Intragenic mutations of the p16(INK4), p15(INK4B) and p18 genes in primary non-small-cell lung cancers

A Novel HCC Prognosis Predictor EEF1E1 Is Related to Immune Infiltration and May Be Involved in EEF1E1/ATM/p53 Signaling

BACKGROUND

EEF1E1 has been reported to play a role in ovarian cancer, breast cancer, non-small cell lung cancer and other cancers, but its role and mechanism in hepatocellular carcinoma (HCC) are still unknown.

METHODS

EEF1E1 expression in human HCC was analyzed via the GTEx and TCGA database. Logistic regression analysis was used to analyze the clinicopathological correlation of EEF1E1 expression. The correlation between EEF1E1 expression and patients' prognosis was analyzed in HCC, shown by forest plots, nomogram and Kaplan-Meier curves. Hazard ratio (HR) with 95% confidence intervals and log-rank p-value were calculated via multivariate/univariate survival analyses. Moreover, the correlation between EEF1E1 and tumor immune infiltration was analyzed using the gsva package with the ssgsea algorithm. Pearson correlation was used to investigate the correlation between EEF1E1 expression and p53 pathway genes expression. Two third-party databases were used to validate the content of EEF1E1 protein and mRNA expression patterns and prognosis analysis. The immunohistochemistry and multiplex immunohistochemistry was used to verify the bio-informatics results.

RESULTS

EEF1E1 mRNA and protein expression in tumor was statistically higher than normal (EEF1E1 mRNA: p < 0.001; EEF1E1 protein: p < 0.01). Results from paired t-test (cancer and adjacent tissues) exhibited consistent trend (t = 7.572, p < 0.001). Immunohistochemistry showed that EEF1E1 is highly expressed in cancer. The expression of EEF1E1 was positively correlated with body weight, BMI, tumor status, vascular invasion, AFP, logistic grade, T stage and pathological stage. The univariate Cox model revealed that high EEF1E1 expression was strongly associated with worse OS (HR=2.581; 95% CI: 1.782-3.739; p < 0.001), as was T stage, pathologic stage, Histologic grade. High EEF1E1 expression was the only independent prognostic factor associated with OS (HR=2.57; 95% CI: 1.715-3.851; p < 0.001) in the multivariate analysis. EEF1E1 was significantly correlated with various immune cells, including cytotoxic cells, DC, macrophages, neutrophils, NK cd56bright, TFH, Tgd, Th17, Th2, Treg. Multiplex immunohistochemistry showed that the EEF1E1 protein level is positively correlated to the CD3, CD4, PD1 and is negatively correlated to the CD8. The expression level of EEF1E1 in HCC was significantly correlated with the key genes involved in the p53 pathway. The expression of EEF1E1, ATM, p53 and CASPASE3 in HCC tissues was significantly higher than that in adjacent tissues.

CONCLUSION

EEF1E1 is highly expressed in cancer tissues in HCC. EEF1E1's high expression is significantly correlated with worse prognosis and immune cell infiltration of HCC. EEF1E1 may be participating in EEF1E1/ATM/p53 signaling pathway in HCC.

Detection of FHIT and p16 mRNA deletion in biopsy specimens obtained by bronchoscopy for the diagnosis of lung cancer

The purpose of this study was to investigate the diagnostic value of the deletion of fragile histidine triad (FHIT) and p16INK4a (p16) mRNA in biopsies obtained by bronchoscopy. Biopsies were analyzed using RT-PCR in 52 patients with lung cancer and 19 patients with benign lung disease. The results showed that the detection rates of FHIT and p16 gene transcript deletion were significantly higher in lung cancer patients than in patients with benign lung disease (65.4% versus 10.5%, p=0.001 and 59.6% versus 5.3%, p<0.001, respectively). The sensitivities for detecting FHIT and p16 transcript deletion in biopsies were 65.4% and 59.6% (combined 80.8%), respectively, which were markedly better than those of histology and cytology (42.3% and 34.6%, respectively; combined 57.7%). In 22 lung cancer patients with negative histology and cytology at initial bronchoscopy, FHIT and p16 mRNA loss was detected in 40.9% (9/22) and 36.4% (8/22) cases, respectively. FHIT mRNA loss was associated with smoking status in lung cancer patients. In conclusion, deletion of FHIT and p16 mRNA can be identified in biopsies obtained during bronchoscopic procedures. FHIT and p16 mRNA deletion can be used as biomarkers in the clinical diagnosis of lung cancer and may serve as adjuncts to histology and cytology in lung cancer diagnosis.

