Suppression of p53 function in normal human mammary epithelial cells increases sensitivity to extracellular matrix-induced apoptosis.

Little is known about the fate of normal human mammary epithelial cells (HMECs) that lose p53 function in the context of extracellular matrix (ECM)-derived growth and polarity signals. Retrovirally mediated expression of human papillomavirus type 16 (HPV-16) E6 and antisense oligodeoxynucleotides (ODNs) were used to suppress p53 function in HMECs as a model of early breast cancer. p53+ HMEC vector controls grew exponentially in reconstituted ECM (rECM) until day 6 and then underwent growth arrest on day 7. Ultrastructural examination of day 7 vector controls revealed acinus-like structures characteristic of normal mammary epithelium. In contrast, early passage p53- HMEC cells proliferated in rECM until day 6 but then underwent apoptosis on day 7. p53- HMEC-E6 passaged in non-rECM culture rapidly (8-10 passages), lost sensitivity to both rECM-induced growth arrest and polarity, and also developed resistance to rECM-induced apoptosis. Resistance was associated with altered expression of alpha3-integrin. Treatment of early passage p53- HMEC-E6 cells with either alpha3- or beta1-integrin function-blocking antibodies inhibited rECM-mediated growth arrest and induction of apoptosis. Our results indicate that suppression of p53 expression in HMECs by HPV-16 E6 and ODNs may sensitize cells to rECM-induced apoptosis and suggest a role for the alpha3/beta1-heterodimer in mediating apoptosis in HMECs grown in contact with rECM.

Human papillomavirus type 16 E6 inactivation of p53 in normal human mammary epithelial cells promotes tamoxifen-mediated apoptosis.

Aberrant p53 expression is frequently observed in mammary epithelial cells obtained from women at high risk for developing breast cancer and is a predictor for the subsequent development of malignancy. Tamoxifen has recently been shown to reduce the incidence of noninvasive breast cancer in high-risk women, but the molecular mechanism of tamoxifen chemoprevention in mammary epithelial tissue that does not overexpress the estrogen receptor is poorly understood. We suppressed p53 expression by retroviral-mediated expression of human papillomavirus type-16 E6 protein (HPV-16 E6) in human mammary epithelial cells (HMECs) to develop an in vitro model of tamoxifen chemoprevention in the context of p53 loss. Early passage p53(-) HMEC-E6-transduced cells treated with 1.0 microM tamoxifen rapidly underwent apoptosis. In contrast, early passage p53(+) HMEC-LXSN vector controls treated with 1.0 microM tamoxifen underwent G1-G0-phase arrest but did not undergo apoptosis. p53(-) HMEC-E6 cells rapidly acquired resistance to tamoxifen-mediated apoptosis after 10 passages in culture (in the absence of tamoxifen). Both p53(+) and p53(-) HMECs exhibited a low level of estrogen receptor staining and minimal estrogen binding, characteristic of proliferating normal luminal mammary epithelial cells. Tamoxifen-mediated apoptosis in p53(-) HMEC-E6 cells was not blocked by inhibitors of transcription and protein synthesis. These data suggest that the acute loss of p53 function in HMECs by expression of HPV-16 E6 results in marked sensitivity to tamoxifen-mediated apoptosis but that resistance to apoptosis rapidly develops within 10 passages in vitro. Observations in our model system predict a critical role for the early institution of tamoxifen chemoprevention.

Tamoxifen but not 4-hydroxytamoxifen initiates apoptosis in p53(-) normal human mammary epithelial cells by inducing mitochondrial depolarization.

Despite the widespread clinical use of tamoxifen as a breast cancer prevention agent, the molecular mechanism of tamoxifen chemoprevention is poorly understood. Abnormal expression of p53 is felt to be an early event in mammary carcinogenesis. We developed an in vitro model of early breast cancer prevention to investigate how tamoxifen and 4-hydroxytamoxifen may act in normal human mammary epithelial cells (HMECs) that have acutely lost p53 function. p53 function was suppressed by retrovirally mediated expression of the human papillomavirus type 16 E6 protein. Tamoxifen, but not 4-hydroxytamoxifen, rapidly induced apoptosis in p53(-) HMEC-E6 cells as evidenced by characteristic morphologic changes, annexin V binding, and DNA fragmentation. We observed that a decrease in mitochondrial membrane potential, mitochondrial condensation, and caspase activation preceded the morphologic appearance of apoptosis in tamoxifen-treated early passage p53(-) HMEC-E6 cells. p53(-) HMEC-E6 cells rapidly developed resistance to tamoxifen-mediated apoptosis within 10 passages in vitro. Resistance to tamoxifen in late passage p53(-) HMEC-E6 cells correlated with an increase in mitochondrial mass and a lack of mitochondrial depolarization and caspase activation following tamoxifen treatment. We hypothesize that an early event in the induction of apoptosis by tamoxifen involves mitochondrial depolarization and caspase activation, and this may be important for effective chemoprevention.

