The WWOX gene in brain development and pathology.

IMPACT STATEMENT: WW domain-containing oxidoreductase encoded by the WWOX gene is a transcription regulator and a key player in a number of cellular and biological processes such as tumor suppression, cell proliferation, apoptosis induction, steroid metabolism, and central nervous system development. This review provides a comprehensive summary of currently known roles and discusses the importance of WWOX gene for CNS development and functioning.

Boundary spanning at the science-policy interface: the practitioners' perspectives.

Cultivating a more dynamic relationship between science and policy is essential for responding to complex social challenges such as sustainability. One approach to doing so is to "span the boundaries" between science and decision making and create a more comprehensive and inclusive knowledge exchange process. The exact definition and role of boundary spanning, however, can be nebulous. Indeed, boundary spanning often gets conflated and confused with other approaches to connecting science and policy, such as science communication, applied science, and advocacy, which can hinder progress in the field of boundary spanning. To help overcome this, in this perspective, we present the outcomes from a recent workshop of boundary-spanning practitioners gathered to (1) articulate a definition of what it means to work at this interface ("boundary spanning") and the types of activities it encompasses; (2) present a value proposition of these efforts to build better relationships between science and policy; and (3) identify opportunities to more effectively mainstream boundary-spanning activities. Drawing on our collective experiences, we suggest that boundary spanning has the potential to increase the efficiency by which useful research is produced, foster the capacity to absorb new evidence and perspectives into sustainability decision-making, enhance research relevance for societal challenges, and open new policy windows. We provide examples from our work that illustrate this potential. By offering these propositions for the value of boundary spanning, we hope to encourage a more robust discussion of how to achieve evidence-informed decision-making for sustainability.

The influence of the WWOX gene on the regulation of biological processes during endometrial carcinogenesis.

The purpose of the present study was to investigate the role of WW domain containing oxidoreductase (WWOX) downregulation in biological cancer-related processes in normal (non-malignant) and cancer endometrial cell lines. We created an in vitro model using the normal endometrial cell line, THESC, and 2 endometrial cancer cell lines with varying degrees of differentiation, the Ishikawa (well-differentiated) and the MFE296 (moderately differentiated) cells, in which the WWOX tumor suppressor gene was silenced using Gipz lentiviral shRNA. In this model, we examined the changes in invasiveness via biological assays, such as zymography, migration through a basement membrane, the adhesion of cells to extracellular matrix proteins, anchorage-independent growth and colony formation assay. We also evaluated the correlation between the mRNA expression of the WWOX gene and genes involved in the processes of carcinogenesis, namely catenin beta-1 (CTNNB1) and zinc finger E-box binding homeobox 1 (ZEB1) (gene transcription), cadherin 1 (CDH1) and ezrin (EZR) (cell adhesion), vimentin (VIM) (structural proteins), as well as phosphatase and tensin homolog (PTEN) (tumor suppression) and secreted protein, acidic, cysteine-rich (osteonectin) (SPARC) (SPARC) (cell growth regulation) by RT-qPCR. Downregulation of the WWOX gene in the moderately differentiated MFE296 cell line caused decreased migratory capacity, and a reduction of matrix metalloproteinase-2 (MMP-2) activity. However, these cells grew in semisolid medium and exhibited higher expression of CDH1 and EZR (cell adhesion) and secreted protein, acidic, cysteine-rich (osteonectin) (SPARC) (cell growth regulation). Moreover, in the well-differentiated endometrial cancer (Ishikawa) cell line, WWOX gene silencing resulted in an increased ability of the cells to proliferate indefinitely. Additionally, WWOX regulated changes in adhesion potential in both the normal and cancer cell lines. Our results suggest that the WWOX tumor suppressor gene modulated the processes of cell motility, cell adhesion, gene expression and remodeling in endometrial cell lines.

Correlation between depression and burden observed in informal caregivers of people suffering from dementia with time spent on caregiving and dementia severity.

