Steffi Oesterreich

Hsp27 overexpression inhibits doxorubicin–induced apoptosis in human breast cancer cells

Previously we demonstrated that heat shock protein 27 (hsp27) overexpression confers resistance to the chemotherapeutic agent doxorubicin in MDA–MB–231 breast cancer cells. Since induction of apoptosis is one underlying mechanism of chemotherapeutic drug action, we investigated the effect of hsp27 overexpression on doxorubicin–induced apoptosis, finding that hsp27 protects MDA–MB–231 cells from apoptosis. We also examined expression of the doxorubicin target, topoisomerase II (topo II), in control and hsp27–overexpressing stable transfectants, as topo II expression is important for both drug sensitivity and the initiation of apoptosis by doxorubicin. The relative levels of both topo IIα and β were higher in the controls than the hsp27–overexpressing clones, suggesting that the apoptotic protective effect of hsp27 overexpression in MDA–MB–231 cells is associated with altered topo II expression.abstract

Heat shock proteins and drug resistance

SummaryHeat shock proteins (hsps) are induced in cells when exposed to different environmental stressful conditions. We have found that breast cancer cells sometimes express high levels of several hsps, which may both augment the aggressiveness of these tumors and make them more resistant to treatment. We have shown that hsp70 is an ominous prognostic sign as detected by Western blot assays in node-negative breast tumors, and that hsp27 increases specific resistance to doxorubicin in breast cancer cell lines. These findings have direct clinical application, and suggest that modulating hsp expression may be a therapeutic target for reversal of hsp-associated detrimental cellular effects.

Novel nuclear matrix protein HET binds to and influences activity of the HSP27 promoter in human breast cancer cells

Since the small heat shock protein hsp27 enhances both growth and drug resistance in breast cancer cells, and is a bad prognostic factor in certain subsets of breast cancer patients, we have characterized the transcriptional regulation of hsp27, with the long‐term goal of targeting its expression clinically. The majority of the promoter activity resides in the most proximal 200 bp. This region contains an imperfect estrogen response element (ERE) that is separated by a 13‐bp spacer that contains a TATA box. Gel‐shift analysis revealed the binding of a protein (termed HET for Hsp27‐ERE‐TATA‐binding protein) to this region that was neither the estrogen receptor nor TATA‐binding protein. We cloned a complete cDNA (2.9 kb) for HET from an MCF‐7 cDNA library. To confirm the identity of the HET clone, we expressed a partial HET clone as a glutathione S‐transferase fusion protein, and showed binding to the hsp27 promoter fragment in gel‐retardation assays. The HET clone is almost identical to a recently published scaffold attachment factor (SAF‐B) cloned from a HeLa cell cDNA library. Scaffold attachment factors are a subset of nuclear matrix proteins (NMP) that interact with matrix attachment regions. Analyzing how HET could act as a regulator of hsp27 transcription and as a SAF/NMP, we studied its subnuclear localization and its effect on hsp27 transcription in human breast cancer cells. We were able to show that HET is localized in the nuclear matrix in various breast cancer cell lines. Furthermore, in transient transfection assays using hsp27 promoter‐luciferase reporter constructs, HET overexpression resulted in a dose‐dependent decrease of hsp27 promoter activity in several cell lines. J. Cell. Biochem. 67:275–286, 1997.

Constitutive overexpression of the 27,000 dalton heat shock protein in late passage human breast cancer cells

We present evidence that the mechanisms controlling induction of heat shock transcription factors (HSFs) and mRNA expression of the 27,000 molecular weight heat shock protein, hsp27, are diverse in human breast cancer cells. Heat shock accumulation of hsp27 RNA is associated with the activation of HSF in MDA-MB-231 cells. We have later passage MCF-7 breast cancer cell lines with elevated, constitutive expression of hsp27 mRNA, perhaps due to hsp 27 gene amplification. Estradiol and heat shock treatment no longer affect the level of hsp27 mRNA in these cells. Heat induction of HSF is inhibited in cells overexpressing hsp27, although metal ions and amino acid analogs are still capable of activating HSF. These cells will provide a useful system for characterizing alternative pathways in HSF inhibition and activation.

