Characterization and expression analysis of TNF-related apoptosis inducing ligand (TRAIL) in grass carp Ctenopharyngodon idella

TRAIL (Apo2 ligand) described as a type II transmembrane protein belonging to the TNF superfamily can induce apoptotic cell death in a variety of cell types. In the present study, a putative cDNA sequence encoding the 299 amino acids of TRAIL (GC-TRAIL) and its genomic organization were identified in grass carp Ctenopharyngodon idella. The predicted GC-TRAIL sequence showed 44 and 41% identities to chicken and human TRAILs, respectively. In a domain search, a tumor necrosis factor homology domain (THD) was identified in the C-terminal portion of TRAILs. The GC-TRAIL gene consists of five exons, with four intervening introns, spaced over approximately 4 kb of genomic sequence. Analysis of GC-TRAIL promoter region revealed the presence of a number of putative transcription factor binding sites, such as Sp1, NF-kappaB, AP-1, GATA, NFAT, HNF, STAT, P53 and IRF1 sequences which are important for the expression of other TNF family members. Phylogenetic analysis placed GC-TRAIL and the putative zebrafish (Danio rerio) TRAIL obtained from searching the zebrafish database into one separate cluster near mammalian TRAIL genes, but apart from the reported zebrafish TRAIL-like protein, indicating that the GC-TRAIL is an authentic fish TRAIL. Expression analysis revealed that GC-TRAIL is expressed in many tissues, such as in gills, liver, trunk kidney, head kidney, intestine and spleen.

Investigation of the Booroola (FecB) and Inverdale (FecX(I)) mutations in 21 prolific breeds and strains of sheep sampled in 13 countries

Twenty-one of the world's prolific sheep breeds and strains were tested for the presence of the FecB mutation of BMPR1B and the FecX(I) mutation of BMP15. The breeds studied were Romanov (2 strains), Finn (2 strains), East Friesian, Teeswater, Blueface Leicester, Hu, Han, D'Man, Chios, Mountain Sheep (three breeds), German Whiteheaded Mutton, Lleyn, Loa, Galician, Barbados Blackbelly (pure and crossbred) and St. Croix. The FecB mutation was found in two breeds, Hu and Han from China, but not in any of the other breeds. The 12 Hu sheep sampled were all homozygous carriers of FecB (FecB(B)/FecB(B)) whereas the sample of 12 Han sheep included all three genotypes (FecB(B)/FecB(B), FecB(B)/FecB+, FecB+/FecB+) at frequencies of 0.33, 0.58 and 0.08, respectively. There was no evidence of FecX(I) in any of the breeds sampled.

Isolation and characterization of rice mutants compromised in Xa21-mediated resistance to X. oryzae pv. oryzae

The rice gene, Xa21, confers resistance to diverse races of Xanthomonas oryzae pv. oryzae (Xoo) and encodes a receptor-like kinase with leucine-rich repeats in the extra-cellular domain. To identify genes essential for the function of the Xa21 gene, 4,500 IRBB21 ( Xa21 isogenic line in IR24 background) mutants, induced by diepoxybutane and fast neutrons, were screened against Philippine race six (PR6) Xoo for a change from resistance to susceptibility. From two greenhouse screens, 23 mutants were identified that had changed from resistant to fully (6) or partially (17) susceptible to PR6. All fully susceptible mutants carried rearrangements at the Xa21 locus as detected by PCR and Southern hybridization. For the partially susceptible mutants, no changes were detected at the Xa21 locus based on Southern and PCR analyses. However, two of these mutants were confirmed via genetic analysis to have mutations at the Xa21 locus. Partially susceptible mutants exhibited variation in level of susceptibility to different Xoo strains, suggesting that they may carry different mutations required for the Xa21-mediated resistance. The mutants identified in this study provide useful materials for dissecting the Xa21-mediated resistance pathway in rice.

