Overexpression of candidate tumor suppressor gene FUS1 isolated from the 3p21.3 homozygous deletion region leads to G1 arrest and growth inhibition of lung cancer cells

Frequent inactivation of RASSF1A, BLU, and SEMA3B on 3p21.3 by promoter hypermethylation and allele loss in non-small cell lung cancer

Non-small cell lung cancer frequently shows loss of heterozygosity of the chromosome 3p21.3 region and several genes such as RASSF1A, BLU, and SEMA3B have been identified as candidate tumor suppressor genes at this region since their downregulation and hypermethylation at their promoter regions were frequently detected in lung cancer. To determine whether these three genes are simultaneously inactivated during lung cancer development, we studied 138 primary non-small cell lung cancers for the promoter methylation status of these genes and allelic loss of the chromosome 3p21.3 region. We found promoter hypermethylation at 32% in RASSF1A, 30% in BLU, and 47% in SEMA3B. Allelic loss of 3p21.3 was detected in 54 (58%) of 93 informative tumors. Despite the weak association of methylation status among these three genes, there was no correlation between the methylation status of each gene and loss of heterozygosity. We also studied possible genes downstream of RASSF1A in 16 primary non-small cell lung cancers and found that the expressions of SM22 and SPARC were significantly downregulated in RASSF1A-hypermethylated tumors. Our results showed that, while candidate tumor suppressor genes at this locus can be simultaneously inactivated by epigenetic alterations, loss of heterozygosity without any hypermethylation of the three genes can also occur in some cases, suggesting that just one allelic loss might also be sufficient for the inactivation of any of these genes for lung cancer development.

Gene expression changes in the course of neural progenitor cell differentiation

The molecular changes underlying neural progenitor differentiation are essentially unknown. We applied cDNA microarrays with 13,627 clones to measure dynamic gene expression changes during the in vitro differentiation of neural progenitor cells that were isolated from the subventricular zone of postnatal day 7 mice and grown in vitro as neurospheres. In two experimental series in which we withdrew epidermal growth factor and added the neurotrophins Neurotrophin-4 or BDNF, four time points were investigated: undifferentiated cells grown as neurospheres, and cells 24, 48, and 96 hr after differentiation. Expression changes of selected genes were confirmed by semiquantitative RT-PCR. Ten different groups of gene expression dynamics obtained by cluster analysis are described. To correlate selected gene expression changes to the localization of respective proteins, we performed immunostainings of cultured neurospheres and of brain sections from adult mice. Our results provide new insights into the genetic program of neural progenitor differentiation and give strong hints to as yet unknown cellular communications within the adult subventricular zone stem cell niche.

Myristoylation of the fus1 protein is required for tumor suppression in human lung cancer cells

FUS1 is a novel tumor suppressor gene identified in the human chromosome 3p21.3 region that is deleted in many cancers. Using surface-enhanced laser desorption/ionization mass spectrometric analysis on an anti-Fus1-antibody-capture ProteinChip array, we identified wild-type Fus1 as an N-myristoylated protein. N-myristoylation is a protein modification process in which a 14-carbon myristoyl group is cotranslationally and covalently added to the NH2-terminal glycine residue of the nascent polypeptide. Loss of expression or a defect of myristoylation of the Fus1 protein was observed in human primary lung cancer and cancer cell lines. A myristoylation-deficient mutant of the Fus1 protein abrogated its ability to inhibit tumor cell-induced clonogenicity in vitro, to induce apoptosis in lung tumor cells, and to suppress the growth of tumor xenografts and lung metastases in vivo and rendered it susceptible to rapid proteasome-dependent degradation. Our results show that myristoylation is required for Fus1-mediated tumor-suppressing activity and suggest a novel mechanism for the inactivation of tumor suppressors in lung cancer and a role for deficient posttranslational modification in tumor suppressor-gene-mediated carcinogenesis.

