p53-dependent and p53-independent activation of apoptosis in mammary epithelial cells reveals a survival function of EGF and insulin

EGF inhibits expression of WDNM1 and sulfated glycoprotein-2 genes in mammary epithelial cells

We have previously shown that expressions of ferritin heavy chain (FHC), WDNM1, and sulfated glycoprotein-2 (SGP-2) genes are induced at an involution stage of mammary gland. Here we studied the effect of lactogenic hormones and EGF on the expression of involution-induced genes in HC11 mammary epithelial cells. Insulin, dexamethasone, prolactin, and its combinations did not affect expression of the genes. When cells were cultured in growth medium containing EGF, expression of WDNM1 and SGP-2 genes was strongly inhibited in a dose- and time- dependent manner, whereas expression of FHC gene was not influenced by EGF. Results demonstrate that EGF inhibits expression of WDNM1 and SGP-2 genes in mammary epithelial cells.

Cell cycle control is aberrant in Chinese hamster ovary cell mutants exhibiting apoptosis after serum deprivation

We isolated mutants of Chinese hamster ovary cells that exhibit excessive apoptosis after serum deprivation. In the medium containing 10% serum, the growth rates of the mutants were 1.4 to 1.5-fold faster than those of wild-type cells. Whereas the cell cycle of wild-type cells was arrested at the G1 phase after serum deprivation, the cell cycle of the mutant cells was not fully arrested at this phase, suggesting that cell cycle regulation was disorganized in the mutants. The mutants were highly sensitive to a nucleotide-analogue 5-fluorouracil in the absence of serum, whereas wild-type cells were resistant to the drug. Based on the sensitivity to the drug after serum deprivation, we could classify the mutants into dominant groups and at least two recessive complementation groups. Thus, these mutants presumably contain different lesions in gene(s) required for cell cycle regulation and apoptosis.

Target to apoptosis: a hopeful weapon for prostate cancer

BACKGROUND

Prostate cancer is the most commonly diagnosed neoplasm and the second leading cause of male death in this country. Multiple genetic and epigenetic factors have been implicated in the oncogenesis and progression of prostate cancer. However, the molecular mechanisms underlying the disease remain largely unknown. The major difficulty in the clinical management of prostate cancer stems from the reality that reliable and accurate diagnostic/prognostic biomarkers are not available and that effective treatment regimens for hormone-resistant prostate cancers are yet to be developed.

METHODS

The present review, through extensive literature research, summarizes the most recently accumulated experimental and clinical data on the relationship between apoptosis and prostate cancer. We analyze the possibility of inducing prostate cancer cell apoptosis by: 1) androgen ablation by castration or biochemical antagonists: 2) chemotherapeutic drugs or natural/synthetic chemicals; 3) manipulation of apoptosis-related oncoproteins; and 4) modulation of intracellular signal transducers.

RESULTS

1) Prostate cancer, like most other solid tumors, represents a very heterogeneous entity. Most prostate cancers, at the time of clinical diagnosis, present themselves as mixtures of androgen-dependent and androgen-independent cells. 2) Most prostate cancers respond initially to androgen ablation since the population of androgen-dependent cells undergoes rapid apoptosis upon androgen withdrawal. However, androgen ablation rarely cures patients, most of whom will experience recurrence due to takeover of the tumor mass by androgen-independent tumor cells as well as the emergence of apoptosis-resistant clones as a result of further genetic alterations such as bcl-2 amplification. 3) On the other hand, although androgen-independent prostate cancer cells do not undergo apoptosis upon androgen blocking, they do maintain the appropriate molecular machinery of apoptosis. Therefore, certain conventional chemotherapy drugs can eliminate androgen-independent cancer cells by inducing apoptosis. 4) However, most drugs used in chemotherapy induce apoptosis or mediate cytotoxicity only in proliferating cancer cells. Human prostate cancer cells demonstrate very slow growth kinetics. Thus, novel chemical/natural products need be identified to eradicate those nonproliferating cancer cells. In this regard, the angiogenesis inhibitor, linomide, and a plant extract, beta-lapachone, demonstrate very promising apoptosis-inducing effects on prostate cancer cells in a proliferation-independent manner. 5) An alternative way to modulate the apoptotic response is by interfering with the expression levels of essential regulatory molecule of apoptosis. Bcl-2 and p53 represent two prime targets for such manipulations. 6) Finally, modulation of signal transduction pathways (e.g., intracellular Ca2+ levels, PKC activity) involved in apoptosis may also induce and/or enhance the apoptotic response of prostate cancer cells.

