Protective function of p27(KIP1) against apoptosis in small cell lung cancer cells in unfavorable microenvironments

N-Myc transcriptionally activates Skp2 to suppress p27 expression in small cell lung cancer

BACKGROUND

Small cell lung cancer (SCLC) is characterized by a high proliferative rate, a strong predilection for early metastasis and poor prognosis. Novel SCLC biomarkers are urgently required to improve current diagnostic and treatment modalities. MYCN encodes the proto-oncogene N-Myc that is overexpressed in SCLC, but its downstream effectors are poorly characterized. Here, we investigated the role of the N-Myc/Skp2/p27 axis during SCLC progression.

METHODS

Immunohistochemistry (IHC) and western blotting were performed to evaluate N-Myc/Skp2/p27 expression. SCLC cell apoptosis was investigated through TUNEL staining. Wound healing and transwell assays were performed to detect the migratory and invasive potential of SCLC cells. N-Myc and Skp2 binding was confirmed through luciferase reporter and ChIP assays. Xenograft models were developed to investigate the function of Skp2 during SCLC tumor growth in vivo.

RESULTS

N-Myc and Skp2 were overexpressed in SCLC, whilst p27 expression was suppressed. Skp2 facilitated SCLC progression by protecting cells from apoptosis and facilitating cell migration and invasion. N-Myc was found to bind to the promoter region of Skp2 to enhance its expression. Skp2 enhanced tumor growth in vivo through the suppression of p27. Skp2 silencing reversed the pro-oncogenic effects of N-myc in SCLC tumors.

CONCLUSION

We show that N-Myc enhances Skp2 to regulate p27 expression during SCLC progression. We therefore highlight the N-Myc/Skp2/p27 axis as a novel diagnostic and much-needed therapeutic target in SCLC.

Peroxisome Proliferator Activated Receptor Gamma Sensitizes Non-small Cell Lung Carcinoma to Gamma Irradiation Induced Apoptosis

The nuclear receptors known as peroxisome proliferator activated receptor gamma (PPARG) are lipid-activated transcription factors that have emerged as key regulators of inflammation. PPARG ligands have been shown to have an anti-proliferative effect on a variety of cancers. These ligands can induce apoptosis via TP53 (Tumor protein p53) or ERK1/2 (Extracellular signal-regulated kinases 1/2) (EPHB2) pathways. However, the exact mechanism is not known. PPAR, a type II nuclear hormone receptor deserves attention as a selective target for radiotherapy. Our study examines the potential of selective agonism of PPARG for radiation therapy in non-small cell lung carcinoma (NSCLC). We found that the overexpression of PPARG protein as well as its induction using the agonist, rosiglitazone was able to stimulate radiation-induced cell death in otherwise radio resistant NSCLC A549 cell line. This cell death was apoptotic and was found to be BAX (BCL2 associated X) mediated. The treatment also inhibited radiation-induced AKT (Protein Kinase B) phosphorylation. Interestingly, the ionising radiation (IR) induced apoptosis was found to be inversely related to TP53 levels. A relatively significant increase in the levels of radiation induced apoptosis was observed in H1299 cells (TP53 null) under PPARG overexpression condition further supporting the inverse relationship between apoptosis and TP53 levels. The combination of PPARG agonist and radiation was able to induce apoptosis at a radiation dose at which A549 and H1299 are radioresistant, thus confirming the potential of the combinatorial strategy. Taken together, PPARG agonism was found to invigorate the radiosensitising effect and hence its use in combination with radiotherapy is expected to enhance sensitivity in otherwise resistant cancer types.

