BRCA1 transactivates the cyclin-dependent kinase inhibitor p27(Kip1)

Progesterone up-regulates p27 through an increased binding of the progesterone receptor-A-p53 protein complex onto the non-canonical p53 binding motif in HUVEC

We previously demonstrated that progesterone (P4) up-regulated p53 expression, which in turn increased p21 and p27 expression, and finally resulted in proliferation inhibition in human umbilical vein endothelial cells (HUVEC). While a direct transcriptional activation of p21 by p53 protein has been clearly elucidated, the mechanism by which p53 induces p27 expression has not been documented. In this study, we identified three putative p53 protein binding domains at the p27 promoter. Luciferase assay showed that the activity of ectopically introduced p27 promoter constructs containing the potential p53 protein binding region was significantly increased by P4. Immunoblotting analysis indicated that P4 increased the level of p53 protein. Treatment with pifithrin-α-HBr (PFTα), a specific blocker of p53-responsive gene transactivation, reduced the P4-increased p27 promoter activity and p27 protein expression. Transfection with dominant-negative mutants of p53 (C135Y, R175H and R248 W) abolished the P4-increased p27 promoter activity. Moreover, deletion or TCCT nucleotide sequence fill-in at the core site of any of p53 protein binding domains led to the irresponsiveness of the p27 promoter to P4 treatment. Interestingly, immunoprecipitation and chromatin-immunoprecipitation analyses demonstrated that P4 increased the complex of p53-P4 receptor (PR) protein in the nucleus and the assembly of PR protein to the p53 protein binding region of the p27 promoter. Ectopic co-overexpression of p53 and PR-A constructs further augmented the P4-increased p27 promoter activity. Taken together, the results from the present study suggest that P4-increased p53 expression might directly up-regulate p27 transactivation, and PR-A protein might promote this effect by forming complex with p53 protein.

MYCN promotes neuroblastoma malignancy by establishing a regulatory circuit with transcription factor AP4

Amplification of the MYCN oncogene, a member of the MYC family of transcriptional regulators, is one of the most powerful prognostic markers identified for poor outcome in neuroblastoma, the most common extracranial solid cancer in childhood. While MYCN has been established as a key driver of malignancy in neuroblastoma, the underlying molecular mechanisms are poorly understood. Transcription factor activating enhancer binding protein-4 (TFAP4) has been reported to be a direct transcriptional target of MYC. We show for the first time that high expression of TFAP4 in primary neuroblastoma patients is associated with poor clinical outcome. siRNA-mediated suppression of TFAP4 in MYCN-expressing neuroblastoma cells led to inhibition of cell proliferation and migration. Chromatin immunoprecipitation assay demonstrated that TFAP4 expression is positively regulated by MYCN. Microarray analysis identified genes regulated by both MYCN and TFAP4 in neuroblastoma cells, including Phosphoribosyl-pyrophosphate synthetase-2 (PRPS2) and Syndecan-1 (SDC1), which are involved in cancer cell proliferation and metastasis. Overall this study suggests a regulatory circuit in which MYCN by elevating TFAP4 expression, cooperates with it to control a specific set of genes involved in tumor progression. These findings highlight the existence of a MYCN-TFAP4 axis in MYCN-driven neuroblastoma as well as identifying potential therapeutic targets for aggressive forms of this disease.

Identification and frequency of the rs12516 and rs8176318 BRCA1 gene polymorphisms among different populations

Genetic mutation of breast cancer 1 (BRCA1) is one of the most notable factors responsible for a proportion of breast cancer cases. BRCA1 encodes a 1,863-amino acid protein and functions as a negative regulator of tumor growth. Thus, investigation of the underlying mechanisms that regulate BRCA1 gene expression provide further insight into possible targets for breast cancer therapy. Previous studies have demonstrated that the genetic variants in the BRCA1 3' untranslated region (3'UTR), in addition to the cytosine-phosphate-guanine (CpG) islands in the promoter region, are significantly associated with breast cancer risk; however, the role of single nucleotide polymorphisms (SNPs) in the BRCA1 3'UTR remains unclear. The present study aimed to investigate the association between SNPs and BRCA1 mRNA expression levels. Bioinformatics analysis demonstrated that 2 SNPs in the BRCA1 3'UTR (rs12516 and rs8176318 with putative microRNA binding sites) were significantly correlated with mRNA expression in lymphoblastoid cell lines (P=2.55×10-4 and P=8.78×10^-5, respectively). Furthermore, the genotype frequency distribution varied between populations worldwide. In addition, 3 CpG islands and several transcription factor binding sites in the BRCA1 promoter region were established. The identification of such polymorphisms and CpG islands may aid in designing improved therapeutic strategies to treat patients with BRCA1-associated breast cancer.

BRCA1 regulates transforming growth factor-β (TGF-β1) signaling through Gadd45a by enhancing the protein stability of Smad4

BRCA1 is a well established tumor suppressor gene, which is involved in many cellular processes, including DNA damage repair, cell cycle control, apoptosis, as well as transcriptional control. In this work, we have found that BRCA1 is involved in regulating TGF-β1/Smad pathway. The loss of endogenous BRCA1 greatly attenuated TGF-β1-induced growth inhibition and cell cycle G1 arrest. BRCA1 greatly maintains stability of Smad4 protein, and the loss of BRCA1 results in Smad4 down-regulation, which is likely related to its downstream gene Gadd45a. Gadd45a is able to interact with β-Trcp1, a-F-box protein of SCF E3 ligase, and consequently suppresses the ubiquitin-degradation of Smad4 by SCF(β-trcp1), as reflected by the observations that the induction of Gadd45a substantially stabilizes Smad4 protein. In addition, exogenous expression of Gadd45a can largely rescue the protein level of Smad4 in BRCA1 deficient cells. These results further demonstrate that BRCA1 may act as an important negative regulator in cell cycle progression and tumorigenesis through regulating the stability of Smad4, and define a novel link that connects BRCA1 to TGF-β1/Smad pathway.

BRCA1 functions as a novel transcriptional cofactor in HIV-1 infection

Background

Viruses have naturally evolved elegant strategies to manipulate the host’s cellular machinery, including ways to hijack cellular DNA repair proteins to aid in their own replication. Retroviruses induce DNA damage through integration of their genome into host DNA. DNA damage signaling proteins including ATR, ATM and BRCA1 contribute to multiple steps in the HIV-1 life cycle, including integration and Vpr-induced G₂/M arrest. However, there have been no studies to date regarding the role of BRCA1 in HIV-1 transcription.