OBJECTIVE: The aim of the study is to compare data on the examined population of informal caregivers of people suffering from dementia with previous studies, as well as to assess the correlation between (i) depression determined on the basis of the Center for Epidemiologic Studies Depression Scale and (ii) caregiver burden measured by means of the Zarit Caregiver Burden Scale and some chosen parameters, such as total time devoted to caregiving, time of caregiving in hours per week and level of dementia severity measured by Global Deterioration Scale. PATIENTS AND METHODS: 41 informal caregivers of people suffering from dementia from different backgrounds were evaluated using the Zarit Caregiver Burden Scale and the Center for Epidemiologic Studies Depression Scale. Demographic data about the time devoted to caregiving and the number of hours spend on caregiving weekly were gathered. The type of dementia and its stage were registered using the Global Deterioration Scale (GDS). With the aid of the Statistica StatSoft program, mutual correlations between the parameters were measured. The study was conducted within the framework of AAL UnderstAID--a platform that supports and helps to understand and assist caregivers in the care of a relative with dementia. The international project is co-founded by the Joint Programme Ambient Assisted Living (Grant code: ESR-aal 2012 5 107). RESULTS: No significant correlations between the level of depression severity evaluated in caregivers and the total time of taking care of a demented person or time of caregiving in hours per week were observed. Similarly, no significant correlation between depression severity level and dementia severity level measured on the GDS scale were noted. There was also no significant correlation between Zarit Caregiver Burden Scale scores and the above-mentioned parameters. CONCLUSIONS: The level of depression among caregivers do not depend on socio-demographic factors.

WWOX, the tumour suppressor gene affected in multiple cancers.

WWOX is a tumour suppressor gene affected in multiple cancers, especially in breast, prostate and ovary. This gene is located at the chromosomal area 16q23.3-24.1, which was identified as a common chromosomal fragile site FRA16D. WWOX turned out to possess tumour suppressor features despite the fact that the most basic (classical) way of tumour suppressor gene inactivation involves both alleles (e.g. through deletions, point mutations and promoter methylation), which is very rare event in a case of WWOX, occurring only in few cell lines. A large number of papers corroborate the phenomenon of correlation between the loss of WWOX expression and more aggressive/worse prognosis in many different types of tumours, for example breast cancer, nonsmall cell lung cancer, bladder cancer, gastric cancer or sporadic meningiomas. Ectopically increased WWOX expression promotes migration through basal membrane, however suppresses anchorage independent growth and induces normal-like colony formation in matrigel.

Evaluation of oestrogen receptor expression in breast cancer by quantification of mRNA.

AIMS: cDNA microarrays have subclassified breast carcinomas into molecular subtypes with oestrogen receptor-alpha (ER) gene expression as a main marker. The aim was to compare ER expression in 97 patients with operable breast cancer estimated by real-time reverse transcriptase-polymerase chain reaction (real-time RT-PCR) and by routine immunohistochemistry, and to determine which method was reliable for molecular subtyping in relation to basal-type keratins and HER2 gene expression. METHODS AND RESULTS: Frozen tumour samples were analysed by real-time RT-PCR for the expression of ER, HER2, keratin 5 and keratin 17 genes. In a group of 27 tumours with a low level of ER mRNA (<1.00), there were eight ER+ cases as assessed by immunohistochemistry, and of 70 cases with a high level of ER mRNA (>or=1.00), 26 were ER- by immunohistochemistry (P = 0.003). Lack of prognostic relevance of ER mRNA level was demonstrated, whereas assessment by immunohistochemistry was related to clinical outcome. Expression of basal keratins and HER2 genes differed significantly between ER+ and ER- tumours based on immunohistochemistry, but not on mRNA level. CONCLUSIONS: These results throw doubt on the assessment of ER mRNA as a key factor in the molecular distinction between breast tumours.

Primary cutaneous marginal zone B-cell lymphoma in a patient with chronic lymphocytic leukaemia.

Primary cutaneous marginal zone B-cell lymphoma (PCMZL) is a low-grade malignant lymphoma that presents in the skin with no evidence of extracutaneous localization at diagnosis. We present an 80-year-old woman with B-cell chronic lymphocytic leukaemia (CLL) who developed multifocal PCMZL lesions 14 months after CLL diagnosis. PCMZL was clonally similar to the original bone marrow (BM) CLL cells. The specific translocation t(14;18) (q32;q21) with breakpoints in IGH and BCL2 loci was found in a skin specimen, but was absent in BM and peripheral blood (PB) cells. In contrast, a 13q deletion was found in BM and PB CLL cells. The patient was treated with chlorambucil and complete response of PCMZL was achieved. To our knowledge this is the first patient with CLL in whom PCMZL has been diagnosed.

Cyclin E expression in breast cancer correlates with negative steroid receptor status, HER2 expression, tumor grade and proliferation.