Molecular biology of lung cancer: Diagnosis and management of lung cancer, 3rd ed: American College of Chest Physicians evidence-based clinical practice guidelines

Based on recent bench and clinical research, the treatment of lung cancer has been refined, with treatments allocated according to histology and specific molecular features. For example, targeting mutations such as epidermal growth factor receptor (EGFR) with tyrosine kinase inhibitors has been particularly successful as a treatment modality, demonstrating response rates in selected patients with adenocarcinoma tumors harboring EGFR mutations that are significantly higher than those for conventional chemotherapy. However, the development of new targeted therapies is, in part, highly dependent on an improved understanding of the molecular underpinnings of tumor initiation and progression, knowledge of the role of molecular aberrations in disease progression, and the development of highly reproducible platforms for high-throughput biomarker discovery and testing. In this article, we review clinically relevant research directed toward understanding the biology of lung cancer. The clinical purposes of this research are (1) to identify susceptibility variants and field molecular alterations that will promote the early detection of tumors and (2) to identify tumor molecular alterations that serve as therapeutic targets, prognostic biomarkers, or predictors of tumor response. We focus on research developments in the understanding of lung cancer somatic DNA mutations, chromosomal aberrations, epigenetics, and the tumor microenvironment, and how they can advance diagnostics and therapeutics.

Genomic impact of cigarette smoke, with application to three smoking-related diseases

There is considerable evidence that inhaled toxicants such as cigarette smoke can cause both irreversible changes to the genetic material (DNA mutations) and putatively reversible changes to the epigenetic landscape (changes in the DNA methylation and chromatin modification state). The diseases that are believed to involve genetic and epigenetic perturbations include lung cancer, chronic obstructive pulmonary disease (COPD), and cardiovascular disease (CVD), all of which are strongly linked epidemiologically to cigarette smoking. In this review, we highlight the significance of genomics and epigenomics in these major smoking-related diseases. We also summarize the in vitro and in vivo findings on the specific perturbations that smoke and its constituent compounds can inflict upon the genome, particularly on the pulmonary system. Finally, we review state-of-the-art genomics and new techniques such as high-throughput sequencing and genome-wide chromatin assays, rapidly evolving techniques which have allowed epigenetic changes to be characterized at the genome level. These techniques have the potential to significantly improve our understanding of the specific mechanisms by which exposure to environmental chemicals causes disease. Such mechanistic knowledge provides a variety of opportunities for enhanced product safety assessment and the discovery of novel therapeutic interventions.

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.

Retinoblastoma deficiency increases chemosensitivity in lung cancer

The retinoblastoma (RB) tumor suppressor is mutated or functionally inactivated in the majority of human malignancies, and p16(INK4a)-cyclin D1-cyclin-dependent kinase 4-RB pathway aberrations are present in nearly all cases of non-small cell lung cancer (NSCLC). Here, the distinct role of RB loss in tumorigenic proliferation and sensitivity to chemotherapeutics was determined in NSCLC cells. Attenuation of RB led to a proliferative advantage in vitro and aggressive tumorigenic growth in xenograft models. Clinically, such aggressive disease is treated with genotoxic and cytotoxic chemotherapeutic agents. In vitro analysis showed that RB deficiency resulted in bypass of the checkpoint response to multiple chemotherapeutic challenges concomitant with an elevated apoptotic response. Correspondingly, RB deficiency in xenograft models led to increased chemosensitivity. However, this response was transient, and a durable response was dependent on prolonged chemotherapeutic administration. Together, these findings show that although RB deficiency enhances sensitivity to chemotherapeutic challenge, efficient and sustainable response is highly dependent on the specific therapeutic regimen, in addition to the molecular environment.

Clinical significance of the detection of the homozygous deletion of P16 gene in malignant pleural effusion

OBJECTIVE

To assess the role of the p16 gene exon 2 homozygous deletion in malignant pleural effusions.

METHODS

The homozygous deletion of p16 gene was determined in 34 pleural effusions due to non-small cell lung cancer (NSCLC) and in 21 cases with tuberculous pleuritis by polymerase chain reaction (PCR), compared with the determination of exfoliated cytology in the same specimens.

RESULTS

The PCR analysis showed that the homozygous deletion of p16 exon 2 was identified in 15 of 34 malignant pleural effusions (44.11%), including 8 negative cytology and it was not found any tuberculous pleural effusions. The exfoliated cytology of pleural effusion was positive in 19 of 34 malignant cases (55.88%). By combining two methods, the diagnostic sensitivity was enhanced, from 55.88% (19/34) to 79.41% (27/34), whose positive rate was higher than only determination of p16 exon2 homozygous deletion or exfoliated cytology in malignant pleural effusions (p<0.001, p<0.05 respectively).

CONCLUSION

Our data suggested that combining the examination of exfoliated cytology and homozygous deletion of p16 gene exon2 in pleural effusion can recruit and enhance the diagnostic value of pleural effusion cytology. The detection of the homozygous deletion of the p16 gene in pleural effusion may be a useful adjunct to the cytological and histological examinations of pleural effusion. In cases of undiagnosed exudative pleural effusion with a high clinical suspicion for malignancy, it is reasonable to examine the homozygous deletion of pleural fluid p16 gene. With p16 gene homozygous deletion in pleural effusion, it may be strongly highly likely to be malignant and have a higher metastatic potential.