Genetic and physical mapping of Pi5(t), a locus associated with broad-spectrum resistance to rice blast

To gain an understanding of the molecular basis for resistance to rice blast (Magnaporthe grisea), we have initiated a project to clone Pi5(t), a locus associated with broad-spectrum resistance to diverse blast isolates. AFLP-derived markers linked to Pi5(t)-mediated resistance were isolated using bulked segregant analysis of F(2) populations generated by crossing three recombinant inbred lines (RILs), RIL125, RIL249, and RIL260 with the susceptible line CO39. The most tightly linked AFLP marker, S04G03, was positioned on chromosome 9 of the fingerprint-based physical map of Nipponbare, a well-characterized rice genotype. Flanking BAC-based Nipponbare markers were generated for saturation mapping using four populations, the three initial RILs and an additional one derived from a cross between M202 and RIL260. A BIBAC (binary BAC) library was constructed from RIL260. Using these resources Pi5(t) was mapped to a 170-kb interval, and a contiguous set of BIBAC clones spanning this region was constructed. It had previously been suggested that Pi3(t) and Pi5(t) might be allelic, due to their identical resistance spectrum and tight linkage. We therefore compared genomic regions for lines containing Pi3(t) using the Pi5(t)-linked markers. DNA gel-blot analyses indicated that the region around Pi3(t) is identical to that of Pi5(t), suggesting that Pi3(t) and Pi5(t) are the same resistance gene.

Dissection of defence response pathways in rice

The cloning of major resistance genes has led to a better understanding of the molecular biology of the steps for induction of resistance, yet much remains to be discovered about the downstream genes that collectively confer resistance, i.e. the defence response (DR) genes. We are dissecting the pathways contributing to resistance in rice by identifying a collection of mutants with deletions or other structural rearrangements in DR genes. The collection of rice mutants has been screened for many characters, including increased susceptibility or resistance to Magnaporthe grisea and Xanthomonas oryzae pv. oryzae. A collection of enhanced sequence tags (ESTs) and putative DR genes has been established to facilitate detection of mutants with deletions in DR genes. Arrays of DR genes will be used to create gene expression profiles of interesting mutants. Successful application of the mutant screen will have broad utility in identifying candidate genes involved in disease response and other metabolic pathways.

[Effects of medium and culture conditions on polysaccharide synthesis by suspension cell culture of Gardenia jasminoides Eills]

The effects of medium and culture condition on polysaccharide synthesis by suspension culture of Gardenia jasminoides Eills were studied. The results show that B5 was the optimum medium, 5-10 days was suitable for subculture periods, and an inoculum of 80 g/L wet cell was better to cell growth and polysaccharide accumulation. For carbon source, it was better to use glucose than sucrose on cell growth, but due to the higher price of glucose, 45 g/L compound carbon source combined sucrose with glucose (1:1) was the optimum. The effect of different kinds of nitrogen source on cell growth and polysaccharide synthesis was not so big, and 40-50 mmol/L nitrogen was optimum, lower concentration of nitrogen source could inhibit the synthesis of polysaccharides. In addition, by controlling the harvest time of the polysaccharide in the suspension culture, the accumulation of yellow pigment could be prevented, which is easier to the polysaccharide purification.

alpha-Adducin gene and essential hypertension in China

Adducin is a membrane skeletal protein that is involved in the regulation of membrane ion transport and cellular signal transduction. Essential hypertension has been linked to alpha-adducin gene locus, and association of a polymorphism of the gene has been found in some studies, but results of linkage or association studies on alpha-adducin gene are controversial among different populations. This study was designed to examine the linkage between alpha-adducin gene locus and essential hypertension and to reveal the relationship between an alpha-adducin gene polymorphism (Gly460Trp) and essential hypertension in a Chinese population. For the linkage study, one hundred and six Chinese nuclear families were recruited, including 417 hypertensive patients in all 474 individuals. Those samples were genotyped at D4S412 and D4S3038. The distances between the two microsatellite markers and the alpha-adducin gene locus are less than 3cM. Parametric, non-parametric linkage (NPL) analyses using the GENEHUNTER software were carried out. Sib transmission-dise- quilibrium test (S-TDT), as well as transmission-disequilibrium test (TDT). was also implemented with TDT/S-TDT Program 1.1. Serum levels of uric acid, creatinine, blood urea nitrogen (BUN), fasting glucose and lipids were determined as phenotypes. In an association study, 138 hypertensive and 121 normotensive subjects were genotyped at Gly460Trp of the alpha-adducin gene to examine a possible association between this polymorphism and blood pressure or other phenotypes. We fail to find the linkage between the two markers and essential hypertension by parametric, NPL analysis or TDT/S-TDT study. With the use of the simple association and the multivariate logistic regression analyses, we also fail to reveal a significant association between the Gly460Trp polymorphism in alpha-adducin gene and the blood pressure variation, or blood biochemical indices studied. The frequency of the 460Trp allele in Chinese (46-48%) is similar to that found in Japanese (54-60%) while the allele frequency is less common in Caucasian (13%-23%). These findings suggest that in our Chinese population, alpha-adducin 460Trp variant may not play an important role in the etiology of EH. And the negative results of linkage and TDT/ S-TDT further supports this conclusion.