The main objective of this retrospective study was to investigate relations between cyclin E and pathoclinical factors in patients with operable breast cancer. Expression of cyclin E was analyzed by immunohistochemistry in specimens of invasive ductal breast cancer tissue obtained from 189 women during radical mastectomy. Overall, 110 tumor samples were regarded to be cyclin E positive. Cyclin E expression was more often seen in tumors with: negative steroid receptor status (p<0.0001), higher proliferative index (p=0.0014), higher tumor grade (p=0.0017), and presence of HER2 (p=0.0171). With a median follow-up of 58 months, expression of cyclin E together with negative steroid receptor status determined poor prognosis with a 5-year cancer-specific survival rate of 58%. It differed significantly from a survival curve of cyclin E negative and steroid receptor positive patients (87%, p=0.0005). No significant difference was observed in comparison with survival of cyclin E positive and steroid receptor positive patients (68%, p=0.221). We demonstrated that cyclin E expression in breast cancer cells was associated with negative steroid receptor status, HER2 presence, higher tumor grade and higher proliferation index. Expression of cyclin E together with lack of steroid receptors determined poor prognosis.

WWOX--the FRA16D cancer gene: expression correlation with breast cancer progression and prognosis.

AIMS: WWOX is a tumour suppressor gene involved in various tumours including breast cancer. High chromosomal abnormalities in a genomic region spanned by WWOX are associated with the fact that this gene covers approximately 1 million base pairs of the second most affected among common chromosomal fragile sites FRA16D. We evaluated WWOX expression levels in breast cancer samples in association with diagnostics-prognostics markers. METHODS: We performed quantitative real-time RT-PCR to analyse levels of expression of WWOX in 132 cases of breast cancer. We evaluated the relationship between WWOX mRNA levels, clinico-pathological factors, expression of aberrant WWOXDelta6-8 mRNA and other cancer related genes. RESULTS: Expression of WWOX was higher in patients younger than 50 years old, in ER and PR positive tumours vs negative for those receptors and tumours without lymph node metastasis vs LN+. WWOX mRNA levels were also higher in tumours with higher apoptotic index (Bcl2/Bax ratio). Negative associations were found between WWOX expression and cytokeratins 5/6 and 17 (P<0.05). High level expression of WWOX was also associated with better disease free survival. Presence of WWOXDelta6-8 transcripts were accompanied with lower WWOX wild type mRNA level. CONCLUSIONS: Reduced WWOX expression commonly observed in various neoplasias in cases of breast cancer is associated with markers of bad prognosis. Our findings reveal additional evidence that WWOX may be involved in steroid (estrogens) metabolism and signaling pathways. WWOX can be considered as a new target for gene therapy development due to the association of high WWOX expression with improved disease free survival.

GADD45A and EPB41 as tumor suppressor genes in meningioma pathogenesis.

Deletions of 1p occur in approximately 30% of meningiomas. Based on loss of heterozygosity (LOH) analysis, two regions on 1p have been suspected to be carriers of tumor suppressor genes. We chose the GADD45A and EPB41 genes as tumor suppressor candidates based on their function and chromosomal localization. We analyzed 19 cases of meningioma with LOH of 1p by means of sequencing of the GADD45A gene and Western blotting of the GADD45a protein. Twenty cases of meningioma without 1p LOH were also analyzed by Western blotting to find out if changes of the GADD45a protein expression occurred. Nineteen samples with 1p LOH (12 grade I; 7 grade II, WHO classification) and 20 samples without 1p LOH (18 grade I; 2 grade II) were also analyzed by means of real-time polymerase chain reaction to find abnormalities in EPB41 mRNA levels in meningioma. LOH analysis was performed using seven microsatellite markers: D1S508 (1p36.2), D1S199 (1p36.1) D1S2734 (1p36.1), D1S2720 (1p34), D1S197 (1p32), D1S162 (1p32), D1S429 (1p11). LOH analysis confirmed previously described localization of putative tumor suppressor genes on 1p and involvement in meningioma pathogenesis (1p36 and 1p32). The open reading frame of GADD45A and intron splicing sites showed neither mutations nor polymorphisms. GADD45a protein molecular weight and expression level were unaltered in meningiomas with and without 1p LOH. We conclude that the GADD45A gene is not involved in meningioma tumorigenesis. EPB41 gene expression was unchanged in all analyzed meningiomas. This suggests that involvement of the EPB41 gene (4.1R protein) in meningioma pathogenesis should be reconsidered.

