Mutational analysis of p73 and p53 in human cancer cell lines

Analyses of p73 Protein Oligomerization and p73-MDM2 Interaction in Single Living Cells Using In Situ Single Molecule Spectroscopy

Protein oligomerization and protein-protein interaction are crucial to regulate protein functions and biological processes. p73 protein is a very important transcriptional factor and can promote apoptosis and cell cycle arrest, and its transcriptional activity is regulated by p73 oligomerization and p73-MDM2 interaction. Although extracellular studies on p73 oligomerization and p73-MDM2 interaction have been carried out, it is unclear how p73 oligomerization and p73-MDM2 interaction occur in living cells. In our study, we described an in situ method for studying p73 oligomerization and p73-MDM2 interaction in living cells by combining fluorescence cross-correlation spectroscopy with a fluorescent protein labeling technique. Lentiviral transfection was used to transfect cells with a plasmid for either p73 or MDM2, each fused to a different fluorescent protein. p73 oligomerization was evaluated using brightness per particle, and the p73-MDM2 interaction was quantified using the cross-correlation value. We constructed a series of p73 mutants in three domains (transactivation domain, DNA binding domain, and oligomerization domain) and MDM2 mutants. We systematically studied p73 oligomerization and the effects of p73 oligomerization and the p73 and MDM2 structures on the p73-MDM2 interaction in single living cells. We have found that the p73 protein can form oligomers and that the p73 structure changes in the oligomerization domain significantly influence its oligomerization. p73 oligomerization and the structure changes significantly affect the p73-MDM2 interaction. Furthermore, the effects of inhibitors on p73 oligomerization and p73-MDM2 interaction were studied.

The dominant-negative interplay between p53, p63 and p73: A family affair

The tumor suppression activity of p53 is frequently impaired in cancers even when a wild-type copy of the gene is still present, suggesting that a dominant-negative effect is exerted by some of p53 mutants and isoforms. p63 and p73, which are related to p53, have also been reported to be subjected to a similar loss of function, suggesting that a dominant-negative interplay might happen between p53, p63 and p73. However, to which extent p53 hotspot mutants and isoforms of p53, p63 and p73 are able to interfere with the tumor suppressive activity of their siblings as well as the underlying mechanisms remain undeciphered. Using yeast, we showed that a dominant-negative effect is widely spread within the p53/p63/p73 family as all p53 loss-of-function hotspot mutants and several of the isoforms of p53 and p73 tested exhibit a dominant-negative potential. In addition, we found that this dominant-negative effect over p53 wild-type is based on tetramer poisoning through the formation of inactive hetero-tetramers and does not rely on a prion-like mechanism contrary to what has been previously suggested. We also showed that mutant p53-R175H gains the ability to inhibit p63 and p73 activity by a mechanism that is only partially based on tetramerization.

Hyper-O-GlcNAcylation induces cisplatin resistance via regulation of p53 and c-Myc in human lung carcinoma

Aberrant metabolism in hexosamine biosynthetic pathway (HBP) has been observed in several cancers, affecting cellular signaling and tumor progression. However, the role of O-GlcNAcylation, a post-translational modification through HBP flux, in apoptosis remains unclear. Here, we found that hyper-O-GlcNAcylation in lung carcinoma cells by O-GlcNAcase inhibition renders the cells to apoptosis resistance to cisplatin (CDDP). Profiling of various key regulatory proteins revealed an implication of either p53 or c-Myc in the apoptosis regulation by O-GlcNAcylation, independent of p53 status. Using co-immunoprecipitation and correlation analyses, we found that O-GlcNAcylation of p53 under certain cellular contexts, i.e. high p53 activation, promotes its ubiquitin-mediated proteasomal degradation, resulting in a gain of oncogenic and anti-apoptotic functions. By contrast, O-GlcNAcylation of c-Myc inhibits its ubiquitination and subsequent proteasomal degradation. Gene manipulation studies revealed that O-GlcNAcylation of p53/c-Myc is in part a regulator of CDDP-induced apoptosis. Accordingly, we classified CDDP resistance by hyper-O-GlcNAcylation in lung carcinoma cells as either p53 or c-Myc dependence based on their molecular targets. Together, our findings provide novel mechanisms for the regulation of lung cancer cell apoptosis that could be important in understanding clinical drug resistance and suggest O-GlcNAcylation as a potential target for cancer therapy.

Lovastatin causes FaDu hypopharyngeal carcinoma cell death via AMPK-p63-survivin signaling cascade

Statins are used widely to lower serum cholesterol and the incidence of cardiovascular diseases. Growing evidence shows that statins also exhibit beneficial effects against cancers. In this study, we investigated the molecular mechanisms involved in lovastatin-induced cell death in Fadu hypopharyngeal carcinoma cells. Lovastatin caused cell cycle arrest and apoptosis in FaDu cells. Lovastatin increased p21^cip/Waf1 level while the survivin level was decreased in the presence of lovastatin. Survivin siRNA reduced cell viability and induced cell apoptosis in FaDu cells. Lovastatin induced phosphorylation of AMP-activated protein kinase (AMPK), p38 mitogen-activated protein kinase (MAPK) and transcription factor p63. Lovastatin also caused p63 acetylation and increased p63 binding to survivin promoter region in FaDu cells. AMPK-p38MAPK signaling blockade abrogated lovastatin-induced p63 phosphorylation. Lovastatin’s enhancing effect on p63 acetylation was reduced in HDAC3- or HDAC4- transfected cells. Moreover, transfection of cells with AMPK dominant negative mutant (AMPK-DN), HDAC3, HDAC4 or p63 siRNA significantly reduced lovastatin’s effects on p21^cip/Waf1 and survivin. Furthermore, lovastatin inhibited subcutaneous FaDu xenografts growth in vivo. Taken together, lovastatin may activate AMPK-p38MAPK-p63-survivin cascade to cause FaDu cell death. This study establishes, at least in part, the signaling cascade by which lovastatin induces hypopharyngeal carcinoma cell death.

Proteasome inhibitors suppress the protein expression of mutant p53

Tumor suppressor p53 is one of the most frequently mutated genes in cancer, with almost 50% of all types of cancer expressing a mutant form of p53. p53 transactivates the expression of its primary negative regulator, HDM2. HDM2 is a ubiquitin ligase, which initiates the proteasomal degradation of p53 following ubiquitination. Proteasome inhibitors, by targeting the ubiquitin proteasome pathway inhibit the degradation of the majority of cellular proteins including wild-type p53. In contrast, in this study we found that the protein expression of mutant p53 was suppressed following treatment with established or novel proteasome inhibitors. Furthermore, for the first time we demonstrated that Arsenic trioxide, which was previously shown to suppress mutant p53 protein level, exhibits proteasome inhibitory activity. Proteasome inhibitor-mediated suppression of mutant p53 was partially rescued by the knockdown of HDM2, suggesting that the stabilization of HDM2 by proteasome inhibitors might be responsible for mutant p53 suppression to some extent. This study suggests that suppression of mutant p53 is a general property of proteasome inhibitors and it provides additional rationale to use proteasome inhibitors for the treatment of tumors with mutant p53.

