Hypoxia induces the expression of transketolase-like 1 in human colorectal cancer.

BACKGROUND AND AIMS: Transketolase-like (TKTL) 1 is one of the key enzymes for anaerobic sugar degradation even in the presence of oxygen (aerobic glycolysis). Transketolase-dependent reactions supply malignant tumors with ribose and NADPH. Therefore, TKTL1 activity could be crucial for tumor proliferation and survival. The aim of the study was to evaluate the expression of TKTL1 in colorectal cancer (CRC) and its regulation under hypoxic conditions. METHODS: We studied TKTL1 mRNA and protein expression in CRC cell lines and human CRC biopsies by quantitative real-time PCR, Western blotting and immunohistochemistry. Regulation of TKTL1 under oxygen depletion was analyzed by cultivating cells either in a three-dimensional spheroid model or in a hypoxia incubator chamber. RESULTS: TKTL1 mRNA was heterogeneously expressed in monolayers of cells with high levels in HT-29 and SW480. TKTL1 protein was also clearly detectable in HT-29 and SW480. Hypoxia-inducible factor (HIF)-1α protein expression correlated with TKTL1 protein expression in SW480 spheroids over time. On the one hand, induction of hypoxia in T84 spheroids did not induce TKTL1; on the other hand, hypoxia by incubation at 1% O2 in a hypoxia incubator chamber clearly showed an upregulation of TKTL1. In 50% of CRC patients, TKTL1 protein expression was upregulated in tumor compared to non-tumor tissue. The immunohistochemical staining of TKTL1 in CRC patient samples resulted in 14 positive and 30 negative samples. CONCLUSIONS: TKTL1 expression correlated with HIF-1α protein expression and was induced upon hypoxic conditions which could facilitate energy supply to tumors under these circumstances.

A gene mutated in X-linked myotubular myopathy defines a new putative tyrosine phosphatase family conserved in yeast.

X-linked recessive myotubular myopathy (MTM1) is characterized by severe hypotonia and generalized muscle weakness, with impaired maturation of muscle fibres. We have restricted the candidate region to 280 kb and characterized two candidate genes using positional cloning strategies. The presence of frameshift or missense mutations (of which two are new mutations) in seven patients proved that one of these genes is indeed implicated in MTM1. The protein encoded by the MTM1 gene is highly conserved in yeast, which is surprising for a muscle specific disease. The protein contains the consensus sequence for the active site of tyrosine phosphatases, a wide class of proteins involved in signal transduction. At least three other genes, one located within 100 kb distal from the MTM1 gene, encode proteins with very high sequence similarities and define, together with the MTM1 gene, a new family of putative tyrosine phosphatases in man.

A human homologue of the Drosophila tumour suppressor gene l(2)gl maps to 17p11.2-12 and codes for a cytoskeletal protein that associates with nonmuscle myosin II heavy chain.

Inactivation of the tumour suppressor gene lethal(2) giant larvae (D-lgl) of Drosophila leads to malignant transformation of the presumptive adult optic centers in the larval brain and tumours of the imaginal discs. These malignancies result from the disorganization of a cytoskeletal network in which the D-LGL protein participates. Here we describe the isolation of a cDNA encoding the human homologue to the D-lgl gene designated as hugl. The hugl cDNA detects a locus spanning at least 25 kilobases (kb) in human chromosome band 17p11.2-12, which is centromeric to the p53 gene and recognizes a 4.5 kb RNA transcript. The hugl gene is expressed in brain, kidney and muscle but is barely seen in heart and placenta. Sequence analysis of the hugl cDNA demonstrates a long open reading frame, which has the potential to encode a protein of 1057 amino acids with a predicted molecular weight of 115 kDaltons (kD). To further substantiate and identify the HUGL protein, we have prepared polyclonal rabbit antibodies against synthetic peptides corresponding to the amino and carboxyl termini of the conceptual translation product of the hugl gene. The affinity-purified anti-HUGL antibodies recognize a single protein with an apparent molecular weight of approximately 115 kD. Similar to the Drosophila protein, HUGL is part of a cytoskeletal network and, is associated with nonmuscle myosin II heavy chain and a kinase that specifically phosphorylates HUGL at serine residues.