Methods

Here we performed various transcriptional analyses to assess the role of BRCA1 in HIV-1 transcription by overexpression, selective depletion, and treatment with small molecule inhibitors. We examined association of Tat and BRCA1 through in vitro binding assays, as well as BRCA1-LTR association by chromatin immunoprecipitation.

Results

BRCA1 was found to be important for viral transcription as cells that lack BRCA1 displayed severely reduced HIV-1 Tat-dependent transcription, and gain or loss-of-function studies resulted in enhanced or decreased transcription. Moreover, Tat was detected in complex with BRCA1 aa504-802. Small molecule inhibition of BRCA1 phosphorylation effector kinases, ATR and ATM, decreased Tat-dependent transcription, whereas a Chk2 inhibitor showed no effect. Furthermore, BRCA1 was found at the viral promoter and treatment with curcumin and ATM inhibitors decreased BRCA1 LTR occupancy. Importantly, these findings were validated in a highly relevant model of HIV infection and are indicative of BRCA1 phosphorylation affecting Tat-dependent transcription.

Conclusions

BRCA1 presence at the HIV-1 promoter highlights a novel function of the multifaceted protein in HIV-1 infection. The BRCA1 pathway or enzymes that phosphorylate BRCA1 could potentially be used as complementary host-based treatment for combined antiretroviral therapy, as there are multiple potent ATM inhibitors in development as chemotherapeutics.

Undifferentiated embryonic cell transcription factor-1 (UTF1) inhibits the growth of cervical cancer cells by transactivating p27Kip1

Undifferentiated embryonic cell transcription factor-1 (UTF1) is an important transcription factor during development, which plays critical roles in cell fate determination. However, its expression and function in somatic tissues remain unclear. Here, we investigated the expression pattern of the UTF1 in the human normal and cancerous lesions of cervix and found that UTF1 was downregulated in cervical carcinogenesis, which was related to the hypermethylation of UTF1 promoter. Exogenous expression of UTF1 resulted in the significant inhibition of cell proliferation in vitro and tumorigenesis in vivo through attenuating cell cycle arrest via increasing the level of p27 (Kip1) . Luciferase reporter assay indicated that the region containing an intact activating transcription factor site between nucleotides -517 and -388 of the p27 (Kip1) promoter was indispensable for its activation by UTF1. Chromatin immunoprecipitation analysis confirmed the physical interaction between UTF1 and the p27 (Kip1) promoter. Taken together, our findings reveal that UTF1 attenuates cell proliferation and is inactivated in cervical carcinogenesis through epigenetic modification, which strongly supports that UTF1 is a potential tumor suppressor.

Down-regulation of estrogen receptor α (ERα) transcriptional activity by p27 is mediated by inhibition of ERα nuclear localization and modulation of the ERα transcriptional complex

To investigate the role of p27 on estrogen receptor (ER)α-mediated transcription, we generated MCF-7 cells with knocked down p27 via retroviral delivery of p27 shRNA. Suppression of p27 expression in MCF-7 cells resulted in up-regulation of ERα-mediated transcription by estradiol compared to the levels in control MCF-7 cells. Accordingly, transient transfection studies in 293T cells revealed that overexpression of p27 reduced ERα-mediated transcription. The effect of p27 on ERα transcriptional activity was independent of cell cycle arrest by p27, as cell cycle arrest induced by serum starvation did not significantly affect ERα-mediated transcription. Further, we observed that p27 inhibited nuclear localization of ERα, and that p27 was associated with ERα in the cytoplasm. We also investigated the role of p27 in the modulation of ERα transcriptional activity in the nucleus. We found that p27 negatively modulated ERα transcriptional activity by inhibiting association of cyclin D1 with ERα and recruiting BRCA1 to ERα transcriptional complex. Taken together, these data suggest that p27 inhibits ERα transcriptional activity by two independent mechanisms, namely, physical nuclear exclusion of ERα, and modulation of the ERα transcriptional complex.

The molecular pathogenesis of hereditary ovarian carcinoma: alterations in the tubal epithelium of women with BRCA1 and BRCA2 mutations

BACKGROUND

BRCA1 or BRCA2 (BRCA1/2)-mutated ovarian carcinomas may originate in the fallopian tube. The authors of this report investigated alterations in BRCA1/2 tubal epithelium to define the molecular pathogenesis of these carcinomas.

METHODS

Tubal epithelium was evaluated from 31 BRCA1/2 mutation carriers with gynecologic carcinomas (BRCA CA), 89 mutation carriers who underwent risk-reducing salpingo-oophorectomy (RRSO), and 87 controls. Ki-67 expression and p53 foci (≥10 of 12 consecutive staining cells) were scored by 2 investigators who were blinded to patient designations. Expression levels of p27 and p21 were evaluated within p53 foci. Loss of heterozygosity at the BRCA1/2 mutation site was evaluated in microdissected p53 foci and tubal neoplasms.

RESULTS

Background tubal proliferation as measured by Ki-67 staining was increased in the BRCA1 RRSO group (P = .005) compared with the control group. Women who had BRCA1/2 mutations had more p53 foci identified per tubal segment than women in the control group (P = .02). Levels of p27 were decreased in 12 of 28 p53 foci from women with BRCA1 mutations and in 0 of 16 p53 foci from controls (P = .002). There was no loss of the wild type BRCA1/2 allele in 5 tested p53 foci. Tubal neoplasia lost the wild type allele in 6 of 6 foci (P = .002).

CONCLUSIONS

The current results suggested a model of tubal carcinogenesis in women with BRCA1/2 mutations. Increased proliferation occurred globally in at-risk tubal epithelium. A mutation in the tumor protein p53 gene TP53 with clonal proliferation and loss of p27 occurred before neoplastic proliferation. Loss of the wild type BRCA1/2 allele occurred with neoplastic proliferation and before invasion.

The genesis and evolution of high-grade serous ovarian cancer

Germline mutation in either BRCA1 or BRCA2 is associated with an increased risk of ovarian cancer, particularly the most common invasive histotype - serous carcinoma. In addition, serous ovarian cancers have an unusually high frequency of other molecular events involving BRCA pathway dysfunction. Recent findings show a high frequency of TP53 mutation, chromosomal instability, distinct molecular subtypes and DNA copy number-driven changes in gene expression. These findings suggest a model in which homologous recombination repair deficiency initiates a cascade of molecular events that sculpt the evolution of high-grade serous ovarian cancer and dictate its response to therapy.