The prognostic relevance of p16 inactivation in head and neck cancer

The inactivation of the tumor suppressor gene p16 plays an important role in the development of malignant tumors. p16 loss can result from point mutations, loss of heterozygosity (LOH) or methylation of the promoter region. A total of 67 samples of tumor tissue from squamous cell carcinoma of the oral cavity, the pharynx and the larynx were analyzed for an inactivation of p16. The results of the molecular-biological investigations were correlated with the known clinical prognostic parameters after a follow-up period of approximately 3 years. Methylation of the promoter region and LOH were the main mechanisms of p16 inactivation. Point mutations presented as rare events. An inactivation of p16 did not have any statistical influence on tumor prognosis. Patients with a p16 gene inactivated by promoter methylation appeared to have a slightly lower tendency for local and regional recurrences. The inactivation of the tumor suppressor gene p16 plays a role in the carcinogenesis of head and neck cancer.

Regulation of the G1/S phase of the cell cycle and alterations in the RB pathway in human lung cancer

The retinoblastoma (RB)-Cyclin (CCN)D1-p16 cell cycle pathway has a crucial role in lung tumorigenesis. Impairment of the RB pathway has been shown to occur in almost all lung tumors. A deregulation at any level of this core RB pathway seems to make cells insensitive to the mitogenic signaling that is required for cell cycle progression. To date, almost all participants in this pathway have been shown to be altered to a various degree in lung tumors. Some of the alterations are mutually exclusive, including RB and p16INK4A . In small cell lung cancer, the RB tumor suppressor gene is inactivated in almost 90% of the tumors, whereas in non-small cell lung cancer, the cyclin-dependent kinase (CDK)4 inhibitor p16INK4A is inactivated in 40-60% of the tumors. Many mechanisms may be responsible for activating the RB-Cyclin D1 pathway, including activating (CDK4) and inactivating mutations (p16INK4A ), deletions (RB and p16INK4A ), amplifications (CCND1 and CDK4), silencing methylation (p16INK4A and RB), and hyper-phosphorylation (RB). As some of these alterations, such as p16INK4A methylation, can also be detected in bronchial lavage and serum, they could potentially serve as useful markers for the early detection of lung cancer. This review summarizes recent experiments describing the variable roles of key-player molecules of the RB pathway and different mechanisms by which the RB pathway can be altered in lung cancer.

Inhibition of retinoblastoma tumor suppressor activity by RNA interference in lung cancer lines

BACKGROUND

Inactivation of retinoblastoma (RB) tumor suppressor function occurs frequently in lung cancer. Short-hairpin RNA can be constructed to target specific sequences and efficiently knock down protein expression. We developed a short-hairpin RNA approach to specifically target Rb in lung cancer cells to determine the influence of RB knockdown on proliferation.

METHODS

NCI-H520 human lung cancer cells (wild-type Rb) were transfected with pMSCVpuro-Rb3C, a plasmid containing a short-hairpin sequence targeted to human Rb. Transfectants harboring the construct were selected with puromycin. Loss of RB expression in selected cell populations was determined by immunoblotting. Proliferating cells were counted to establish growth rates. Retinoblastoma-proficient and RB-deficient tumor growth was monitored in nude mice.

RESULTS

Transfection with pMSCVpuro-Rb3C dramatically diminished RB expression and led to aberrant expression of RB-regulated genes. Cells harboring pMSCVpuro-Rb3C grew at an increased rate compared with control cells: 480.6 +/- 37.7 versus 159.4 +/- 36.2 (relative cell count at 12 days). Tumor growth in nude mice also increased with RB knockdown compared with control mice: 135.2 +/- 73.6 mm3 versus 40.0 +/- 17.0 mm3 (tumor volume at 10 days).

CONCLUSIONS

Inhibition of RB expression is efficiently achieved in lung cancer cells with short-hairpin RNA. Genetic targets of RB are deregulated with RB knockdown. Retinoblastoma depletion increases growth in vitro and in murine xenografts. These studies indicate that even in the context of an established tumor cell line, RB limits tumorigenic proliferation. Additionally, this model will serve as an ideal system to evaluate the role of RB activity on therapeutic response.

Role of cell-cycle regulators in lung cancer

Lung cancer is the leading cause of cancer death worldwide. Histologically, 80% of lung cancers are classified as non-small-cell lung cancer (NSCLC), and the remaining 20% as small-cell lung cancer (SCLC). Lung carcinoma is the result of molecular changes in the cell, resulting in the deregulation of pathways controlling normal cellular growth, differentiation, and apoptosis. This review summarizes some of the most recent findings about the role of cell-cycle proteins in lung cancer pathogenesis and progression.

