Caroline Holm

Oestrogen receptors alpha and beta show different associations to clinicopathological parameters and their co-expression might predict a better response to endocrine treatment in breast cancer.

Aims: The majority of all breast cancers are hormone responsive, traditionally defined by the expression of oestrogen receptor (ER) α and/or progesterone receptors. In contrast to ERα, the clinical significance of the relatively recently identified ERβ is still unclear. This study aimed to define the relationship between ERβ and clinicopathological parameters in a mixed cohort of breast cancer and, furthermore, to investigate the impact of ERβ expression on disease outcome. Methods: The immunohistochemical expression of ERα and ERβ was analysed in tissue microarrays containing a total number of 512 tumours with all incident breast cancers diagnosed at the Malmö University Hospital between 1988 and 1992. Results: 78% of the tumours were ERα positive and 50% were ERβ positive. ERβ correlated positively with ERα (p = 0.001). In contrast to ERα, ERβ was not associated with any important clinicopathological variables. Furthermore, no overall prognostic significance could be demonstrated for ERβ. In the ERα-positive subgroup, however, a low expression of ERβ correlated with a decreased disease-free survival in patients receiving endocrine treatment (p = 0.003). Conclusions: Although interrelated, ERα and ERβ seem to be differentially associated to clinicopathological parameters, and this would support the fact that they might have different functions in vivo. Furthermore, ERβ might be a predictive marker of response to endocrine therapy, although this needs to be confirmed in additional studies, preferably randomised trials.

Phosphorylation of the oestrogen receptor alpha at serine 305 and prediction of tamoxifen resistance in breast cancer.

Phosphorylation of oestrogen receptor α at serine 305 (ERαS305‐P) induces tamoxifen resistance in experimental studies, but does not influence response to other endocrine agents, such as fulvestrant. We evaluated ERαS305‐P using immunohistochemistry in 377 breast carcinomas from premenopausal participants of a randomized trial (n = 248) and patients with advanced disease (n = 129). Among the premenopausal patients, adjuvant tamoxifen improved recurrence‐free survival (RFS) for ERαS305‐P‐negative tumours (multivariate HR = 0.53, 95% CI 0.32–0.86, p = 0.010), but not for ERαS305‐P‐positive tumours (multivariate HR = 1.01, 95% CI 0.33–3.05, p = 0.99) (interaction p = 0.131). Notably, ERαS305‐P was not significantly associated with RFS in patients not treated with tamoxifen (multivariate HR = 0.64, 95% CI 0.30–1.37, p = 0.248), indicating that ERαS305‐P is a marker for treatment outcome rather than tumour progression. Given the direct experimental link between ERαS305‐P and tamoxifen resistance and these first clinical data suggesting that premenopausal patients with ERαS305‐P‐positive breast cancer are resistant to adjuvant tamoxifen, further research is encouraged to study whether alternative endocrine treatment should be considered for this subgroup. Copyright

Breast cancer-amplified sequence 3, a target of metastasis-associated protein 1, contributes to tamoxifen resistance in premenopausal patients with breast cancer.

Lysine acetylation occurs in many protein targets, including core histones, transcription factors, and other proteins. Metastasis-associated protein 1 (MTA1) is implicated in the progression and metastasis of various epithelial tumors. Because MTA1 functions as a transcriptional coregulator, much of its role in cancer promoting processes are likely to involve its ability to regulate the transcription of downstream target genes that encode effector proteins. We recently showed that MTA1 could be posttranslationally modified by acetylation, which modulates its function as a coregulator molecule. We also defined a chromatin target of MTA1, namely, breast cancer–amplified sequence 3 (BCAS3), in the context of which MTA1 behaves as a transcriptional coactivator in breast cancer cells. Because the phenotypic effect of BCAS3 overexpression in tumors has not been defined, we investigated the consequence of increased expression of BCAS3 in human breast tumors. Here, we report that BCAS3 overexpression in hormone receptor–positive premenopausal breast cancer seemed to be associated with impaired responses to tamoxifen.. Our findings have implications for endocrine therapy.