In vitro cytotoxic and pro-apoptotic effects of water extracts of Tulbaghia violacea leaves and bulbs

ETHNOPHARMACOLOGICAL RELEVANCE

Infusions of Tulbaghia violacea (wild garlic) in water are used in traditional medicine in Southern Africa to treat numerous diseases, including cancer. Several studies have previously demonstrated the cytotoxic activities of extracts of T. violacea in cultured cancer cells. Their findings support the potential anti-cancer properties of this plant. However, these studies made use of organic solvent extraction methods, while the traditional use of the plant involves the preparation of infusions in water.

MATERIALS AND METHODS

In the current study, we investigated the potential anti-cancer properties of infusions of T. violacea. We also performed a comparative study investigating the cytotoxic activities of T. violacea bulbs and leaves. A panel of four cancer cell lines (HepG2, MCF7, H157, and HT29) and one non-cancerous cell line (KMST6) was treated with the two extracts and the effects of the extracts on the growth of the cells were evaluated. We also investigated whether the growth inhibitory effects were associated with the induction of apoptosis and whether the mechanism of cell death is the result of oxidative stress and the activation of caspase-3.

RESULT

We found that extracts of the leaves and not the bulbs have growth inhibitory effects and that this is the result of the induction of apoptosis, which is associated with the production of Reactive Oxygen Species (ROS) and the activation of caspase-3. The leaf extract demonstrated variable selective toxicity towards the cancer lines. Although the extract also induced cell death in the non-cancerous cell line (KMST6), we found that the levels of toxicity were lower in this cell line.

CONCLUSION

this study confirms that infusions of T. violacea have potential anti-cancer activity and that this bioactivity is contained in the leaf extract. This study lends support to claims that this plant can be used to treat cancer.

Effect of combined 5-aza-2'deoxycytidine and cisplatin treatment on the P15 lung adenocarcinoma cell line

Aberrant promoter hypermethylation resulting in the epigenetic silencing of apoptosis-associated genes is a key process in the chemotherapeutic treatment of cancer. The nucleoside analog, 5-aza-2'deoxycytidine (DAC), inhibits the activity of DNA methyltransferase enzymes and is able to restore the expression levels of genes that have been silenced by aberrant DNA methylation. The aim of the present study was to investigate the effect of combined treatment with DAC and cisplatin (CDDP) on the lung adenocarcinoma cell line, P15. Growth inhibition was examined using a clone formation assay and growth inhibitory activities by cell counting during treatment with DAC alone, CDDP alone or DAC followed by CDDP. In addition, changes in the mRNA expression levels of various apoptosis-associated genes following treatment with increasing concentrations of DAC were determined using reverse transcription-polymerase chain reaction. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) analysis was used to detect the number of apoptotic P15 tumor cells following treatment with DAC and/or CDDP. The results indicated that DAC treatment alone restored the mRNA expression levels of p73, p16^INK4a , B-cell lymphoma (Bcl)-2-associated agonist of cell death and Bcl-2-associated X protein. In addition, combined therapy with DAC and CDDP was found to significantly suppress the growth of P15 tumor cells compared with DAC or CDDP treatment alone. In conclusion, DAC may enhance the chemosensitivity of the P15 cell line to treatment with CDDP.

Local mitochondrial-endolysosomal microfusion cleaves voltage-dependent anion channel 1 to promote survival in hypoxia

The oxygen-limiting (hypoxic) microenvironment of tumors induces metabolic reprogramming and cell survival, but the underlying mechanisms involving mitochondria remain poorly understood. We previously demonstrated that hypoxia-inducible factor 1 mediates the hyperfusion of mitochondria by inducing Bcl-2/adenovirus E1B 19-kDa interacting protein 3 and posttranslational truncation of the mitochondrial ATP transporter outer membrane voltage-dependent anion channel 1 in hypoxic cells. In addition, we showed that truncation is associated with increased resistance to drug-induced apoptosis and is indicative of increased patient chemoresistance. We now show that silencing of the tumor suppressor TP53 decreases truncation and increases drug-induced apoptosis. We also show that TP53 regulates truncation through induction of the mitochondrial protein Mieap. While we found that truncation was independent of mitophagy, we observed local microfusion between mitochondria and endolysosomes in hypoxic cells in culture and in patients' tumor tissues. Since we found that the endolysosomal asparagine endopeptidase was responsible for truncation, we propose that it is a readout of mitochondrial-endolysosomal microfusion in hypoxia. These novel findings provide the framework for a better understanding of hypoxic cell metabolism and cell survival through mitochondrial-endolysosomal microfusion regulated by hypoxia-inducible factor 1 and TP53.

Interferon-α acts on the S/G2/M phases to induce apoptosis in the G1 phase of an IFNAR2-expressing hepatocellular carcinoma cell line

Interferon-α (IFN-α) is used clinically to treat hepatocellular carcinoma (HCC), although the detailed therapeutic mechanisms remain elusive. In particular, IFN-α has long been implicated in control of the cell cycle, but its actual point of action has not been clarified. Here, using time lapse imaging analyses of the human HCC cell line HuH7 carrying a fluorescence ubiquitination-based cell cycle indicator (Fucci), we found that IFN-α induced cell cycle arrest in the G0/G1 phases, leading to apoptosis through an IFN-α type-2 receptor (IFNAR2)-dependent signaling pathway. Detailed analyses by time lapse imaging and biochemical assays demonstrated that the IFN-α/IFNAR2 axis sensitizes cells to apoptosis in the S/G2/M phases in preparation for cell death in the G0/G1 phases. In summary, this study is the first to demonstrate the detailed mechanism of IFN-α as an anticancer drug, using Fucci-based time lapse imaging, which will be informative for treating HCC with IFN-α in clinical practice.

Alterations of p63 and p73 in human cancers

p53 and its related genes, p63 and p73 constitute the p53 gene family. While p53 is the most frequently mutated gene in human tumors, p63 and p73 are rarely mutated or deleted in cancers. Many studies have reported p63/p73 overexpression in human cancers while others showed that a loss of p63/p73 is associated with tumor progression and metastasis. Thus, whether p63 or p73 is a tumor suppressor gene or an oncogene has been a matter of debate. This controversy has been attributed to the existence of multiple splicing isoforms with distinct functions; the full-length TA isoform of p63 has structural and functional similarity to wild-type p53, whereas the ΔNp63 acts primarily in dominant-negative fashion against all family members of p53. Differential activities of TA and ΔN isoforms have been shown in vivo by creating isform-specific gene knockout mice. All p53, p63, p73 proteins bind to and activate target genes with p53-response elements; p63 also binds to distinct p63-response elements and regulate expression of specific target genes involved in skin, limb, and craniofacial development. Interestingly, several studies have shown that both p63 and p73 are involved in cellular response to cancer therapy and others have indicated that both of these molecules are required for p53-induced apoptosis, suggesting functional interplay among p53 family proteins. Consistent with these findings, aberrant splicing that result in ΔNp63 or ΔNp73 overexpression are frequently found in human cancers, and is associated with poor clinical outcomes of patients in the latter. Thus immunohistochemical staining of tumor specimen with ΔNp73-specific antibody might have diagnostic values in cancer clinics.