Dysregulated expression of cyclin D1 in normal human mammary epithelial cells inhibits all-trans-retinoic acid-mediated G0/G1-phase arrest and differentiation in vitro.

Overexpression of cyclin D1 protein is observed in the majority of breast cancers, suggesting that dysregulated expression of cyclin D1 might be a critical event in breast cancer carcinogenesis. We investigated whether retroviral-mediated expression of cyclin D1 might affect all-trans-retinoic acid (ATRA)-mediated growth inhibition and differentiation of normal cultured human mammary epithelial cells (HMECs). HMECs treated with 1.0 microM ATRA undergo irreversible growth inhibition starting at 24 h and complete G0/G1-phase arrest by Day 3. Cyclin D1 protein levels are observed to decrease in association with the initiation of growth arrest starting at 24 h and then increase by approximately 35% on Day 3. Concomitant with this observed increase in cyclin D1, HMECs undergo morphologic changes consistent with progression to a more differentiated phenotype, including an increase in cell size, increased cell spreading, increased tonofilaments, and accumulation of cytoplasmic vesicles containing lipid. Dysregulated expression of cyclin D1 in HMECs results in inhibition of G0/G1-phase arrest mediated by ATRA. In addition, HMECs expressing exogenous cyclin D1 are resistant to differentiation by ATRA. Our results suggest that coordinated expression of cyclin D1 may be critical for normal mammary epithelial cell homeostasis, and dysregulated expression of cyclin D1 might result in retinoid resistance and promote mammary carcinogenesis.

Inhibition of retinoic acid receptor function in normal human mammary epithelial cells results in increased cellular proliferation and inhibits the formation of a polarized epithelium in vitro.

The expression of retinoic acid receptor-beta (RAR beta) mRNA is absent or down-regulated in a majority of breast cancers, suggesting that loss of retinoic acid receptor function may be a critical event in breast cancer carcinogenesis. We developed an in vitro system to investigate whether the loss of retinoic acid receptor (RAR) function might affect the proliferation and structural differentiation of normal cultured human mammary epithelial cells (HMECs). Utilizing a truncated retinoic acid receptor (RAR)-alpha construct exhibiting dominant-negative activity against retinoic acid receptor isoforms alpha, beta, and gamma (DNRAR), we inhibited normal retinoic acid receptor function in HMECs. Suppression of RAR function in HMECs resulted in reduced growth inhibition mediated by all-trans-retinoic acid (ATRA). Moreover, the doubling time of HMECs expressing the DNRAR was significantly shortened, associated with a decrease in the percentage of cells in G1 and an increase in the percentage of cells in S-phase relative to controls. In addition, HMECs expressing the DNRAR cultured in prepared extracellular matrix exhibited a loss of extracellular matrix-induced growth arrest and formation of a polarized ductal epthelium. Our results suggest that ATRA and RARs may play an important role in regulating the proliferation of HMECs and in promoting differentiation.

All-trans-retinoic acid mediates G1 arrest but not apoptosis of normal human mammary epithelial cells.

Retinoids mediate the normal growth of a variety of epithelial cells and may play an important role in the chemoprevention of certain malignancies. Loss of retinoic acid (RA) receptor-beta function may be an important event in mammary carcinogenesis, because the majority of breast cancers, in contrast to normal mammary epithelial cells, fail to express this receptor. We previously reported that all-trans-RA mediates G1 arrest as well as apoptosis in certain RAR beta-transduced breast cancer cell lines. We now report the effect of RA on normal human mammary epithelial cells (HMECs), which express functionally active retinoid receptors. We observe that RA induces growth suppression and G1 arrest of these HMECs but find no evidence that RA mediates apoptosis in these normal cell strains. This RA-induced G1 arrest is temporally associated with decreased levels of hyperphosphorylated retinoblastoma protein without any significant changes in c-myc, p53, p21, or p27 expression. Expression of cyclin D1, cyclin-dependent kinase 4, and cyclin E proteins, however, decreased in association with RA-mediated G1 arrest. Our studies suggest that growth inhibition, rather than apoptosis, may be a mechanism by which RA and RA receptors act to prevent the malignant transformation of normal mammary epithelial cells. The molecular target(s) of the activated RA receptors that mediate this G1 arrest in HMECs appear to be associated with a retinoblastoma-dependent pathway.

Regional blood flow and metabolism in ovine fetuses during severe cord occlusion.

