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Int. J. Cancer (Pred. Oncol.): 89, 39 – 43 (2000)
© 2000 Wiley-Liss, Inc.
Publication of the International Union Against Cancer
CORRELATION OF CYCLIN D1 MRNA LEVELS WITH
CLINICO-PATHOLOGICAL PARAMETERS AND CLINICAL OUTCOME IN
HUMAN BREAST CARCINOMAS
Toshiaki UTSUMI1*, Noriko YOSHIMURA2, Morito MARUTA1, Shinji TAKEUCHI3, Jiro ANDO4, Yoshikazu MIZOGUCHI5
and Nobuhiro HARADA2
1
Department of Surgery, Fujita Health University School of Medicine, Toyoake, Japan
2
Department of Biochemistry, Fujita Health University School of Medicine, Toyoake, Japan
3
Marumo Hospital, Nagoya, Japan
4
Department of Surgery, Tochigi Cancer Center, Utsunomiya, Japan
5
Department of Pathology, Fujita Health University School of Medicine, Toyoake, Japan
In order to evaluate the prognostic significance of cyclin D1
mRNA expression in mammary neoplasia, its levels were
measured in 97 breast cancers by reverse transcription-polymerase chain reaction (PCR) using fluorescent primer and
standard RNA along with estrogen receptor (ER). The median value of cyclin D1 mRNA was 1.60 amol/␮g RNA (range,
0.01 to 5.63 amol/␮g RNA). ER mRNA was detectable in 70
breast cancer samples (72.2%) and cyclin D1 mRNA levels
were significantly higher in ER mRNA-positive than in ER
mRNA-negative tumors (p ⴝ 0.009). Furthermore, cyclin D1
mRNA levels were significantly (p ⴝ 0.001) lower in patients
who experienced a recurrence during the follow-up period
(mean of 40.8 months, median of 39 months) compared with
those with no evidence of recurrent disease (mean of 49.2
months, median of 48 months), and in those who died from
disease (mean follow-up period of 30.5 months, median of 26
months) than in the survivors (mean of 50.5 months and
median of 48 months) (p ⴝ 0.005). Setting the median value
(ⴝ1.60 amol/␮g RNA) as the cutoff point, expression was
significantly associated with relapse-free survival (p ⴝ 0.002).
Similarly, a significant correlation was observed between the
cyclin D1 mRNA level and overall survival (p ⴝ 0.015). The
expression was found to be an independent factor for predicting relapse-free survival using multivariate analysis. Int.
J. Cancer (Pred. Oncol.) 89:39 – 43, 2000.
© 2000 Wiley-Liss, Inc.
D-type cyclins are strongly implicated in controlling progression through the G1 phase of the cell cycle. Three closely related
human D-type cyclins activate cyclin-dependent kinases (Cdks),
Cdk4 and Cdk6, although they have specialized functions in distinct cell types (reviewed by Sherr, 1993). As a G1 cyclin, cyclin
D1 was identified originally as a putative proto-oncogene, BCL1/
PRAD1, located on chromosome 11q13, as a suppressor of yeast
G1 cyclin mutations and as a delayed early response gene induced
by colony-stimulating factor 1 (Sherr, 1993). Remarkable overexpression of cyclin D1 has been observed in human neoplasms
(reviewed by Donnellan and Chetty, 1998). It is likely to promote
cell proliferation and differentiation by shortening the G1-S transition (reviewed by Sherr, 1994). A further hint that cyclin D1
could be associated with tumorigenesis came from the fact that it
is inducible by activated myc oncogene (Daksis et al., 1994).
Cyclin D1 may also be a mediator of apoptotic neuronal cell death
(Kranenburg et al., 1996), and Pagano et al. (1994) have shown
that a transient overexpression in fibroblasts arrests the cells in the
G1-phase of the cell cycle. In senescent fibroblasts, an increased
level of cyclin D1 has been found (Dulic et al., 1993). These
reports indicate 2 opposing impacts of cyclin D1 overexpression in
cell cycle control.