Validation of molecular and immunological factors with predictive importance in lung cancer

Histological classification and staging are cornerstones of diagnosis in lung cancer. Treatment options have been enriched in the last few years by the development of a number of new drugs, and therapy is now increasingly being carried out within multimodal concepts and at earlier stages. Still, outcome of the disease is far from satisfactory and progress in clinical and preclinical research is time-consuming. With the whole variety of potent new therapeutic compounds including classical cytostatics and biological factors at hand, many now believe that a clear improvement of treatment results will be derived from a better understanding of the biology of these tumours and a resulting improvement of diagnosis. Biological factors reflecting the underlying tumour biology and aspects of clinically important pathomechanisms may not only better predict outcome of the disease but also of its treatment, serving as surrogate markers for a more appropriate general intensification of therapy and ideally for specific "targeted" interventions. This article describes the different insights in the biology of these tumours in relation with the representing surrogate markers, and opens routes to possible diagnostic and therapeutic consequences.

Activation of protein kinase C promotes human cancer cell growth through downregulation of p18INK4c

p18(INK4c), a member of INK4 family of cyclin-dependent kinase inhibitors, negatively regulates the cyclin D-cyclin-dependent kinase 4/6 complexes which promote G1/S transition by phosphorylating the retinoblastoma tumor-suppressor gene product. Several recent studies using p18(INK4c)-null mice revealed that the p18(INK4c) plays an important role in cell proliferation and tumor development. We report here that 12-O-tetradecanoylphorbol-13-acetate (TPA), widely used as a protein kinase C (PKC) activator, suppresses the expression of p18(INK4c) through its promoter, accompanied by the induction of human cancer cell growth. Reduction of p18(INK4c) using small interfering RNA (siRNA) also enhanced cell growth, suggesting that p18(INK4c) is a critical target of TPA. Ro 31-8425, a potent and highly specific PKC inhibitor abrogated the suppressive effect of TPA on p18(INK4c) gene expression. However, the expression of dominant-negative c-Jun (TAM-67) did not inhibit the action of TPA on p18(INK4c). These findings suggest that activation of PKC promotes human cancer cell growth through downregulation of p18(INK4c) in an AP-1 activation-independent manner. These results suggest that the accelerated cellular proliferation of some human tumors caused by enhanced PKC activity at least partially involves the suppression of p18(INK4c), which is a ubiquitously expressed cyclin-dependent kinase inhibitor.

K-ras and p16INK4Aalterations in sputum of NSCLC patients and in heavy asymptomatic chronic smokers

NSCLC rates among the most frequent and lethal neoplasm world-wide and a significant decrease in morbidity and mortality relies only upon effective early diagnostic strategies. We investigated K-ras mutations and p16(INK4A) hypermethylation in tumor tissue and sputum of 50 patients with NSCLC and correlated them with sputum cytology and with tumor staging, grading and location, to ascertain, in sputum, their potential diagnostic impact. The same genetic/epigenetic abnormalities and cytological features were also evaluated in sputum from 100 chronic heavy smokers. Genetic analysis identified molecular abnormalities in 64% tumors (14/50 K-ras mutations and 24/50 p16(INK4A) hypermethylation) and in 48% sputum (11/50 K-ras mutations and 16/50 p16(INK4A) hypermethylation). In tumors K-ras mutations and p16(INK4A) hypermethylation were mostly mutually exclusive, being found in the same patients in 3 cases only. Genetic abnormalities in sputum were detected only in molecular abnormal tumors. Molecular changes in sputum had rates of detection similar to cytology (42%) but the cyto-molecular combination increased the diagnostic yield up to 60%. Interestingly, the rate of detection of genetic changes in sputum of tumors at early stage (T1) was not significantly different from that of tumors at more advanced stage (T2-T4). In fact K-ras point mutations were frequently recognised in tumors at early stage while p16(INK4A) inactivation prevailed in tumors at advanced stage ( P=0.0063). As expected, diagnostic cytological findings were more frequently found in tumors at advanced stage (P=0.004). No correlation was found between tumor grading and location (central versus peripheral) and molecular changes. p16(INK4A) hypermethylation, but not K-ras mutations, was documented in sporadic cases of asymptomatic heavy smokers (4%) where it was uncoupled from cytological abnormalities. In conclusion the cyto-molecular diagnostic strategy adopted in this study was able to detect the majority of tumors but in order to be proposed as effective and early diagnostic tool, this molecular panel needs to be tested in prospective studies with adequate follow-up.