CONCLUSIONS

Modulation of apoptotic response represents a novel mechanism-based approach which may help identify novel drugs and/or develop new therapeutic regimens for the treatment of prostate cancers.

Regulation of apoptosis resistance and ontogeny of age-dependent diseases

Diseases of the elderly, including neurodegenerative and cardiovascular disorders and cancer, may develop through the accumulation of "hits" composed of genetic and epigenetic risk factors. The "iceberg" buildup of these hits over time may exceed the tolerance threshold of a particular tissue, thus precipitating disease. Resistance to apoptosis, a self-eliminating cellular program, is one risk factor; it is attributed to persistent survival factors, or the absence of killer factors, which form a "Yin-Yang" mechanism directing cells to either live or die. Most apoptosis-associated genes can be categorized into four groups, providing signals, signal processors, activators, or substrates for the apoptotic pathway. Senescent human fibroblasts resist apoptosis, perhaps through the lack of key G1-phase gene expressions, also necessary for apoptosis initiation; they also lack key proteolytic activity, and maintain high levels of survival factor bcl2, reflecting a triple blockage to apoptosis. Accumulations of these apoptosis-resistant fibroblasts in aging individuals may impair proper tissue function, not only as noncontributing members, but also as the seed for the buildup of further hits. With time, these cells with multiple hits and apoptosis resistance may induce susceptibility to developing age-dependent diseases.

Comparative studies of the mitogenic effects of epidermal growth factor and transforming growth factor-alpha and the expression of various growth factors in neoplastic and non-neoplastic prostatic cell lines

BACKGROUND

The role of growth factors in prostate cell growth has been investigated as these peptides may be involved in the autonomous growth of hormone-independent prostate cancer.

METHODS

Responses of neoplastic (PC-3 and CPA) and non-neoplastic (CAPE) prostatic cell lines to epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) were determined using clonogenic and growth curve analysis. The constitutive expression of EGF, TGF-alpha, and TGF-beta 1-3 mRNA was examined using Northern blotting and EGF and TGF-alpha protein levels were determined immunohistochemically.

RESULTS

Growth curve and clonogenic analysis indicated that EGF and TGF-alpha were mitogenic in each cell line. The magnitude of the clonogenic response varied between the cell lines, with CPA cells showing the greatest growth increases. CPA cells also displayed the highest levels of EGF and TGF-alpha mRNA and protein. TGF-beta 1 mRNA was detected in the order of magnitude, PC-3 > CPA > CAPE. Furthermore, PC-3 and CPA cells expressed TGF-beta 3 and TGF-beta 2 transcripts respectively. In each cell line, the expression of any growth factor mRNA was not affected by exogenous EGF.

CONCLUSIONS

The growth responses of the cell lines to EGF and TGF-alpha did not correlate with their constitutive levels of EGF and TGF-alpha mRNA and protein, thus whilst growth factors may be important in malignant cell growth, other pathways may also be involved in the autocrine regulation of cell proliferation.

