α (RXRα). The expression findings were correlated with the clinicopathological parameters.
Results: Of the total 60 cases, 26 cases (43.3%) were of advanced stage with the presence of tumor beyond
the prostatic capsule. Histopathological examination revealed that 38 cases (63.3%) had Gleason score (5–7).
Clinically, 45 (75%) cases were found to be hormone sensitive while 15 (25%) cases were hormone refractory.
Immunohistochemically, 43 cases (71.6%) were positive for AR while RARα and RXRα expressions were positive
in 36 (60%) and 34 (56.6%) cases. Immunohistochemical expression of AR was found insignificant in relation
with Gleason score (P = 0.2) and hormone response (P = 0.6). The association between AR and tumor staging
was found significant with 82.4% positivity in localized cancer (P = 0.03). Association of RARα expression with
Gleason score, tumor staging and hormone response were found significant (P = 0.2, P = 0.1 and P = 0.2).
RXRα expression however had a significant correlation with tumor stage with 67.6% of localized cancer showing
positivity (P = 0.05). Its correlation with Gleason score and hormone response however was not significant (P = 0.3).
Conclusions: RXR expression decreases with the advancing stage of prostate cancer. These findings possibly
predict their implications on diagnostic and therapeutic strategies in prostate cancer.
Key words:
Androgen receptor, prostate cancer, retinoic acid receptor, retinoid X receptor
Introduction
P
Department of
Pathology, National
Institute of Pathology
(ICMR), Safdarjang
Hospital Campus,
New Delhi, India
Address for
correspondence:
Dr. Anju Bansal,
3126, Sector‑D,
Pocket‑3, Vasant Kunj,
New Delhi ‑ 110 070, India.
E‑mail: dranjubansal@
yahoo.com
Submission: 28‑12‑2015
Accepted: 10‑03‑2016
rostate cancer appears to be an increasingly
common but complex entity. It is the second
most common cancer in men worldwide.[1] In
India, Although its incidence has been less, but
in recent years, it has been progressively rising.[2]
It is complex because it shows wide geographical
variations ranging up to 25‑fold in spite of no
discernible discriminating factors. In addition,
there is a wide variation in the clinical course
ranging from an indolent tumor to a rapidly
metastasizing tumor with poor prognosis.
Prostate cancer is the fifth leading cause of
death from cancer in men accounting for 307,000
deaths in 2012, with less variation in mortality
worldwide.[1] Traditionally, the management
has constituted androgen deprivation with
or without surgery since the tumor is initially
androgen‑dependent. In the course of its progress,
the tumor becomes androgen‑ independent,
treatment refractory and thereafter has rapidly
downhill often fatal course. Efforts have been
made to identify the various markers and
receptors which may address the prognosis and
the reason why these tumors become refractory
© 2016 Oncobiology and Targets | Published by Wolters Kluwer - Medknow
to androgen modulation. Determination of
androgen receptors (ARs) and their correlation
with the conventional parameters of tumor
grading and tumor staging has been one such
effort. Newer markers and receptors are under
investigation overall the world. One such group
of receptors are the retinoid receptors. In this
study, we undertook to analyze the status of
retinoic acid receptor α (RARα) and retinoid X
receptor α (RXRα) in various grades and stages
of prostate cancer immunohistochemically. We
also looked for the AR status in a similar manner.
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How to cite this article: Bansal A, Hora H. Retinoic
acid receptor α and retinoid X receptor α: Do they
have a role in prognostication of prostate cancer?.
Oncobiol Targets 2016;3:5.