Crystal structures and magnetic properties of new cyano-bridged two-dimensional grid-like bimetallic assemblies [Ni(tn)2]2[Cr(CN)5((NO)]OH*H2O and [NI(tn)2]2[Co(CN)6]NO3*2H2O (tn=1,3-propanediamine)

Two bimetallic assemblies, [Ni(tn)(2)](2)[Cr(CN)(5)(NO)]OH.H(2)O (1) and [Ni(tn)(2)](2)[Co(CN)(6)]NO(3).2H(2)O (2) (tn = 1,3-diaminopropane), have been prepared and structurally and magnetically characterized. Crystal data for 1 (2): space group P1 (P1), a = 8.698(3) (8.937(2)) A, b = 10.001(2) (9.863(1)) A, c = 10.158(2) (10.064(1)) A, alpha = 87.40(2) (86.064(10)) degrees, beta = 65.10(2) (65.489(10)) degrees, gamma = 81.63(2) (81.572(12)) degrees and Z = 1 (1). Both structures consist of two-dimensional grid-like polycations containing Ni-N triple bond C-M linkages (M = Cr or Co) and counteranions (OH, NO(3)). Magnetic studies of 1 showed that the complex displays a metamagnetic behavior originating from intralayer ferromagnetic and interlayer antiferromagnetic interactions. Long-range antiferromagnetic ordering was observed at T(N) = 3.3 K. Complex 2 exhibits intramolecular ferromagnetic interactions through the diamagnetic N triple bond C-Co-N triple bond C bridges, owing to superexchange involving the empty d(sigma) orbital of the diamagnetic Co(III) ion.

[Studies on X-ray diffraction pattern of traditional Chinese medicinal materials]

Traditional Chinese medicine(TCM) as prescribed by Chinese traditional physicians is usually available as "decoction slices" which calls for a ready method for assessment of quantity or even genuineness. Three groups of TCM drugs (radix Rubiae, bulbus Fritillariae and rhizoma Dioscoreae) were selected by using powder X-ray diffraction analysis with complete absorption profile. Topological regularity and characteristic peaks of the absorption profile were obtained as fingerprint in X-ray diffraction diagrams of the pertinent medicinal materials. We have discovered the similarities of 3 radix Rubiae samples gathered from different localities and their differences with Rubia tinctorum, the similarities and differences between 7 species belonging to Fritillaria Genus, the similarities of 2 rhizoma Dioscoreae samples from different localities and their differences with 2 counterfeits. The result points to a promising prospect in achieving an objective assessment of genuineness at TCM drugs.

Rice ESTs with disease-resistance gene- or defense-response gene-like sequences mapped to regions containing major resistance genes or QTLs

The chromosomal locations of 109 rice expressed sequence tags (ESTs) in the rice genome were determined using a doubled haploid mapping population. These ESTs show high similarity to disease resistance genes or to defense response genes. Nine of the ESTs were mapped to three regions that contain genetically defined resistance genes on chromosomes 6 and 11. Clustering of the ESTs in the rice genome was observed at several chromosomal regions. Some of the clusters were located in regions where quantitative trait loci (QTL) associated with partial resistance to rice blast, bacterial blight and sheath blight are known to lie. Three ESTs that were mapped to the regions containing blast resistance genes Pi2 and Pia were chosen for Northern analysis after inoculation of plants with the blast fungus. Two of them, which code for a receptor-like kinase and a putative membrane channel protein, respectively, and were mapped to the Pi2 locus, were induced by rice blast infection as early as 4 h after inoculation. Transcription of another EST, which codes for a homolog of a putative human tumor suppressor and was mapped to the region containing Pia, was repressed after blast infection. These findings demonstrate that the candidate-gene approach is an efficient way of mapping resistance genes or resistance QTLs in rice.