Cell-cell contact and specific cytokines inhibit apoptosis of colonic epithelial cells: growth factors protect against c-myc-independent apoptosis

In this study we sought factors that determine the survival of human colonic epithelial cells. Normal colonic epithelial cells are dependent on cell-cell contacts and survival factors for the inhibition of apoptosis whereas, during colorectal tumorigenesis, cells develop mechanisms to evade these controls. The ability to survive loss of cell-cell contacts and/or growth factor deprivation is a marker of tumour progression. Many adenoma (premaligant) cultures survive only if cell-cell contacts are maintained in vitro and die by apoptosis if trypsinized to single cells. This also occurs in adenomas derived from familial adenomatous polyposis (FAP) patients, therefore APC mutations do not confer resistance to cell death in response to loss of cell-cell contacts. We show here that if cell-cell contacts are maintained such cells are capable of survival in suspension. Adenoma cells also undergo apoptosis in response to removal of serum and growth factors from the medium. After removal of serum and growth factors c-myc is down-regulated within 2 h. Therefore, the induction of apoptosis is not an inappropriate response of the cells due to a deregulated c-myc gene. The apoptotic response is also p53 independent. Such cultures have been used to determine specific survival factors for colonic epithelial cells. Insulin, the insulin-like growth factors I and II, hydrocortisone and epidermal growth factor (EGF) protect cells from the induction of apoptosis in the absence of serum over a short-term period of 24 h. This approach may give insight into the factors governing growth and survival of colonic epithelial cells in vivo. This is the first report of specific growth factors protecting against apoptosis in human colonic epithelial cells.

Apoptosis and proliferation in thyroid carcinoma: correlation with bcl-2 and p53 protein expression

The aim of this study was to determine the apoptotic cell death in 92 thyroid carcinomas of different histotypes (42 papillary, PTC; 12 poorly differentiated, PDC: 21 undifferentiated, UC; and 17 medullary, MC) by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end labelling (TUNEL). Apoptotic index (Al, evaluated as a percentage of TUNEL-positive cells of neoplastic cells) was calculated in each tumour. The AI was very low in all subtypes of thyroid carcinoma, ranging from a median value of 0.2 in PTC to 1.4 in UC. The proliferative activity was determined by immunohistochemistry using monoclonal antibody, MIB-1. The percentage of proliferating cells was significantly different among the histotypes, increasing with tumour aggressiveness (from the mean value of 3.1 for PTC to 5.6 for PDC and 51.8 for UC). In addition, the ratio between proliferative activity and apoptosis was significantly higher in UC than in the other histotypes. The expression of bcl-2 and p53 protein (important in the modulation of cell death) was correlated (bcl-2, inverse correlation, r2 = 0.1, P = 0.04; p53, direct correlation, r2 = 0.11, P = 0.02) with apoptotic index in PTC.

Morphologic effects of neoadjuvant chemotherapy in locally advanced breast cancer

The use of chemotherapy as primary treatment in early and locally advanced breast cancer is rising. As a result, many resected tumors were exposed to cytotoxic drugs in vivo. To study resulting histopathologic changes, we examined 61 patients with locally advanced stage III breast cancer who had been treated with a standardized neoadjuvant polychemotherapy regimen before undergoing surgical resection 3 months later. Matched pairs of pre- and posttherapy breast tissue were evaluated for morphologic changes in the residual malignant and benign breast tissue compartment. A potential correlation between changes and the original p53 immunophenotype was examined as well. In 11 cases (18%), complete pathologic remission with no residual tumor in the mastectomy specimen was achieved. This response was not correlated to the original p53 status. The remaining 50 cases showed residual tumor. The most prominent histologic change was an increase in nuclear atypia of tumor cells (51% of the cases). This effect was independent of the presence or absence of nuclear p53 accumulation in the pre-treatment specimens. Nuclear atypia was frequently accompanied by tumor cell enlargement (in 49% of the cases). Most commonly, a tumor with relatively small cells presented with large epithelioid apocrine features after treatment. In 6 cases (13%), the mitotic rate decreased significantly, while in 12 cases (26%) the mitotic rate increased after chemotherapy. Elston histogrades remained unchanged in 70% of the cases but increased in 17% and decreased in 13%, mainly due to changes in mitotic rates. Extensive tumor cell vacuolization, a common change seen after radiotherapy, was a minor finding but was seen focally. Within the non-malignant compartment, lobular atrophy with hyalinization and minimal epithelial atypia of lobules and ducts were common. We conclude that changes in residual tumor and normal breast are common following systemic cytotoxic therapy. As neoadjuvant chemotherapy becomes mainstream management for locally advanced breast cancer, pathologists are required to recognize treatment induced changes. For correct histopathologic assessment, therapy induced morphologic alterations need to be distinguished from tumor-intrinsic morphologic features.