Methylation of the tumor suppressor protein, BRCA1, influences its transcriptional cofactor function

BACKGROUND

Approximately half of hereditary breast cancers have mutations in either BRCA1 or BRCA2. BRCA1 is a multifaceted tumor suppressor protein that has implications in processes such as cell cycle, transcription, DNA damage response and chromatin remodeling. This multifunctional nature of BRCA1 is achieved by exerting its many effects through modulation of transcription. Many cellular events are dictated by covalent modification of proteins, an important mechanism in regulating protein and genome function; of which protein methylation is an important posttranslational modification with activating or repressive effects.

METHODS/PRINCIPAL FINDINGS

Here we demonstrate for the first time that BRCA1 is methylated both in breast cancer cell lines and breast cancer tumor samples at arginine and lysine residues through immunoprecipitation and western blot analysis. Arginine methylation by PRMT1 was observed in vitro and the region of BRCA1 504-802 shown to be highly methylated. PRMT1 was detected in complex with BRCA1 504-802 through in vitro binding assays and co-immunoprecipitated with BRCA1. Inhibition of methylation resulted in decreased BRCA1 methylation and alteration of BRCA1 binding to promoters in vivo as shown through chromatin immunoprecipitation assays. Knockdown of PRMT1 also resulted in increased BRCA1 binding to particular promoters in vivo. Finally, following methylation inhibition, Sp1 was found to preferentially associate with hypo-methylated BRCA1 and STAT1 was found to preferentially associate with hyper-methylated BRCA1.

CONCLUSIONS/SIGNIFICANCE

These results suggest that methylation may influence either the ability of BRCA1 to bind to specific promoters or protein-protein interactions which alters the recruitment of BRCA1 to these promoters. Thus, given the importance of BRCA1 to genomic stability, methylation of BRCA1 may ultimately affect the tumor suppressor ability of BRCA1.

Mitogenic regulation of p27(Kip1) gene is mediated by AP-1 transcription factors

The abundance of cyclin-dependent kinase inhibitor p27(Kip1) during the cell cycle determines whether cells will proliferate or become quiescent. Although the post-translational regulation of p27(Kip1) is well established, its transcriptional regulation is poorly understood. Here, we report that mitogenic stimulation of quiescent HEK293 and Huh7 cells showed a rapid decline in the levels of p27(Kip1) transcript by 2.4 +/- 0.1-fold. Inhibition of the p27(Kip1) gene in response to mitogens involved transcriptional down-regulation and required newly synthesized protein(s). Mutation of the AP-1 element at position -469 in the human p27(Kip1) promoter abrogated the effect of mitogens. The recruitment of the AP-1 complex to the p27(Kip1) promoter was confirmed by in vitro DNA binding and chromatin immunoprecipitation studies. Reporter gene analysis combined with enforced expression of Jun/Fos proteins suggested the involvement of Jun/Fos heterodimer in the transrepression process. Both MAPK and phosphatidylinositol 3-kinase signaling pathways appeared to mediate p27(Kip1) transcription. Furthermore, hepatitis B virus X protein-mediated down-regulation of p27(Kip1) in a transgenic environment correlated with an increase in c-Fos levels, reiterating the physiological relevance of AP-1 in the transcriptional regulation of p27(Kip1). Collectively, our studies present the first evidence demonstrating the role of the AP-1 complex in transcriptional down-regulation of the p27(Kip1) gene following mitogenic stimulation.

Transcriptional downregulation of p27KIP1 through regulation of E2F function during LMP1-mediated transformation

LMP1 induces the phenotypic transformation of fibroblasts and affects regulators of the cell cycle during this process. LMP1 decreases expression of the cyclin-dependent kinase inhibitor p27 and increases the levels and phosphorylation of cyclin-dependent kinase 2 and the retinoblastoma protein. In the present study, the effects of LMP1 on cell cycle progression and the mechanism of p27 downregulation by LMP1 were determined. Although p27 is frequently regulated at the posttranscriptional level during cell cycle progression and in cancer, LMP1 did not decrease ectopically expressed p27. However, LMP1 did decrease p27 RNA levels and inhibited the activity of p27 promoter reporters. The LMP1-regulated promoter element was mapped to a region containing two E2F sites. Electrophoretic mobility shift assays determined that the regulated cis element bound an inhibitory E2F complex containing E2F4 and p130. These findings indicate that LMP1 decreases p27 transcription through effects on E2F family transcription factors. This property likely contributes to the ability of LMP1 to stimulate cell cycle progression.

P21 and p27: roles in carcinogenesis and drug resistance

Human cancers arise from an imbalance of cell growth and cell death. Key proteins that govern this balance are those that mediate the cell cycle. Several different molecular effectors have been identified that tightly regulate specific phases of the cell cycle, including cyclins, cyclin-dependent kinases (CDKs) and CDK inhibitors. Notably, loss of expression or function of two G1-checkpoint CDK inhibitors - p21 (CDKN1A) and p27 (CDKN1B) - has been implicated in the genesis or progression of many human malignancies. Additionally, there is a growing body of evidence suggesting that functional loss of p21 or p27 can mediate a drug-resistance phenotype. However, reports in the literature have also suggested p21 and p27 can promote tumours, indicating a paradoxical effect. Here, we review historic and recent studies of these two CDK inhibitors, including their identification, function, importance to carcinogenesis and finally their roles in drug resistance.

Evaluation of unclassified variants in the breast cancer susceptibility genes BRCA1 and BRCA2 using five methods: results from a population-based study of young breast cancer patients

INTRODUCTION

Efforts are ongoing to determine the significance of unclassified variants (UVs) in the breast cancer susceptibility genes BRCA1/BRCA2, but no study has systematically assessed whether women carrying the suspected deleterious UVs have characteristics commonly seen among women carrying known deleterious or disease-causing mutations in BRCA1/BRCA2.

METHODS

We sequenced BRCA1/BRCA2 in 1,469 population-based female breast cancer patients diagnosed between the ages of 20 and 49 years. We used existing literature to classify variants into known deleterious mutations, polymorphic variants, and UVs. The UVs were further classified as high risk or low risk based on five methods: allele frequency, Polyphen algorithm, sequence conservation, Grantham matrix scores, and a combination of the Grantham matrix score and sequence conservation. Furthermore, we examined whether patients who carry the variants classified as high risk using these methods have risk characteristics similar to patients with known deleterious BRCA1/BRCA2 mutations (early age at diagnosis, family history of breast cancer or ovarian cancer, and negative estrogen receptor/progesterone receptor).