1
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Bansal and Hora: Retinoic acid receptors in prostate cancer
Materials and Methods
In this study, we examined the immunohistochemical
expression of AR, RARα, and RXRα in tissue samples of sixty
prostate carcinoma patients. The approval of the Institutional
Ethics Committee was obtained. Formalin‑fixed sections of
prostate carcinoma were deparaffinized followed by incubation
with 1% hydrogen peroxide in methanol for 30 min to block
endogenous peroxidase activity. For antigen retrieval, they
were microwaved for 15 min. Immunohistochemical staining
was performed using primary antibodies against AR (clone
F39.4.1, 1/100; BioGenex); RARα ([C‑20]: sc‑551, 1/50; Santa
Cruz Biotech); and RXRα ([D‑20]: sc‑553, 1/50; Santa Cruz
Biotech). Overnight incubation of the specimens was done
with the primary antibodies, rinsed in PBS (Phosphate Buffered
Saline). Biotin–avidin system was used for detecting antibody
binding. Nuclei were then counterstained with hematoxylin.
Negative and positive control sections were used for checking
the specificity of immunohistochemical techniques. Nuclear
reactivity was noted for AR antibody while cytoplasmic and/
or nuclear reactivity was noted for RARα as well as RXRα. Cases
exhibiting more than 10% positivity for the antibody were
taken as positive cases. Staining was assessed by two observers
analyzing ten high-power fields. Statistical analysis was done
using Statistical Package for Social Sciences (SPSS, IBM).
Chi‑square test and test for mean difference by independent
sample t‑test were applied for testing the significance of the
findings. A P ≤ 0.05 was considered statistically significant.
a
b
Figure 1: Carcinoma prostate showing nuclear positivity for androgen receptor
antibody (a: ×100, b: ×200)
a
Results
The age of the patients ranged from 48 to 97 years, the median
being 72 years. However, the majority of the cases (87%)
were more than 60 years old. Tumor staging was done
based on the American Joint Committee on Cancer manual.
Thirty‑four (56.6%) cases were localized to the prostate,
and 26 cases were advanced tumors extending beyond the
prostatic capsule. Histopathological grading was done by
Gleason scoring. Of the 60 cases, 4 (6.6%) had Gleason score
2–4, 38 (63.3%) had 5–7, and 18 (30%) had 8–10. Further,
45 cases (75%) were hormone sensitive, and 15 cases (25%)
were hormone refractory. As regards immunohistochemistry,
AR was localized in nucleus [Figure 1a and b] while RARα
[Figure 2a and b] and RXRα [Figure 3a and b] were localized
in cytoplasm and/or nucleus. Immunohistochemical analysis
showed that AR was positive in 71.6% cases while RARα and
RXRα were positive in 60% and 56.6% cases, respectively.
An attempt was made to correlate AR and RARα/RXRα
with the conventional prognostic indices, Gleason score, and
hormone responsiveness. While no significant correlation
could be found between AR and Gleason score (P = 0.2) or
hormone response (P = 0.6) it significantly correlated with
tumor stage with 82.4% patients of localized tumor staining
positively for AR (P = 0.03). A similar analysis was done
in respect of RARα expression and Gleason score, tumor
staging, and hormone response; none of which were found to
be significant (P = 0.2, P = 0.1, and P = 0.2). RXRα expression
however had significant correlation with tumor stage with
67.6% of localized cancer showing positivity (P = 0.05). Its
correlation with Gleason score and hormone response however
was not significant (P = 0.3). The relations of AR, RARα, and
RXRα with Gleason score [Table 1], tumor stage [Table 2] and
2
b
Figure 2: Carcinoma prostate showing cytoplasmic and nuclear positivity for
retinoic acid receptor α antibody (a: ×100, b: ×200)
a
b
Figure 3: Carcinoma prostate showing cytoplasmic and nuclear positivity for
retinoic X receptor α antibody (a: ×100, b: ×200)
hormone response [Table 3] are listed in the accompanying
tables.