Aberrant methylation of the CDKN2a/p16INK4a gene promoter region in preinvasive bronchial lesions: a prospective study in high-risk patients without invasive cancer

Among the identified factors involved in malignant transformation, abnormal methylation of the CDKN2A/p16(INK4a) gene promoter has been described as an early event, particularly in bronchial cell cancerization. Precancerous bronchial lesions (n = 70) prospectively sampled during fluorescence endoscopy in a series of 37 patients at high risk for lung cancer were studied with respect to the methylation status of the CDKN2A gene. Methylation-specific polymerase chain reaction was performed on DNA extracted from pure bronchial cell populations derived from biopsies and detection of p16 protein was studied by immunohistochemistry on contiguous parallel biopsies. Aberrant methylation of the CDKN2A gene promoter was found in 19% of preinvasive lesions and its frequency increased with the histologic grade of the lesions. Methylation in at least 1 bronchial site was significantly more frequent in patients with cancer history, although there was no difference in the outcome of patients with or without methylation in bronchial epithelium. The other risk factors studied (tobacco and asbestos exposure) did not influence the methylation status. There was no relationship between CDKN2A methylation and the evolutionary character of the lesions. Our results confirm that abnormal methylation of the CDKN2A gene promoter is an early event in bronchial cell cancerization, which can persist for several years after carcinogen exposure cessation, and show that this epigenetic alteration cannot predict the evolution of precancerous lesions within a 2-year follow-up.

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.

Tumor p16M is a possible marker of advanced stage in non-small cell lung cancer

BACKGROUND AND OBJECTIVES

The inactivation of the tumor suppressor gene p16 by methylation (p16M) has been recognized recently as an important process in the oncogenesis for a variety of carcinomas. There have been few reports of its use in lung cancer. We investigate p16M in patients with non-small cell lung cancer (NSCLC).

METHODS

p16M in tumor, plasma, and pleural lavage fluid from patients with resectable NSCLC were investigated by using methylation-specific polymerase chain reaction.

RESULTS

Of the 33 patients studied, 14 (42%) had p16M tumors. There was a significant association between p16M tumors and advanced TNM staging (stage III or IV, P=0.047, Fisher exact test). Circulating p16M was identified in 2 of the 14 patients with p16M tumor and was also associated with advanced TNM staging (P=0.049). The presence of plasma p16M in NSCLC patients and in p16M tumor patients was associated with poor survival and shorter disease-free survival (P=0.0028, P=0.0039, Kaplan-Meier log rank). In addition, p16M was present in three preresectional and four postresectional lavage samples. Preresectional p16M was associated with poor survival and shorter disease-free survival (P=0.0085). p16M tumor involving the visceral pleura was significantly associated with positive p16M postresectional lavage.

CONCLUSIONS

Positive tumor and plasma p16M indicate advanced staging in NSCLC. Patients with plasma and preresection pleural lavage p16M have shorter survival. Further research in this direction is warranted.

Expression of p15 and p15.5 products in neuroendocrine lung tumours: relationship with p15(INK4b) methylation status

The cell cycle inhibitor p15(INK4B) is frequently inactivated by homozygous deletions together with p16(INK4a)/p14(ARF) in many tumour types. Although it is now well established that p16(INK4a) and p14(ARF) act as tumour suppressor genes, the role of p15(INK4b) remains to be well defined. In order to explore the possibility of a selective deregulation of p15(INK4b) in human lung carcinogenesis, we studied p15(INK4b) status in neuroendocrine (NE) lung tumours where homozygous deletions of the p16(INK4a)/p14(ARF) locus are rarely observed. Expressions of p15 and p15.5 protein isoforms were analysed in a series of eight control normal lung, 12 tumour-associated normal lung, five low grade and 15 high grade neuroendocrine (NE) lung tumours and relationship with a specific p15(INK4b) methylation status was studied. Using Western blot analysis, we showed that p15 and p15.5 isoforms displayed a high heterogeneous pattern of expression in both normal and tumour tissues. P15 and p15.5 expressions were correlated in control normal lung (P<0.04) whereas they were not in tumours and associated normal lung. The level of p15.5 was significantly higher in associated normal lung and in tumours (P<0.02 respectively), specially in low grade tumours (P<0.01), than in control normal lung. Furthermore, p15.5 expression was more variable in tumours than in normal lung (P<0.01) and in low grade than in high grade NE lung tumours (P<0.02). Levels of p15 and p15.5 were distinct (up- or downregulated) from those observed in paired normal lung in 4/12 (33%) and 10/12 (83%) tumours respectively. Aberrant methylation at the 5' end of p15(INK4b) gene was observed in 15% of NE lung tumours using PCR-based assay, in a region proximal to the translation start where methylation did not occur in control and associated normal lung. However, no correlation could be assessed with protein status. MSP analysis of CpG islands proximal to the transcription start revealed methylation in all normal and tumour samples. No correlation was found between p15(INK4b) and p16(INK4a) or p14(ARF) status. These data suggest that complex deregulation of p15.5 is implicated in the carcinogenesis of human NE lung tumours independently of p16(INK4a) and p14(ARF) status.