LncRNA pathway involved in premature preterm rupture of membrane (PPROM): an epigenomic approach to study the pathogenesis of reproductive disorders

Preterm birth (PTB) is a live birth delivered before 37 weeks of gestation (GW). About one-third of PTBs result from the preterm premature rupture of membranes (PPROM). Up to the present, the pathogenic mechanisms underlying PPROM are not clearly understood. Here, we investigated the differential expression of long chain non-coding RNAs (lncRNAs) in placentas of PTBs with PPROM, and their possible involvement in the pathogenic pathways leading to PPROM. A total number of 1954, 776, and 1050 lncRNAs were identified with a microarray from placentas of PPROM (group A), which were compared to full-term birth (FTB) (group B), PTB (group C), and premature rupture of membrane (PROM) (group D) at full-term, respectively. Instead of investigating the individual pathogenic role of each lncRNA involved in the molecular mechanism underlying PPROM, we have focused on investigating the metabolic pathways and their functions to explore what is the likely association and how they are possibly involved in the development of PPROM. Six groups, including up-regulation and down-regulation in the comparisons of A vs. B, A vs. C, and A vs. D, of pathways were analyzed. Our results showed that 22 pathways were characterized as up-regulated 7 down-regulated in A vs. C, 18 up-regulated and 15 down-regulated in A vs. D, and 33 up-regulated and 7 down-regulated in A vs. B. Functional analysis showed pathways of infection and inflammatory response, ECM-receptor interactions, apoptosis, actin cytoskeleton, and smooth muscle contraction are the major pathogenic mechanisms involved in the development of PPROM. Characterization of these pathways through identification of lncRNAs opened new avenues for further investigating the epigenomic mechanisms of lncRNAs in PPROM as well as PTB.

Mechanism of T-oligo-induced cell cycle arrest in Mia-PaCa pancreatic cancer cells

DNA oligonucleotides with sequence homology to human telomeric DNA (T-oligo) induce cell cycle arrest, followed by apoptosis, senescence, or autophagy in a human cancer cell type-specific manner. T-oligo has potential as a new therapeutic strategy in oncology because of its ability to target certain types of tumor cells while sparing normal ones. In the present study, we demonstrate the T-oligo-induced S-phase cell cycle arrest in four pancreatic cancer cell lines. To further contribute to the mechanistic understanding of T-oligo, we also identify cyclin dependent kinase 2 (cdk2) as a functional mediator in the T-oligo-induced cell cycle arrest of pancreatic cancer cells. Ectopic expression of a constitutively active cdk2 mutant abrogates T-oligo-induced cell cycle arrest in these tumor cells while knockdown of cdk2 expression alone recapitulates the T-oligo effect. Finally, we demonstrate the dispensability of T-oligo-induced ATM/ATR-mediated DNA damage response-signaling pathways, which have long been considered functional in the T-oligo signaling mechanism.

Reactivation of p53 mutants by prima-1 [corrected] in thyroid cancer cells

Most undifferentiated thyroid carcinomas express p53 mutants and thereafter, are very resistant to chemotherapy. p53 reactivation and induction of massive apoptosis (Prima-1) is a compound restoring the tumor-suppressor activity of p53 mutants. We tested the effect of Prima-1 in thyroid cancer cells harboring p53 mutations. Increasing doses of Prima-1 reduced viability of thyroid cancer cells at a variable extent (range 20-80%). Prima-1 up-regulated p53 target genes (p21(WAF1) , BCL2-associated X protein (Bax), and murine double minute 2 (MDM2)), in BC-PAP and Hth-74 cells (expressing D259Y/K286E and K286E p53 mutants) but had no effect in SW1736 (p53 null) and TPC-1 (expressing wild-type p53) thyroid cancer cells. Prima-1 also increased the cytotoxic effects of either doxorubicin or cisplatin in thyroid cancer cells, including the chemo-resistant 8305C, Hth-74 and BC-PAP cells. Moreover, real-time PCR and Western blot indicated that Prima-1 increases the mRNA of thyroid-specific differentiation markers in thyroid cancer cells. Fluorescence-activated cell sorting analysis revealed that Prima-1 effect on thyroid cancer cells occurs via the enhancement of both cell cycle arrest and apoptosis. Small interfering RNA experiments indicated that Prima-1 effect is mediated by p53 mutants but not by the p53 paralog p73. Moreover, in C-643 thyroid cancer cells, forced to ectopically express wild-type p53, Prima-1 prevented the dominant negative effect of double K248Q/K286E p53 mutant. Finally, co-IP experiments indicated that in Hth-74 cells Prima-1 prevents the ability of p53 mutants to sequestrate the p53 paralog TAp73. These in vitro studies imply that p53 mutant reactivation by small compounds may become a novel anticancer therapy in undifferentiated thyroid carcinomas.

Modulation of the E2F1-driven cancer cell fate by the DNA damage response machinery and potential novel E2F1 targets in osteosarcomas

Osteosarcoma is the most common primary bone cancer. Mutations of the RB gene represent the most frequent molecular defect in this malignancy. A major consequence of this alteration is that the activity of the key cell cycle regulator E2F1 is unleashed from the inhibitory effects of pRb. Studies in animal models and in human cancers have shown that deregulated E2F1 overexpression possesses either "oncogenic" or "oncosuppressor" properties, depending on the cellular context. To address this issue in osteosarcomas, we examined the status of E2F1 relative to cell proliferation and apoptosis in a clinical setting of human primary osteosarcomas and in E2F1-inducible osteosarcoma cell line models that are wild-type and deficient for p53. Collectively, our data demonstrated that high E2F1 levels exerted a growth-suppressing effect that relied on the integrity of the DNA damage response network. Surprisingly, induction of p73, an established E2F1 target, was also DNA damage response-dependent. Furthermore, a global proteome analysis associated with bioinformatics revealed novel E2F1-regulated genes and potential E2F1-driven signaling networks that could provide useful targets in challenging this aggressive neoplasm by innovative therapies.