Apoptosis in the terminal endbud of the murine mammary gland: a mechanism of ductal morphogenesis

Ductal morphogenesis in the rodent mammary gland is characterized by the rapid penetration of the stromal fat pad by the highly proliferative terminal endbud and subsequent formation of an arborized pattern of ducts. The role of apoptosis in ductal morphogenesis of the murine mammary gland and its potential regulatory mechanisms was investigated in this study. Significant apoptosis was observed in the body cells of the terminal endbud during the early stage of mammary ductal development. Apoptosis occurred predominately in defined zones of the terminal endbud; 14.5% of the cells within three cell layers of the lumen were undergoing apoptosis compared to 7.9% outside this boundary. Interestingly, DNA synthesis in the terminal endbud demonstrated a reciprocal pattern; 21.1% outside three cell layers and 13.8% within. Apoptosis was very low in the highly proliferative cap cell laver and in regions of active proliferation within the terminal endbud. In comparison to other stages of murine mammary gland development, the terminal endbud possesses the highest level of programmed cell death observed to date. These data suggest that apoptosis is an important mechanism in ductal morphogenesis. In p53-deficient mice, the level of apoptosis was reduced, but did not manifest a detectable change in ductal morphology, suggesting that p53-dependent apoptosis is not primarily involved in formation of the duct. Immunohistochemical examination of the expression of the apoptotic checkpoint proteins, Bcl-x, Bax and Bcl-2, demonstrated that they are expressed in the terminal endbud. Bcl-x and Bcl-2 expression is highest in the body cells and lowest in the nonapoptotic cap cells, implying that their expression is associated with increased apoptotic potential. Bax expression was distributed throughout the terminal endbud independent of the observed pattern of apoptosis. A functional role for Bcl-2 family members in regulating endbud apoptosis was demonstrated by the significantly reduced level of apoptosis observed in WAP-Bcl-2 transgenic mice. The pattern of apoptosis and ductal structure of endbuds in these mice was also disrupted. These data demonstrate that p53-independent apoptosis may play a critical role in the early development of the mammary gland.

P53 protein expression in pancreatic tumors and its relationship to clinicopathological factors and prognosis

We examined the expression of p53 protein by immunohistochemical method in a series of pancreatic tumors and evaluated its relationships to the clinicopathological factors and prognosis. The study involved 108 cases of pancreatic tumors (79 ductal carcinomas, 1 acinar cell carcinoma, 14 endocrine tumors, 6 solid cystic tumors, 8 benign ductal tumors) and 8 chronic pancreatitides. Thirty-nine cases of pancreatic ductal carcinoma (49.4%) were positive for p53 protein. Analysis of the Cox hazards model identified p53 positivity and stage at the initial operation as an independent prognostic factor. Patients with p53 positive ductal carcinomas had a greater risk of death compared to p53 negative cases (P < 0.05). There was, however, no statistically significant correlation between p53 protein expression and other clinicopathological factors. Cases of stage III and IVb with positive p53 showed a bleak prognosis compared to p53 negative cases (P < 0.05). Our results suggest that p53 expression is common in invasive pancreatic ductal carcinomas and may have a prognostic value.