New pyrazolo[3,4-d]pyrimidine SRC inhibitors induce apoptosis in mesothelioma cell lines through p27 nuclear stabilization

Malignant mesothelioma (MM) is a highly aggressive tumor of the serous membranes for which there is currently no effective curative modality. Recent data suggest that hyperactivation of the tyrosine kinase SRC has a key role in MM development and therefore this kinase represents an important molecular target for MM therapy. We tested new pyrazolo[3,4-d]pyrimidine SRC inhibitors on a panel of MM cell lines expressing the active form of SRC. These SRC inhibitors exerted a significant proapoptotic effect on MM cells without affecting the normal mesothelial cell line MET-5A, supporting a possible use of these SRC inhibitors for a safe treatment of MM. We also showed that SRC inhibitor-induced apoptosis occurred concomitantly with an increase in the nuclear stability of the cyclin-dependent kinase inhibitor p27. This finding is remarkable considering that loss of nuclear p27 expression is a well-established adverse prognostic factor in MM, and p27 nuclear localization is crucial for its tumor-suppressive function. Consistently, SRC inhibition seems to promote the increase in p27 nuclear level also by inactivating the AKT kinase and downregulating cyclin D1, which would otherwise delay p27 nuclear import and provoke its cytoplasmic accumulation. To determine whether p27 stabilization has a direct role in apoptosis induced by SRC inhibition, we stably silenced the CDKN1B gene, encoding p27, in MSTO-211H and REN mesothelioma cells by transduction with lentiviral vectors expressing short hairpin RNAs against the CDKN1B transcript. Strikingly, p27 silencing was able to suppress the apoptosis induced by these SRC inhibitors in both MM cell lines, suggesting that p27 has a crucial proapoptotic role in MM cells treated with SRC inhibitors. Our findings reveal a new mechanism, dependent on p27 nuclear stabilization, by which SRC inhibition can induce apoptosis in MM cells and provide a new rationale for the use of SRC inhibitors in MM therapy.

Resveratrol protects leukemic cells against cytotoxicity induced by proteasome inhibitors via induction of FOXO1 and p27Kip1

BACKGROUND

It was reported recently that resveratrol could sensitize a number of cancer cells to the antitumoral effects of some conventional chemotherapy drugs. The current study was designed to investigate whether resveratrol could sensitize leukemic cells to proteasome inhibitors.

METHODS

Leukemic cells were treated with MG132 alone or in combination with resveratrol. Cell viability was investigated using MTT assay, and induction of apoptosis and cell cycle distribution was measured using flow cytometry. Western blot and real-time RT-PCR were used to investigate the expression of FOXO1 and p27Kip1. CHIP was performed to investigate the binding of FOXO1 to the p27 Kip1 promoter.

RESULTS

Resveratrol strongly reduced cytotoxic activities of proteasome inhibitors against leukemic cells. MG132 in combination with resveratrol caused cell cycle blockade at G1/S transition via p27Kip1 accumulation. Knockdown of p27Kip1 using siRNA dramatically attenuated the protective effects of resveratrol on cytotoxic actions of proteasome inhibitors against leukemic cells. Resveratrol induced FOXO1 expression at the transcriptional level, while MG132 increased nuclear distribution of FOXO1. MG132 in combination with resveratrol caused synergistic induction of p27Kip1 through increased recruitment of FOXO1 on the p27Kip1 promoter.

CONCLUSIONS

Resveratrol may have the potential to negate the cytotoxic effects of proteasome inhibitors via regulation of FOXO1 transcriptional activity and accumulation of p27Kip1.

Role of cell cycle regulators in lung carcinogenesis

Cellular division is an ordered, tightly regulated process involving multiple checkpoints that assess extracellular growth signals, cell size and DNA integrity. Progression throughout the cell cycle is based on the activation of different CDK-cyclin complexes that prevent cells from entering into a new phase until thay have successfully complete the previous one. In addition, a series of cell cycle checkpoints are designed to preserve genome integrity and chromosomal stability. Neoplastic lung cells develop the ability to bypass several of these checkpoints, and tumor cell proliferation is frequently associated with genetic or epigenetic alterations in key regulators of the cell cycle. The goal of this review is to summarize the knowledge about the dysregulation of major cell cycle regulators in lung cancer pathogenesis and to discuss the use of these proteins as targets for therapeutic intervention.