Richter syndrome first manifesting as cutaneous B-cell lymphoma clonally distinct from primary B-cell chronic lymphocytic leukaemia.

Richter syndrome (RS) is a transformation to high-grade non-Hodgkin lymphoma in patients with chronic lymphocytic leukaemia (CLL). RS may develop in lymph nodes or rarely extranodally. Skin localization of RS has been described in only a few cases. We present a 77-year-old woman who developed isolated diffuse large B-cell lymphoma (LBCL) in the skin of the nose without any other symptoms of RS. The LBCL in the skin was clonally distinct from the original bone marrow CLL cells. Moreover, LBCL cells were positive for LMP-1 segment of Epstein-Barr virus and overexpressed p53 protein. The patient was successfully treated with CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone) and adjuvant local radiotherapy.

WWOX, the common chromosomal fragile site, FRA16D, cancer gene.

Gross chromosomal rearrangements and aneuploidy are among the most common somatic genomic abnormalities that occur during cancer initiation and progression, in particular in human solid tumor carcinogenesis. The loss of large chromosomal regions as consequence of gross rearrangements (e.g. deletions, monosomies, unbalanced translocations and mitotic recombination) have been traditionally associated with the existence of tumor suppressor genes within the areas affected by the loss of genetic material. The long arm of chromosome 16 was identified as being frequently associated with structural abnormalities in multiple neoplasias, that led us to focus attention on the detailed genetic dissection of this region resulting in the cloning of the putative tumor suppressor gene, WWOX (WW domain containing Oxidoreductase). Interestingly, the WWOX gene resides in the very same region as that of the common chromosomal fragile site 16D (FRA16D). The WWOX gene encodes a protein that contains two WW domains, involved in protein-protein interactions, and a short chain dehydrogenase (SDR) domain, possibly involved in sex-steroid metabolism. We have identified the WWOX WW domain ligand as the PPXY motif confirming the biochemical activity of this domain. WWOX normally resides in the Golgi and we will demonstrate that Golgi localization requires an intact SDR. Inactivation of the WWOX gene during tumorigenesis can occur by homozygous deletions and possibly mutation, however, aberrantly spliced forms of WWOX mRNA have been observed even when one allele is still intact. The aberrantly spliced mRNAs have deletions of the exons that encode the SDR and these WWOX protein isoforms display abnormal intracellular localization to the nucleus possibly functioning as dominant negative inhibitors of full length WWOX. Thus, generation of aberrant transcripts of WWOX may represent a novel mechanism to functionally inactivate WWOX without genomic alteration of the remaining allele. In this article we will review the cloning and identification of WWOX as the target of FRA16D. In addition, we will discuss the possible biochemical functions of WWOX and present evidence that ectopic WWOX expression inhibits tumor growth.

WWOX, the FRA16D gene, behaves as a suppressor of tumor growth.

We recently reported the cloning of WWOX, a gene that maps to the common fragile site FRA16D region in chromosome 16q23.3-24.1. It was observed that the genomic area spanned by WWOX is affected by chromosomal translocations and homozygous deletions. Furthermore, the high incidence of allelic loss in breast, ovarian, prostate, and other cancers affecting this region suggests that WWOX is a candidate tumor suppressor gene. Expression of WWOX is highly variable in breast cancer cell lines, with some cases showing low or undetectable levels of expression. In this report, we demonstrate that ectopic WWOX expression strongly inhibits anchorage-independent growth in soft agar of breast cancer cell lines MDA-MB-435 and T47D. Additionally, we observed that WWOX induces a dramatic inhibition of tumorigenicity of MDA-MB-435 breast cancer cells when tested in vivo. We also detected the common occurrence of aberrant WWOX transcripts with deletions of exons 5-8 or 6-8 in various carcinoma cell lines, multiple myeloma cell lines, and primary breast tumors. These aberrant mRNA forms were not detected in normal tissues. Interestingly, we further observed that proteins encoded by such aberrant transcripts display an abnormal nuclear localization in contrast to the wild-type WWOX protein that localizes to the Golgi system. Our data indicate that WWOX behaves as a potent suppressor of tumor growth and suggest that abnormalities affecting this gene at the genomic and transcriptional level may be of relevance in carcinogenesis.