Breast cancer is a worldwide problem which urgently requires
solutions; in many countries it is still the most common cause of
malignancy associated death. Early stage detection and treatment
has become possible, but this has meant difficulty in obtaining
adequate tumor tissues for biological studies of estrogen receptor
(ER) status and also measurement of other prognostic parameters.
However, the development of molecular biology techniques has
allowed various biochemical factors to be assayed in small tissue
specimens, and we have reported the biological significance of
enzymes concerned with estrogen synthesis (Utsumi et al., 1996,
1999). In the present study, to investigate the role of cyclin D1 in
breast cancers, we assessed the mRNA levels of cyclin D1 and ER
using reverse transcription-polymerase chain reaction (RT-PCR)
analysis in 97 cases. Studies in mice and humans have linked
cyclin D1 with steroid-induced proliferation of mammary epithelial cells (Donnellan and Chetty, 1998). Our present results indicate that cyclin D1 expression is associated with ER mRNA levels,
prognostic factors, and patient outcome.
MATERIAL AND METHODS
Patients and samples
Material for this study was obtained from 97 patients with
primary breast carcinomas who underwent curative surgery at
Fujita Health University Hospital, Marumo Hospital, and Tochigi
Cancer Center between 1990 and 1994. The average age of the
patients was 52.2 ⫾ 9.5 years (mean ⫾ standard deviation), with a
range of 33 to 77 years. Fifty patients received adjuvant chemotherapy, and 65 were given adjuvant endocrine therapy. Disease
recurrence was documented on the basis of physical examination,
radiological and laboratory tests and/or other relevant diagnostic
procedures. The median follow-up period for all patients was 46
months, with a range of 7 to 95 months.
The tumor types of the 97 patients were classified by pathologists
according to the World Health Organization scheme for typing breast
tumors. Histologically, there was 1 case each of ductal carcinoma in
situ, mucinous carcinoma, and invasive lobular carcinoma and 94 of
invasive ductal carcinomas. Fifty-two cases were node negative and
45 were node positive. Each tumor, exclusive of 1 ductal carcinoma
in situ and 1 invasive lobular carcinoma, was graded in parallel
according to the criteria of Bloom and Richardson (1957). Tumor size
was measured at surgery by the operating physicians. Immediately
following surgical removal, the specimens were frozen in liquid
nitrogen and then stored at ⫺80°C until use. ERs were assayed by
means of the dextran-coated charcoal method with a cutoff value of 5
fmol/mg protein.
This research project was approved by the Medical Ethics
Committee of Fujita Health University School of Medicine.
Preparation of total RNA
Frozen tissues were homogenized in 5 M guanidine thiocyanate
containing 5 mM sodium citrate and 0.5% sodium sarcosyl, and
total RNA fractions were prepared from the homogenates, as
described previously (Utsumi et al., 1996, 1999). The RNA con*Correspondence to: Department of Surgery, Fujita Health University
School of Medicine, Toyoake, Aichi 470-1192, Japan. Fax: ⫹81-562-938311. E-mail: [email protected]
Received 7 June 1999; Revised 23 July 1999
40
UTSUMI ET AL.
centration was determined from the spectrophotometric absorption
at 260 nm.