αCP-4, Encoded by a Putative Tumor Suppressor Gene at 3p21, But Not Its Alternative Splice Variant αCP-4a, Is Underexpressed in Lung Cancer

alpha CP-4 is an RNA-binding protein coded by PCBP4, a gene mapped to 3p21, a common deleted region in lung cancer. In this study we characterized the expression of alpha CP-4 and alpha CP-4a, an alternatively spliced variant of alpha CP-4, in lung cancer cell lines and non-small cell lung cancer (NSCLC) samples from early stage lung cancer patients. In NSCLC biopsies, an immunocytochemical analysis showed cytoplasmic expression of alpha CP-4 and alpha CP-4a in normal lung bronchiolar epithelium. In contrast, alpha CP-4 immunoreactivity was not found in 47% adenocarcinomas and 83% squamous cell carcinomas, whereas all of the tumors expressed alpha CP-4a. Besides, lack of alpha CP-4 expression was associated with high proliferation of the tumor (determined by Ki67 expression). By fluorescence in situ hybridization, >30% of NSCLC cell lines and tumors showed allelic losses at PCBP4, correlating with the absence of the protein. On the other hand, no mutations in the coding region of the gene were found in any of the 24 cell lines analyzed. By Northern blotting and real-time reverse transcription-PCR, we detected the expression of alpha CP-4 and alpha CP-4a messages in NSCLC and small cell lung cancer cell lines. Our data demonstrate an abnormal expression of alpha CP-4 in lung cancer, possibly associated with an altered processing of the alpha CP-4 mRNA leading to a predominant expression of alpha CP-4a. This may be considered as an example of alternative splicing involved in tumor suppressor gene inactivation. Finally, induction of alpha CP-4 expression reduced cell growth, in agreement with its proposed role as a tumor suppressor, and suggesting an association of this RNA-binding protein with lung carcinogenesis.

MYRbase: analysis of genome-wide glycine myristoylation enlarges the functional spectrum of eukaryotic myristoylated proteins

We evaluated the evolutionary conservation of glycine myristoylation within eukaryotic sequences. Our large-scale cross-genome analyses, available as MYRbase, show that the functional spectrum of myristoylated proteins is currently largely underestimated. We give experimental evidence for in vitro myristoylation of selected predictions. Furthermore, we classify five membrane-attachment factors that occur most frequently in combination with, or even replacing, myristoyl anchors, as some protein family examples show.

Lung cancer. 9: Molecular biology of lung cancer: clinical implications

It has been hypothesised that clinically evident lung cancers have accumulated many different genetic or epigenetic abnormalities in oncogenes and/or tumour suppressor genes. This notion has important clinical ramifications. Recent developments in our knowledge of the molecular biology of lung cancer are reviewed, with particular reference to genetic abnormalities in tumour suppressor gene inactivation and overactivity of growth promoting oncogenes. These changes lead to the "hallmarks of lung cancer". These hallmarks are the new rational targets for early detection, prevention, and treatment of lung cancer.

Molecular genetics of lung cancer

Lung cancer results from multiple changes in the genome of susceptible pulmonary cells caused by exposure to carcinogens found in tobacco smoke, the environment, or the workplace. Recent studies suggest that histologically apparent lung cancer is due to the sequential accumulation of specific genetic and morphologic changes to the normal epithelial cells of the lung. Positive signallers, such as those mediated by the oncogene RAS, and negative signallers, such as those mediated by the tumor suppressor retinoblastoma protein (RB), contribute to unchecked cell growth and proliferation. Other key molecular derangements can also be considered hallmarks of cancer, including evasion of apoptosis and senescence, angiogenesis, tissue invasion, and metastases. Epigenetic inactivation of genes via DNA methylation provides another novel way of evading normal cellular control mechanisms. The new knowledge of the human genome coupled with global methods of detecting genetic abnormalities and profiling gene expression in tumor cells may enable us to understand the signaling pathways of lung cancer cells. These are molecular targets for new cancer therapeutics such as receptor tyrosine kinase inhibitors. This information could advance risk assessment, early detection, prognosis, and therapy for lung cancer.

Detailed characterization of a homozygously deleted region corresponding to a candidate tumor suppressor locus at distal 17p13.3 in human lung cancer

17p13.3 is one of the chromosomal regions most frequently affected by allelic loss in a variety of human neoplasms including lung cancer. A number of loss of heterozygosity (LOH) analyses have suggested the existence of a tumor suppressor gene at 17p13.3, distal to the p53 locus at 17p13.1. In the present study, we characterized a homozygous deletion at 17p13.3 in a small cell lung cancer cell line by constructing a bacterial artificial chromosome (BAC) contig and a restriction map surrounding the region, as well as by utilizing publicly available draft sequences. We defined the breakpoint, assigned and analysed two known genes, 14-3-3 epsilon and CRK, and a novel gene LOST1 within or at the end of the homozygous deletion of about 170 kb in size. Marked reduction of LOST1 expression was detected in 69% (11/16) of lung cancer specimens by quantitative real-time RT-PCR, while significant DNA hypermethylation was observed at the 5' end of the LOST1 gene in four of six lung cancer cell lines with negligible LOST1 expression. We also show here that a polymorphic marker D17S1174, which resides within the homozygous deletion, was apparently located in the middle of the minimum LOH region, providing further supportive evidence for the presence of a tumor suppressor gene(s) in this region.