RESULTS

We identified 262 distinct BRCA1/BRCA2 variants, including 147 UVs, in our study population. The BRCA1 UV carriers, but not the BRCA2 UV carriers, who were classified as high risk using each classification method were more similar to the deleterious mutation carriers with respect to family history than those carriers classified as low risk. For example, the odds ratio of having a first-degree family history for the high-risk women classified using Polyphen was 3.39 (95% confidence interval = 1.16 to 9.94) compared with normal/polymorphic BRCA1 carriers. The corresponding odds ratio of low-risk women was 1.53 (95% confidence interval = 1.07 to 2.18). The odds ratio for high-risk women defined by allele frequency was 2.00 (95% confidence interval = 1.14 to 3.51), and that of low-risk women was 1.30 (95% confidence interval = 0.87 to 1.93).

CONCLUSION

The results suggest that the five classification methods yielded similar results. Polyphen was particularly better at isolating BRCA1 UV carriers likely to have a family history of breast cancer or ovarian cancer, and may therefore help to classify BRCA1 UVs. Our study suggests that these methods may not be as successful in classifying BRCA2 UVs.

The role of BRCA1 in transcriptional regulation and cell cycle control

The exact functions of BRCA1 have not been fully described but it now seems apparent that it has roles in DNA damage repair, transcriptional regulation, cell cycle control and most recently in ubiquitylation. These functions of BRCA1 are most likely interdependent but this review will focus on the role of BRCA1 in relation to transcriptional regulation and in particular how this impacts upon cell cycle control. We will (i) describe the structure of BRCA1 and how it may contribute to its transcription function; (ii) describe the interaction of BRCA1 with the core transcriptional machinery (RNA polII); (iii) describe how BRCA1 may regulate transcription at an epigenetic level through chromatin modification; (iv) discuss the role of BRCA1 in modulating transcription through its association with sequence-specific transcription factors. Finally, we will discuss the possible effects of BRCA1 transcriptional regulation on downstream targets with known roles in cell cycle control.

BRCA1 at the crossroad of multiple cellular pathways: approaches for therapeutic interventions

Approximately 10% of the cases of breast cancer and invasive ovarian cancer are hereditary, occurring predominantly in women with germ-line mutations in the BRCA1 or BRCA2 genes. Low expression of these genes in sporadic tumors extends their significance to sporadic breast and ovarian cancers as well. For over a decade since its identification, extensive research has been directed toward understanding the function of the breast and ovarian tumor suppressor gene BRCA1. The long-term goal has been to identify the biochemical pathways reliant on BRCA1 that can be exploited for developing targeted therapies and benefit mutation carriers. To date, no one specific role has been identified, but rather it is clear that BRCA1 has significant roles in multiple fundamental cellular processes, including control of gene expression, chromatin remodeling, DNA repair, cell cycle checkpoint control, and ubiquitination, and overall is important for maintenance of genomic stability. Major findings and potential BRCA1-dependent therapies will be discussed.

The roles of BRCA1 and BRCA2 and associated proteins in the maintenance of genomic stability

The BRCA1 and BRCA2 proteins are important in maintaining genomic stability by promoting efficient and precise repair of double-strand breaks. The main role of BRCA2 appears to involve regulating the function of RAD51 in the repair by homologous recombination. BRCA1 has a broader role upstream of BRCA2, participating in various cellular processes in response to DNA damage. The DNA repair defect associated with mutations in BRCA1 or BRCA2 could be exploited to develop new targeted therapeutic approaches for cancer occurring in mutation carriers.

A morphogenetic wave of p27Kip1 transcription directs cell cycle exit during organ of Corti development

The molecular mechanisms coordinating cell cycle exit with cell differentiation and organogenesis are a crucial, yet poorly understood, aspect of normal development. The mammalian cyclin-dependent kinase inhibitor p27(Kip1) is required for the correct timing of cell cycle exit in developing tissues, and thus plays a crucial role in this process. Although studies of p27(Kip1) regulation have revealed important posttranscriptional mechanisms regulating p27(Kip1) abundance, little is known about how developmental patterns of p27(Kip1) expression, and thus cell cycle exit, are achieved. Here, we show that during inner ear development transcriptional regulation of p27(Kip1) is the primary determinant of a wave of cell cycle exit that dictates the number of postmitotic progenitors destined to give rise to the hair cells and supporting cells of the organ of Corti. Interestingly, transcriptional induction from the p27(Kip1) gene occurs normally in p27(Kip1)-null mice, indicating that developmental regulation of p27(Kip1) transcription is independent of the timing of cell cycle exit. In addition, cell-type-specific patterns of p27(Kip1) transcriptional regulation are observed in the mature organ of Corti and retina, suggesting that this mechanism is important in differential regulation of the postmitotic state. This report establishes a link between the spatial and temporal pattern of p27(Kip1) transcription and the control of cell number during sensory organ morphogenesis.

The BRCA1 COOH-terminal region acts as an RNA polymerase II carboxyl-terminal domain kinase inhibitor that modulates p21WAF1/CIP1 expression

BRCA1 is involved both in positive and negative regulation of gene activity as well as in numerous other processes, such as DNA damage response and repair. We recently reported that BRCA1 inhibits RNA polymerase II carboxyl-terminal domain (CTD) phosphorylation by TFIIH and decreases serine 5 phosphorylation levels when introduced into a BRCA1(-/-) cell line. Regulation of CTD phosphorylation is crucial for proper gene expression and response to cellular stresses, such as DNA damage and transcription arrest. A key player in this process, P-TEFb, phosphorylates the CTD on serine 2 of transcriptionally engaged RNA polymerase II, and its kinase activity was shown to be up-regulated when cells are exposed to transcriptional stress such as UV irradiation. Here, we investigate the effect of BRCA1 on serine 2 phosphorylation and UV-activated P-TEFb kinase activity. We now show that BRCA1 inhibits immunoprecipitated P-TEFb kinase activity from UV-irradiated cells and preferentially decreases UV-induced serine 2 phosphorylation of soluble, rather than chromatin-bound, RNAPII. We further show that BRCA1 rescues the UV-mediated inhibition of transcriptional activity from nuclear extracts and stimulates endogenous p21 gene expression upon UV irradiation, a function that is dependent of the inhibition of CTD kinase activity. Our results suggest that BRCA1 could act as a CTD kinase inhibitor and, as such, contribute to the regulation of p21 gene expression.