p21Waf1/Cip1REGULATES PROLIFERATION AND APOPTOSIS IN AIRWAY EPITHELIAL CELLS AND ALTERNATIVE FORMS HAVE ALTERED BINDING ACTIVITIES

p21(Waf1/Cip1) plays central roles in proliferation, differentiation, and apoptosis. Alterations in the expression and subcellular localisation of p21 occur during several lung diseases but the roles of p21 in the lung epithelium are unknown. The effects of p21 on proliferation and apoptosis in mouse airway epithelial cells (AECs) were examined using p21-null mice. AECs isolated from p21-null mice had increased proliferation and apoptotic rates compared to AECs from wild-type mice. Alterations in the subcellular localization of the cell cycle regulatory proteins p27, PCNA, and p53 were also evident in p21(-/-) cells. The nuclear and cytoplasmic forms of p21 present in AECs were also examined. Full-length p21 (20 kDa) was detected in nuclear fractions but a C-terminal truncated form (17 kDa) of p21 was present in cytoplasmic fractions. The binding activities of truncated p21 were altered compared to full-length p21. Although the latter was complexed with PCNA, Cdk2, Cdk4, Cdk6, cyclin D3, and cyclin E, truncated p21 was bound only to Cdk4 and cyclin D3. In conclusion, p21 regulates proliferation and protects against apoptosis in AECs. In addition, different forms of p21 are present in AECs and the subcellular localization of these forms reflects differences in p21 activity.

MicroRNA-221/222 confers tamoxifen resistance in breast cancer by targeting p27Kip1

We explored the role of microRNAs (miRNAs) in acquiring resistance to tamoxifen, a drug successfully used to treat women with estrogen receptor-positive breast cancer. miRNA microarray analysis of MCF-7 cell lines that are either sensitive (parental) or resistant (4-hydroxytamoxifen-resistant (OHT(R))) to tamoxifen showed significant (>1.8-fold) up-regulation of eight miRNAs and marked down-regulation (>50%) of seven miRNAs in OHT(R) cells compared with parental MCF-7 cells. Increased expression of three of the most promising up-regulated (miR-221, miR-222, and miR-181) and down-regulated (miR-21, miR-342, and miR-489) miRNAs was validated by real-time reverse transcription-PCR. The expression of miR-221 and miR-222 was also significantly (2-fold) elevated in HER2/neu-positive primary human breast cancer tissues that are known to be resistant to endocrine therapy compared with HER2/neu-negative tissue samples. Ectopic expression of miR-221/222 rendered the parental MCF-7 cells resistant to tamoxifen. The protein level of the cell cycle inhibitor p27(Kip1), a known target of miR-221/222, was reduced by 50% in OHT(R) cells and by 28-50% in miR-221/222-overexpressing MCF-7 cells. Furthermore, overexpression of p27(Kip1) in the resistant OHT(R) cells caused enhanced cell death when exposed to tamoxifen. This is the first study demonstrating a relationship between miR-221/222 expression and HER2/neu overexpression in primary breast tumors that are generally resistant to tamoxifen therapy. This finding also provides the rationale for the application of altered expression of specific miRNAs as a predictive tamoxifen-resistant breast cancer marker.

The potential role of pharmacogenomic and genomic in the adjuvant treatment of early stage non small cell lung cancer