Effects of 1,25 dihydroxyvitamin D3 and its analogues on induction of apoptosis in breast cancer cells

Vitamin D derivatives have been shown both to inhibit the proliferation of cultured breast cancer cells and to cause regression of experimental mammary tumours in vivo. We have investigated the ability of several vitamin D analogues to promote the regression of experimental rat mammary tumours. Our results revealed that one vitamin D compound in particular, EB1089 (1(S),3(R)-dihydroxy-20(R)-5'-ethyl- 5'-hydroxy-hepta-1'(E),3'(E)-dien-1'-yl)-9,10-secopregna-5(Z ),7(E) ,10(19)-triene), was highly effective at inhibiting tumour progression, without causing a significant rise in serum calcium concentration. Tumour regression occurs when the rate of cell death is greater than the rate of cell proliferation. Apoptosis (programmed or active cell death) is an active, energy-dependent process in which a distinct series of biochemical and molecular events leads to the death of cells by specific signals. We have examined effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2(D)3) and the synthetic vitamin D analogue EB1089 on indices of apoptosis in cultured human breast cancer cells. The effects of the vitamin D compounds on the expression of two oncoproteins which may regulate apoptosis, bcl-2 and p53 were examined by Western analysis. In MCF-7 cell cultures treated for six days with 1,25(OH)2(D)3 or EB1089 (1 x 10(-8) M), bcl-2 protein was reduced in comparison to control levels, whereas p53 protein was increased. In addition, the p21 protein, whose gene WAF-1 is induced by wild type p53, was also increased by both vitamin D compounds. Using Northern analysis, it was observed that 24-h treatment of MCF-7 cells with 1 x 10(-8) M 1,25(OH)2(D)3 or EB1089 resulted in an induction of TRPM-2 (clusterin) mRNA, a gene associated with onset of apoptosis in the involuting prostate. Fragmentation of genomic DNA is a characteristic feature of apoptosis. With the terminal deoxynucleotidyl transferase (TdT) assay, 3'-OH DNA breaks indicative of DNA fragmentation were detected histochemically in MCF-7 cells treated with 1 x 10(-8) M 1,25(OH)2(D)3 or EB1089 for four days prior to fixation and TdT reaction. Further evidence of apoptosis was obtained following six days treatment of MCF-7 cell cultures with 5 x 10(-8) M 1,25(OH)2(D)3 or EB1089, utilizing a cell death ELISA assay, which measures the presence of histone-associated oligonucleosome complexes generated from DNA fragmentation. Taken together our findings indicate that vitamin D derivatives may play a role in regulating the expression of genes and protein products implicated in apoptosis.

The role of p53 in cell cycle regulation

The tumor suppressor gene p53, implicated in diverse types of human tumors, functions both as a gene-specific transcription factor as well as a specific inhibitor of the transcription of certain genes. The two physiological outcomes of re-expression of wild type p53 in tumor cells, not expressing wild type p53, are G1 arrest and apoptosis. The mechanism of G1 arrest by p53 is much better documented than its ability to trigger apoptosis. P53 as a transcription factor induces the expression of p21WAF1/CIP1/Sdi1, an inhibitor of the cyclin dependent kinases (CDKs)2, 3, 4 and 6. Thus, a G1 arrest can result simply by the p53 induced expression of p21WAF1/CIP1/Sdi1. Amongst the other genes presently characterized to be regulated by p53 are BAX, a homologue of the BCL-2 gene. Bax does not trigger apoptosis, but simply accelerates the rate at which apoptosis proceeds54. P53 also down regulates the expression of cyclin A, providing a secondary break on cell cycle progression into the through the S phase.