BRCA1 and FOXA1 proteins coregulate the expression of the cell cycle-dependent kinase inhibitor p27(Kip1)

We have previously shown that the breast cancer susceptibility gene, BRCA1, can transcriptionally activate the p27(Kip1) promoter. The BRCA1-responsive element was defined as a 35 bp region from position -545 to -511. We next determined that within this region is also a potential binding site for the transcription factor Forkhead box (FOX)A1. RNA and protein analysis as well as immunohistochemistry showed that expression of FOXA1 correlated with the expression of the estrogen receptor in a panel of breast cancer cell lines and tissues. In transient transfection reporter assays, FOXA1 could activate the p27(Kip1) promoter. Cotransfection of BRCA1 and FOXA1 resulted in a synergistic activation of the p27(Kip1) promoter. Mutation of the FOXA1 DNA-binding site in the p27(Kip1) promoter-luciferase construct significantly diminished the activity of FOXA1 alone or in combination with BRCA1. Cotransfection of FOXA1 and BRCA1 resulted in a greater amount of each protein compared to transfection of each expression vector alone. The half-life of FOXA1 was increased when coexpressed with BRCA1. Electrophoretic mobility shift assay analysis demonstrated that FOXA1 could bind to a wild-type oligonucleotide containing the FOXA1 binding site in the p27(Kip1) promoter, but this binding was lost upon mutation of this FOXA1 binding site. The protein-DNA binding complex could be supershifted with an antibody directed against FOXA1. The activity of the p27(Kip1) promoter as well as FOXA1 expression was reduced in cells treated with BRCA1 siRNA, thus silencing the expression of BRCA1 protein. In summary, we identified a FOXA1 binding site within the BRCA1-responsive element of the p27(Kip1) promoter and showed that FOXA1 activated the promoter alone and in conjunction with BRCA1. Furthermore, we identified high expression of FOXA1 in breast cancer cell lines and tissues, discovered a role for BRCA1 in the regulation of p27(Kip1) transcription and a possible interaction with BRCA1.

Natural selection and mammalian BRCA1 sequences: elucidating functionally important sites relevant to breast cancer susceptibility in humans

Comparison of orthologous gene sequences is emerging as a powerful approach to elucidating functionally important positions in human disease genes. Using a diverse array of 132 mammalian BRCA1 (exon 11) sequences, we evaluated the functional significance of specific sites in the context of selection information (purifying, neutral, or diversifying) as well as the ability to extract such information from alignments that index varying degrees of mammalian diversity. Small data sets of either closely related taxa (Primates) or divergent placental taxa were unable to distinguish sites conserved due to purifying selection from sites conserved due to chance (false-positive rate = 65%-99%). Increasing the number of placental taxa to 57 greatly reduced the potential false-positive rate (0%-1.5%). Using the larger data set, we ranked the oncogenic risk of human missense mutations using a novel method that incorporates site-specific selection level and severity of the amino acid change evaluated against the amino acids present in other mammalian taxa. In addition to sites undergoing positive selection in Marsupialia, Laurasiatheria, Euarchontoglires, and Primates, we identified sites most likely to be undergoing divergent selection pressure in different lineages and six pairs of potentially interacting sites. Our results demonstrate the necessity of including large numbers of sequences to elucidate functionally important sites of a protein when using a comparative evolutionary approach.

Progesterone inhibits human breast cancer cell growth through transcriptional upregulation of the cyclin-dependent kinase inhibitor p27Kip1 gene

The effects of progesterone derivatives on breast cancer development are still controversial, probably accounting for their biphasic, opposed effects on mammary cell-cycle regulation. Here, we demonstrate in vitro that the growth-inhibitory effects of progesterone on breast cancer T-47D cells require the transcriptional upregulation of the cyclin-dependent kinase inhibitor p27(Kip1) (p27) gene. A statistical analysis of human tumor biopsies further indicates that p27 mRNA levels correlate to progesterone receptor (PR) levels. Moreover, p27 gene expression is inversely associated with tumor aggressiveness, and is a prognostic factor of favorable disease outcome. Thus, progesterone derivatives selectively activating the p27 gene promoter could be promising drugs against breast cancer progression.

The MLL fusion gene, MLL-AF4, regulates cyclin-dependent kinase inhibitor CDKN1B (p27kip1) expression

MLL, involved in many chromosomal translocations associated with acute myeloid and lymphoid leukemia, has >50 known partner genes with which it is able to form in-frame fusions. Characterizing important downstream target genes of MLL and of MLL fusion proteins may provide rational therapeutic strategies for the treatment of MLL-associated leukemia. We explored downstream target genes of the most prevalent MLL fusion protein, MLL-AF4. To this end, we developed inducible MLL-AF4 fusion cell lines in different backgrounds. Overexpression of MLL-AF4 does not lead to increased proliferation in either cell line, but rather, cell growth was slowed compared with similar cell lines inducibly expressing truncated MLL. We found that in the MLL-AF4-induced cell lines, the expression of the cyclin-dependent kinase inhibitor gene CDKN1B was dramatically changed at both the RNA and protein (p27kip1) levels. In contrast, the expression levels of CDKN1A (p21) and CDKN2A (p16) were unchanged. To explore whether CDKN1B might be a direct target of MLL and of MLL-AF4, we used chromatin immunoprecipitation (ChIP) assays and luciferase reporter gene assays. MLL-AF4 binds to the CDKN1B promoter in vivo and regulates CDKN1B promoter activity. Further, we confirmed CDKN1B promoter binding by ChIP in MLL-AF4 as well as in MLL-AF9 leukemia cell lines. Our results suggest that CDKN1B is a downstream target of MLL and of MLL-AF4, and that, depending on the background cell type, MLL-AF4 inhibits or activates CDKN1B expression. This finding may have implications in terms of leukemia stem cell resistance to chemotherapy in MLL-AF4 leukemias.

BRCA1 regulation of transcription

BRCA1, a tumor suppressor gene on chromosome 17q21, was identified in 1994 based on its linkage to hereditary breast and ovarian cancer syndromes. The BRCA1 gene encodes a 220 kDa nuclear phosphoprotein. Studies aimed at elucidating the mechanisms of its tumor suppressor activity have revealed, in part, that BRCA1 participates in the DNA damage response and acts to maintain the integrity of the genome. This activity is generic and does not account for the propensity of BRCA1 mutation carriers to develop specific tumor types rather than a broad spectrum of cancers. In addition to genome maintenance, BRCA1 has been found to broadly regulate gene transcription, even though it is not itself a sequence-specific DNA-binding transcription factor. The ability of BRCA1 to function as a coregulator of transcription may underlie some of its tumor suppressor activity and may explain the tissue-specific nature of this activity. This review will focus on how BRCA1 selectively regulates transcription and how this regulatory function may relate to tumor suppression.