Molecular genetic abnormalities in the pathogenesis of human lung cancer

In the past few years our knowledge of the molecular pathogenesis of lung cancer has significantly increased. There are several molecular mechanisms involved in the multistage carcinogenesis through which respiratory epithelial cells become preneoplastic and then invasive cancer. In this review we summarize some of these changes including, genomic alterations such as loss of heterozygosity and microsatellite alterations, autocrine-paracrine loops, alterations in oncogenes and tumor suppressor genes, tumor angiogenesis, aberrant promoter methylation and inherited predisposition to lung cancer. Translation of these findings to the clinic is also discussed.

Frequent loss of 1p32 region but no mutation of the p18 tumor suppressor gene in meningiomas

After chromosome 22 and NF2 inactivation, the loss of chromosome 1p is one of the most frequent abnormalities encountered in meningiomas. However the putative tumor suppressor gene located on 1p inactivated in meningiomas has still to be identified. We screened 68 meningiomas for LOH on chromosome 22 and 1. We found 34 LOH on the NF2 region on chromosome 22 (50%) and 19 LOH on 1p (28%), 16 being associated with loss of chromosome 22. Partial deletions delimited a candidate region located between D1S234 and D1S2797. The p18INK4C tumor suppressor gene, a member of the genes family coding for inhibitors of cyclin-dependent kinases, is located in this region. To determine whether p18 is involved in development of meningiomas, we performed a mutation analysis of the p18 gene and a search for homozygous deletion in the 19 meningiomas with 1p loss. Sequencing analysis of the p18 gene revealed one polymorphism, but no somatic mutations and no homozygous deletions were found. These results confirm that the loss of chromosome 1p32 is a frequent feature in meningiomas, however the p18 tumor suppressor gene which is located in this region, does not seem to be involved.

Limited overlapping roles of P15(INK4b) and P18(INK4c) cell cycle inhibitors in proliferation and tumorigenesis

Entry of quiescent cells into the cell cycle is driven by the cyclin D-dependent kinases Cdk4 and Cdk6. These kinases are negatively regulated by the INK4 cell cycle inhibitors. We report the generation of mice defective in P15(INK4b) and P18(INK4c). Ablation of these genes, either alone or in combination, does not abrogate cell contact inhibition or senescence of mouse embryo fibroblasts in culture. However, loss of P15(INK4b), but not of P18(INK4c), confers proliferative advantage to these cells and makes them more sensitive to transformation by H-ras oncogenes. In vivo, ablation of P15(INK4b) and P18(INK4c) genes results in lymphoproliferative disorders and tumor formation. Mice lacking P18(INK4c) have deregulated epithelial cell growth leading to the formation of cysts, mostly in the cortical region of the kidneys and the mammary epithelium. Loss of both P15(INK4b) and P18(INK4c) does not result in significantly distinct phenotypic manifestations except for the appearance of cysts in additional tissues. These results indicate that P15(INK4b) and P18(IKN4c) are tumor suppressor proteins that act in different cellular lineages and/or pathways with limited compensatory roles.

Molecular analysis of alterations of the p18INK4c gene in human meningiomas

Meningiomas are common primary brain tumours frequently presenting with deleted and/or mutated NF2 gene located on 22q.1p has been reported as the second most commonly deleted chromosomal region in these neoplasms. A new member of the INK4 family of CDK inhibitors, the p18INK4c gene, has recently been mapped to this chromosomal arm. By virtue of its structural and functional similarities with the p16 gene, p18 has been implicated as a tumour suppressor gene in a variety of cancers. In this paper 40 human meningiomas were analysed for loss of heterozygosity (LOH) at the p18 locus, mutations and inactivating methylation of the p18 gene. LOH at D1S193, D1S463 and D1S211 microsatellite marker loci mapped to 1p32 was detected in 13 of 35 (37%), four of 20 (20%), and six of 24 (25%) tumour samples, respectively. One sample presented with homozygous deletion at D1S193. Mutational analysis using single stranded conformational polymorphism (SSCP) and direct sequencing did not detect any missense mutation but revealed a novel silent mutation, G to T, at coding nucleotide 435. Analysis of HgaI, BsaHI, ScrFI and Eco0109I restriction sites of p18 exon 1 revealed absence of inactivating methylation. Immunohistochemistry with p18 monoclonal antibody detected presence of cytoplasmic p18 staining in 21 of 22 examined samples. One sample did not stain and was shown to carry homozygous deletion at D1S193. Despite the high frequency of LOH at 1p32 microsatellite markers, the lack of genetic and epigenetic aberrations in the p18 gene together with the presence of p18 protein in all but one meningioma samples argues against the role of p18 as a tumour suppressor gene important for meningioma development.