Transcriptional activation of the tumor suppressor and differentiation gene S100A2 by a novel p63-binding site

S100A2 is generally found expressed in the epidermis and was recently shown to play a crucial role in the differentiation of keratinocytes. Also known as CaN19, S100A2 was identified as a potential tumor suppressor. Expression of S100A2 is upregulated by p53. The proteins p63 and p73 are related to p53 and are expressed as several splice variants with partially overlapping tasks but also functions different from p53. It had been shown that p63 proteins with mutations in their DNA-binding domain cause severe phenotypes in man as autosomal dominantly inherited disease including EEC, AEC, SHFM, LMS and ADULT syndromes. Here we show that S100A2 is a transcriptional target of p63/p73 family members, particularly the p63 splice variant TAp63γ. The regulation is mediated by a novel transcriptional element in the S100A2 promoter which is bound by TAp63γ but not by p53. Mutant p63 proteins derived from EEC and ADULT syndrome patients cannot activate S100A2 transcription whereas SHFM-related mutants still can stimulate the S100A2 promoter. Consistent with a function in tumor suppression S100A2 expression is stimulated upon DNA damage. After doxorubicin treatment p63γ proteins are recruited to the S100A2 promoter in vivo. This may indicate a function of the p63-dependent S100A2 regulation in tumor suppression.

Molecular markers in lung cancer: prognostic role and relationship to smoking

Epidemiological studies have demonstrated a causal relationship between smoking and lung cancer. Although most lung cancer cases are linked to smoking, only a minority of heavy smokers develop lung cancer, leading to the notion that genetic factors affect individual susceptibility. The principal molecular changes in lung cancer are seen in tumor suppressor genes, proto-oncogenes, growth factors, telomerase activity, and methylation status of promoters. Well-known agents include angiogenesis-stimulating factors (such as vascular endothelial growth factor), as well as factors related to tumor cell proliferation and apoptosis (epidermal growth factor receptor, p53, K-ras, retinoblastoma and BCL-2). Several of these genetic factors have already been investigated, but no single parameter has yet presented sufficient selectivity regarding prognostic value or therapeutic efficacy. Treatment strategies to cure lung cancer should focus on these early genetic lesions in order to promote their repair or to eliminate these lung cancer cells.

Effect of combined therapy with low-dose 5-aza-2'-deoxycytidine and irinotecan on colon cancer cell line HCT-15

BACKGROUND

Aberrant promoter hypermethylation is an epigenetic change that silences the expression of crucial genes, resulting in inactivation of the apoptotic pathway in various cancers. This hypermethylation can be restored by the demethylating agent 5-aza-2'-deoxycytidine (DAC). DAC might increase the tumor sensitivity to chemotherapy through demethylation and restoration of gene expression. We investigated the effect of combined therapy with DAC and irinotecan (CPT-11) on the human colon cancer cell line HCT-15.

METHODS

Human colon cancer cell line HCT-15 was treated with DAC and/or CPT-11 both in vitro and in vivo. The changes in mRNA expression of several apoptosis-related genes were investigated by reverse transcriptase-polymerase chain reaction (PCR). Promoter methylation was detected by methylation-specific PCR and combined bisulfite restriction analysis. Suppression of tumor growth was observed during the treatment with DAC and/or CPT-11 and apoptosis in the tumors was investigated by TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) assay.

RESULTS

Promoter methylation of p14ARF, p16 INK4a, BNIP3, and XAF1 was confirmed, and DAC restored mRNA expression of these genes. Demethylation and restoration of gene expression was observed with low-dose DAC, and demethylation status was sustained for several weeks. Combined therapy with DAC and CPT-11 produced marked suppression in tumor growth compared with DAC or CPT-11 alone, both in vitro and in vivo.

CONCLUSIONS

Pretreatment with low-dose DAC may have the potential to be used as a "biosensitizer" of DNA-damaging agents such as CPT-11 when the apoptotic pathway is inactivated as a result of aberrant promoter methylation in the cancer.

Inhibition of the 53BP2S-mediated apoptosis by nuclear factor kappaB and Bcl-2 family proteins

The p53 binding protein 2 (53BP2) has been identified independently as the interacting protein to p53, Bcl-2, and p65 subunit of nuclear factor kappaB (NF-kappaB). It was demonstrated that over-expression of 53BP2 (renamed as 53BP2S) induces apoptotic cell death. In this study we explored the effect of NF-kappaB activation elicited by a physiological NF-kappaB inducer, interleukin-1beta (IL-1beta), and anti-apoptotic Bcl-2 family proteins on the 53BP2S-mediated apoptosis. We found that both NF-kappaB activation and Bcl-2 family proteins could prevent the 53BP2S-mediated depression of mitochondrial transmembrane potential, activation of caspase-9, cleavage of poly ADP ribose polymerase (PARP), and cell death. These observations suggested that 53BP2S/Bbp and its directly or indirectly interacting proteins might play crucial roles in the regulation of apoptosis and contribute to carcinogenesis. It is also suggested that 53BP2S/Bbp induces apoptosis through the mitochondrial death pathway presumably by counteracting the actions of anti-apoptotic Bcl-2 family proteins. The regulatory network of the 53BP2S-mediated apoptosis cascade including its interacting proteins is discussed.

Effects of inducible overexpression of DNp73alpha on cancer cell growth and response to treatment in vitro and in vivo

The p73 gene has a complex regulation, which leads to the expression of different isoforms, often with opposite biological effects. We have generated in the human colocarcinoma cell line HCT116, expressing a wild-type p53, an inducible DNp73alpha expressing system. Two clones (HCT116/DN3 and HCT116/DN14), upon doxycycline addition, show a strong expression of DNp73alpha. In vitro the two DNp73alpha overexpressing clones grow at similar rate of the control transfected clone (HCT116/8a) and similarly respond to DNA damage. When injected in mice, HCT116/DN3, HCT116/DN14, and HCT116/8a cells grew similarly in the absence or presence of tetracycline. In HCT116/DN3 and HCT116/DN14 tumors, tetracycline induced a strong expression of DNp73alpha both as mRNA and protein. These results indicate that in this system the overexpression of the DNp73alpha does not induce a more aggressive phenotype and does not seem to be associated with a reduced response of the cells to treatment with anticancer agents.

Variation in transcriptional regulation of cyclin dependent kinase inhibitor p21waf1/cip1 among human bronchogenic carcinomas

Background

Cell proliferation control depends in part on the carefully ordered regulation of transcription factors. The p53 homolog p73, contributes to this control by directly upregulating the cyclin dependent kinase inhibitor, p21^waf1/cip1. E2F1, an inducer of cell proliferation, directly upregulates p73 and in some systems upregulates p21 directly. Because of its central role in controlling cell proliferation, upregulation of p21 has been explored as a modality for treating bronchogenic carcinoma (BC). Improved understanding of p21 transcriptional regulation will facilitate identification of BC tissues that are responsive to p21-directed therapies. Toward this goal, we investigated the role that E2F1 and p73 each play in the transcriptional regulation of p21.