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Bansal and Hora: Retinoic acid receptors in prostate cancer
Table 1: Immunoreactivity for androgen receptor,
retinoic acid receptors α, and retinoid X receptor α in
carcinoma prostate in relation to histological grade
Histological grade
Carcinoma
Prostatne Cases
Gleason score 2-4
Gleason score 5-7
Gleason score 8-10
P
Carcinoma
prostate
cases,
n (%)
n=60
AR‑
positive
cases,
n (%)
43 (71.6)
RARα‑
positive
cases,
n (%)
36 (60)
RXRα‑
positive
cases,
n (%)
34 (56.6)
4 (6.6)
38 (63.3)
18 (30)
4 (100)
25 (65.8)
14 (77.8)
0.2
4 (100)
22 (57.9)
10 (55.6)
0.2
3 (75)
19 (50)
12 (66.7)
0.3
RARα:Retinoic acid receptors α, RXRα:Retinoid X receptor α, AR:Androgen
receptor
Table 2: Immunoreactivity for androgen receptor,
retinoic acid receptors α, and retinoid X receptor α in
carcinoma prostate in relation to stage
Stage
Carcinoma
Prostatne Cases
Localized
Advanced
P
Carcinoma
AR‑
RARα‑
prostate
positive positive
cases,
cases,
cases,
n (%)
n (%)
n (%)
n=60
43 (71.6) 36 (60)
34 (56.6)
26 (43.3)
28 (82.4) 23 (67.6)
15 (57.7) 13 (50)
0.03
0.1
RXRα‑
positive
cases,
n (%)
34 (56.6)
23 (67.6)
11 (42.3)
0.05
RARα:Retinoic acid receptors α, RXRα:Retinoid X receptor α, AR:Androgen
receptor
Table 3: Immunoreactivity for androgen receptor,
retinoic acid receptors α, and retinoid X receptor α in
carcinoma prostate in relation to hormone response
Hormone
response
Carcinoma
Prostatne Cases
Hormone sensitive
Hormone refractory
P
Carcinoma
prostate
cases,
n (%)
(n=60)
AR‑
positive
cases,
n (%)
43 (71.6)
RARα‑
positive
cases,
n (%)
36 (60)
RXRα‑
positive
cases,
n (%)
34 (56.6)
45 (75)
15 (25)
33 (73.3)
10 (66.7)
0.6
29 (64.4)
7 (46.7)
0.2
27 (60)
7 (46.7)
0.3
RARα:Retinoic acid receptors α, RXRα:Retinoid X receptor α, AR:Androgen
receptor
(RAREs) and hence regulate the gene expression.[7] There are
several isoforms of both RAR and RXR. The usual functional
unit is a heterodimer consisting of one RAR and one RXR.
It is believed that aberrations in this heterodimer lead to
carcinogenesis of different tissues including pancreas and
prostate.[8,9] A subtle hint regarding the role of retinoids in the
development of prostate is suggested by the fact that Vitamin
A deficiency in mothers leads to squamous metaplasia of
prostate in the offsprings which are reversible on Vitamin
A administration. Early experimental evidence in mice and
thereafter in human cell lines has revealed that RXR is more
important an incriminating marker than RAR.[10] It is believed
that in early stages, retinoid receptors help to induce apoptosis
but in later stages as the cancers become androgen‑independent,
the retinoid receptors decrease.[11] Several authors have shown
that expression of RXR is very common in the normal prostate
cells, diminishes in the preneoplastic stage and is highly
diminished in the advanced grade malignancies.[7,12]
The data on retinoid receptors in prostate are virtually absent
from Asian countries. A PubMed search on the subject returned
no matches. Given, the geographical heterogeneity of prostate
cancer, this area apparently lies unexplored in the Indian
subcontinent. Similar to the previous Western studies, our
study reveals that the RAR receptors could not be correlated
to any of the other factors namely, Gleason score, stage, or
hormone responsiveness. RXR receptors also did not correlate
with the grade of tumor as suggested by Gleason score and
hormone responsiveness. However, there was a significant
correlation between RXR and the stage of the tumor. About
67.6% of the localized tumors showed RXR expression while
only 42.3% of advanced tumors showed its expression. One
of the shortcomings of our study is that we did not study the
retinoid receptors in normal and preneoplastic prostate, but it
may be presumed that these receptors would be mostly present
in these groups. Our study appears to reiterate the fact that as
tumor becomes more advanced in stage, a number of RARs
decrease. Thus, the degree of retinoid receptor positivity may
indicate an early stage of the tumor. In contrast to the Western
studies wherein retinoid receptor status correlated with the
grade of the tumor, the lack of correlation between the grade
of tumor and RXR expression in our study may be possibly a
finding attributable to regional heterogeneity in our part of
the world.
