Tumour metastasis is the principal cause of death for cancer patients. We have identified the nm23 gene, for which RNA levels are reduced in tumour cells of high metastatic potential. In this report we identify the cytoplasmic and nuclear Nm23 protein, and show that it also is differentially expressed in metastatic tumour cells. We also find that the human Nm23 protein has sequence homology over the entire translated region with a recently described developmentally regulated protein in Drosophila, encoded by the abnormal wing discs (awd) gene. Mutations in awd cause abnormal tissue morphology and necrosis and widespread aberrant differentiation in Drosophila, analogous to changes in malignant progression. The metastatic state may therefore be determined by the loss of genes such as nm23/awd which normally regulate development.

No abstract

Inactivation of both alleles of the fruit¯y D. melanogaster brain tumor (brat) gene results in the production of a tumor-like neoplasm in the larval brain, and lethality in the larval third instar and pupal stages. We cloned the brat gene from a transposon-tagged allele and identi®ed its gene product. brat encodes for an 1037 amino acid protein with an N-terminal B-box1 zinc ®nger followed by a B-box2 zinc ®nger, a coiled-coil domain, and a C-terminal b-propeller domain with six blades. All these motifs are known to mediate protein ± protein interactions. Sequence analysis of four brat alleles revealed that all of them are mutated at the bpropeller domain. The clustering of mutations in this domain strongly suggests that it has a crucial role in the normal function of Brat, and de®nes a novel protein motif involved in tumor suppression activity. The brat gene is expressed in the embryonic central and peripheral nervous systems including the embryonic brain. In third instar larva brat expression was detected in the larval central nervous system including the brain and the ventral ganglion, in two glands ± the ring gland and the salivary gland, and in parts of the foregut ± the gastric caecae and the proventriculus. A second brat-like gene was found in D. melanogaster, and homologs were identi®ed in the nematode, mouse, rat, and human. Accumulated data suggests that Brat may regulate proliferation and di erentiation by secretion/transportmediated processes.

Covalent modifications of histone tails modulate gene expression via chromatin organization. As examples, methylation of lysine 9 residues of histone H3 (H3) (H3-K9) is believed to repress transcription by compacting chromatin, whereas methylation of lysine 4 residues of H3 (H3-K4) is believed to activate transcription by relaxing chromatin. The Drosophila trithorax group protein absent, small, or homeotic discs 1 (ASH1) is involved in maintaining active transcription of many genes. Here we report that in extreme ash1 mutants, no H3-K4 methylation is detectable. Within the limits of our assays, this lack of detectable H3-K4 methylation implies that ASH1 is required for essentially all H3-K4 methylation that occurs in vivo. We report further that the 149-aa SET domain of ASH1 is sufficient for H3-K4 methylation in vitro. These findings support a model in which ASH1 is directly involved in maintaining active transcription by conferring a relaxed chromatin structure. C hromatin serves as the template for processing genetic information. The dynamic DNA-protein structure of chromatin is influenced by epigenetic modifications on both the DNA and nucleosomal histones. Chromatin can exist in alternate states: a relaxed state (euchromatin) where underlying DNA becomes accessible to transcription factors, and a condensed state (heterochromatin) where underlying DNA is transcriptionally restricted. The functional organization of chromatin structure is in part the result of targeted covalent modifications on the N-terminal tails of the core histones. The histone code hypothesis suggests that combinations of histone modifications format the chromatin for proper gene regulation (1).Although histone methylation was first described in 1964 (2), its significance for regulating chromatin structure and transcription remained unclear until the discovery of the first histone methyltransferase (HMTase), SUV39H (3), a SET domaincontaining protein. Lysine-directed histone methylation is intriguing, because it is involved in mediating both compacted and relaxed chromatin. Histone H3 (H3) can be methylated at lysine residues 4, 9, 27, and 36. Methylation of lysine 9 modulates gene silencing (3), whereas methylation of lysine 4 appears to function as a signal for gene activation (4). It has been proposed that the combination of methylation on the lysine 4 and 9 residues of histone H3 with methylation on the lysine 20 residue of histone H4 may also serve as a signal for gene activation (5).The SET domain is present in transcriptional regulators that have opposing functions. For example, consider the three Drosophila proteins that originally defined the SET domain: suppressor of variegation 3-9 [SU(VAR)3-9] is involved in heterochromatin-dependent gene silencing (6, 7), enhancer of zeste, is involved in maintaining both activated and repressed transcriptional states (8), and trithorax (TRX) is involved in maintaining gene activation (9). The HMTase function of the SET domain has been implicated in conferring both active and repressed transc...