Results

Among BC samples (N = 21) p21 transcript abundance (TA) levels varied over two orders of magnitude with values ranging from 400 to 120,000 (in units of molecules/10⁶ molecules β-actin). The p21 values in many BC were high compared to those observed in normal bronchial epithelial cells (BEC) (N = 18). Among all BC samples, there was no correlation between E2F1 and p21 TA but there was positive correlation between E2F1 and p73α (p < 0.001) TA. Among BC cell lines with inactivated p53 and wild type p73 (N = 7) there was positive correlation between p73α and p21 TA (p < 0.05). Additionally, in a BC cell line in which both p53 and p73 were inactivated (H1155), E2F1 TA level was high (50,000), but p21 TA level was low (470). Transiently expressed exogenous p73α in the BC cell line Calu-1, was associated with a significant (p < 0.05) 90% increase in p21 TA and a 20% reduction in E2F1 TA. siRNA mediated reduction of p73 TA in the N417 BC cell line was associated with a significant reduction in p21 TA level (p < 0.01).

Conclusion

p21 TA levels vary considerably among BC patients which may be attributable to 1) genetic alterations in Rb and p53 and 2) variation in TA levels of upstream transcription factors E2F1 and p73. Here we provide evidence that p73 upregulates p21 TA in BC tissues and upregulated p21 TA may result from E2F1 upregulation of p73 but not from E2F1 directly.

The role of p53 in treatment responses of lung cancer

Resistance to radio- and chemotherapy is a major problem in treatment responses of lung cancer. In this disease, biological markers, that can be predictive of response to treatment for guiding clinical practice, still need to be validated. Radiotherapy and most chemotherapeutic agents directly target DNA and in response to such therapies, p53 functions as a coordinator of the DNA repair process, cell cycle arrest, and apoptosis. In fact, it participates in the main DNA repair systems operative in cells, including NHEJ, HRR, NER, BER, and MMR. Given the high p53 mutation frequency in lung cancer which likely impairs some of the p53-mediated functions, a role of p53 as a predictive marker for treatment responses has been suggested. In this review, we summarize the conflicting results coming from preclinical and clinical studies on the role of p53 as a predictive marker of responses to chemotherapy or radiotherapy in lung cancer.

Discrete breakpoint mapping and shortest region of overlap of chromosome arm 1q gain and 1p loss in human hepatocellular carcinoma detected by semiquantitative microsatellite analysis

Recurrent chromosomal gain at 1q is one of the most common features of human hepatocellular carcinoma (HCC), but how the gain at 1q contributes to hepatocarcinogenesis is still unclear. To identify the target genes, precise determination of the shortest region of overlap (SRO) and of breakpoints is necessary. Similarly, the role of loss at 1p, which is also a major cytogenetic aberration in HCC, needs to be determined. Fifty HCCs were examined with the aid of 59 microsatellite markers distributed throughout both arms of chromosome 1. To detect allelic gain effectively, the cutoff value of the allelic imbalance index was set at 0.70. Alleles showing imbalance were subjected to multiplex PCR, using a retained allele as an internal control, to determine whether the imbalance was the result of chromosomal gain or loss. The SRO of the gains was defined as D1S2878-D1S2619 (1q23.-q25.3, 16.9 Mb), which involved 36 cases (72%). Gains in the number of copies of certain oncogenes within this region seemed to be critical for the pathogenesis of HCC. In contrast, the centromeric breakpoints of these gains varied, but they tended to occur mainly in the pericentromeric region (26 of 50 cases, 52%). Rearrangement of specific genes associated with the gains is unlikely. On the other hand, the SRO of deletion was defined as D1S2893-D1S450 (1p36.32-p36.22, 5.1 Mb). Four known putative tumor-suppressor genes (TP73, RIZ1, NBL1/DAN, and CDKN2C) were outside the SRO, suggesting the presence of other candidate genes with critical roles in hepatocarcinogenesis.

A naturally occurring p73 mutation in a p73-p53 double-mutant lung cancer cell line encodes p73 alpha protein with a dominant-negative function

p73, a close homolog of p53 tumor suppressor, induces growth arrest and apoptosis. However, its role in cancers is controversial because of the rarity of p73 mutations, lack of tumors in p73-knockout mice, and the presence of multiple isotypes, among which Delta N isotypes inhibit the function of TA isotypes. We analyzed three naturally occurring p73 mutants found in lung cancer cell lines, NCI-H1155, DMS 92 and A427. NCI-H1155 is a cell line that has a p73 mutation [p73(G264W)] in the DNA-binding domain, as well as a p53 mutation [p53(R273H)], which is frequently found in human cancers and has a "gain-of-function" characteristic. p73 alpha(G264W) not only lacks transactivation activity itself, but also suppressed the transactivation activity of the wild-type p73 alpha in a dose-dependent manner, indicating that p73 alpha(G264W) is a dominant-negative mutant. p73 alpha(G264W) failed to suppress colony formation. We tested two other mutations, p73(Del418) in DMS 92 and p73(Del603) in A427. Both mutants retained similar levels of transactivation activity and suppression of colony formation to those of wild-type p73. The biological significance of these two mutations is unclear. In NCI-H1155 cells the coexistence of mutations that abrogate the normal functions of p73 and p53 may indicate that each mutation confers an additive growth advantage upon the cells.

Aberrant promoter methylation of multiple genes in oligodendrogliomas and ependymomas

Promoter hypermethylation represents a primary mechanism in the inactivation of tumor suppressor genes during tumorigenesis. To determine the frequency and timing of hypermethylation during carcinogenesis of nonastrocytic tumors, we analyzed promoter methylation status of 10 tumor-associated genes in a series of 41 oligodendrogliomas (22 World Health Organization [WHO] grade II; 13 WHO grade III; 6 WHO grade II-III oligoastrocytomas) and 7 WHO grade II-III ependymomas, as well as 2 nonneoplastic brain samples, by a methylation-specific polymerase chain reaction. Aberrant CpG island methylation was detected in 9 of 10 genes analyzed, and all but one sample displayed anomalies in at least one gene. The frequencies of hypermethylation for the 10 genes were as follows, in oligodendrogliomas and ependymomas, respectively: 80% and 28% for MGMT; 70% and 28% for GSTP1; 66% and 57% for DAPK; 44% and 28% for TP14(ARF); 39% and 0% for THBS1; 24% and 28% for TIMP3; 24% and 14% for TP73; 22% and 0% for TP16(INK4A); 3% and 14% for RB1; and 0% in both neoplasms for TP53. No methylation of these genes was detected in normal brain tissue samples. We conclude that a high frequency of aberrant methylation of the 5' CpG island of the MGMT, GSTP1, TP14(ARF), THBS1, TIMP3, and TP73 genes is observed in nonastrocytic neoplasms. This aberration seems to occur early in the carcinogenesis process (it is already present in the low-grade forms), although in some instances (DAPK, THBS1, and TP73) it appears also associated with the genesis of anaplastic forms.