Discussion
Conclusions
Androgens are the key molecules which play a significant role
in prostate development and morphogenesis.[3,4] Androgens
however are not the only molecule to regulate prostatic
development. Studies have shown that molecules such as
retinoic acid also contribute toward the control of proliferation
and differentiation of prostate epithelium.[5,6]
It appears that among RARs, RXR do have an association
with carcinoma prostate. This association is with the stage of
malignancy in our population unlike some Western studies
wherein it is associated with grade of tumor. This association
is independent of Gleason score and hormone responsiveness.
These findings have possible therapeutic potential of retinoic
acid in preventing the conversion of hormone responsive
tumors to hormone refractory stage.
Taking a clue from these physiological facts, for several years
now, efforts have been on to find markers that may possibly
identify the prognosis and course of prostate carcinoma. Of
the several markers investigated, the retinoid receptors are an
important class. The retinoid receptors are of two types namely,
RAR and RXR, both of which are encoded by three genes α, β,
and γ. These receptors bind to the retinoic acid response elements
Oncobiology and Targets - Vol 3 | 2016
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
3
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Bansal and Hora: Retinoic acid receptors in prostate cancer
References
1.
2.
3.
4.
5.
6.
4
Torre LA, Bray F, Siegel RL, Ferlay J, Lortet‑Tieulent J, Jemal A.
Global cancer statistics, 2012. CA Cancer J Clin 2015;65:87‑108.
Lalitha K, Suman G, Pruthvish S, Mathew A, Murthy NS.
Estimation of time trends of incidence of prostate cancer – An
Indian scenario. Asian Pac J Cancer Prev 2012;13:6245‑50.
Kellokumpu‑Lehtinen P, Santti RS, Pelliniemi LJ. Development
of human fetal prostate in culture. Urol Res 1981;9:89‑98.
Cunha GR, Lung B. The possible influence of temporal factors
in androgenic responsiveness of urogenital tissue recombinants
from wild‑type and androgen‑insensitive (Tfm) mice. J Exp Zool
1978;205:181‑93.
Seo R, McGuire M, Chung M, Bushman W. Inhibition of
prostate ductal morphogenesis by retinoic acid. J Urol 1997;158
(3 Pt 1):931‑5.
Peehl DM, Wong ST, Stamey TA. Vitamin A regulates proliferation
and differentiation of human prostatic epithelial cells. Prostate
1993;23:69‑78.
Alfaro JM, Fraile B, Lobo MV, Royuela M, Paniagua R, Arenas MI.
Immunohistochemical detection of the retinoid X receptors alpha,
beta, and gamma in human prostate. J Androl 2003;24:113‑9.
8. Albrechtsson E, Ohlsson B, Axelson J. The expression of retinoic
acid receptors and the effects in vitro by retinoids in human
pancreatic cancer cell lines. Pancreas 2002;25:49‑56.
9. Zhang XK. Vitamin A and apoptosis in prostate cancer. Endocr
Relat Cancer 2002;9:87‑102.
10. Zhong C, Yang S, Huang J, Cohen MB, Roy‑Burman P. Aberration
in the expression of the retinoid receptor, RXRalpha, in prostate
cancer. Cancer Biol Ther 2003;2:179‑84.
11. DiPaola RS, Aisner J. Overcoming bcl‑2‑ and p53‑mediated
resistance in prostate cancer. Semin Oncol 1999;26 1 Suppl 2:112‑6.
12. Gyftopoulos K, Perimenis P, Sotiropoulou‑Bonikou G,
Sakellaropoulos G, Varakis I, Barbalias GA. Immunohistochemical
detection of retinoic acid receptor‑alpha in prostate carcinoma:
Correlation with proliferative activity and tumor grade. Int Urol
Nephrol 2000;32:263‑9.
7.
Oncobiology and Targets - Vol 3 | 2016