Quantitation of cyclin D1 mRNA
Quantitative analysis of cyclin D1 mRNA in the RNA fractions
was carried out by RT-PCR using a fluorescent primer as described
previously (Utsumi et al., 1996, 1999). In brief, oligonucleotides
of antisense primer, H-D1-1R (5⬘-GTCACACTTGATCACTCTGG-3⬘) for reverse transcription, and antisense (5⬘-CCAGGTTCCACTTGAGCTTG-3⬘) and sense (5⬘-CCTACTTCAAATGTGTGCAG-3⬘) primers, H-D1-2R and H-D1-3F for PCR, respectively, were synthesized. The sense primer H-D1-3F for PCR was
labeled with a fluorescent dye, FAM (Perkin-Elmer, Norwalk,
CT), after connection with Aminolink 2 (Perkin-Elmer). The coding sequence between the 2 PCR primer sites is located 5⬘ upstream of the reverse transcription primer site in the cyclin D1
transcript, and is interrupted by an intron in the gene. Standard
cyclin D1 RNA was synthesized in vitro with T7 RNA polymerase
using cyclin D1 cDNA as a template, purified on an anion exchange column of Qiagen (Chatsworth, CA), and then quantitated
from the absorbance at 260 nm. Total RNA (1–2 ␮g) and standard
cyclin D1 RNA (0.5 amol) were subjected to reverse transcription
with 5 units of RAV-2 reverse transcriptase (Takara Shuzo, Kyoto,
Japan) and the specific antisense primer H-D1-1R at 42°C for 40
min. The resulting cDNAs were amplified by PCR using the
fluorescent dye-labeled primer H-D1-3F and H-D1-2R. The PCR
conditions were: denaturation at 94°C for 20 sec, annealing at
55°C for 30 sec, and extension at 72°C for 30 sec for 19 cycles.
Fluorescent PCR products were analyzed on 2% agarose gels with
a Gene Scanner 362 Fluorescent Fragment Analyzer (PerkinElmer). The amount of cyclin D1 mRNA in each tissue RNA was
calculated by comparing the peak area of the fluorescent products
with that of standard cyclin D1 RNA.
Similarly, standard ER RNA was synthesized in vitro using ER
cDNA as a template, and quantitative analysis of ER mRNA was
also carried out by RT-PCR, in which the antisense primer (5’GCCTTTGTTACTCATGTGCC-3⬘) was employed for reverse
transcription, and antisense (5⬘-GTGTCTGTGATCTTGTCCAG3⬘) and fluorescent dye-labeled sense (5⬘-CTGATGATTGGTCTCGTCTG-3’) primers for PCR.
RT-PCR analyses were performed under the condition that the
fluorescent peak areas of PCR products corresponding to cyclin D1
and ER mRNAs were proportional to the amounts of total RNAs
added as to templates. This proportionality between their amounts
and their fluolescent peak areas was observed over a wide range of
0.002–10 amol and 0.002–10 amol for cyclin D1 and ER mRNAs,
respectively, in these assays.
Statistics
Statistical analyses were carried out with SAS-REL.6.12. software. The Spearman’s correlation coefficient was used to investigate correlations among different clinico-pathological variables.
Mean levels of cyclin D1 mRNA were compared using the MannWhitney U test. Relapse-free and overall survival curves were
generated using the method of Kaplan and Meier. Survival comparisons were made with the log-rank test, the Wilcoxon test, the
proportional hazards regression model, and proportional hazards
(Cox) multiple regression. The event considered in our analysis of
relapse-free survival was first recurrence of disease. Overall survival refers to survival with or without recurrence of disease.
Relapse-free survival and overall survival were calculated from the
date of first surgery to the date of clinical or pathological relapse
or death. The cutoff for significance was taken as p ⫽ 0.05.
RESULTS
Cyclin D1 mRNA in breast cancer tissues
Cyclin D1 mRNA levels in the breast tissues from 97 patients
with breast cancer were determined by quantitative RT-PCR analysis. Figure 1 shows the distribution of the cyclin D1 mRNA levels
FIGURE 1 – Distribution of cyclin D1 mRNA levels in the 97
primary breast cancer tumors. The class interval is 1 amol/␮g RNA.
The mean of 2.13 amol/␮g RNA is indicated by a solid arrow, and the
median (1.60 amol/␮g RNA) is indicated by an open arrow.
in the 97 breast tissues. The distribution was not normal, and there
was a median value of 1.60 amol/␮g RNA (range, 0.01–5.63
amol/␮g RNA). The mean value was 2.13 ⫾ 1.64 amol/␮g RNA
(mean ⫾ standard deviation).