p16 protein expression is associated with a poor prognosis in squamous cell carcinoma of the lung

An immunohistochemical analysis for p16 protein was performed in 171 patients with non-small-cell lung cancer (NSCLC). Sixty-two carcinomas (36.3%) were classified as p16-negative. p16-negative tumours in squamous cell carcinomas (SCCs) were significantly more than those in adenocarcinomas (P = 0.039). There was no significant difference in survival according to tumour p16 status in patients with NSCLCs or in patients with adenocarcinomas. In contrast, of patients with SCCs, the 5-year survival rate of patients with p16-negative tumours was significantly lower than those with p16-positive tumours (P = 0.001). Especially, the survival of patients with p16-negative tumours was significantly worse than that of patients with p16-positive tumours in the early stage of the SCC, e.g. stage I (P = 0.005). Multivariate analysis showed that p16 status and nodal status were significant prognostic factors for the survival of patients with SCCs of the lung (P = 0.024 and P = 0.008 respectively). In conclusion, our study showed that alteration of p16 was one of the significant factors of a poor prognosis in SCCs of the lung, and that p16 might play an important role in some SCCs of the lung due to its high prevalence and prognostic value.

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.

Alterations of the p16-pRb pathway and the chromosome locus 9p21-22 in non-small-cell lung carcinomas: relationship with p53 and MDM2 protein expression

The p16-pRb and p53-MDM2 pathways represent vital cell cycle checkpoints. Recent studies provide evidence that these pathways are directly linked via MDM2-pRb interaction and p53 suppression of the RB1 gene. In the present study we investigated the alterations of this G1 phase protein network using immunohistochemical and molecular methods in a series of 68 non-small-cell lung carcinomas (NSCLCs) and correlated the findings with clinicopathological features and prognosis of the patients. Aberrant expression (Ab) of p16 and pRb was observed in 33 (49%) and 27 (40%) of the carcinomas, respectively. Analysis of the region that encodes for p16 by deletion mapping, a polymerase chain reaction (PCR)-based methylation assay and PCR single-strand conformation polymorphism (SSCP) analysis revealed that deletions and transcriptional silencing by methylation might represent the main mechanisms of CDKN2/p16ink4a inactivation in NSCLCs. The results of deletion mapping also suggest that other tumor suppressor genes may reside at the 9p21-22 region, which encodes for CDKN2/MTS1/p16ink4a, p14ARF, and MTS2/p15ink4b. In addition, microsatellite instability was observed with a frequency of 16% in the 9p21-22 chromosome area. Overexpression (P) of p53 and MDM2 proteins was found in 39 (58%) and 47 (70%) of the cases, respectively. A highly significant association was observed between p53 overexpression and p53 mutations (P = 0.006). Statistical analysis of the expression patterns of the biologically relevant molecules (p16/pRb, p53/MDM2, MDM2/pRb, and p53/pRb) showed coincident overexpression of p53 and MDM2 (P = 0.04) and that abnormal pRb was correlated with elevated levels of MDM2 (P = 0.013) and p53 (P = 0.01), respectively. We suggest that deregulated expression of these molecules may act synergistically. An important finding of the study was that multiple impairments (three and four molecules affected) of the p16/pRb/p53/MDM2 network occurred in a large proportion (43%) of the carcinomas. This finding in addition to the absence of correlation with clinical stage of the tumors suggests that multiple hits of this network may be a relatively early event in the development of a subset of NSCLCs. The relationship between the factors examined in the present study, clinicopathological features, and survival of the patients did not reveal any significant correlations with the exception of smoking, which was associated with microsatellite alterations (loss of heterozygosity and microsatellite instability) at the 9p21-22 locus (P = 0.04) and the immunophenotypes p53(P)/MDM2(P) (P = 0.04) and p16(Ab)/pRb(Ab)/p53(P)/MDM2(P) (P = 0.03), respectively. We suggest that in a subset of NSCLCs, simultaneous deregulation of the members of this network may represent one way of initiating the oncogenic procedure whereas in other NSCLC subgroups alternative pathways may play this role.

Progress in understanding the molecular pathogenesis of human lung cancer

We review the molecular pathogenesis of lung cancer including alterations in dominant oncogenes, recessive oncogenes/tumor suppressor genes, alterations in growth regulatory signaling pathways, abnormalities in other pathways, such as apoptosis, autocrine and paracrine growth stimulatory loops, angiogenesis, and host immune responses, other mechanisms of genetic changes, such as microsatellite and methylation alterations, and the potential for inherited predisposition to lung cancer. These changes are related to multistage carcinogenesis involving preneoplastic lesions, and lung development and differentiation. The translational applications of these findings for developing new ways of early detection, prevention, treatment, and prognosis of lung cancer are discussed.