Oxamato-bridged trinuclear Ni(II)Cu(II)Ni(II) complexes with irregular spin state structures and a binuclear Ni(II)Cu(II) complex with an unusual supramolecular structure: crystal structure and magnetic properties

Four oxamato-bridged heterotrinuclear Ni(II)Cu(II)Ni(II) complexes of formula ([Ni(bispictn)](2)Cu(pba))(ClO(4))(2).2.5H(2)O (1), ([Ni(bispictn)](2)Cu(pbaOH))(ClO(4))(2).H(2)O (2), ([Ni(cth)](2)Cu(pba))(ClO(4))(2) (3), and ([Ni(cth)](2)Cu(opba))(ClO(4))(2).H(2)O (4) and a binuclear Ni(II)Cu(II) complex of formula [Cu(opba)Ni(cth)].CH(3)OH (5) have been synthesized and characterized by means of elemental analysis, IR, ESR, and electronic spectra, where pba = 1,3-propylenebis(oxamato), pbaOH = 2-hydroxyl-1,3-propylenebis(oxamato), opba = o-phenylenebis(oxamato), bispictn = N,N'-bis(2-pyridylmethyl)-1,3-propanediamine, and cth = rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. The crystal structures of 1, 3, and 5 have been determined. The structures of complexes 1 and 3 consist of trinuclear cations and perchlorate anions, and that of 5 consists of neutral binuclear molecules which are connected by hydrogen bonds and pi-pi interactions to produce a unique supramolecular "double" sheet. In the three complexes, the copper atom in a square-planar or axially elongated octahedral environment and the nickel atom in a distorted octahedral environment are bridged by the oxamato groups, with Cu.Ni separations between 5.29 and 5.33 A. The magnetic properties of all five complexes have been investigated. The chi(M)T versus T plots for 1-4 exhibit the minimum characteristic of antiferromagnetically coupled NiCuNi species with an irregular spin state structure and a spin-quartet ground state. The chi(M)T versus T plot for 5 is typical of an antiferromagnetically coupled NiCu pair with a spin-doublet ground state. The Ni(II)-Cu(II) isotropic interaction parameters for the five complexes were evaluated and are between 102 and 108 cm(-)(1) (H = -JS(Cu).S(Ni)).

[Response of lithium fluoride detector to charged particle LET]

Response of LiF thermoluminescence (TL) detector to charged particle is dependent on particles' LET. High LET can cause reduction of detector response and underestimation of radiation dose. This paper summarized the response of LiF detector to charged particles' LET, and suggested a new approach to solve the dose contribution of high LET charged particles.

GATA-4 and serum response factor regulate transcription of the muscle-specific carnitine palmitoyltransferase I beta in rat heart

Transcriptional regulation of nuclear encoded mitochondrial proteins is dependent on nuclear transcription factors that act on genes encoding key components of mitochondrial transcription, replication, and heme biosynthetic machinery. Cellular factors that target expression of proteins to the heart have been well characterized with respect to excitation-contraction coupling. No information currently exists that examines whether parallel transcriptional mechanisms regulate nuclear encoded expression of heart-specific mitochondrial isoforms. The muscle CPT-Ibeta isoform in heart is a TATA-less gene that uses Sp-1 proteins to support basal expression. The rat cardiac fatty acid response element (-301/-289), previously characterized in the human gene, is responsive to oleic acid following serum deprivation. Deletion and mutational analysis of the 5'-flanking sequence of the carnitine palmitoyltransferase Ibeta (CPT-Ibeta) gene defines regulatory regions in the -391/+80 promoter luciferase construct. When deleted or mutated constructs were individually transfected into cardiac myocytes, CPT-I/luciferase reporter gene expression was significantly depressed at sites involving a putative MEF2 sequence downstream from the fatty acid response element and a cluster of heart-specific regulatory regions flanked by two Sp1 elements. Each site demonstrated binding to cardiac nuclear proteins and competition specificity (or supershifts) with oligonucleotides and antibodies. Individual expression vectors for Nkx2.5, serum response factor (SRF), and GATA4 enhanced CPT-I reporter gene expression 4-36-fold in CV-1 cells. Although cotransfection of Nkx and SRF produced additive luciferase expression, the combination of SRF and GATA-4 cotransfection resulted in synergistic activation of CPT-Ibeta. The results demonstrate that SRF and the tissue-restricted isoform, GATA-4, drive robust gene transcription of a mitochondrial protein highly expressed in heart.

Linkage of hypertension to chromosome 2q14-q23 in Chinese families

OBJECTIVES

To identify chromosome regions containing hypertension susceptibility genes in Chinese.