ER mRNA expression and ER protein status
In our series, 57 cases were ER protein positive, 37 were ER
negative, and 3 were unknown. The ER mRNA levels in the breast
tissues from 97 patients with breast cancer were also determined
by RT-PCR analysis. The ER calculated from the peak area of the
fluorescent PCR product by comparison with that of a standard ER
RNA (0.5 amol). The distribution of ER mRNA was not normal
(data not presented), and ER mRNA were detectable in 70 samples
(72.2%) and 27 (27.8%) were negative. A positive correlation was
observed between the ER mRNA expression and the ER protein
status assessed by the dextran-coated charcoal method (p ⫽
0.0001, r ⫽ 0.670, n ⫽ 94).
Correlation of cyclin D1 mRNA expression
with clinico-pathological features
Table I shows the clinical profiles of the 97 patients, comparing
cases at or above the median cyclin D1 mRNA level with those
below the median. Cyclin D1 mRNA expression was not found to
be significantly correlated with any clinical parameters except ER
mRNA expression and endocrine therapy history. There was no
significant association between cyclin D1 mRNA and age
(p ⫽ 0.240, r ⫽ ⫺0.121, n ⫽ 97), menopausal status (p ⫽ 0.086,
r ⫽ 0.175, n ⫽ 97), tumor size (p ⫽ 0.485, r ⫽ 0.072, n ⫽ 97),
nodal status (p ⫽ 0.361, r ⫽ 0.094, n ⫽ 97), chemotherapy history
(p ⫽ 0.131, r ⫽ 0.154, n ⫽ 97) or histological grade (p ⫽ 0.080,
r ⫽ 0.181, n ⫽ 95). There was a significant but only weak association between cyclin D1 mRNA and ER mRNA status (p ⫽ 0.004,
r ⫽ 0.293, n ⫽ 97) and endocrine therapy history (p ⬍ 0.001,
r ⫽ 0.344, n ⫽ 97). The relation between cyclin D1 and endocrine
therapy history may not be relevant, since endocrine therapy is
usually given to patients on the basis of their ER status which was
associated with the cyclin D1 status.
The levels of cyclin D1 mRNA in ER mRNA-positive tumors were
significantly (p ⫽ 0.009) higher than those in ER mRNA-negative
tumors (Table II). There were also significantly (p ⬍ 0.001) higher
cyclin D1 mRNA levels in ER protein positive breast cancers compared with ER protein negative tumors (data not shown).
A total of 20 patients had recurrent disease, and 15 had died by
the time of the analyses. Cyclin D1 mRNA on the basis of the
median and the mean was then examined in association with the
disease recurrence and death during the follow-up period (Table
III). There were significantly (p ⫽ 0.001) lower cyclin D1 mRNA
levels in patients who experienced a recurrence during the fol-
CYCLIN D1 EXPRESSION IN HUMAN BREAST CANCER
41
TABLE I – CLINICAL PROFILES OF THE 97 BREAST CANCER PATIENTS
Cyclin D1 mRNA
Number of patients
Mean age (years)
ER mRNA
Negative
Positive
Tumor size
ⱕ2.0 cm
ⱖ2.1 cm
Nodal status
Negative
Positive
Histological grade
1
2
3
Adjuvant chemotherapy
No
Yes
Adjuvant endocrine therapy
No
Yes
Number of recurrences
Number of deaths during
follow-up
Number of survivors during
follow-up
Mean follow-up time for deceased
patients (months)
Mean follow-up time for survivors
(months)
ⱕ1.6 amol/␮g
RNA
⬎1.6 amol/␮g
RNA
49
51.0 ⫾ 9.0
48
53.4 ⫾ 9.9
20 (40.8%)
29 (59.2%)
7 (14.6%)
41 (85.4%)
17 (33.3%)
32 (66.7%)
20 (41.8%)
28 (58.2%)
24 (49.0%)
25 (51.0%)
28 (56.4%)
20 (43.6%)
5 (10.4%)