Although notable progress has been made in the treatment of non-small-cell lung cancer (NSCLC) in recent years, this disease is still associated with a poor prognosis. Despite early-stage NSCLC is considered a potentially curable disease following complete resection, the majority of patients relapse and eventually die after surgery. Adjuvant chemotherapy prolongs survival, altough the absolute improvement in 5-year overall survival is only approximately 5%.Trying to understand the role of genes which could affect drug activity and response to treatment is a major challenge for establishing an individualised chemotherapy according to the specific genetic profile of each patient. Among genes involved in the DNA repair system, the excision repair cross-complementing 1 (ERCC1) is a useful markers of clinical resistance to platinum-based chemotherapy. In the International Lung Cancer Trial (IALT) adjuvant chemotherapy significantly prolonged survival among patients with ERCC1 negative tumors but not among ERCC1-positive patients. BRCA1 and ribonucleotide reductase M1 (RRM1), two other key enzymes in DNA synthesis and repair, appear to be modulators of drug sensitivity and may provide additional information for customizing adjuvant chemotherapy.Several clinical trials suggest that overexpression of class III beta-tubulin is an adverse prognostic factor in cancer since it could be responsible for resistance to anti-tubulin agents. A retrospective analysis of NCIC JBR.10 trial showed that high tubulin III expression is associated with a higher risk of relapse following surgery alone but also with a higher probability of benefit from adjuvant cisplatin plus vinorelbine chemotherapy.Finally, the use of gene expression patterns such as the lung metagene model could provide a potential mechanism to refine the estimation of a patient's risk of disease recurrence and could affect treatment decision in the management of early stage of NSCLC.In this review we will discuss the potential role of pharmacogenomic approaches to guide the medical treatment of early stage NSCLC.

Expression of p21Cip1/Waf1 and p27Kip1 in Small Cell Neuroendocrine Carcinoma of the Uterine Cervix

Small-cell neuroendocrine carcinoma of the uterine cervix (SCCC), a rare but malignant cervical neoplasm, has a highly aggressive phenotype that requires more intensive treatment than other cervical tumors. Immunohistochemical methods were used to compare the expression of p21Cip1/Waf1 and p27Kip1 in SCCC and squamous cell carcinoma, the most common type of cervical cancer. In SCCC, p21 expression was significantly reduced compared with squamous cell carcinoma, whereas expression of p27 was similar in both carcinomas. Reduced expression of p21 could be a helpful diagnostic marker and may contribute to the invasive phenotype of SCCC.

Cell cycle regulators and outcome of adjuvant cisplatin-based chemotherapy in completely resected non-small-cell lung cancer: the International Adjuvant Lung Cancer Trial Biologic Program

PURPOSE

The International Adjuvant Lung Cancer Trial (IALT) demonstrated that adjuvant cisplatin-based chemotherapy improves the survival of patients with completely resected non-small-cell lung cancer (NSCLC). The purpose of our study was to determine whether cell cycle regulators are of prognostic and/or predictive value in patients who were enrolled onto the IALT.

PATIENTS AND METHODS

Expression of p27Kip1, p16INK4A, cyclin D1, cyclin D3, cyclin E, and Ki-67 was immunohistochemically assessed in tumor specimens obtained from 778 IALT patients. Prognostic and predictive analyses were based on Cox models adjusted for clinical and pathologic parameters.

RESULTS

There was a relationship between p27Kip1 status and benefit of cisplatin-based chemotherapy (test for interaction, P = .02). Among patients with p27Kip1-negative tumors, cisplatin-based chemotherapy resulted in longer overall survival compared with controls (adjusted hazard ratio [HR] for death = 0.66; 95% CI, 0.50 to 0.88; P = .006). In patients with p27Kip1-positive tumors, overall survival was not different between patients treated with cisplatin-based chemotherapy and controls (adjusted HR for death = 1.09; 95% CI, 0.82 to 1.45; P = .54). The other cell cycle regulators and Ki-67 did not predict benefit of adjuvant cisplatin-based chemotherapy. None of these biomarkers was significantly associated with overall survival of the patients in the total study population.

CONCLUSION

NSCLC patients with p27Kip1-negative tumors benefit from adjuvant cisplatin-based chemotherapy after complete tumor resection. Before establishing p27Kip1 as a routine marker for selection of patients for adjuvant chemotherapy, the predictive value of p27Kip1 has to be confirmed in patients from other trials.