p53 stimulates promoter activity of the sgk. serum/glucocorticoid-inducible serine/threonine protein kinase gene in rodent mammary epithelial cells

sgk is a novel member of the serine/threonine protein kinase gene family that is transcriptionally regulated by serum and glucocorticoids in mammary epithelial cells. To functionally determine if the sgk promoter is regulated by the p53 tumor suppressor protein in mammary cells, a series of sgk promoter fragments with 5'-deletions were linked to the bacterial chloramphenicol acetyltransferase gene (sgk-CAT) and transiently co-transfected into nontumorigenic NMuMG or transformed Con8Hd6 mammary epithelial cells with p53 expression plasmids. Wild-type p53, but not mutant p53, strongly stimulated sgk promoter activity in both mammary epithelial cell lines. These effects were mediated by specific regions within the sgk promoter containing p53 DNA-binding sites. The sgk p53 sequence at-1380 to-1345 (site IV) was sufficient to confer p53-dependent transactivation to a heterologous promoter, and p53 was capable of binding to this sequence in vitro as assessed by gel shift analysis. In the nontumorigenic NMuMG epithelial cell line, cotransfection of wild-type p53 strongly stimulated the activities of both the sgk promoter and the well characterized p53-responsive p21/Waf1 promoter, whereas in Rat-2 fibroblasts, wild-type p53 repressed the basal activities of both promoters, revealing that sgk and p21/Waf1 are similarly regulated in a cell type-specific manner. Taken together, these results demonstrate that sgk is a new transcriptional target of p53 in mammary epithelial cells and represent the first example of a hormone-regulated protein kinase gene with a functionally defined p53 promoter recognition element.

Epidermal growth factor, but not hepatocyte growth factor, suppresses the apoptosis induced by transforming growth factor-beta in fetal hepatocytes in primary culture

We studied whether the TGF-beta-induced apoptosis in fetal hepatocyte primary cultures may be modulated by the presence of mitogenic stimuli, such as EGF or HGF. EGF prevented cell death, showing a dose dependence that was identical to that observed for its effect on DNA synthesis stimulation. HGF, in contrast, had no effect, even at high concentrations. EGF blocked apoptosis, since in the presence of this factor cells did not show DNA fragmentation. Moreover, EGF, but not HGF, blocked c-fos induction associated with the apoptotic process induced by TGF-beta in these cells.

Decreased DNA repair but normal apoptosis in ultraviolet-irradiated skin of p53-transgenic mice

p53 tumor suppressor plays a vital role in the cellular responses to genotoxic stress. It is believed that p53 regulates the cell cycle by activating the G1 checkpoint after exposure to agents like ionizing radiation, ultraviolet (UV) radiation, or genotoxic chemicals. Recently, it is conjectured that p53 may have additional functions in DNA repair and apoptosis. Previously, we demonstrated that p53-transgenic mice that carry mutant alleles of a p53 gene developed twice as many skin tumors as control mice after UV exposure. To elucidate the molecular mechanisms of mutant p53 in skin cancers, we studied DNA repair efficiency and the rate of apoptosis in murine keratinocytes after UV irradiation. In this report, we show that mutant p53-transgenic mouse skin has reduced repair of UV-induced DNA damage in both in vivo and in vitro radioimmunoassays. In control mice, DNA repair is associated with increased amounts of wild-type P53 protein. Unexpectedly, mutant p53-transgenic mice had slightly increased apoptosis after UV irradiation, suggesting that the wild-type p53 protein in the cells still functions in inducing apoptosis, or that this cell death results from p53-independent mechanisms. These results suggest that mutant p53 interferes with wild-type p53 in the repair of UV-induced DNA damage but not in apoptosis.

Growth factor and sex steroid interactions in breast cancer

Mitogenic and inhibitory growth factors and steroid ovarian hormones play important roles as selective modulators of normal mammary development and in the onset and the progression of human breast cancer. The focus of this article is to review past and current research on the interactions of these two classes of effectors in mammary gland development and neoplasia. Steroid hormones regulate synthesis of growth stimulatory and inhibitory growth factors, growth factor receptors, and growth factor binding proteins. In turn, growth factor pathways may modulate phosphorylation and function of steroid receptors and potentiate or inhibit the mitogenic actions of steroids. Ultimately, during the progression of the malignant mammary epithelial cell to hormonal autonomy, overexpression, mutation, or disregulation of key elements of growth factor signal transduction pathways all may play critical roles.