28 (58.3%)
15 (31.3%)
7 (14.9%)
34 (72.3%)
6 (12.8%)
20 (40.8%)
29 (59.2%)
27 (56.3%)
21 (43.7%)
24 (49.0%)
25 (51.0%)
17
13
8 (16.7%)
40 (83.3%)
3
2
36
46
32.0 ⫾ 20.6
21.0
58.2 ⫾ 17.3
44.5 ⫾ 11.0
TABLE II – CYCLIN D1 MRNA VALUES IN BREAST CANCER PATIENTS
WITH RESPECT TO ER MRNA EXPRESSION
ER
mRNA
Number
Negative
Positive
27
70
Cyclin D1 mRNA (amol/␮g RNA)
Mean ⫾ SD
Median
1.42 ⫾ 1.33
2.41 ⫾ 1.68
0.97
1.91
p value
0.009
TABLE III – CYCLIN D1 MRNA VALUES IN BREAST CANCER PATIENTS
WITH RESPECT TO CLINICAL OUTCOME WITHIN THE FOLLOW-UP PERIOD
Number
Recurrence
No
Yes
Deceased
No
Yes
Cyclin D1 mRNA (amol/␮g RNA)
p value
Mean ⫾ SD
Median
77
20
2.40 ⫾ 1.64
1.12 ⫾ 1.24
1.88
0.75
0.001
82
15
2.32 ⫾ 1.64
1.12 ⫾ 1.33
1.88
0.57
0.005
low-up period (mean of 40.8 months and median of 39 months)
compared with those with no evidence of disease (mean of 49.2
months, median of 48 months). We further found that the subset,
who died after recurrence during the follow-up period (mean of
30.5 months, median of 26 months), had significantly (p ⫽ 0.005)
lower cyclin D1 mRNA compared with the survivors (mean of
50.5 months, median of 48 months).
Prognostic analysis
For statistical evaluation, the patients were divided into 2 groups
on the basis of the level of cyclin D1 mRNA expression. Most
prognostic factors are usually considered as dichotomized, discontinuous variables. Therefore, to evaluate the cyclin D1 mRNA
level as a prognostic factor of relapse-free survival in breast
cancer, the median value was used as a cutoff to define “low” and
“high” expression. Figure 2 shows Kaplan-Meier survival curves
FIGURE 2 – Relapse-free and overall survival of 97 patients with
breast cancer according to their cyclin D1 mRNA levels. The cutoff
value for low cyclin D1 mRNA was the median. There were 48
patients in the high group, and 49 patients in the low group. Both
curves were generated using the method of Kaplan-Meier.
for relapse-free survival dichotomized by cyclin D1 mRNA levels.
Patients with high levels of cyclin D1 mRNA showed significantly
better relapse-free survival compared with those with low levels of
the mRNA. The intergroup relationships were significantly different by both the log-rank (p ⫽ 0.002) and the Wilcoxon tests
(p ⫽ 0.003). When a more optimal cutoff value (⫽1.30 amol/␮g
RNA) derived by the minimum p-value approach (Altman et al.,
1994) was used, the difference between the 2 groups was more
distinct (p ⬍ 0.001, log-rank test). Overall survival was also positively correlated with the tissue level of cyclin D1 mRNA and
reached significance when the median level of cyclin D1 mRNA
was used as the cutoff value (p ⫽ 0.015, log-rank test and
p ⫽ 0.022, Wilcoxon test). When cyclin D1 mRNA groups were
divided into tertiles [bottom tertile, ⱕ0.95 amol/␮g RNA
(n ⫽ 32); middle tertile, ⱕ2.90 amol/␮g RNA (n ⫽ 32); upper
tertile, ⬎2.90 amol/␮g RNA (n ⫽ 33)], intergroup differences in
relapse-free survival was also distinct (p ⫽ 0.008, log-rank test
and p ⫽ 0.013, Wilcoxon test; Fig. 3). Overall survival was also
positively correlated with the tissue levels of cyclin D1 mRNA and
reached significance when the groups were divided into tertiles
(p ⫽ 0.040, log-rank test and p ⫽ 0.060, Wilcoxon test).