Reduction of Cytosolic p27Kip1Inhibits Cancer Cell Motility, Survival, and Tumorigenicity

We generated a p27(Kip1) mutant (p27deltaNLS) that localized exclusively in cell cytosol. Expression of p27deltaNLS in MCF7 breast cancer cells down-regulated RhoA and increased motility, survival, and Akt levels without an effect on cell cycle distribution. RNA interference of p27 in U87 glioma cells, which express p27 predominantly in the cytoplasm, inhibited motility and survival. Conversely, knockdown of p27 in COS7 cells, with >95% nuclear p27 expression, accelerated proliferation but had no effect on motility or survival. U87 cells in which p27 had been eliminated by RNA interference exhibited lower Akt levels, shorter Akt turnover, and markedly impaired tumorigenicity in vivo. These xenografts were less invasive and exhibited increased apoptosis compared with p27-expressing tumors. Expression of cytosolic p27 in primary human breast carcinomas correlated linearly with Akt content as measured by immunohistochemistry. These data suggest that cytoplasmic p27 can exert oncogenic functions by modulating Akt stability, cell survival, and tumorigenicity.

Suppression of PI3K/mTOR pathway rescues LLC cells from cell death induced by hypoxia

Cancer cells in solid tumors are challenged by various microenvironmental stresses, including hypoxia, and cancer cells in hypoxic regions are resistant to current cancer therapies. To investigate the mechanism of resistance to hypoxia in cancer cells, we examined mouse Lewis lung carcinoma (LLC) cells, which died due to necrosis at high density under hypoxic but not under normoxic conditions. Levels of mammalian target of rapamycin (mTOR), a central regulator of cellular energy, are reported to be suppressed in hypoxia. We found that phosphorylation of two molecules downstream to it, ribosomal p70 S6 kinase (S6K) and ribosomal protein S6, was markedly suppressed by hypoxia. Overexpression of the active form of S6K increased the sensitivity of LLC cells to hypoxia. On the other hand, inhibition of PI3K or mTOR dramatically reduced hypoxia-induced cell death under hypoxic conditions. Under hypoxic conditions, blockade of the PI3K or mTOR pathway increased levels of intracellular ATP and delayed decreases in pH and glucose level in culture medium, without affecting the cell cycle.

High-Grade Neuroendocrine Carcinoma of the Ampulla of Vater

We describe the clinical and pathologic features of 14 cases of high-grade neuroendocrine carcinoma (HGNEC) of the ampulla of Vater classified according to WHO classification of lung tumors into small cell carcinoma (SCC, 6 cases) and large cell neuroendocrine carcinoma (LCNEC, 8 cases) types. The immunohistochemical findings were compared with those of 13 cases of primary poorly differentiated ampullary adenocarcinomas (PDACA) lacking neuroendocrine morphology. The mean age of 10 males and 4 females was 70 years. The mean tumor size was 2.5 cm. Ten of 13 patients had lymph node metastases (mean, 2.3 nodes involved). Documented sites of distant metastases included brain and liver. Overall, 64% of patients with ampullary HGNEC died of disease (mean follow-up, 14.5 months). Four patients had no evidence of disease after resection (mean, 20 months). Half of the tumors were associated with adenomas of the adjacent mucosa, 2 with high-grade dysplasia. Two HGNECs were combined with a conventional adenocarcinoma and another with a squamous cell carcinoma component. By immunohistochemistry, the HGNECs were positive for cytokeratins (AE1/AE3, 100%; Cam5.2, 67%; CK7, 87%; CK20, 38%), similar to the pattern found in PDACAs. p27 expression was lost in 1 case of HGNEC and in all PDACAs. Retinoblastoma (Rb) protein expression was lost in 60% of HGNECs and in none of the PDACA cases. In conclusion, HGNECs of the ampulla are rare (2%-3% of ampullary tumors in our material). The clinical course parallels that of their pulmonary counterparts and appears to be worse than that of locally advanced ampullary adenocarcinomas. The association with adenoma and or conventional adenocarcinoma components may suggest a common pathway in the initial carcinogenesis of these two types of tumors. Loss of Rb expression, a characteristic finding in pulmonary SCCs, is present in almost half of ampullary HGNECs. In contrast, p27 expression is lost in PDACAs and retained in most HGNECs. Thus, there are differences in the molecular phenotypes of these two types of ampullary carcinoma, supporting the distinction of poorly differentiated carcinomas with a neuroendocrine phenotype from those without.