The role of BRCA1 in the cellular response to chemotherapy

Germline mutations of the BRCA1 gene account for approximately 5% of breast and ovarian cancer cases, and lower than normal BRCA1 expression or function may be an important contributing factor in sporadic cancers. The major role of BRCA1 is to respond to DNA damage by participating in cellular pathways for DNA repair, mRNA transcription, cell cycle regulation, and protein ubiquitination. Because most chemotherapeutic agents function by directly or indirectly damaging DNA, the role of BRCA1 as a regulator of chemotherapy-induced DNA damage has been the subject of an increasing number of investigations. We review published preclinical and clinical evidence that the level of BRCA1 function in an individual patient's tumor can guide the choice of chemotherapeutic agents for breast and ovarian cancer. We conclude that a loss of BRCA1 function is associated with sensitivity to DNA-damaging chemotherapy and may also be associated with resistance to spindle poisons. We recommend that prospective clinical studies investigating the role of BRCA1 in the response to chemotherapy be conducted.

Role of BRCA1 and BRCA2 as regulators of DNA repair, transcription, and cell cycle in response to DNA damage

BRCA1 (BReast-CAncer susceptibility gene 1) and BRCA2 are tumor suppressor genes, the mutant phenotypes of which predispose to breast and ovarian cancers. Intensive research has shown that BRCA proteins are involved in a multitude of pivotal cellular processes. In particular, both genes contribute to DNA repair and transcriptional regulation in response to DNA damage. Recent studies suggest that BRCA proteins are required for maintenance of chromosomal stability, thereby protecting the genome from damage. New data also show that BRCAs transcriptionally regulate some genes involved in DNA repair, the cell cycle, and apoptosis. Many of these functions are mediated by a large number of cellular proteins that interact with BRCAs. The functions of BRCA proteins are also linked to distinct and specific phosphorylation events; however, the extent to which phosphorylation-activated molecular pathways contribute to tumor suppressor activity remains unclear. Finally, the reasons why mutations in BRCA genes lead to the development of breast and ovarian cancers are not clearly understood. Elucidation of the precise molecular functions of BRCAs is expected to improve our understanding of hereditary as well as sporadic mammary carcinogenesis.

Gene expression profiling after radiation-induced DNA damage is strongly predictive of BRCA1 mutation carrier status

PURPOSE

The impact of the presence of a germ-line BRCA1 mutation on gene expression in normal breast fibroblasts after radiation-induced DNA damage has been investigated.

EXPERIMENTAL DESIGN

High-density cDNA microarray technology was used to identify differential responses to DNA damage in fibroblasts from nine heterozygous BRCA1 mutation carriers compared with five control samples without personal or family history of any cancer. Fibroblast cultures were irradiated, and their expression profile was compared using intensity ratios of the cDNA microarrays representing 5603 IMAGE clones.

RESULTS

Class comparison and class prediction analysis has shown that BRCA1 mutation carriers can be distinguished from controls with high probability (approximately 85%). Significance analysis of microarrays and the support vector machine classifier identified gene sets that discriminate the samples according to their mutation status. These include genes already known to interact with BRCA1 such as CDKN1B, ATR, and RAD51.

CONCLUSIONS

The results of this initial study suggest that normal cells from heterozygous BRCA1 mutation carriers display a different gene expression profile from controls in response to DNA damage. Adaptations of this pilot result to other cell types could result in the development of a functional assay for BRCA1 mutation status.

BRCA1 can modulate RNA polymerase II carboxy-terminal domain phosphorylation levels

A high incidence of breast and ovarian cancers has been linked to mutations in the BRCA1 gene. BRCA1 has been shown to be involved in both positive and negative regulation of gene activity as well as in numerous other processes such as DNA repair and cell cycle regulation. Since modulation of the RNA polymerase II carboxy-terminal domain (CTD) phosphorylation levels could constitute an interface to all these functions, we wanted to directly test the possibility that BRCA1 might regulate the phosphorylation state of the CTD. We have shown that the BRCA1 C-terminal region can negatively modulate phosphorylation levels of the RNA polymerase II CTD by the Cdk-activating kinase (CAK) in vitro. Interestingly, the BRCA1 C-terminal region can directly interact with CAK and inhibit CAK activity by competing with ATP. Finally, we demonstrated that full-length BRCA1 can inhibit CTD phosphorylation when introduced in the BRCA1(-/-) HCC1937 cell line. Our results suggest that BRCA1 could play its ascribed roles, at least in part, by modulating CTD kinase components.

FLT3 receptors with internal tandem duplications promote cell viability and proliferation by signaling through Foxo proteins

In about 30% of the patients with acute myeloid leukemia, activating FLT3 receptor mutations have been identified, often as in-frame internal tandem duplications (ITD) at the juxtamembrane domain of the receptor. FLT3-ITD receptors exhibit constitutive tyrosine kinase activity in the absence of FLT3 ligand (FL) binding, and when expressed in cytokine-dependent cell lines and primary hematopoietic cells suppress programmed cell death and increase cell division. However, the signaling pathways important for transformation, in particular the nuclear targets, are unknown. Here we demonstrate that FLT3-ITD expression in Ba/F3 cells results in activation of Akt and concomitant phosphorylation of the Forkhead family member Foxo3a. Phosphorylation of Foxo proteins through FLT3-ITD signaling promotes their translocation from the nucleus into the cytoplasm, which requires the presence of conserved Akt phosphorylation sites in Forkhead transcription factors and PI3K activity. Induction of Foxo3a phosphorylation by FLT3-ITD receptors in Ba/F3 cells correlates with the suppression of Foxo-target genes p27Kip1 and the proapoptotic Bcl-2 family member Bim. Specifically, FLT3-ITD expression prevents Foxo3a-mediated apoptosis and upregulation of p27Kip1 and Bim gene expression. These data indicate that the oncogenic tyrosine kinase FLT3 can negatively regulate Foxo transcription factors, thereby promoting cell survival and proliferation.

Primary fibroblasts from BRCA1 heterozygotes display an abnormal G1/S cell cycle checkpoint following UVA irradiation but show normal levels of micronuclei following oxidative stress or mitomycin C treatment

PURPOSE

There is evidence to suggest that the breast cancer predisposing gene, BRCA1, is involved in cell cycle control and the response to damage but mouse brca1+/- heterozygotes have no distinctive phenotype. Here the response to the three forms of cellular stress was examined in primary human fibroblasts from individuals with a +/+ or +/- genotype for BRCA1.