SUBJECTS AND METHODS

A three-stage study was carried out in Chinese siblings ascertained through outpatient clinics. In the first stage, 283 affected sib-pairs from 79 nuclear families were subjected to a genome-wide scan with 240 microsatellite marker loci. The second stage focused on chromosome 2 with additional markers resulting in an average distance of 5 cM and used an independent sample of 637 affected sib-pairs from 161 families. In the third stage, a fine-scale mapping study on the suggestive region was performed in an independent set of 777 affected sib-pairs from 106 families. Fourteen markers were used with an average distance less than 2 cM. Non-parametric linkage analyses (NPL), parametric linkage analyses and transmission-disequilibrium tests were used to assess evidence for linkage and association.

RESULTS

Three markers (D2S168 at 27.06 cM, D2S151 at 152.04 cM and D2S142 at 161.26 cM) on chromosome 2 with suggestive linkage to hypertension susceptibility genes were identified in the genome-wide scan. In stage II, the suggestive region around D2S151 and D2S142 was replicated, while the linkage around D2S168 was not. In the stage III fine-scale mapping study, multipoint linkage analyses showed LOD scores greater than 2.0 throughout a region between 157.16 cM and 162.46 cM (all P < 0.001) with a maximum peak of 2.24 (P= 0.00067) at 160.52 cM. We also observed a NPL Z-score peak of 3.27 at 157.55 cM (P= 0.00086).

CONCLUSIONS

The results of a suggestive region on chromosome 2q14-q23 (D2S112-D2S2370) were consistent between each of the three studies. Interestingly, this region overlaps a syntenic region that contains blood pressure quantitative trait loci identified in rat models of hypertension. These data suggest that the region near D2S142 and D2S151 deserves to be further screened for hypertension susceptibility genes.

Characterizing rice lesion mimic mutants and identifying a mutant with broad-spectrum resistance to rice blast and bacterial blight

Many plant mutants develop spontaneous lesions that resemble disease symptoms in the absence of pathogen attack. In several pathosystems, lesion mimic mutations have been shown to be involved in programmed cell death, which in some instances leads to enhanced disease resistance to multiple pathogens. We investigated the relationship between spontaneous cell death and disease resistance in rice with nine mutants with a range of lesion mimic phenotypes. All nine mutations are controlled by recessive genes and some of these mutants have stunted growth and other abnormal characteristics. The lesion mimics that appeared on the leaves of these mutants were caused by cell death as measured by trypan blue staining. Activation of six defense-related genes was observed in most of the mutants when the mimic lesions developed. Four mutants exhibited significant enhanced resistance to rice blast. One of the mutants, spl11, confers non-race-specific resistance not only to blast but also to bacterial blight. The level of resistance in the spl11 mutant to the two pathogens correlates with the defense-related gene expression and lesion development on the leaves. The results suggest that some lesion mimic mutations in rice may be involved in disease resistance, and cloning of these genes may provide a clue to developing broad-spectrum resistance to diverse pathogens.

[Site-directed mutagenesis of melittin gene and its expression in Escherichia coli]

The cDNA encoding promelittin was obtained from the total RNA of bee poison gland by RT-PCR. Moreover, hydroxylamine clearage site was arranged before the melittin sequences by site-directed mutagenesis. The expression vector containing the mutagenic promelittin sequence with partial sequence of beta-galactosidase was constructed. The result of DNA sequence analysis demonstrated that the obtained cDNA sequence include the desired codon and the reading frame of fusion gene was correct. The induced protein was expressed in Escherichia coli.

[Measurements of proton response of two lithium fluoride detectors with different thicknesses]

OBJECTIVE

To study the response characteristics of LiF detectors to proton fluence rate and energy, and to observe the thickness effect of the detector.

METHOD

Protons were generated by an accelerator. Proton energy was changed in two ways, i.e. changing the accelerator energy directly, or using detector stacks to absorb the proton energy. The incident proton energy on each chip of detector stacks was calculated according to proton range in LiF.

RESULT

The response of the detector to proton fluence rate was almost constant; when proton energy was above 9 MeV, the response of the detector to proton energy was constant (less than 10% errors). When proton energy was below 9 MeV, the response reduced gradually with the decrease of proton energy. Thickness effect for LiF thicknesses of 0.4mm and 0.8mm was not obvious.

CONCLUSION

The homemade LiF detector is suitable for measurement of space radiation dose. When proton component (below 9 MeV) was abundant in radiation field, the decrease of the relative thermoluminescence efficiency should be taken into consideration.