Histone deacetylase inhibitor BL1521 induces a G1-phase arrest in neuroblastoma cells through altered expression of cell cycle proteins

Histone deacetylase inhibitors (HDACi) have been discovered as potential drugs for cancer treatment. The effect of BL1521, a novel HDACi, on the cell cycle distribution and the induction of apoptosis was investigated in a panel of MYCN single copy and MYCN amplified neuroblastoma cell lines. BL1521 arrested neuroblastoma cells in the G1 phase and induced up to 30% apoptosis. Downregulation of CDK4, upregulation of p21(WAF1/CIP1) and an increase of hypophosphorylated retinoblastoma protein were observed, indicating a possible mechanism for the cell-cycle arrest. BL1521 also induced downregulation of p27, which may underlie the observed induction of apoptosis.

Nutritional deficiency affects cell cycle status and viability in A549 cells: role of p27Kip1

We investigated how nutritional deficiency affects cell cycle and cell viability in A549 lung adenocarcinoma cells. Deprivation of various amino acids or glucose induced cell cycle arrest and cell death in a different manner. Cell death on deprivation of these nutrients was increased by downregulating of p27Kip1 with RNA interference. It was also observed that intrinsic p27Kip1 was segregated in cytoplasm in a glucose-deprived situation. In conclusion, amino acid or glucose deprivation induced cell cycle arrest and cell death, part of which is thought to be rescued by the existence of cytoplasmic p27Kip1.

Hypoxia inhibits human bladder smooth muscle cell proliferation: a potential mechanism of bladder dysfunction

AIMS

Recent animal studies have suggested that bladder outflow obstruction causes bladder wall hypoxia during both the filling and the voiding phases of the micturition cycle. We have previously demonstrated that mechanical deformation of human detrusor leads to smooth muscle (SM) cell hypertrophy and hyperplasia, which may then contribute to hypoxia in the dysfunctional bladder. We hypothesise that the detrusor's response to a hypoxic environment contributes to bladder dysfunction. The aim of this study was to evaluate the effect of hypoxia on detrusor cell survival and growth.

METHODS

Normal human detrusor muscle was obtained at radical cystectomy and primary cultures were established. Cells were then cultured in the presence of 1% oxygen in a hypoxic chamber for different times. Apoptosis was assessed by propidium iodide DNA staining and flow cytometry. Proliferation was assessed by radiolabelled thymidine incorporation. Cell supernatants were retained for growth factor estimation by enzyme linked immuno-sorbent assay (ELISA), and total cell and nuclear extracts were isolated for Western blotting.

RESULTS

SM cells responded to the presence of hypoxia through significant upregulation of survival factors hypoxia inducible factor (HIF 1alpha) and vascular endothelial growth factor (VEGF) in a time-dependent manner. Hypoxia did not induce cell death, but significantly reduced the rate of proliferation over time, associated with an increase in the cell cycle inhibitor p27kip1.

CONCLUSIONS

In an in vitro human detrusor cell culture model, cells demonstrate a resistance to hypoxia-induced apoptosis but proliferation is inhibited. We suggest that the anti-proliferative effects of hypoxia may limit the ability of detrusor cells to respond to, and compensate for, alterations in their environment contributing to bladder dysfunction.

P27kip1 regulates the apoptotic response of gastric epithelial cells to Helicobacter pylori

BACKGROUND

Helicobacter pylori infection increases the risk of gastric cancer but the molecular mechanisms responsible are not well understood. Gastric cells chronically exposed to H pylori in vitro develop resistance to apoptosis associated with low levels of p27, a cyclin dependent kinase inhibitor and haplo insufficient tumour suppressor gene that is downregulated in gastric cancer.

AIM

To determine whether the low level of p27 protein is responsible for the resistance to apoptosis of gastric cancer cells.