Undamming rivers: a review of the ecological impacts of dam removal.

Dam removal continues to garner attention as a potential river restoration tool. The increasing possibility of dam removal through the FERC relicensing process, as well as through federal and state agency actions, makes a critical examination of the ecological benefits and costs essential. This paper reviews the possible ecological impacts of dam removal using various case studies. Restoration of an unregulated flow regime has resulted in increased biotic diversity through the enhancement of preferred spawning grounds or other habitat. By returning riverine conditions and sediment transport to formerly impounded areas, riffle/pool sequences, gravel, and cobble have reappeared, along with increases in biotic diversity. Fish passage has been another benefit of dam removal. However, the disappearance of the reservoir may also affect certain publicly desirable fisheries. Short-term ecological impacts of dam removal include an increased sediment load that may cause suffocation and abrasion to various biota and habitats. However, several recorded dam removals have suggested that the increased sediment load caused by removal should be a short-term effect. Pre-removal studies for contaminated sediment may be effective at controlling toxic release problems. Although monitoring and dam removal studies are limited, a continued examination of the possible ecological impacts is important for quantifying the resistance and resilience of aquatic ecosystems. Dam removal, although controversial, is an important alternative for river restoration.

The level of magnesium in the serum of children hospitalized for severe respiratory infections.

The objective of the studies was evaluation of the level of magnesium in children hospitalized for severe respiratory infections (mainly pneumonia and bronchitis). The criterion for the evaluation of the magnesium level in the serum of the children hospitalized for severe respiratory infections were the following parameters: general condition of the child at the time of admittance, feeding pattern and psychosomatic development in the children with respiratory infection. The level of magnesium in the serum of the children admitted with median general condition was higher than that of the children admitted with poor general condition. The level of magnesium in the serum of breastfed children and those with correct psychosomatic development was higher than the level of magnesium in children fed artificially and representing backward psychosomatic development.

Outcome of revision hip arthroplasty.

Background. Clinical material collected from 1989 to 1999 from three orthopedic centers is discussed: the Orthopedic Clinic at the Center for Postgraduate Medical Education in Otwock, the Orthopedic Clinic at the Lublin Academy of Medicine, and the Orthopedic Clinic at the Warsaw Academy of Medicine.
Material and methods. During this period 511 patients with an average age of 66 were treated. The authors explain the reasons for aseptic loosening of hip prostheses, the types of implants replaced, and the methods of surgical treatment.
Analysis of results. The importance of correct surgical technique and modern cementing methods during primary arthroplasty for the duration of good prosthesis functioning is discussed. A good outcome from revision arthroplasty can be expected only when the decision to treat is made early. The authors confirm the usability of impacted camcellous allografts for revision hip arthroplasty. Complications during and after surgery are also discussed. Difficulties in the clinical and radiological evaluation of treatment outcomes caused by differing criteria used in each orthopedic treatment are also discussed in this article.
Conclusions. In the conclusion the authors propose rules for surgical treatment to reduce the number of revision procedures.

Film badges for personal dosimetry of roentgen radiation.

The paper describes the calibration procedure for and data obtained from routine X-ray dosimetry service in Poland. In 1998 the number of readouts amounted to 152,000. The dosimetry concerned 31,281 workers in 3,113 enterprises. The annual collective dose was assessed to be 16.7 man.Sv. The analysis of the calibration quality is discussed as well. Only 2.9% of all points lay outside the quality curve while the number of the acceptable outliers was 5%.

Effects of estrogen on global gene expression: identification of novel targets of estrogen action.