Primary adenocarcinomas of lower esophagus, esophagogastric junction and gastric cardia: in special reference to China

Gastric cardia adenocarcinoma (GCA) is an under-studied subject. The pathogenesis, molecular changes in the early stage of carcinogenesis and related risk factors have not been well characterized. There is evidence, however, that GCA differs from cancer of the rest of the stomach in terms of natural history and histopathogenesis. Adenocarcinomas of the lower esophagus, esophagogastric junction (EGJ) and gastric cardia have been given much attention because of their increasing incidences in the past decades, which is in striking contrast with the steady decrease in distal stomach adenocarcinoma. In China, epidemiologically, GCA shares very similar geographic distribution with esophageal squamous cell carcinoma (SCC), especially in Linzhou (formerly Linxian County), Henan Province, North China, the highest incidence area of esophageal SCC in the world. Historically, both GCA and SCC in these areas were referred to as esophageal cancer (EC) by the public because of the common syndrome of dysphagia. In Western countries, Barrett's esophagus is very common and has been considered as an important precancerous lesion of adenocarcinoma at EGJ. Because of the low incidence of Barrett's esophagus in China, it is unlikely to be an important factor in early stage of EGJ adenocarcinoma development. However, Z line up-growth into lower esophagus may be one of the characteristic changes in these areas in early stage of GCA development. Whether intestinal metaplasia (IM) is a premalignant lesion for GCA is still not clear. Higher frequency of IM observed at adjacent GCA tissues in Henan suggests the possibility of IM as a precancerous lesion for GCA in these areas. Molecular information on GCA, especially in early stage, is very limited. The accumulated data about the changes of tumor suppressor gene, such as p53 mutation, and ontogeny, such as C-erbB2, especially the similar alterations in GCA and SCC in the same patient, indicated that there might be some similar risk factors, such as nitrosamine, involved in both GCA and SCC in Henan population. The present observations also suggest that GCA should be considered as a distinct entity.

Induction of apoptosis by the p53-related p73 and partial inhibition by the baculovirus-encoded p35 in neuronal cells

To better understand whether the p53-related p73 gene could induce neuronal apoptosis, we tested whether p73 induced cell killing in three neuronal cell lines and whether apoptosis could be inhibited by p35, a baculovirus-encoded protein that blocks caspase 3. Recombinant adenoviruses carrying the hemagglutinin (HA)-tagged p73beta or p35, or the green fluorescent protein gene driven by the cytomegalovirus immediate-early promoter were constructed, and used to infect human SK-N-AS and SK-N-SH neuroblastoma, and rat PC12 pheochromocytoma cells. Infection with Adp73beta virus resulted in p73beta over-expression and substantial reduction of cell viability due to apoptosis in all three neuronal cell lines as compared with the control AdGFP virus. These results indicate that p73beta over-expression in neuronal cells could induce apoptotic cell death regardless of the endogenous expression of p73. The p73 effect was partially blocked by co-expression of the wild-type p35, suggesting caspase-mediated cell killing. Insertion of a hemagglutinin (HA) tag at the N-terminus of p35 markedly reduced its ability to inhibit the p73 effect compared with the wild-type p35, while insertion of an HA tag to the C-terminus of p35 had no appreciable effect. Taken together, our results suggest that the N-terminal structure of p35 is critical for its anti-apoptotic activity on p73-induced apoptosis in neuronal cells.

Molecular and cellular biology of small cell lung cancer

For any tumor to become cancerous, various genetic mutations and biologic alterations must occur in the cell that in combination render it a malignant neoplasm. Small cell lung cancer (SCLC) is a neoplasm associated with several molecular and cellular abnormalities. SCLC is associated with early and frequent metastasis as well as a poor ultimate response to chemotherapy. New and novel therapies based on understanding the mechanisms of transformation are needed. SCLC is associated with multiple chromosomal abnormalities, the most common of which is chromosome 3p deletion, as well as with abnormal oncogenes and tumor-suppressor genes. Along with the genetic alterations, SCLC has been shown to overexpress various cell surface receptors, including receptor tyrosine kinases (RTKs), G-protein-coupled receptors, integrins, and others. Some downstream molecules are also activated, such as phosphatidylinositol 3'-kinase, and would serve as good candidates for therapeutic strategies.

The p53 network in lung carcinogenesis

The p53 tumor suppressor gene lies at the crossroads of multiple cellular response pathways that control a cell's fate in response to endogenous or exogenous stresses. Positive and negative regulatory loops both upstream and downstream of p53 cooperate to finely tune its functions as a transcription factor, a DNA damage sensor, and possibly, a protein-assembly scaffold. Through this plethora of activities, p53 is a major determinant of cell survival and a safeguard against genetic instability. Functional inactivation of p53 pathways through genetic and epigenetic events affecting the p53 gene itself and/or its interacting partners occur with a high frequency in lung cancer. The p53 mutational spectrum provides molecular evidence of the etiology of lung cancer and supports abundant epidemiological data indicating the role of tobacco smoke in the causation of this disease.

Role for the double-stranded RNA activated protein kinase PKR in E2F-1-induced apoptosis

The transcription factor E2F-1 induces cell cycle progression at the G1/S checkpoint, and deregulation of E2F-1 provokes apoptosis in a wide variety of malignant cells. To date only p14(ARF) and p73, a p53 homologue, have been identified as E2F-1-inducible genes capable of mediating an apoptotic response. Here we show that adenovirus-mediated E2F-1 overexpression in cancer cells induces expression and autophosphorylation of the double-stranded RNA-dependent protein kinase PKR leading to phosphorylation of its downstream target, the alpha-subunit of the eukaryotic translation initiation factor 2 (eIF-2alpha) and to apoptotic cell death. This PKR-dependent apoptosis occurs in cell lines with mutated p53 and in cell lines with mutated p53 and p73, and is significantly reduced by the chemical inhibition of PKR activation. Further, PKR(-/-) mouse embryo fibroblasts, but not PKR(+/+) mouse embryo fibroblasts, demonstrate significant resistance to E2F-1-induced apoptosis. We conclude that an important pathway of E2F-1-mediated apoptosis is dependent on PKR activation and does not require p53 or p73.