New alternating ferro- and antiferromagnetic one-dimensional complexes. Synthesis, characterization, crystal structure, and magnetic properties of

The preparation, X-ray crystal structure, and magnetic properties of alternating 1,1- and 1,3-azido-bridged copper(II) complex [Cu(4,4'-dmbpy)(N3)2]n (1, 4,4'-dmbpy = 4,4'-dimethylbipyridine) have been reported. It crystallizes in triclinic system, space group P1, a = 7.9903(1) A, b = 9.3545(9) A, c = 10.754(2) A, alpha = 113.485(1) degrees, beta = 101.399(1) degrees, gamma = 101.897(1) degrees, Z = 2. The magnetic properties of 1 have been investigated in the temperature range 1.5-300 K. Alternating antiferromagnetic (-J = 191.0 cm(-1)) interaction through a 1,3-N3- bridge and ferromagnetic (J = 297.1 cm(-1)) interaction through a 1,1-N3- bridge are obtained for 1 by analyzing the magnetic susceptibility data with the Hamiltonian H = -Jsigma(S2iS2i-1--alphaS2iS2i+1). It's derivatives ([Mn(4,4'-dmbpy)(N3)2]n (2), [Ni(4,4'-dmbpy)(N3)2]n (3), and [Fe(4,4'-dmbpy)(N3)2]n (4) and the heterometallic derivatives [NiMn(4,4'-dmbpy)2(N3)4]n (5) and [CuMn(4,4'-dmbpy)2(N3)4]n (6) have also been synthesized and characterized by electronic and IR spectra. The X-ray powder diffraction and the magnetic properties of 6 have also been discussed.

[An analysis on thickness effect of lithium fluoride detector in proton measurement]

OBJECTIVE

To theoretically analyze the thickness effect of a LiF detector for proton measurement.

METHOD

Thickness effect of the detector was calculated by using the definition of the detector dose under ideal and reasonable hypothesis.

RESULT

The thickness effect of the detector was not obvious when protons could penetrate the detector: when proton energy was above 12 MeV, the thickness effect was obvious only on condition that the detector thickness approaches proton range, when proton energy was less than 12 MeV, the thickness effect was not obvious. The thickness effect of the detector was obvious, when protons could not penetrate the detector.

CONCLUSION

Thin detectors should be used in low energy proton measurements to avoid thickness effect of the detector.

[Cloning and expression of tyrosinase gene from Pseudomonas maltophilia in E. coli]

The enzyme tyrosinase, encoded by tyrosinase gene (mel), is responsible for melanin formation. In a shotgun cloning experiment, a SalI-digested DNA fragment coding for tyrosinase was cloned from Pseudomonas maltophilia DNA into plasmid vector (pUC18) to generate the hybrid plasmid (pWSY). The recombinant plasmid imparted the ability of melanin synthesis to an E. coli host (HB101). The foreign DNA fragment (0.7 kb) possessed no recognition sites for BamHI, HindIII, EcoRI or BclI. Hybridization studies confirmed that the small fragment cloned in pWSY was from P. maltophilia DNA. Nucleotide sequence analysis identified an ORF of 504 nt coding tyrosinase. SDS-PAGE analysis also revealed an additional protein of 18 kDa, which was equal to the putative tyrosinase according to the size of mel fragment, was expressed in the E. coli recombinant carrying the plasmid pWSY.

Inhibiting tumorigenic potential by restoration of p16 in nasopharyngeal carcinoma

The p16 gene, encodes a key checkpoint protein p16 in the cell cycle, has been reported inactivation in a wide variety of human cancers. We have previously demonstrated high frequency of p16 alterations in primary nasopharyngeal carcinoma (NPC), xenografts and cell lines. The finding implied that inactivation of the p16 gene may play an important role in the NPC development. To investigate the tumour suppressor function of p16 in NPC, we transfected p16-deficient NPC cell line, NPC/HK-1, with a wild-type p16 expression construct, and evaluated growth and tumorigenic properties of the clones stably expressing exogenous p16. Expression of the exogenous wild-type p16 significantly inhibited cell growth by more than 70% when compared to that of the parental and empty vector-transfected cells. This growth inhibition was attributable to a significant proportion of p16-expressing cells arrested at G1 phase in the cell cycle as revealed by flow cytometric analysis. By anchorage-independent colony forming assay, we found that the ability to form colonies in soft agar was highly reduced in cells expressing p16. NPC/HK1 cells expressing functional p16 also showed suppressed tumorigenicity in athymic nude mice. Taken together, our results provide strong evidence for a tumour suppressor role of p16 in NPC.