Differential transcriptional regulation of the monocyte-chemoattractant protein-1 (MCP-1) gene in tumorigenic and non-tumorigenic HPV 18 positive cells: the role of the chromatin structure and AP-1 composition.

The expression of the monocyte-chemoattractant-protein-1 (MCP-1) is closely linked with a non-tumorigenic phenotype in somatic cell hybrids made between the human papillomavirus type 18 (HPV 18) positive cervical carcinoma cell line HeLa and normal human fibroblasts. In contrast, MCP-1 transcription is absent in tumorigenic segregants derived from the same hybrids or in parental HeLa cells. Selectivity of MCP-1 transcription, which is regulated at the level of initiation of transcription, is mainly based on differences in the location and extension of DNAse I-hypersensitive regions (DHSR) at both ends of the gene. While TNF-alpha only moderately increases the sensitivity of pre-existing 5'-DHSRs, a 3'-end DHSR became strongly induced exclusively in non-malignant hybrids. DNA sequencing showed that the 3'-DHSR coincides with an additional AP-1 site located approximately 600 bp downstream of the polyadenylation site. Analyses of AP-1 composition revealed that MCP-1 is only expressed in those cells where jun-family members were mainly heterodimerized with the fos-related protein fra-1. In contrast, in tumorigenic cells the 1: 1 ratio between jun and fra-1 is disturbed and the MCP-1 gene is no longer expressed. Hence, alterations in the heterodimerization pattern of AP-1 and its selective accessibility to opened chromatin may represent a novel regulatory pathway in the regulation of chemokines in malignant and non-malignant HPV-positive cells.

The genomic structure of the DMBT1 gene: evidence for a region with susceptibility to genomic instability.

Increasing evidence has accumulated for an involvement of the inactivation of tumour suppressor genes at chromosome 10q in the carcinogenesis of brain tumours, melanomas, and carcinomas of the lung, the prostate, the pancreas, and the endometrium. The gene DMBT1 (Deleted in Malignant Brain Tumours 1) is located at chromosome 10q25.3-q26.1, within one of the putative intervals for tumour suppressor genes. DMBT1 is a member of the scavenger-receptor cysteine-rich (SRCR) superfamily and displays homozygous deletions or lack of expression in glioblastoma multiforme, medulloblastoma, and in gastrointestinal and lung cancers. Based on these properties, DMBT1 has been proposed to be a candidate tumour suppressor gene. We have determined the genomic sequence of DMBT1 to allow analyses of mutations. The gene has at least 54 exons that span a genomic region of about 80 kb. We have identified a putative exon with coding potential for a transmembrane domain. Our data further suggest that alternative splicing gives rise to isoforms of DMBT1 with a differential utilization of SRCR domains and SRCR interspersed domains. The major part of the gene harbours locus specific repeats. These repeats may point to the DMBT1 locus as a region susceptible to chromosomal instability.

Isolation, differential splicing and protein expression of a DNase on the human X chromosome.

A systematic search for genes differentially expressed in human tissues resulted in the isolation of a gene encoding a protein with high homology to DNase I. In addition to the recently described cDNA sequence (Parrish et al., 1995) we have isolated a transcript, alternatively spliced in the 5' noncoding region. The gene is located between the QM and the XAP-2 gene in Xq28 and encodes a 302 amino acid protein with 39% identity to human DNase I. Besides a high homology at the nucleotide and amino acid level, most exon-intron boundaries of DNase I and DNase X are identical, indicating that both genes may have evolved from a common ancestor. The predicted function was verified by expression of a recombinant protein in an inducible bacterial system and detection of DNase activity. In contrast to DNase I a 18 kdal amino terminal fragment of the full length 35 kdal protein exhibited DNase activity.

The relationship between allelic imbalance on 17p, p53 mutation and p53 overexpression in head and neck cancer.

