Discovery of widespread tumour growth gene holds promise for effective cancertrtment

[Lani]

Discovery of widespread tumour growth gene holds promise for effective anti-cancer treatment [European Cancer Organization]
Barcelona, Spain: Italian scientists will announce today (Monday September 24) that they have found a new and promising target for anti-tumour therapy in cancer. Professor Saverio Alberti, from the CESI, University of Chieti Foundation, Chieti, will tell the European Cancer Conference (ECCO 14) that he and his team have found a widespread mechanism for the stimulation of tumour growth in man, and that this is leading to the development of novel diagnostic and therapeutic procedures.
Professor Alberti and his team have discovered the function of the Trop-2 gene, a product of the TACTD2 gene, which is expressed in placenta, an 'invasive' normal tissue. "The function of Trop-2 was a mystery until now," says Professor Alberti, "but knowing its expression in the trophoblast (cells forming the outer layer of the blastocyst - the stage between the fertilised egg and the embryo) during pregnancy, we thought that it might well be involved in another invasive function - tumour growth.
" The scientists analysed the genes in human tumours and found that Trop-2 was expressed in the vast majority of human cancers, for example, breast, colon, stomach, lung, prostate, ovary, endometrium, uterine cervix and pancreas. Over-expression of the Trop-2 gene was also found when immunohistochemical (IHC) analysis of 1,755 tumours was undertaken. IHC analysis looks at the interaction of antibodies and antigens in tissues, and has the advantage of showing exactly where in a tissue a given protein is located. "This has allowed us to develop anti-Trop-2 monoclonal antibodies for immunotherapy (modulation of the immune system to reject and destroy tumours) of Trop-2 expressing tumours," explains Professor Alberti.
Trop-2 over-expression was found in between 65% and 90% of the tumour types analysed, with an average of 74% across the board. "These figures are high," explains Professor Alberti. "In comparison, telomerase over-expression, possibly the most fundamental mechanism for cell immortalisation, is observed in 80% of all tumours. Telomerase is an enzyme that adds specific DNA repeats to the ends of chromosomes, so not strictly comparable. When we come to look at genes, her2/neu is a key determinant of breast cancer aggressiveness and is over-expressed in 25% of the cancers, and amplified in only a subgroup of them; and p53, possibly the most fundamental of tumour suppressors, is mutated and/or over-expressed in 50% of tumours. Mutations of the epidermal growth factor receptor gene (EGFR) are relatively infrequent in most cancers, reach 30% of the non small-cell lung cancers and are present at frequencies of around 75% in only a small subgroup of the latter. Most other markers known to date show lower figures and/or can be detected at high frequency in only a subgroup of tumours, for example PSA in prostate cancer. So Trop-2 really stands out."
"It is also a unique marker of cancer metastases in different tumour types - including colon, stomach, breast, and ovary in man - and across a number of species," he says. In man, most metastases in lymph nodes or down-stream organs, for example liver in colon cancer, express higher levels of Trop-2 compared with the primary tumours. Trop-2 induces these metastases through mechanisms that the scientists are beginning to unravel. The most intriguing of these findings, they say, is the presence of two sequence elements in the Trop-2 cytoplasmic tail, the signalling engine of Trop-2, which act as, respectively, an enhancer and a silencer of metastatic propensity. This may be the key to the identification of signalling molecules that promote or inhibit the formation of metastases.
"If we can identify such molecules we will be approaching a situation where we could influence their activity and hence either encourage or prevent it," says Professor Alberti. "This could be an important step towards stopping cancer in its tracks.
" In addition, the scientists want to extend their knowledge of the cell changes induced by receptor activation, or signal transduction pathways, triggered by Trop-2. "This will be crucial for the better understanding of the way in which tumour growth is regulated by the gene, and will also provide additional targets for anti-cancer drugs," says Professor Alberti. "We are very excited about the prospects for therapy which we can see arising from this discovery."
ABSTRACT: TROP2 is a novel, potent stimulator of tumour growth and of metastatic spreading of human cancer [European Cancer Organization]
Background: Trop-2 is a transmembrane calcium signal transducer, that plays a role in cell-cell and cell-substrate adhesion.
Material and Methods: We investigated the expression pattern of Trop-2 by DNA array, SAGE, Northern and Western blotting, flow cytometry, confocal microscopy and IHC analysis in experimental systems and in man. We explored its functional role by overexpression or down-regulation and by directed mutagenesis in transformed and/or metastatic cells in vivo.
Results: DNA array, EST, SAGE, RT-PCR and Northern blot analysis of human tumors revealed expression of the TROP2 gene in the vast majority of human cancers. A corresponding overexpression of the Trop-2 protein was demonstrated by a large scale IHC analysis of human tumors (1755 cases). Trop-2 was demonstrated to potently stimulate the growth of tumor cells, and its down-regulation by siRNA inhibited it. Deletion of the cytoplasmic region of Trop-2 abolished its growth stimulatory capacity, as mutagenesis of the S303 PKC phosphorylation site did. Proteomic and phosphoproteomic analysis demonstrated a Trop-2-dependent activation of PKC?, FAK and Raf1, modulation of ERK, MEK and p38 MAPK, and upregulation of NF-?B. In vivo imaging demonstrated a dynamic colocalization of PKC? and Trop-2 in membrane ruffles and podosomes. Dominant negative PKC? and PKC? siRNAs selectively abolished the Trop-2-induced growth demonstrating that PKC? plays a key role in Trop-2 signaling. Strikingly, comparative global gene expression analysis revealed that TROP2 was the only gene up-regulated across different metastatic models, tumor types and animal species. IHC analysis revealed a dramatic up-regulation in metastases from colon, stomach, breast and ovary tumors in man. To assess if Trop-2 plays a causal role in metastatic spreading, the metastatic potential of TROP2-transfected KM12SM colon cancer cells, orthotopically injected in nude mice, was assessed. TROP2-overexpressing cells indeed demonstrated a profoundly increased metastatic potential to the liver. Deletion of the HIKE domain of Trop-2 severely diminished, whereas that of the whole cytoplasmic region vastly increased metastatic diffusion, indicating the existence of metastatic enhancers and silencers in the Trop-2 cytoplasmic tail.
Conclusions: Our findings demonstrate the existence of a previously unsuspected, strikingly widespread mechanism of stimulation of tumor growth and of metastatic spreading in man, and candidate Trop-2 for novel diagnostic and therapeutic procedures.