METHODS

The effects of increasing the expression of p27 protein were examined by transiently and stably transfecting a plasmid encoding full length p27 mRNA into apoptosis resistant gastric cancer cell lines with low p27 expression that were derived from AGS gastric cancer cells by chronic H pylori coculture followed by dilutional cloning.

RESULTS

Low p27 expression in the apoptosis resistant derivative cell lines was associated with an approximate 30% decrease in p27 mRNA and an 80% decrease in p27 protein that was not due to increased proteasome dependent degradation of p27 protein. Transient or stable transfection with p27 constructs partially restored the sensitivity of the apoptosis resistant cells to 5-fluorouracil and H pylori induced apoptosis without altering spontaneous apoptotic cell death.

CONCLUSIONS

These results demonstrate that p27 positively regulates, at least in part, the apoptotic response of gastric epithelial cells to H pylori. Low gastric p27 may promote gastric carcinogenesis associated with H pylori infection by inhibiting apoptotic pathways.

The cyclin-dependent kinase inhibitor p27 (Kip1) regulates both DNA synthesis and apoptosis in mammary epithelium but is not required for its functional development during pregnancy

Decreased expression of the cyclin-dependent kinase (CDK) inhibitor p27(Kip1) is common in breast cancer and is associated with poor prognosis. p27 is also an important mediator of steroidal regulation of cell cycle progression. We have therefore investigated the role of p27 in mammary epithelial cell proliferation. Examination of the two major functions of p27, assembly of cyclin D1-Cdk4 complexes and inhibition of Cdk2 activity, revealed that cyclin D1-Cdk4 complex formation was not impaired in p27-/- mammary epithelial cells in primary culture. However, cyclin E-Cdk2 activity was increased approximately 3-fold, indicating that the CDK inhibitory function of p27 is important in mammary epithelial cells. Increased epithelial DNA synthesis was observed during pregnancy in p27-/- mammary gland transplants, but this was paralleled by increased apoptosis. During pregnancy and at parturition, development and differentiation of p27+/+ and p27-/- mammary tissue were indistinguishable. These results demonstrate a role for p27 in both the proliferation and survival of mammary epithelial cells. However, the absence of morphological and cellular defects in p27-/- mammary tissue during pregnancy raises the possibility that loss of p27 in breast cancer may not confer an overall growth advantage unless apoptosis is also impaired.

Fludarabine-induced apoptosis of B chronic lymphocytic leukemia cells includes early cleavage of p27kip1 by caspases

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of growth arrested clonal B lymphocytes that undergo apoptosis when treated with fludarabine. To further explore the mechanism for the cell cycle arrest, we examined the expression and activity of cyclin-dependent kinases and inhibitors in primary B-CLL cells. We observed high levels of p27kip1, cyclin D2, cyclin E, cdk2, and cdk4 expression in freshly isolated B-CLL cells. Despite high levels of cyclins and cdks, little cdk2 or cdk4 activity was observed with p27kip1 in complex with cyclinD2/cdk4 and cyclin E/cdk2. Remarkably, when B-CLL cells were treated in vitro with fludarabine, p27kip1 underwent caspase-specific degradation accompanied by an increase in cdk4 activity. We conclude that the G0/G1 arrest of B-CLL cells may protect against apoptosis and that the decrease in p27kip1 expression by caspase cleavage may be a key step in chemotherapy-induced apoptosis in B-CLL.

Expression of p27KIP1 in human gliomas: relationship between tumor grade, proliferation index, and patient survival