Practical uses for ecdysteroids in mammals including humans: an update

Ecdysteroids are widely used as inducers for gene-switch systems based on insect ecdysteroid receptors and genes of interest placed under the control of ecdysteroid-response elements. We review here these systems, which are currently mainly used in vitro with cultured cells in order to analyse the role of a wide array of genes, but which are expected to represent the basis for future gene therapy strategies. Such developments raise several questions, which are addressed in detail. First, the metabolic fate of ecdysteroids in mammals, including humans, is only poorly known, and the rapid catabolism of ecdysteroids may impede their use as in vivo inducers. A second set of questions arose in fact much earlier with the pioneering "heterophylic" studies of Burdette in the early sixties on the pharmacological effects of ecdysteroids on mammals. These and subsequent studies showed a wide range of effects, most of them being beneficial for the organism (e.g. hypoglycaemic, hypocholesterolaemic, anabolic). These effects are reviewed and critically analysed, and some hypotheses are proposed to explain the putative mechanisms involved. All of these pharmacological effects have led to the development of a wide array of ecdysteroid-containing preparations, which are primarily used for their anabolic and/or "adaptogenic" properties on humans (or horses or dogs). In the same way, increasing numbers of patents have been deposited concerning various beneficial effects of ecdysteroids in many medical or cosmetic domains, which make ecdysteroids very attractive candidates for several practical uses. It may be questioned whether all these pharmacological actions are compatible with the development of ecdysteroid-inducible gene switches for gene therapy, and also if ecdysteroids should be classified among doping substances.

Tumor suppressor genes on chromosome 3p involved in the pathogenesis of lung and other cancers

Loss of heterozygosity (LOH) involving several chromosome 3p regions accompanied by chromosome 3p deletions are detected in almost 100% of small (SCLCs) and more than 90% of non-small (NSCLCs) cell lung cancers. In addition, these changes appear early in the pathogenesis of lung cancer and are found as clonal lesions in the smoking damaged respiratory epithelium including histologically normal epithelium as well as in epithelium showing histologic changes of preneoplasia. These 3p genetic alterations lead to the conclusion that the short arm of human chromosome 3 contains several tumor suppressor gene(s) (TSG(s)). Although the first data suggesting that 3p alterations were involved in lung carcinogenesis were published more than 10 years ago, only recently has significant progress been achieved in identifying the candidate TSGs and beginning to demonstrate their functional role in tumor pathogenesis. Some of the striking results of these findings has been the discovery of multiple 3p TSGs and the importance of tumor acquired promoter DNA methylation as an epigenetic mechanism for inactivating the expression of these genes in lung cancer. This progress, combined with the well known role of smoking as an environmental causative risk factor in lung cancer pathogenesis, is leading to the development of new diagnostic and therapeutic strategies which can be translated into the clinic to combat and prevent the lung cancer epidemic. It is clear now that genetic and epigenetic abnormalities of several genes residing in chromosome region 3p are important for the development of lung cancers but it is still obscure how many of them exist and which of the numerous candidate TSGs are the key players in lung cancer pathogenesis. We review herein our current knowledge and describe the most credible candidate genes.

Cre-loxP chromosome engineering of a targeted deletion in the mouse corresponding to the 3p21.3 region of homozygous loss in human tumours

Chromosomal deletions are a common feature of epithelial tumours and when further defined by homozygous deletions, are often the location of tumour suppressor genes. Deletions within the short arm of chromosome 3 occur very frequently in human carcinomas: a minimal region of loss at 3p21.3 (the Luca) region has been defined by overlapping homozygous deletions in lung and breast cancer cell lines. Using a rapid strategy for Cre-loxP chromosome engineering, a deletion of approximately 370 kb was created in the mouse germline corresponding to the deleted region at 3p21.3. The deletion when homozygous is embryonic lethal. Heterozygotes develop normally despite being haplo-insufficient for twelve genes including the candidate tumour suppressor gene Rassf1. Because damage to 3p21.3 often occurs very early in the sequence of genetic changes that lead to malignancy, particularly in lung and breast cancer, further genetic damage to these mice will provide the opportunity to model multi-step tumorigenesis of these tumours.