Extranuclear Coactivator Signaling Confers Insensitivity to Tamoxifen

Purpose: Tamoxifen is one of many standard therapeutic options currently available for estrogen receptor-α–positive breast cancer patients. Emerging data have suggested that levels of estrogen receptor coregulatory proteins play a significant role in acquiring resistance to antiestrogen action. It has been suggested that high levels of estrogen receptor coactivators and its mislocalization may enhance the estrogen agonist activity of tamoxifen and contribute to tamoxifen resistance. Experimental Design: In an effort to understand the impact of nongenomic signaling and its contribution to hormone resistance in a whole-animal setting, we generated a transgenic mouse expressing a cytoplasmic version of proline-, glutamic acid–, and leucine-rich protein–1 (PELP1) mutant defective in its nuclear translocation (PELP1-cyto) and implanted these mice with tamoxifen pellets to assess its responsiveness. Results: We show that mammary glands from these mice developed widespread hyperplasia with increased cell proliferation and enhanced activation of mitogen-activated protein kinase and AKT as early as 12 weeks of age. Treatment with tamoxifen did not inhibit this hyperplasia; instead, such treatment exaggerated hyperplasia with an enhanced degree of alteration, indicative of hypersensitivity to tamoxifen. Analysis of molecular markers in the transgenic mammary glands from the tamoxifen-treated transgenic mice showed higher levels of proliferation markers proliferating cell nuclear antigen and activated mitogen-activated protein kinase than in untreated PELP1-cyto cell-derived mice. We also found that nude mice with MCF-7/PELP1-cyto cell-derived tumor xenografts did not respond to tamoxifen. Using immunohistochemical analysis, we found that 43% of human breast tumor samples had high levels of cytoplasmic PELP1, which shows a positive correlation between tumor grade and proliferation. Patients whose tumors had high levels of cytoplasmic PELP1 exhibited a tendency to respond poorly to tamoxifen compared with patients whose tumors had low levels of cytoplasmic PELP1. Conclusions: These findings suggest that PELP1 localization could be used as a determinant of hormone sensitivity or vulnerability. The establishment of the PELP1-cyto transgenic mouse model is expected to facilitate the development of preclinical approaches for effective intervention of breast tumors using cytoplasmic coregulators and active nongenomic signaling.

Expression of cyclin A1 and cell cycle proteins in hematopoietic cells and acute myeloid leukemia and links to patient outcome.

Abstract:  Abnormal expression of several key regulators essential for G1/S transitions has been implicated in tumorigenesis. A critical role of cyclin A1 in the development of acute myeloid leukemia (AML) has previously been demonstrated in transgenic mice. Our present study focused on the expression and prognostic significance of cyclin A1 and a panel of cell cycle regulatory proteins including cyclin A2, cyclin B1, cyclin E, CDK1, CDK2, p21 and p27 in bone marrow samples from 40 patients with AML. Freshly isolated CD34+ hematopoietic cells and bone marrow samples from 10 healthy donors were also assessed for cell type‐ and subcellular‐specific expression of the cell cycle regulatory proteins. The level of cyclin A1 expression was the only factor that showed a significant correlation with patient outcome. In log‐rank test stratified by levels of cyclin A1 expression, patients with high levels of cyclin A1 had significantly worse overall survival (OS) (P = 0.012) compared to those with low levels. Further, patients with high levels of cyclin A1 had significantly lower disease‐free survival (DFS) (P = 0.028). Multivariate analysis indicated that cyclin A1 protein expression was an independent prognostic factor for predicting DFS (P = 0.035) and OS (P = 0.045). No correlation between cyclin A1 expression and age was found. However, expression of cyclin A2, cyclin B1, cyclin E, CDK1, CDK2, p21 and p27 did not show prognostic significance in these AML patients.

Regulation of the cyclin A1 protein is associated with its differential subcellular localization in hematopoietic and leukemic cells

An important role of the cell cycle regulatory protein cyclin A1 in the development of acute myeloid leukemia (AML) was previously demonstrated in a transgenic mouse model. We have now turned our attention to study specific aspects of the activity and subcellular distribution of cyclin A1 using bone marrow samples from normal donors and patients with AML, as well as leukemic cell lines. We show that the localization of cyclin A1 in normal hematopoietic cells is nuclear, whereas in leukemic cells from AML patients and cell lines, it is predominantly cytoplasmic. In leukemic cell lines treated with all-trans retinoic acid (ATRA), cyclin A1 localized to the nucleus. Further, there was a direct interaction between cyclin A1 and cyclin-dependent kinase 1, as well as a major ATRA receptor, RARα, in ATRA-treated cells but not in untreated leukemic cells. Our results indicate that the altered intracellular distribution of cyclin A1 in leukemic cells correlates with the status of the leukemic phenotype.