The INK4a/ARF tumor suppressor: one gene--two products--two pathways

Functional inactivation of the retinoblastoma (RB) and p53 pathways appears to be a rite of passage for all cancerous cells and results in disruption of cell-cycle regulation and deactivation of the apoptotic response that normally ensues. The INK4a/ARF locus sits at the nexus of these two growth-control pathways, by virtue of its ability to generate two distinct products: the p16INK4a protein, a cyclin-dependent kinase inhibitor that functions upstream of RB; and the p19ARF protein, which blocks MDM2 inhibition of p53 activity. This 'one gene--two products--two pathways' arrangement provides a basis for the prominence of INK4a/ARF in tumorigenesis.

Association of CDKN2A(p16)/CDKN2B(p15) alterations and homozygous chromosome arm 9p deletions in human lung carcinoma

To elucidate the possibility of the existence of multiple tumor suppressor genes on chromosome arm 9p, we performed genetic and epigenetic analyses of the CDKN2A/p16/MTS1 and CDKN2B/p15/MTS2 genes as well as homozygous deletion mapping of 9p in human lung carcinoma. To avoid overlooking genetic alterations due to contamination of noncancerous cells, we examined 32 non-small cell lung carcinoma (NSCLC) and 16 cell small cell lung carcinoma (SCLC) cell lines. (CDKN2A was mutated or homozygously deleted in 20 (63%) of 32 NSCLC cell lines, and methylation of the CpG island in the CDKN2A gene was detected in six of the 12 cell lines carrying the wild-type CDKN2A gene. Although homozygous deletions of the CDKN2B gene were also detected in NSCLC cell lines with CDKN2A deletions, mutation and methylation in the CDKN2B gene were infrequent. Thus, it was indicated that the CDKN2A gene rather than the CDKN2B gene plays a critical role as a tumor suppressor gene in NSCLC. Homozygous deletions on 9p were detected in 14 (44%) NSCLC cell lines. It is of note that two common regions of homozygous deletions were mapped proximal to the CDKN2A and CDKN2B loci, suggesting that tumor suppressor genes other than CDKN2A are present on 9p. In contrast to NSCLC, homozygous deletions on 9p as well as CDKN2A and CDKN2B alterations were infrequent in SCLC. Therefore, the pathogenetic significance of 9p alterations is likely to differ between SCLC and NSCLC.

Structure of the gene encoding the human cyclin-dependent kinase inhibitor p18 and mutational analysis in breast cancer

The cyclin-dependent kinase (CDK) inhibitor p18 blocks progression of the cell cycle by associating with the cyclin D-dependent kinases CDK6 and CDK4. To better understand the regulation of p18 gene expression, we isolated full-length cDNA clones from a human BT-20 breast cancer cell cDNA library. These clones were then used to isolate the human gene from a human genomic DNA library. The human p18 gene spans at least 7.5 kb and is composed of three exons, two of which encode the p18 protein. The genomic clone we isolated contained 5 kb of putative promotor sequence which directed expression of the luciferase reporter gene in transient transfection experiments. The longest cDNA that we isolated from BT-20 cells contained 2103 nucleotides which corresponds to the size of the major RNA transcript detected by Northern analysis in these cells. Transcription start sites mapping to the 5' end of the putative full-length cDNA were identified by ribonuclease protection assays. A novel polymorphism was identified in the 3' untranslated region of BT-20 cell cDNA clones that contained the previously described codon 72 mutation. The codon 72 mutation was also detected in 3 of 35 breast tumors analyzed using a mismatch PCR/RFLP strategy.

p16INK4 gene mutations are relatively frequent in ampullary carcinomas

A high incidence of gene mutations or deletions of p16INK4, a cell cycle regulator which inhibits the activity of cyclin-dependent kinase 4/cyclin D complex and blocks the G1-to-S transition, has been reported in pancreato-biliary tract cancers. In order to investigate p16INK4 gene alterations in sporadic ampullary carcinomas, 17 sporadic ampullary carcinomas were examined. After histological diagnosis, DNA samples extracted separately from both cancerous and normal paraffin-embedded tissues were investigated. Loss of heterozygosity (LOH) was investigated utilizing 3 microsatellite markers on 9p21-22, and a mutational analysis was performed by cloning and sequencing. LOH was observed in 3 cases (17.6%) and somatic mutations with retention of heterozygosity were found in 7 cases (41.2%). Of note was that two mutations resulted in truncated incomplete proteins and one was a point mutation at the consensus site in the conserved ankyrin repeats, which would be crucial for function. Although two-hit inactivation was not evident in any of the mutation cases and further investigation would be needed to elucidate the role of altered p16INK4, these results suggest that the p16INK4 gene mutations are relatively frequent and its inactivation might be important in ampullary carcinogenesis.