Glutathione transferase GSTπ in breast tumors evaluated by three techniques

The glutathione transferases are involved in intracellular detoxification reactions. One of these, GST pi, is elevated in some breast cancer cells, particularly cells selected for resistance to anticancer agents. We evaluated GST pi expression in 60 human breast tumors by three techniques, immunohistochemistry. Northern hybridization, and Western blot analysis. There was a significant positive correlation between the three methods, with complete concordance seen in 64% of the tumors. There was strong, inverse relationship between GST pi expression and steroid receptor status with all of the techniques utilized. In addition, there was a trend toward higher GST pi expression in poorly differentiated tumors, but no correlation was found between tumor GST pi content and DNA ploidy or %S-phase. GST pi expression was also detected in adjacent benign breast tissue as well as infiltrating lymphocytes; this expression may contribute to GST pi measurements using either Northern hybridization or Western blot analysis. These results suggest that immunohistochemistry is the method of choice for measuring GST pi in breast tumors.

Induction of heat shock protein 27 by hydroxyurea and its relationship to experimental metastasis.

Treatment of tumor cells with hydroxyurea (HU) has been shown to increase the experimental metastatic potential of these cells. We have previously described the induction of stress proteins (antioxidants) by in B16 murine melanoma cells and their relationship to the metastatic process. We have now investigated the induction by HU of another set of stress proteins, the heat shock proteins, and their role in experi-mental metastasis. HU markedly increased the cellular content of heat shock protein (hsp) 27 but not hsp 90, 72/73, or 60 as measured by immunoblotting. The induction of hsp27 protein was preceded specific increase in hsp27 mRNA. Furthermore, HU-treated cells were more thermotolerant. To investigate the functional role of hsp27, human hsp27 cDNA was constitutively overexpressed in B16 cells at seen in HU-treated cells. In separate experiments, we induced a global increase in hsps by heat shock. Neither the hsp27 transfectants nor the heat-shocked cells demonstrated an increase in their experimental metastatic capacity. We conclude that hsp27 protein is increased by HU by the specific induction of hsp27 mRNA in B16 melanoma cells but increased hsp27 protein is not responsible for the increase in experimental metastasis. Since high levels of hsp27 are associated with metastatic disease in breast and ovarian cancers, but not in our experimental system, the functional role of hsp27 in metastasis requires further study.

Low Cell Motility Induced by hsp27 Overexpression Decreases Osteolytic Bone Metastases of Human Breast Cancer Cells In Vivo

The mechanisms controlling the formation of osteolytic bone metastases in patients with breast cancer are still poorly understood. To explore the role of motility in the establishment of osteolytic bone metastases, we have used a model of bone metastasis in which MDA‐MB‐231 breast cancer cells exhibiting low (hsp27‐transfectants) and high (control‐transfectant) endogenous cell motility were compared. We found that MDA‐MB‐231 cells exhibiting low cell motility were less capable of establishing osteolytic lesions. The number and the area of the osteolytic lesions in mice inoculated with low motility cells were both significantly smaller. Histomorphometry of bone lesions also demonstrated less tumor area in mice bearing hsp27 transfectants although there was no difference in the osteoclast number per square millimeter of tumor–bone interface. These data suggest that cell motility may be an important mechanism in the metastatic cascade of breast cancer cells to the bone and that controlling cell motility may be a useful target to prevent the establishment of osteolytic bone metastases.

Estrogen receptor variants in early breast disease and breast cancer progression

Summary As a downstream mediator of estrogen action, the ER can have a number of pleiotropic effects on a variety of cell types. The critical importance of estrogen in both normal and breast cancer growth has made the ER a matter of intense study, and still its complete mode of action is unclear. One of the discoveries to come out of recent work is the finding that the ER is often altered at the RNA level in both normal and malignant breast tissue. When the interaction of these variants with the growing number of regulators of wild-type ER activity are studied in detail, we may get a clearer picture of the role of variant ERs in breast cancer disease and progression.