Apoptosis: molecular regulation of cell death

The field of apoptosis is unusual in several respects. Firstly, its general importance has been widely recognised only in the past few years and its surprising significance is still being evaluated in a number of areas of biology. Secondly, although apoptosis is now accepted as a critical element in the repertoire of potential cellular responses, the picture of the intra-cellular processes involved is probably still incomplete, not just in its details, but also in the basic outline of the process as a whole. It is therefore a very interesting and active area at present and is likely to progress rapidly in the next two or three years. This review emphasises recent work on the molecular mechanisms of apoptosis and, in particular, on the intracellular interactions which control this process. This latter area is of crucial importance since dysfunction of the normal control machinery is likely to have serious pathological consequences, probably including oncogenesis, autoimmunity and degenerative disease. The genetic analysis of programmed cell death during the development of the nematode Caenorhabditis elegans has proved very useful in identifying important events in the cell death programme. Recently defined genetic connections between C. elegans cell death and mammalian apoptosis have emphasised the value of this system as a model for cell death in mammalian cells, which, inevitably, is more complex. The signals inducing apoptosis are very varied and the same signals can induce differentiation and proliferation in other situations. However, some pathways appear to be of particular significance in the control of cell death; recent analysis of the apoptosis induced through the cell-surface Fas receptor has been especially important for immunology. Two gene families are dealt with in particular detail because of their likely importance in apoptosis control. These are, first, the genes encoding the interleukin-1 beta-converting enzyme family of cysteine proteases and, second, those related to the proto-oncogene bcl-2. Both of these families are homologous to cell death genes in C. elegans. In mammalian cells the number of members of both families which have been identified is growing rapidly and considerable effort is being directed towards establishing the roles played by each member and the ways in which they interact to regulate apoptosis. Other genes with established roles in the regulation of proliferation and differentiation are also important in controlling apoptosis. Several of these are known proto-oncogenes, e.g. c-myc, or tumour suppressors, e.g. p53, an observation which is consistent with the importance of defective apoptosis in the development of cancer. Viral manipulation of the apoptosis of host cells frequently involves interactions with these cellular proteins. Finally, the biochemistry of the closely controlled cellular self-destruction which ensues when the apoptosis programme has been engaged is also very important. The biochemical changes involved in inducing phagocytosis of the apoptotic cell, for example, allow the process to be neatly integrated within the tissues, under physiological conditions. Molecular defects in this area too may have important pathological consequences.

p53 mediated tumor cell response to chemotherapeutic DNA damage: a preliminary study in matched pairs of breast cancer biopsies

Wild type p53 plays a crucial role in maintaining genomic stability in both normal and tumor cells in vitro. When DNA damage occurs, p53 acts as a cell cycle checkpoint and induces a cellular response that aims at restoring genomic integrity. p53 may either allow the repair of damaged DNA by inducing a transient G1 arrest or may eliminate the damaged cells by triggering apoptosis. Mutant p53 fails to mediate any of these effects. From this, a p53 status-dependent response to therapy might be expected when tumors are treated with DNA-damaging genotoxic agents: Although wild type p53-harboring tumors have an intact checkpoint that might allow them to restore genomic integrity back to a pre-exposure level, mutant p53 tumors have a corrupted checkpoint that could lead to an accelerated loss of genomic stability. Until now, no studies have been described that examine such a p53-mediated effect in vivo. The authors tested this response model in vivo comparing 32 matched biopsy pairs from patients with breast cancer before and after rigorously standardized polychemotherapy. Four of the five drugs specifically induce a wild type p53-mediated checkpoint response. Tumor tissue from matched pairs of untreated and treated biopsies of the same patient were analyzed for treatment-associated changes of p53 protein expression by immunocytochemistry and, in a few available specimens, of p53 genotype changes by polymerase chain reaction-based DNA analysis. Treatment-associated changes of the p53 immunophenotype, which the authors speculate to reflect clonal selection, occurred in 39% (12 of 31) of the specimens. One specimen was not informative. Most tumors undergoing clonal selection originally harbored mutant p53 (nine of 12), and only three of 12 tumors were wild type. This study shows that exposure to genotoxic agents is commonly associated with a change in p53 immunophenotype. Although the limited material in this cohort prevented direct analysis of genetic instability, these results suggest that tumors with altered p53 may be genomically less stable and, therefore, may be more likely to undergo treatment-induced clonal changes than wild type tumors. This study also shows that the rigorous matched sample approach, although difficult to obtain, is an important tool that allows the in vivo assessment of the tumor response to genotoxic therapy in a controlled fashion.