METHODS AND MATERIALS

Fibroblasts from individuals carrying mutations in the BRCA1 gene were compared with those from those wild-type for BRCA1 in their response to long wavelength uv (UVA), hydrogen peroxide, and mitomycin C (MMC). Cell cycle progression and micronucleus formation (MN) were used as end points.

RESULTS

After UVA treatment there was no difference between +/- and +/+ cells in the initial fall in DNA synthetic activity (G(1) arrest) but the reentry into S-phase was restored at a faster rate in the BRCA1+/- cells after UVA exposure. Thus, for three normal (+/+) cell lines irradiated in monolayer, S-phase values averaged 15 +/- 3.7% 14 h post-UVA (1 x 10(5) J/m(2)), as compared with 35.7 +/- 1.9 (range) for two BRCA1(+/-) strains. Because a defective G(1)/S checkpoint in BRCA1 heterozygotes could lead to a greater proportion of S-phase cells with unrepaired DNA damage (strand breaks) and a resultant increase in chromosomal instability, the frequency of micronuclei induced by UVA was examined. Three normal (+/+) and three mutant (+/-) strains (two of which were used in the cell cycle experiments) produced mean micronuclei frequencies of 0.077 +/- 0.016 and 0.094 +/- 0.04/binucleate cell respectively (not statistically significant), 48 h after UVA exposure. No differences were found between BRCA1+/+ and +/- cells in MN formation after treatment with MMC or hydrogen peroxide.

CONCLUSION

Our data suggest a defective G(1)/S checkpoint in cells from BRCA1 heterozygotes in response to UVA although this is not reflected in genomic instability as measured by micronuclei induction after oxidative stress or MMC treatment.

Role of the CDK inhibitor p27 (Kip1) in mammary development and carcinogenesis: insights from knockout mice

The cyclin-dependent kinase inhibitor p27 (Kip1) is an important cell cycle regulatory gene in breast cancer, and decreased p27 expression is associated with poor prognosis. Some investigations of its role in mammary development have demonstrated reduced cyclin D1 expression and consequent lack of lobuloalveolar development, but others have found increased cyclin E-Cdk2 activity and increased proliferation balanced by increased apoptosis. It is unclear at present why these apparently divergent results have been obtained. Mice with reduced p27 gene dosage alone do not develop mammary carcinomas but do display substantially shorter tumor latency upon overexpression of erbB2, consistent with a role for p27 as a mammary tumor suppressor gene. In this review we summarize these and other data addressing the role of p27 in normal mammary epithelium and experimental models of mammary carcinogenesis.

BRCA1 Associates with Processive RNA Polymerase II

The human BRCA1 tumor suppressor interacts with transcriptional machinery, including RNA polymerase II (RNA pol II). We demonstrated that interaction with RNA pol II is a conserved feature of BRCA1 proteins from several species. We found that full-length BRCA1 proteins universally fail to activate transcription in classic GAL4-UAS one-hybrid assays and that the activity associated with the human BRCA1 C terminus was poorly conserved in closely related homologs of the gene. Fractionation studies demonstrated that BRCA1 proteins from all species tested interacted specifically with hyperphosphorylated pol II (IIO), in preference to hypophosphorylated RNA pol II (IIA) expected at promoters. BRCA1-RNA pol II complexes showed evidence of a multiply phosphorylated heptad repeat domain in the catalytic subunit (p220) of RNA pol II, and the complex was highly functional in transcriptional run-off assays. Interestingly, endogenous BRCA1 associated with a large fraction of the processive RNA pol II activity present in undamaged cells, and the interaction was disrupted by DNA-damaging agents. Preferential interaction with processive RNA pol II in undamaged cells places BRCA1 in position to link late events in transcription with repair processes in eukaryotic cells.

Novel consensus DNA-binding sequence for BRCA1 protein complexes

Increasing evidence continues to emerge supporting the early hypothesis that BRCA1 might be involved in transcriptional processes. BRCA1 physically associates with more than 15 different proteins involved in transcription and is paradoxically involved in both transcriptional activation and repression. However, the underlying mechanism by which BRCA1 affects the gene expression of various genes remains speculative. In this study, we provide evidence that BRCA1 protein complexes interact with specific DNA sequences. We provide data showing that the upstream stimulatory factor 2 (USF2) physically associates with BRCA1 and is a component of this DNA-binding complex. Interestingly, these DNA-binding complexes are downregulated in breast cancer cell lines containing wild-type BRCA1, providing a critical link between modulations of BRCA1 function in sporadic breast cancers that do not involve germline BRCA1 mutations. The functional specificity of BRCA1 tumor suppression for breast and ovarian tissues is supported by our experiments, which demonstrate that BRCA1 DNA-binding complexes are modulated by serum and estrogen. Finally, functional analysis indicates that missense mutations in BRCA1 that lead to subsequent cancer susceptibility may result in improper gene activation. In summary, these findings establish a role for endogenous BRCA1 protein complexes in transcription via a defined DNA-binding sequence and indicate that one function of BRCA1 is to co-regulate the expression of genes involved in various cellular processes.

BRCA1 in hormone-responsive cancers

Mutations of the breast cancer susceptibility gene BRCA1 are linked to hereditary early onset breast and breast-ovarian cancer syndromes. These mutations confer an increased risk for other hormone-dependent cancers, including those of the uterus, cervix and prostate. BRCA1 expression is decreased or absent in a significant proportion of sporadic breast and ovarian cancers, suggesting a wider role in these tumor types. Multiple functions for BRCA1 have been identified, including roles in DNA repair, cell-cycle progression and apoptosis. These functions are consistent with a tumor suppressor activity, but they do not explain why BRCA1 mutation carriers develop hormone-responsive cancer types. Recent studies indicate that BRCA1 interacts with and regulates the activity of estrogen receptor alpha (ER alpha) and the androgen receptor. Its expression is regulated by carcinogens and anticarcinogens that modulate ER alpha signaling, suggesting a molecular linkage between BRCA1 and hormone-responsive cancers.