On univariate analysis, several variables, including the cyclin
D1 mRNA level, showed significant correlation with prognosis.
Nodal status, cyclin D1 mRNA, and histological grade were found
to be correlated with relapse-free survival (p ⫽ 0.003, p ⫽ 0.006
and p ⫽ 0.033, respectively; Table IV). There was also a significant correlation between overall survival and nodal status, cyclin
42
UTSUMI ET AL.
D1 mRNA, and histological grade (p ⫽ 0.005, p ⫽ 0.029 and
p ⫽ 0.019, respectively) in this population of patients.
All variables were taken into account through a stepwise analysis. Nodal status emerged as a strong independent predictor of
relapse-free survival [p ⫽ 0.008, relative risk ⫽ 4.410, 95% confidence interval (CI) ⫽ 1.471–13.221], and cyclin D1 mRNA level
came next (p ⫽ 0.012, relative risk ⫽ 4.919, 95% CI ⫽ 1.411–
17.142), whereas histological grade was not significant (Table IV).
On multivariate analysis of overall survival, the model gave nodal
status (p ⫽ 0.002, relative risk ⫽ 13.354, 95% CI ⫽ 2.696 –
66.136) and ER mRNA status (p ⫽ 0.025, relative risk ⫽ 3.823,
95% CI ⫽ 1.187–12.317) as independent prognostic factors,
whereas histological grade and cyclin D1 mRNA status were not
significant.
DISCUSSION
In many types of human tumor cells, overexpression of cyclin
D1 or deregulation of cyclin D1 contributes to oncogenic transformation in vitro and in vivo (Sherr, 1993; Donnellan and Chetty,
1998). To examine to what extent expression of cyclin D1 might
be relevant to clinical outcome, in cases of breast cancers the
present quantitative RT-PCR analysis was performed. Although
expression varied widely among individuals, statistical analysis
provided evidence that the level of cyclin D1 transcripts in human
breast cancers may be a useful prognostic indicator. In the present
study, using molecular biology techniques, we showed a good
correlation between cyclin D1 mRNA expression and relapse-free
or overall survival. However, we were not able to show any
significant correlation with age, histological grade, tumor size, or
node metastasis.
There is at present much controversy surrounding the potential
role of cyclin D1 in human neoplasia. In laryngeal and head and
neck carcinomas, its overexpression has been shown to be associated with advanced local invasion and presence of lymph node
metastasis (Donnellan and Chetty, 1998). In breast cancer, previous immunohistochemical studies indicated a positive correlation
between cyclin D1-positivity and good clinical outcome (Gillett et
al., 1996; Pelosio et al., 1996). This was, however, not confirmed
by other investigators (Michalides et al., 1996; van Diest et al.,
1997).
The mechanism of action of cyclin D1 is not fully understood
and is now being intensively studied. Nevertheless, it is clear that
the D-type cyclins are critical modulators of the G1 phase of the
cell cycle and transition through the G1/S restriction point (Sherr,
1994). Mitogenic growth factors such as epidermal growth factor,
basic fibroblast growth factor, and insulin-like growth factor-I
promote progression of the cell cycle by enhancing cyclin D-Cdk4
and cyclin D-Cdk6 complex formation and kinase activities during
the G1 phase (Sherr, 1994; Grana and Reddy, 1995). Cyclin D
proteins, most notably cyclin D1, are thus at a key step in determining whether a cell commits to mitogenesis, and several observations suggest that it also has an important role in promoting the
growth of certain human malignancies and in maintaining the
transformed phenotype (Donnellan and Chetty, 1998).