The important role played by the sex hormone estrogen in disease and physiological processes has been well documented. However, the mechanisms by which this hormone elicits many of its normal as well as pathological effects are unclear. To identify both known and unknown genes that are regulated by or associated with estrogen action, we performed serial analysis of gene expression on estrogen-responsive breast cancer cells after exposure to this hormone. We examined approximately 190,000 mRNA transcripts and monitored the expression behavior of 12,550 genes. Expression levels for the vast majority of those transcripts were observed to remain constant upon 17beta estradiol (E2) treatment. Only approximately 0.4% of the genes showed an increase in expression of > or =3-fold by 3 h post-E2 treatment. We cloned five novel genes (E2IG1-5), which were observed up-regulated by the hormonal treatment. Of these the most highly induced transcript, E2IG1, appears to be a novel member of the family of small heat shock proteins. The E2IG4 gene is a new member of the large family of leucine-rich repeat-containing proteins. On the basis of architectural and domain homology, this gene appears to be a good candidate for secretion in the extracellular environment and, therefore, may play a role in breast tissue remodeling and/or epithelium-stroma interactions. Several interesting genes with a potential role in the regulation of cell cycle progression were also identified to increase in expression, including Pescadillo and chaperonin CCT2. Two putative paracrine/autocrine factors of potential importance in the regulation of the growth of breast cancer cells were identified to be highly up-regulated by E2: stanniocalcin 2, a calcium/phosphate homeostatic hormone; and inhibin-beta B, a TGF-beta-like factor. Interestingly, we also determined that E2IG1 and stanniocalcin 2 were exclusively overexpressed in estrogen-receptor-positive breast cancer lines, and thus they have the potential to serve as breast cancer biomarkers. This data provides a comprehensive view of the changes induced by E2 on the transcriptional program of human E2-responsive cells, and it also identifies novel and previously unsuspected gene targets whose expression is affected by this hormone.

WWOX, a novel WW domain-containing protein mapping to human chromosome 16q23.3-24.1, a region frequently affected in breast cancer.

Studies were conducted with the final goal of identifying genes of interest mapping to the chromosome region 16q23.3-24.1, an area commonly affected by allelic losses in breast cancer. To this end we generated a detailed physical map of the genomic region spanning between sequence-tagged site markers D16S518 and D16S516. To identify candidate genes, we used shotgun genomic sequencing as well as isolation and analysis of transcripts mapping to the area of interest. We identified and cloned a novel gene, the genomic structure of which spans the whole region of interest. We named this gene WWOX because it contains two WW domains coupled to a region with high homology to the short-chain dehydrogenase/reductase family of enzymes. The ORF of WWOX is 1245 bp long, encoding a 414-amino acid protein. This gene is composed of nine exons. We performed a mutation screening of WWOX exons in a panel of breast cancer lines, most of which are hemizygous for the 16q genomic region indicated. We found no evidence of mutations, thus indicating that WWOX is probably not a tumor suppressor gene. However, we observed that one case of homozygous deletion as well as two previously described translocation breakpoints map to intronic regions of this gene. We speculate that WWOX may span the yet uncharacterized common fragile site FRA16D region. In expression studies we found overexpression of WWOX in breast cancer cell lines when compared with normal breast cells and tissues. The highest normal expression of WWOX was observed in hormonally regulated tissues such as testis, ovary, and prostate. This expression pattern and the presence of a short-chain dehydrogenase/reductase domain and specific amino acid features suggest a role for WWOX in steroid metabolism. Interestingly, the presence of WW domains in the structure of WWOX indicate the likelihood that this protein physically interacts with other proteins. The unique features of WWOX and its possible association with cancer processes make it an interesting target for further investigation.

Suppression of cell proliferation and telomerase activity in 4-(hydroxyphenyl)retinamide-treated mammary tumors.

The detection of telomerase activity has been proposed as a biomarker of breast cancer development and progression. In this study, we used cell proliferation and telomerase in MNU (N-methyl-N-nitrosourea)-induced mammary carcinomas as targets for assessing the response of tumor cells to 4-(hydroxyphenyl)retinamide (4-HPR), a known inhibitor of mammary carcinogenesis in animal models and premenopausal women. In mammary tumors of rats treated for 1, 2, 4 or 6 weeks with 4-HPR, we observed that telomerase activity decreased progressively with the extension of 4-HPR administration. A marked reduction in telomerase activity was already observed by 2 weeks after treatment and the lowest level was found at 6 weeks after initiation of 4-HPR treatment. The changes in telomerase activity were preceded and accompanied by a significant decrease in the percentage of proliferating cells as evaluated by 5-bromodeoxyuridine (BrdU)-labeling. However, when the values of telomerase activity in the individual tumors were compared with the percentage of proliferating cells, no significant correlation was found. These data suggest that the decreased telomerase activity in the animals treated with 4-HPR is not a simple consequence of the changes in cell proliferation, but a more complex phenomenon involving different cellular mechanisms and pathways. The time-dependent and consistent decrease of telomerase activity in the tumors treated with 4-HPR suggests that, in addition to the percentage of proliferating cells, telomerase activity could also be used as an endpoint in breast cancer chemotherapy studies.