Transcriptional inactivation of TP73 expression in oligodendroglial tumors

The TP73 gene, located on chromosome 1p36.3, encodes a product that shares significant structural homology with the tumor suppressor TP53. The aim of this study was to investigate whether TP73 is involved in the development of oligodendroglial tumors, which frequently carry deletions involving 1p36.3. Semi-quantitative reverse transcription-polymerase chain reaction was used to determine TP73 transcript levels. Ten of 24 (42%) tumors showed negligible to more than 5-fold reduction in TP73 expression when compared to normal brain level. To identify potential mechanisms that may modulate TP73 transcription in oligodendroglial tumors, we performed mutation analysis on the TP73 gene. No somatic mutations were however detected in the gene sequence. We then evaluated the possible involvement of epigenetic change in TP73 expression. Bisulfite genomic sequencing detected aberrant hypermethylation at the 5' region upstream and including the first exon of the TP73 gene in 17 of 44 (39%) oligodendroglial tumors, whereas normal brain tissues showed no methylation in the same region examined. Moreover, 6 of 10 (60%) tumors with negligible or decreased levels of TP73 transcripts were methylation-positive. In conclusion, our results showed that inactivation of TP73 occurs at the transcriptional level and is associated with promotor hypermethylation. Loss of or reduced TP73 transcript expression may contribute to the tumorigenesis of oligodendroglial tumors.

Molecular biology of lung cancer: clinical implications

This review summarizes the rapidly expanding knowledge of the molecular pathogenesis of lung cancer. It is clear that respiratory epithelial cells require many genetic alterations to become invasive and metastatic cancer. Much more is to be learned, but with modern technology. Clinicians can detect "field cancerized" regions and preneoplastic and malignant cells, therefore offering the opportunity to intercede with biomarker-monitored prevention and early detection efforts. Such molecular screening and detection efforts will likely be coupled to advances in low-dose computed tomographic imaging, positron emission tomography scans, and other imaging modalities. Although this molecular marker approach has great potential, there is not yet a molecular marker validated in large prospective trials that has major independent predictive prognostic value. There is an urgent need for large, adequately powered, carefully designed prospective studies to identify clinically useful new biomarkers. Finally, new therapeutic strategies with genetic manipulation, small molecules, antibodies, vaccines, and, particularly, new drugs targeting specific biologic pathways found to be abnormal in lung provide for future optimism. Researchers need to define their individual value, especially when integrated with standard therapies.

p73 is over-expressed in vulval cancer principally as the Delta 2 isoform

p73 was studied in squamous cancers and precursor lesions of the vulva. Over-expression of p73 occurred commonly in both human papillomavirus (HPV)-positive and -negative squamous cell cancers (SCC) and high-grade premalignant lesions. Whereas expression in normal vulval epithelium was detected only in the basal and supra-basal layers, expression in neoplastic epithelium increased with grade of neoplasia, being maximal at both protein and RNA levels in SCC. p73 Delta 2 was the principal over-expressed isoform in the majority of cases of vulval SCC and often the sole form expressed in SCC. Over-expression of p73 was associated with expression of HPV-encoded E7 or with hypermethylation or mutation of p16(INK4a) in HPV-negative cases. There was a close correlation between expression of p73 and p14(ARF) in cancers with loss of p53 function. The frequent over-expression of p73 Delta 2 in neoplastic but not normal vulval epithelium, and its co-ordinate deregulation with other E2F-1 responsive genes suggests a role in the oncogenic process.

Germline mutations in the p73 gene do not predispose to familial prostate-brain cancer

BACKGROUND

Analysis of high-risk prostate cancer (PC) families with at least one confirmed case of primary brain cancer (BC) has identified a region of genetic linkage on chromosome 1p36 termed CAPB. The p36 region of chromosome one has been reported to have frequent loss of heterozygosity (LOH) in brain and central nervous system (CNS) tumors and epidemiological studies have shown an increased relative risk of BC and tumors of the CNS in PC families. In 1997 a reported tumor suppressor with high homology to p53, termed p73, was mapped to the p36 region of chromosome one. Here, we examine the p73 gene as a potential candidate for CAPB.

METHODS

Ninety-four members from the 12 prostate-brain cancer families in which linkage was originally found were examined. The complete coding region and intron-exon boundaries of the p73 gene were analyzed for germline mutations by Single Stranded Conformational Polymorphism analysis (SSCP) and direct DNA sequencing.

RESULTS

Silent nucleotide substitutions only were detected within the coding regions of the gene in affected individuals. Nucleotide changes were detected in introns 1, 6, 8, 9, and 10, but all were located >or=16 base pairs from the splice site, and are thus unlikely to be deleterious mutations.

CONCLUSIONS

Germline mutations in the p73 gene are unlikely to be critical for inherited susceptibility to PC in this specified subset of families.

Analysis of p73 gene in meningiomas with deletion at 1p

The p73 gene has been mapped to 1p36.33, a chromosome region that is frequently deleted in a wide variety of neoplasms including meningiomas. The protein encoded by p73 shows structural and functional similarities to p53 and may thus represent a candidate tumor suppressor gene. To determine whether p73 is involved in the development of meningiomas, we examined 30 meningioma samples with proven 1p deletion for mutations of p73. Sequence analysis of the entire coding region of the p73 gene revealed previously reported polymorphisms in eight cases. A tumor-specific missense mutation as a result of an A-to-G transition with an Asn204Ser change was found in one meningioma that nevertheless retained the normal allele. These results suggest that if p73 plays a role in meningioma carcinogenesis, it must be in a manner different from the Knudson two-hit model.

p73 is not mutated in meningiomas as determined with a functional yeast assay but p73 expression increases with tumor grade

The p53 gene is normally wild type in meningiomas. Since all three members of the p53 gene family recognize the same DNA sequence, tumors containing wild type p53 could decrease transactivation of p53 target genes by mutating either p63 or p73. In meningiomas the most likely target is p73, because loss of heterozygosity of the chromosomal band containing p73 is the commonest genetic lesion in these tumors. To screen p73 for mutations we have developed a functional assay which tests the ability of p73 to activate transcription from a p53-responsive promoter in yeast. The assay correctly identified p73 mutants with mutations equivalent to hotspot mutations in p53, demonstrating that the assay can detect transcriptionally inactive p73. No mutations in p73 were identified in meningiomas. p73 RNA level was higher in more advanced tumors, but there was no correlation between the expression level of p73 and p21, a known p53 target gene. The yeast assay was also used to measure the intrinsic sensitivity of the p73 protein to mutagenesis. Like p53, p73 is exceptionally easy to inactivate as a transcription factor by point mutation. Taken together, these results indicate that p53 and p73 serve very different functions in tumors.