OBJECTIVE: Our purpose was to compare the ovine fetal response to severe, damaging asphyxia resulting from umbilical cord occlusion with that seen in uterine artery occlusion. STUDY DESIGN: Six ovine fetuses were exposed to severe asphyxia produced by partial umbilical cord occlusion for 90 minutes. Fetal blood pressure and heart rate, blood gases, acid base status, electrocorticogram, and electromyogram were recorded. Regional blood flow (radioactive microspheres) measurements were performed at control and 30, 60, and 90 minutes of occlusion and 30 minutes after release. RESULTS: During the period of occlusion pH fell from 7.37 +/- 0.01 (mean +/- SEM) to 6.82 +/- 0.03 at 90 minutes, base excess from 5 +/- 1 to -22 +/- 2 mEq.L-1 and oxygen content from 3.3 +/- 0.4 mmol.L-1 to a nadir of 1.6 +/- 0.4 mmol.L-1 (p < 0.05). There was no significant long-term change in fetal heart rate or blood pressures. The fetal electrocorticogram was profoundly suppressed during asphyxia, and seizure activity was documented after release of occlusion in all surviving animals. Umbilical blood flow fell to 21% +/- 5% of control by 60 minutes of occlusion and remained depressed until release. Brain and adrenal blood flows increased during asphyxia. Heart and intestinal blood flows did not change significantly from control values. Combined ventricular output and spleen, kidney, and carcass blood flow fell during the insult. Oxygen uptake by the cerebral cortex remained stable during occlusion. Oxygen uptake by the lower carcass fell to 15% +/- 7% of control. CONCLUSION: Umbilical cord occlusion produces similar levels of asphyxia and evidence of encephalopathy (seizures), compared with previous experiments with uterine artery occlusion. The fetal response with respect to blood flow redistribution and organ oxygen uptake, however, differs. These differences may signify that with uterine artery occlusion the brain may be more vulnerable, whereas with umbilical cord occlusion the heart may be at greater risk.

Subarachnoid morphine and fentanyl for labor analgesia. Efficacy and adverse effects.

BACKGROUND AND OBJECTIVES: The study was designed to compare analgesic efficacy and associated adverse effects between a group of parturients receiving subarachnoid opioids via the combined spinal-epidural (CSE) technique with a group receiving epidural analgesia alone for labor. METHODS: The authors studied 59 healthy parturients admitted for labor and delivery. Group 1 consisted of 26 consecutive patients who received the CSE technique, initially receiving subarachnoid morphine sulfate 0.25 mg, and fentanyl 25 micrograms, for labor analgesia. If patients requested additional analgesia, epidural analgesia was initiated. Group 2 was comprised of 33 consecutive patients who received conventional epidural analgesia. All patients were monitored for the occurrence and treatment of peripartum nausea and vomiting (N/V), pruritus, postdural puncture headache, and respiratory depression. RESULTS: Additional analgesia was requested by 20/26 (76%) patients in group 1. Group 1 reported more N/V (50% versus 15%, P = .01) and required more therapy for N/V (31% versus 0%, P < .01) than group 2. Furthermore, group 1 reported having more pruritus (50% versus 3%, P < .01), and required more treatment for pruritus (35% versus 3%, P < .01), than group 2. No patient developed significant respiratory depression. Only one patient in group 1 developed a postdural puncture headache, following unintentional dural puncture with the 18 gauge Tuohy needle. CONCLUSIONS: The combination of subarachnoid morphine 0.25 mg and fentanyl 25 micrograms, when used for labor analgesia as part of the CSE technique, was associated with a higher incidence of clinically significant nausea and vomiting and pruritus, compared to conventional epidural anesthesia. Furthermore, the combination of subarachnoid morphine and fentanyl proved ineffective in providing adequate pain relief for the duration of labor and delivery for the majority of patients. The authors recommend that subarachnoid morphine and fentanyl serve a limited role in the treatment of labor pain.

The ultrastructure of the human epidermis in chronic graft-versus-host disease.

The epidermal ultrastructure of 11 allogeneic bone marrow recipients with chronic graft-versus-host disease (GVHD) was compared with that of 4 recipients without chronic GVHD. This electron microscope study revealed three patterns of epidermal injury typical of chronic GVHD. The first type was a nonacantholytic (nondissecting) injury with a prominent cellular infiltrate consisting primarily of lymphocytes accompanied by a few macrophages. The second type was an acantholytic (dissecting) injury with a prominent infiltrate, while the third was a nondissecting injury with a sparse infiltrate. Broad-zone contact was observed between lymphocytes and all epidermal cell types as well as between other lymphocytes and macrophages. Point contact was only observed between lymphocytes and epidermal cells. Lymphocytes appeared to detach desmosomes from adjacent keratinocytes by isolating them with cytoplasmic projections, a phenomenon not previously described. Typical damage to the epidermal cells in the basal and spinous layers consisted of either swelling of the organelles or condensation of the cytoplasm and nucleus. In the keratinocyte, the condensation reaction resulted in the formation of colloid bodies, some of which were phagocytized by macrophages. Besides the cytolytic events, a concurrent stimulatory reaction occurred in the epidermal cells. The number of melanosomes in melanocytes and of Langerhans cell granules and dense bodies in the Langerhans cells all increased. Extensive areas of replication and disruption of the basal lamina were subjacent to areas of necrosis in the basal layer.