The huge majority of head and neck squamous cell carcinoma (HNSCC) show alterations of p53 either on the genetic level or on the protein level. Allelic imbalance (AI)/loss of heterozygosity (LOH) on 17p at the p53 locus is frequent in HNSCC. However, the complex relationship between these phenomena is poorly understood in HNSCC. We investigated one group of 39 HNSCC for: a) allelic imbalance on 17p using 4 microsatellite markers located throughout this chromosomal arm; b) mutations of p53 in exons 5-9; and c) overexpression of p53 using two antibodies located on opposite ends of the protein. AI/LOH was detected in 44% at the locus TP53, rising to 69% when regarding all 4 markers on 17p. Therefore, our data are in line with the assumption of additional tumour suppressor genes on 17p in HNSCC. A nuclear accumulation of p53 (51%) was independent from the antibody and the recognised epitope. At the first glance there was no correlation between overall p53 mutation (36%) and overexpression. However, it appeared that, with very few exceptions, only nonsense mutations did not lead to p53 overexpression, while missense mutations did. As overexpression of p53 was 15% more frequent than p53 mutations and only 35% of the tumours with p53 overexpression carried a p53 mutation, our data support the hypothesis of additional mechanisms of p53 overexpression. AI/LOH at the p53 locus in 83% of all tumours with a p53 mutation is in line with Knudson's theory of inactivation of tumour suppressor genes.

Genetic discordance between primary tumours and metastases of head and neck cancer detected by microsatellite analysis.

Very little is known about possible intra-tumoural genetic heterogeneity between primary tumours and lymph node metastases in head and neck squamous cell carcinoma (HNSCC). To investigate this phenomenon, we analysed 96 micro-dissected tumour samples for allelic imbalance at four of the most frequently altered chromosomal locations in HNSCC (3p14.2; 9p21; 11q23.3; 17p13.1) using microsatellite markers. From 23 patients, matched pairs of primary tumour and lymph node metastasis were analysed. Discordance in the allelic distribution was identified in 8 cases (35%). With one exception, the metastasis contained a more balanced allelic status than the primary tumour. In contrast, in a group of 25 tumours with two anatomically different samples from the primary tumour site, discordance was identified in only 3 tumours (13%). These results are compatible with the dissemination of subclones from the primary tumour site with a more balanced allelotype in the metastasis. In our opinion, several scenarios could explain this phenomenon. From a clinical point of view, genetic discordance between the metastasis and the primary tumour must be taken into consideration when establishing molecular biologic markers for choice of therapy and prognosis in head and neck cancer.

Salivary gland carcinosarcoma: immunohistochemical, molecular genetic and electron microscopic findings.

Salivary gland carcinosarcoma, or true malignant mixed tumor, is a very rare and extremely aggressive neoplasm. The clonality and clonal origin of this tumor are discussed controversially. We report a carcinosarcoma of the left parotid gland in a patient who subsequently died of cutaneous, lymphatic and pulmonary metastases. Immunohistochemical staining, electron micrograph analysis, loss of heterozygosity (LOH) analysis and sequence analysis were performed on this tumor with an adenocarcinomatous and a predominant spindle cell-like component. While smooth muscle actin was undetectable by immunohistochemistry, cytoplasmatic myoepithelial structures could be detected by electron microscopy. LOH analysis at 12 genomic locations detected complete deletion of one allele at 17p13.1, 17q21. 3, and 18q21.3 indicating allelic loss in both components of the tumor. Double strand sequencing of the remaining allele of the p53 tumor suppressor gene revealed a wild-type allele. Based on our results, we favor the hypothesis of monoclonal origin of this salivary gland carcinosarcoma with a common stem cell that could be the myoepithelial cell and an inactivated tumor suppressor gene on chromosome 17 other than p53.

Fhit expression is absent or reduced in a subset of primary head and neck cancer.

BACKGROUND: The inactivation of the FHIT gene at 3p14.2 by various mechanisms might be of importance in head and neck squamous cell carcinoma (HNSCC). Most reports are based on DNA and RNA findings of intragenic deletions and abnormal transcripts. MATERIAL AND METHODS: To study the protein expression of this putative tumour suppressor gene, we analysed 48 HNSCCs by immunohistochemistry using a polyclonal antibody (ZR44). The results were compared with mutation analysis, clinical data and loss of heterozygosity (LOH) data at 3p14.2. RESULTS: Complete absence of Fhit expression was detected in 8 out of 48 of tumours (17%) and 3 tumours (6%) showed heterogenous staining. The overall frequency of LOH for microsatellite D3S1234 was 64% and 5/7 of Fhit negative tumours exhibited LOH. CONCLUSION: Our findings provide further evidence that FHIT is inactivated in a subtype of HNSCC; however, the incidence of lack of Fhit expression compared to the high frequency of LOH on chromosome 3p supports the notion of additional tumour suppressor genes at 3p14.