Mutation analysis of the p73 gene in nonastrocytic brain tumours

Loss of heterozygosity (LOH) involving the distal chromosome 1 p36 region occurs frequently in nonastrocytic brain tumours, but the tumour suppressor gene targeted by this deletion is unknown. p73 is a novel gene that has high sequence homology and similar gene structure to the p53 gene; it has been mapped to 1 p36, and may thus represent a candidate for this tumour suppressor gene. To determine whether p73 is involved in nonastrocytic brain tumour development, we analysed 65 tumour samples including 26 oligodendrogliomas, 4 ependymomas, 5 medulloblastomas, 10 meningiomas, 2 meningeal haemangiopericytomas, 2 neurofibrosarcomas, 3 primary lymphomas, 8 schwannomas and 5 metastatic tumours to the brain, for p73 alterations. Characterization of allelic loss at 1 p36-p35 showed LOH in about 50% of cases, primarily involving oligodendroglial tumours (22 of 26 cases analysed; 85%) and meningiomas (4 of 10; 40%). PCR-SSCP and direct DNA sequencing of exons 2 to 14 of p73 revealed a missense mutation in one primary lymphoma: a G-to-A transition, with Glu291Lys change. 8 additional cases displayed no tumour-specific alterations, as 3 distinct polymorphic changes were identified: a double polymorphic change of exon 5 was found in one ependymoma and both samples derived from an oligodendroglioma, as follows: a G-to-A transition with no change in Pro 146, and a C-to-T variation with no change in Asn 204: a delG at exon 3/+12 position was identified in 4 samples corresponding to 2 oligodendrogliomas, 1 ependymoma and 1 meningioma, and a C-to-T change at exon 2/+10 position was present in a metastatic tumour. Although both LOH at 1 p36 and p73 sequence changes were evidenced in 4 cases, it is difficult to establish a causal role of the p73 variations and nonastrocytic brain tumours development.

Loss of p73 gene expression in lymphoid leukemia cell lines is associated with hypermethylation

The expression of the p73 gene and the methylation status was examined in 61 acute lymphoblastic leukemia (ALL) cell lines and lymphocytes from seven healthy individuals. p73 mRNA was not expressed in 19 (31.1%) of 61 ALL cell lines, including 11 (31.4%) of 35 B-precursor ALL cell lines, 2 (16.7%) of 12 B-ALL/Burkitt lymphoma (BL) cell lines (totally 27.7% of B-lineage cell lines), 6 (42.9%) of 14 T-ALL cell lines, and expressed in all of normal lymphocytes, by reverse transcriptase-polymerase chain reaction (RT-PCR). Restriction-enzyme related PCR (REP) and methylation-specific PCR (MSP) revealed that the cell lines lacking p73 mRNA expression were hypermethylated. In contrast, normal lymphocytes and most cell lines that expressed detectable p73 mRNA were not hypermethylated with the exception of five cell lines. Furthermore, bisulfite genomic sequencing confirmed the results obtained by REP and MSP. Our results suggest that p73 inactivation may be involved in the pathogenesis of both T- and B-ALLs, and that hypermethylation is the predominant mechanism of inactivation of the p73 gene in ALL.

Evaluation of 1p losses in primary carcinomas, local recurrences and peripheral metastases from colorectal cancer patients

Cytogenetic and molecular genetic analyses of colorectal adenomas and carcinomas have shown that loss of the distal part of chromosome arm 1p is common, particularly in tumors of the left colon. Because the importance of 1p loss in colorectal cancer metastases is unknown, we compared the frequency, exact site and extent of 1p deletions in primary carcinomas (n=28), local recurrences (n=19) and metastases (n=33) from 67 colorectal cancer patients using 14 markers in an allelic imbalance study. Loss of 1p was found in 50% of the primary carcinomas, 33% of the local recurrences, and 64% of the metastases, revealing a significant difference between the local recurrences and the metastases (P=.04). The smallest region of 1p deletion overlap (SRO) defined separately for each group of lesions had the region between markers D1S2647 and D1S2644, at 1p35-36, in common. The genes PLA2G2A (1p35.1-36) and TP73 (1p36.3) were shown to lie outside this consistently lost region, suggesting that neither of them are targets for the 1p loss. In the second part of the study, microdissected primary carcinomas and distant metastases from the same colorectal cancer patients (n=18) were analyzed, and the same 1p genotype was found in the majority of patients (12/18, 67%). The finding that primary carcinoma cells with metastatic ability usually contain 1p deletions, and that some cases lacking 1p alterations in the primary tumor acquire such changes during growth of a metastatic lesion, supports the notion that 1p loss may be important both early and late in colorectal carcinogenesis, with the apparent exception of local recurrences.

Molecular pathogenesis of lung cancer

Lung cancer is the largest cancer killer of men and women in the united states. In addition to the progress made from antismoking primary prevention measures, new tools to help treat patients with lung cancer are emerging from the rapid advances in knowledge of the molecular pathogenesis of lung cancer. These tools include molecular and cellular biology and are starting to provide an insight into how the tumor cell, by altering oncogenes and tumor suppressor genes, achieves growth advantage, uncontrolled proliferation and metastatic behavior via disruption of key cell-cycle regulators and signal transduction cascades. Moreover, new knowledge is being developed in terms of the molecular definition of individual susceptibility to tobacco smoke carcinogens. These tools are being translated into clinical strategies to complement surgery, radiotherapy, and chemotherapy and also to assist in primary and secondary prevention efforts. This review summarizes current knowledge of the molecular pathogenesis of lung cancer. From this we know that respiratory epithelial cells require many genetic alterations to become invasive and metastatic cancer. We can detect cells with a few such changes in current and former smokers, offering the opportunity to intercede with a biomarker-monitored prevention and early detection effort. This will be coupled with new advances in computed tomography-based screening. Finally, because the molecular alterations are known, new mechanism-based therapies are being developed and brought to the clinic, including new drugs, vaccines, and gene therapy, which also must be integrated with standard therapies.

Comparative analysis of p73 and p53 regulation and effector functions

p53 is mutated in approximately 50% of human cancers, whereas mutations of the related p73 gene are rare. p73 can activate p53-responsive promoters and induce apoptosis when overexpressed in certain p53-deficient tumor cells. We show that p73 isoforms, p73alpha and p73beta, can each induce permanent growth arrest with markers of replicative senescence when overexpressed in a tetracycline-regulatable manner in human cancer cells lacking functional p53. Human homologue of mouse double minute 2 gene product (hMDM2), but not an NH(2)-terminal deletion mutant, coimmunoprecipitated with p73alpha or p73beta, and inhibited p73 transcriptional activity as with p53. In contrast to p53, ectopically expressed hemagglutinin (HA)-tagged p73 proteins were not stabilized by treatment with several DNA damaging agents. Furthermore, unlike normal p53, which increases in response to DNA damage due to enhanced protein stability in MCF7 cells, endogenous p73 protein levels were not increased in these cells under the same conditions. Thus, although p73 has an ability, comparable to that of p53, to suppress tumor cell growth in p53-deficient cells, p73 induction is regulated differently from p53. These findings suggest that the selective pressures for p53 rather than p73 inactivation in tumors may reflect their differential responses to stresses such as DNA damage, rather than their capacities to induce permanent growth arrest or apoptosis programs.