No abstract

The third-chromosome mutation Killer of prune (K-pn) causes no phenotype by itself, but causes lethality in individuals homozygous for the nonlethal X-chromosome mutation prune (pn). We have recovered 12 gammaray-induced revertants of Killer o[prune. All of the revertants fail to complement a recessive cell lethal mutation in the abnormal wing ddscs (awd) gene. We present evidence that Killer o[prune is a mutation in the awd gene. First, revertant awd r's14 leads to reduced accumulation of the awd gene product, but does not affect flanking genes. Second, when a copy of the awd gene is cloned from Killer o[prtme homozygous flies and injected into embryos, transformants express the lethal interaction with prune. In individuals of the genotype pn; awdX'~°/awd+ the awd mRNA is present at normal levels but the awd polypeptide fails to accumulate. The absence of the awd gene product in such individuals is the cause of death. Although the awd polypeptide is a subunit of a cytoplasmic protein, its sequence is similar to subunit V of yeast cytochrome oxidase.

We analyzed how cells from tumors caused by mutations in either lgl or brat use matrix metalloproteinases (MMPs) to facilitate metastasis in Drosophila. MMP1 accumulation is dramatically increased in lgl larval imaginal discs compared to both wild type and brat mutants. Removal of Mmp1 gene activity in lgl brain tumor cells reduced their frequency of ovarian micro-metastases after transplantation; whereas, removal of Mmp1 gene activity in brat tumor cells had no such effect. Host ovaries showed increased Mmp1 gene expression in response to transplantation of brat tumors but not of lgl tumors. Reduction of MMP activity in host ovaries by ectopic expression of TIMP significantly reduced both lgl and brat metastases in that organ. These results highlight the mechanisms that lgl and brat tumor cells use to metastasize. Our interpretation of these data is that secretion of MMP1 from lgl tumor cells facilitates their metastasis, while secretion of MMP1 from host ovaries facilitates brat tumor metastasis. This study is the first demonstration that Drosophila tumors utilize MMP activity to metastasize.

More than 50 genes have been identified in Drosophila by loss-of-function mutations that lead to overgrowth of specific tissues. Loss-of-function mutations in the lethal giant larvae, discs large, or brain tumor genes cause neoplastic overgrowth of larval brains and imaginal discs. In the present study, the growth and metastatic potential of tumors resulting from mutations in these genes were quantified. Overgrown brains and imaginal discs were transplanted into adults and beta-galactosidase accumulation was used as a marker to identify donor cells. Mutations in these three genes generated tumors with similar metastatic patterns. For brain tumors, the metastatic index (a measure we defined as the fraction of hosts that acquired secondary tumors normalized for the amount of primary tumor growth) of each of the three mutants was similar. Analysis of cell proliferation in mutant brains suggests that the tumors arise from a population of several hundred cells which represent only 1-2% of the cells in third instar larval brains. For imaginal disc tumors from lethal giant larvae and brain tumor mutants, it is shown for the first time that they can be metastatic and invasive. Primary imaginal disc tumors from lethal giant larvae and brain tumor mutants formed secondary tumors in 43 and 53% of the hosts, respectively, although the secondary tumors were, in general, smaller than the secondary tumors derived from primary brain tumors.