Numerous studies examining the prognostic significance of p27KIP1 expression in human cancer have shown that decreased expression often is an independent prognostic factor associated with worse survival. However, the prognostic value of p27KIP1 expression in gliomas is less well established. To further address this issue, we evaluated the relationship between p27KIP1 protein expression in a series of 50 astrocytomas with clinicopathologic parameters including age, tumor grade, MIB-1 proliferation index, and patient survival using both Western blot analysis and immunohistochemistry. The level of p27KIP1 protein expression in 9 nonneoplastic brain tissue specimens served as a control. Sixteen high-grade astrocytomas were analyzed by Western blot, and 26 high-grade astrocytomas were analyzed by immunohistochemistry for levels of p27KIP1 protein expression. Regardless of the technique used to measure p27KIP1, approximately 50% of the high-grade tumors were low expressors and the other 50% were high expressors. Thus, expression of p27KIP1 was independent of tumor grade. Loss of p27KIP1 expression is often associated with an increase in proliferative activity. We measured the rate of tumor cell proliferation using MIB-1 immunostaining in 16 high-grade astrocytomas to determine whether there was an inverse correlation between p27KIP1 expression and proliferation. No correlation between p27KIP1 expression and MIB-1 labeling index or patient survival was found. Using immunohistochemistry, we noted that the staining pattern of p27KIP1 in glioblastomas was mainly in the pseudopalisading cells that outline areas of necrosis. Because p27KIP1 can be up-regulated by hypoxia, this staining pattern would be consistent with our observation that hypoxia-inducible factor 1alpha is expressed primarily in pseudopalisading tumor cells around necrotic zones. It has been shown that a high level of p27KIP1 prevents apoptosis in hypoxic cells. Thus, maintenance of high levels of p27KIP1 in gliomas could result from the hypoxic microenvironment present within the tumor. No correlation was found between p27KIP1 expression and any of the clinicopathologic parameters tested, including patient age and tumor grade, the 2 strongest predictors of survival among glioma patients.

Genetic alterations of multiple tumor suppressors and oncogenes in the carcinogenesis and progression of lung cancer

Lung cancer has become the leading cause of cancer death in many economically well-developed countries. Recent molecular biological studies have revealed that overt lung cancers frequently develop through sequential morphological steps, with the accumulation of multiple genetic and epigenetic alterations affecting both tumor suppressor genes and dominant oncogenes. Cell cycle progression needs to be properly regulated, while cells have built-in complex and minute mechanisms such as cell cycle checkpoints to maintain genomic integrity. Genes in the p16INK4A-RB and p14ARF-p53 pathways appear to be a major target for genetic alterations involved in the pathogenesis of lung cancer. Several oncogenes are also known to be altered in lung cancer, leading to the stimulation of autocrine/paracrine loops and activation of multiple signaling pathways. It is widely acknowledged that carcinogens in cigarette smoke are deeply involved in these multiple genetic alterations, mainly through the formation of DNA adducts. A current understanding of the molecular mechanisms of lung cancer pathogenesis and progression is presented in relation to cigarette smoking, an absolute major risk factor for lung cancer development, by reviewing genetic alterations of various tumor suppressor genes and oncogenes thus far identified in lung cancer, with brief summaries of their functions and regulation.

Persistent increase in chromosome instability in lung cancer: possible indirect involvement of p53 inactivation

Karyotype and fluorescence in situ hybridization analyses have demonstrated the frequent presence of an altered static state of the number of chromosomes (ie, aneuploidy) in lung cancer, but it has not been directly established whether aneuploidy is in fact associated with a persistent increase in the rate of chromosomal losses and gains (ie, chromosome instability, or CIN). The study presented here used a panel of 10 lung cancer cell lines to provide for the first time direct evidence that CIN is a common feature in lung cancer cell lines in association with the presence of significant aneuploidy. In addition, we found that the CIN phenotype correlates well with the presence of p53 mutations. However, human papilloma virus 16-E6-directed inactivation of p53 in a representative non-CIN lung cancer cell line did not result in the induction of CIN, at least up to the 25th generation, suggesting that inactivation of p53 itself is unlikely to directly induce CIN in lung cancer cells. Interestingly, however, significant CIN could be induced in conjunction with the generation of aneuploid populations when the mitotic spindle formation was transiently abrogated in p53-inactivated cells. These results suggest that inactivation of p53 may allow lung cancer cells to go through an inappropriate second division cycle under certain forms of mitotic stresses, which would result in the induction of the CIN phenotype in conjunction with the generation of aneuploidy.