Bovine BRCA1 shows classic responses to genotoxic stress but low in vitro transcriptional activation activity

Human BRCA1 has a genetically demonstrated role in DNA repair, and has been proposed to act as a transcriptional activator in a limited number of specialized settings. To gain insight into biologically conserved functional motifs, we isolated an ortholog of BRCA1 from cattle (Bos taurus). The predicted protein product shows 72.5% sequence identity with the human protein and conservation of amino acids involved in BRCA1 structure and function. Although the bovine C-terminus is truncated by seven amino acids as compared to human, bovine BRCA1 protein exhibited a similar cell cycle-regulated nuclear expression pattern. Expression was characteristically low and diffuse in the nucleus of G1/G0 cells, followed by increasing BRCA1-positive nuclear speckles in late S phase and G2/M phase cells. Bovine BRCA1 was phosphorylated and nuclear speckling was enhanced in response to DNA-damaging agents. Consistent with evidence from studies of human BRCA1, bovine BRCA1 was shown to interact with RNA polymerase II in vivo, an activity that was mapped to the C-terminal domain (CTD) (bBRCA(1364-1849)). Interestingly, when tested in the GAL4 transcriptional activation assay, full-length bovine and human BRCA1 lacked any ability to act as transcriptional activators and the CTD of bovine BRCA1 had five-fold lower activity when compared to the more acidic human C-terminus. These results provide evidence that phosphorylation and nuclear relocalization are highly conserved features of the BRCA1 response to genotoxic stress. In addition, bovine BRCA1 binds the RNA polymerase II holoenzyme, but this interaction lacks significant ability to correctly orient or recruit RNA polymerase II for transcription in the classic GAL4 transcriptional activation system.

BRCA1 augments transcription by the NF-kappaB transcription factor by binding to the Rel domain of the p65/RelA subunit

BRCA1 is a tumor suppressor gene mutated in cases of hereditary breast and ovarian cancer. BRCA1 protein is involved in apoptosis and growth/tumor suppression. In this study, we present evidence that p65/RelA, one of the two subunits of the transcription factor NF-kappaB, binds to the BRCA1 protein. Treatment of 293T cells with the cytokine tumor necrosis factor-alpha induces an interaction between endogenous p65/RelA and BRCA1. GST-protein affinity assay experiments reveal that the Rel homology domain of the p65/RelA subunit of NF-kappaB interacts with multiple sites within the N-terminal region of BRCA1. Transient transfection of BRCA1 significantly enhances the ability of the tumor necrosis factor-alpha or interleukin-1beta to activate transcription from the promoters of NF-kappaB target genes. Mutation of the NF-kappaB-binding sites in the NF-kappaB reporter blocks the effect of BRCA1 on transcription. Also the ability of BRCA1 to activate NF-kappaB target genes is inhibited by a super-stable inhibitor of NF-kappaB and by the chemical inhibitor SN-50. These data indicate that BRCA1 acts as a co-activator with NF-kappaB. In addition, we show that cells infected with an adenovirus expressing BRCA1 up-regulate the endogenous expression of NF-kappaB target genes Fas and interferon-beta. Together, this information suggests that BRCA1 may play a role in cell life-death decisions following cell stress by modulation of the activity of NF-kappaB.

BRCA1 gene in breast cancer

The BRCA1 gene was identified and cloned in 1994 based its linkage to early onset breast cancer and breast-ovarian cancer syndromes in women. While inherited mutations of BRCA1 are responsible for about 40-45% of hereditary breast cancers, these mutations account for only 2-3% of all breast cancers, since the BRCA1 gene is rarely mutated in sporadic breast cancers. However, BRCA1 expression is frequently reduced or absent in sporadic cancers, suggesting a much wider role in mammary carcinogenesis. Since BRCA1 was cloned in 1994, its molecular function has been the subject of intense investigation. These studies have revealed multiple functions of the BRCA1 that may contribute to its tumor suppressor activity, including roles in: cell cycle progression, several highly specialized DNA repair processes, DNA damage-responsive cell cycle check-points, regulation of a set of specific transcriptional pathways, and apoptosis. Many of these functions are linked to protein:protein interactions involving different portions of the 1,863 amino acid (aa) BRCA1 protein. BRCA1 functions in cell cycle progression and the DNA damage response appear to be regulated by distinct and specific phosphorylation events, but the molecular pathways activated by these phosphorylations are only beginning to be unraveled. In addition, the reason that BRCA1 mutation carriers develop specific tumor types (breast and ovarian cancers in women and possibly prostate cancers in men) is not clearly understood. Elucidation of the precise molecular functions of the BRCA1 gene product will greatly enhance our understanding of the pathogenesis of hereditary as well as sporadic mammary carcinogenesis.

Breast cancer gene 1 (BRCA1): role in cell cycle regulation and DNA repair--perhaps through transcription

Mutations of BRCA1 gene are associated with more than half the cases of hereditary breast cancer. Breast cancer formation in BRCA1 mutation carriers is generally accompanied by loss of the wild-type allele, suggesting that BRCA1 protein may function as a tumor suppressor. The human BRCA1 gene encodes a nuclear protein of 1863 amino acids. Although several lines of evidences suggest that BRCA1 protein may have a role to play in cell cycle regulation, DNA repair, and other processes, the exact mechanism of functioning by BRCA1 protein is not clear. Recent evidences from several laboratories suggest that BRCA1 may regulate the expression of many genes like p21(WAF1/CIP1), Gadd45, Cyclin B1, DBB2, XPC, 14-3-3ó and others at the level of transcription. These BRCA1-regulated gene products have been implicated directly or indirectly in cell cycle regulation and DNA repair. Thus a plausible model is proposed in which BRCA1 protein may bring its effects on cell cycle and DNA repair through its ability to modulate gene expression at the level of transcription.

The prognostic impact of hormone receptors and c-erbB-2 in pregnancy-associated breast cancer and their correlation with BRCA1 and cell cycle modulators

A population-based series of 122 patients with pregnancy-associated breast carcinomas was histologically revised and the relationship between hormone receptors, c-erbB-2, BRCA1, p27, cyclin E, and cyclin D1 was studied. The 5-year overall survival was 41%; 70% had tumor size >20 mm; 72% had metastasized to regional lymph nodes; 95% were histologic grade II or III; 66% and 75% were negative for estrogen and progesterone receptor, respectively; and c-erbB-2 expression was high (44%). BRCA1 expression was reduced in 33% of the cases. The expression of p27, cyclin D1, and cyclin E was low, 11%, 9%, and 16%, respectively. Cyclin D1 was positively associated with the hormone receptors (p< or =0.01). In multivariate analysis, lymph node status, progesterone receptor, and c-erbB-2 were significant prognostic factors. In subdividing the group according to lymph node status, c-erbB-2 and progesterone receptor retained a prognostic significance in the node positive group only. In conclusion, pregnancy-associated breast carcinomas are aggressive tumors, with low expression of hormone receptors, BRCA1, p27, and cyclin E and D1, and high expression of c-erbB-2.