Glucocorticoid and progesterone inhibit involution and programmed cell death in the mouse mammary gland

Milk production during lactation is a consequence of the suckling stimulus and the presence of glucocorticoids, prolactin, and insulin. After weaning the glucocorticoid hormone level drops, secretory mammary epithelial cells die by programmed cell death and the gland is prepared for a new pregnancy. We studied the role of steroid hormones and prolactin on the mammary gland structure, milk protein synthesis, and on programmed cell death. Slow-release plastic pellets containing individual hormones were implanted into a single mammary gland at lactation. At the same time the pups were removed and the consequences of the release of hormones were investigated histologically and biochemically. We found a local inhibition of involution in the vicinity of deoxycorticosterone- and progesterone-release pellets while prolactin-release pellets were ineffective. Dexamethasone, a very stable and potent glucocorticoid hormone analogue, inhibited involution and programmed cell death in all the mammary glands. It led to an accumulation of milk in the glands and was accompanied by an induction of protein kinase A, AP-1 DNA binding activity and elevated c-fos, junB, and junD mRNA levels. Several potential target genes of AP-1 such as stromelysin-1, c-jun, and SGP-2 that are induced during normal involution were strongly inhibited in dexamethasone-treated animals. Our results suggest that the cross-talk between steroid hormone receptors and AP-1 previously described in cells in culture leads to an impairment of AP-1 activity and to an inhibition of involution in the mammary gland implying that programmed cell death in the postlactational mammary gland depends on functional AP-1.

The human papilloma virus 16E6 gene sensitizes human mammary epithelial cells to apoptosis induced by DNA damage

Programmed cell death (apoptosis) is a normal physiological process, which could in principle be manipulated to play an important role in cancer therapy. The key importance of p53 expression in the apoptotic response to DNA-damaging agents has been stressed because mutant or deleted p53 is so common in most kinds of cancer. An important strategy, therefore, is to find ways to induce apoptosis in the absence of wild-type p53. In this paper, we compare apoptosis in normal human mammary epithelial cells, in cells immortalized with human papilloma virus (HPV), and in mammary carcinoma cell lines expressing wild-type p53, mutant p53, or no p53 protein. Apoptosis was induced with mitomycin C (MMC), a DNA cross-linking and damaging agent, or with staurosporine (SSP), a protein kinase inhibitor. The normal and HPV-transfected cells responded more strongly to SSP than did the tumor cells. After exposure to MMC, cells expressing wild-type p53 underwent extensive apoptosis, whereas cells carrying mutated p53 responded weakly. Primary breast cancer cell lines null for p53 protein were resistant to MMC. In contrast, two HPV immortalized cell lines in which p53 protein was destroyed by E6-modulated ubiquitinylation were highly sensitive to apoptosis induced by MMC. Neither p53 mRNA nor protein was induced in the HPV immortalized cells after MMC treatment, although p53 protein was elevated by MMC in cells with wild-type p53. Importantly, MMC induced p21 mRNA but not p21 protein expression in the HPV immortalized cells. Thus, HPV 16E6 can sensitize mammary epithelial cells to MMC-induced apoptosis via a p53- and p21-independent pathway. We propose that the HPV 16E6 protein modulates ubiquitin-mediated degradation not only of p53 but also of p21 and perhaps other proteins involved in apoptosis.