How can the present results be explained in view of the outcome
of our prognostic study? The reasons for the paradoxical behavior
of cyclin D1 are unclear but under certain circumstances, cyclin
D1 can act as a negative rather than a positive factor. Indeed, it has
been argued that an excess of cyclin D1 may be toxic to cells
(Quelle et al., 1993). Overexpression may indeed reduce viability.
In the present study, we found that cyclin D1 mRNA levels were
significantly higher in ER mRNA-positive tumors than in negative
ones, in agreement with previous immunohistochemical findings
(Michalides et al., 1996; van Diest et al., 1997). The mechanisms
FIGURE 3 – Relapse-free and overall survival of 97 the patients
with breast cancer by tertiles of cyclin D1 mRNA (see text). There
were 32 patients in the lower tertile, 32 patients in the middle tertile,
and 33 patients in the upper tertile.
TABLE IV – MULTIVARIATE ANALYSIS OF DESCRIPTORS WITH RESPECT TO RELAPSE-FREE AND OVERALL SURVIVAL
Relapse-free survival
Multivariate1
Variable
Univariate
p value
p value
Cyclin D1 mRNA (low/high)
Nodal status (positive/negative)
ER mRNA (negative/positive)
Tumor size (ⱖ2.1 cm/ⱕ2.0 cm)
Histological grade3 (3/1 and 2)
Menopausal status (pre-/post-)
Age (⬍50 years/ⱖ50 years)
0.006
0.003
0.400
0.093
0.033
0.338
0.740
0.012
0.008
⬎0.2
0.174
0.144
⬎0.2
⬎0.2
Overall survival
Multivariate1
Relative risk
Univariate
p value
p value
Relative risk
4.919 (1.411–17.142)2
4.410 (1.471–13.221)2
—
—
—
—
—
0.029
0.005
0.058
0.202
0.019
0.172
0.389
0.106
0.002
0.025
0.137
0.122
⬎0.2
⬎0.2
—
13.354 (2.696–66.136)2
3.823 (1.187–12.317)2
—
—
—
—
1
Ninety-five patients were analyzed since in 2 cases information of histological grade was lacking.–2Values in parentheses are 95 percent
confidence intervals.–3A case of ductal carcinoma in situ and a case of invasive lobular carcinoma were excluded from this analysis.
CYCLIN D1 EXPRESSION IN HUMAN BREAST CANCER
underlying increase of cyclin D1 expression in human breast
cancer remain unknown at present. The cyclin D1 gene is known
to be often amplified or over-expressed in human breast carcinomas. Barbareschi et al. (1997) showed that gene amplification of
cyclin D1 is related to high immunocytochemical expression of
cyclin D1 and pRB, and that high cyclin D1 expression is associated with positive ER immunoreactivity, suggesting that overexpression of cyclin D1 observed in breast carcinomas may be more
frequently due to ER-related up-regulation than to gene amplification. Treatment of breast cancer cells with anti-estrogens inhibits
pRB phosphorylation (Watts et al., 1995), while estrogen induces
significant phosphorylation of this key component of cyclin-Cdk
complexes (Altucci et al., 1996; Prall et al., 1997). This indicates
43
that cyclin-Cdk complexes are likely to be targets of estrogen
action. In particular, cyclin D1, which activates both Cdk4 and
Cdk6, would be expected to be implicated in estrogen-induced
progression through the cell cycle. In breast cancers, D-type cyclins might play a role in mediating signals from a diverse group
of mitogens including growth factors and steroid hormones.
In conclusion, we report here that cyclin D1 mRNA expression
is well correlated with prognosis in human breast cancer. RT-PCR
analysis of this parameter may thus have clinical advantage especially when only small tissue specimens are available from surgical operation. Our findings also have important implications in
considering the biological functions of cyclin D1.
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