Dans de nombreux cancers, l’expression du gène Fhit (Fragile Histidine Triad) estfréquemment altérée. Fhit est décrit comme un important gène suppresseur de tumeur de parson rôle pro-apoptotique et anti-prolifératif. Nous avons mis en évidence que, in vivo et invitro, la diminution de l’expression de Fhit est associée au caractère infiltrant des cellulestumorales bronchiques, ce qui suggère que Fhit pourrait être impliqué dans le processusd’invasion tumorale. Nous avons en effet montré que la surexpression et l’inhibition de Fhitinduisent respectivement une diminution et une augmentation des capacités migratoires etinvasives des cellules bronchiques. Nous avons aussi mis en évidence que Fhit contrôlel’invasion des cellules tumorales bronchiques en régulant l’expression d’éléments clés de latransition épithélio-mésenchymateuse (TEM) tels que l’organisation des jonctions serrées etadhérentes, l’expression des métalloprotéinases matricielles et de la vimentine. De plus, Fhitrégule la TEM via une cascade de signalisation impliquant le récepteur au TGF-β, lesrécepteurs à tyrosine kinase (RTK), Src, Erk et Slug. Le double rôle de Fhit en tant quesuppresseur de tumeur et d’invasion renforce l’idée que Fhit pourrait représenter un nouveaubiomarqueur d’agressivité tumorale et pourrait constituer une nouvelle cible thérapeutiquedans le traitement des cancers broncho-pulmonaires. / In many types of cancers, Fhit (Fragile histidine triad) expression is frequentlydecreased or lost. Fhit is described as a tumor suppressor gene by its ability to induceapoptosis and to inhibit proliferation of tumor cells. We have demonstrated that a low Fhitexpression is associated with in vivo and in vitro invasiveness of lung tumor cells. Then, wehave shown that Fhit controls the invasive phenotype of lung tumor cells by regulating keyelements of epithelial-mesenchymal transition (EMT) such as cell-cell adhesion molecules,matrix metalloproteinase and vimentin expression. Our results provide also evidence that Fhitcontrols EMT by regulating several signaling pathways implying TGF-βR, RTK, Src, ERKand Slug. The dual function of Fhit as a tumor and invasion suppressor gene strengthens theidea that Fhit could represent a new biomarker of aggressiveness of lung cancer and couldconstitute a new therapeutic target to limit tumor progression.

Dans les cancers du poumon, une des altérations les plus souvent observées est la perte ou l’atténuation de l’expression du gène FHIT (Fragile Histidine Triad). Nous avons précédemment montré que FHIT est un suppresseur d’invasion tumorale. En effet, FHIT contrôle l’invasion des cellules tumorales bronchiques en régulant négativement l'expression de gènes associés à la transition épithélio-mésenchymateuse (TEM), en particulier la vimentine et la MMP-9 via l’inhibition d’une voie orchestrée par l’EGFR. Un intérêt particulier a donc été porté aux relations entre FHIT et un autre membre de la famille de l’EGFR : HER2. Nous avons non seulement mis en évidence, in vivo et in vitro, une corrélation inverse entre les taux de FHIT et l’activité du récepteur HER2 dans les CBNPC mais également montré que FHIT est capable de réguler l’activité du récepteur HER2 dans les cellules tumorales pulmonaires et ce grâce à sa dimérisation avec HER3. De plus, l’utilisation de deux inhibiteurs spécifiques d’HER2, le Trastuzumab et l’Irbinitinib, nous a permis de mettre en évidence, que l’activation du récepteur HER2 lors de l’inhibition de FHIT, participe à l’acquisition par les cellules tumorales bronchiques de caractéristiques invasives via la régulation de certaines cibles de la TEM, telles la vimentine, la MMP-14 ou encore le facteur de transcription TWIST-1. Ces résultats montrent que FHIT régule l’activité d’HER2 dans les cellules tumorales pulmonaires et que les inhibiteurs d’HER2 sont capables de limiter l’invasion induite par l’inhibition de FHIT. Cette étude laisse envisager de nouvelles perspectives thérapeutiques pour le cancer du poumon. / The lack or decrease of FHIT (fragile histidine triad) expression is a common event in lung cancer. We recently showed that FHIT acts as a suppressor of tumor invasion. Indeed, FHIT controls the invasive phenotype of lung tumor cells by regulating the expression of genes associated with epithelial-mesenchymal transition (EMT) such as vimentin or MMP-9 through an EGFR signaling pathway. Accordingly, we focused on the relationships between FHIT and another member of this tyrosine kinase receptor family: HER2. First, we observed in vivo and in vitro a negative correlation between FHIT expression and the activated form of HER2 in lung tumor cells. Moreover, FHIT controls HER2 activation through its dimerization with HER3. The use of HER2 specific inhibitors, Trastuzumab and Irbinitinib, allowed to demonstrate that the in vitro invasion induced by FHIT inhibition is HER2-dependent. Furthermore, FHIT controls the HER2-dependent invasion by regulating genes associated with EMT such as vimentin, MMP-14 or TWIST-1. In conclusion, we showed that FHIT regulates HER2 activity in lung tumor cells and that HER2 inhibitors reduce invasion induced by FHIT inhibition. This study would allow for the identification of new therapeutic leads for lung cancer.

No description available.

The FHIT gene is located on the most fragile site in the human genome. FHIT gene deletions are among the earliest and most frequent events in carcinogenesis, particularly in carcinogen-exposed tissue. Previous work in mouse and cell culture models established FHIT to be an authentic tumor suppressor. Re-expression of FHIT in cell culture causes cell death via initiation of apoptosis, but the precise mechanism underlying this process is unclear. It is well established that cellular transition from normal to transformed occurs in multiple steps and requires the accumulation of several genetic changes. Relying on the compelling phenotype of tumor development in FHIT knockout mice, this project aimed to elucidate a mechanism through which FHIT-deficient cells are primed to survive multiple genetic and environmental stresses, and promote progression of cancer. My work indicates that FHIT expression is required for the normal cellular response to oxidative stress, and presents evidence that in the absence of FHIT, an oxidative stress response pathway is superinduced. When FHIT is depleted from cells exposed to cigarette smoke, the expression of a subset of oxidative stress response genes is enhanced. Enhanced activation of these genes can occur as an adapative response to stress induced by reactive oxygen species production, and is frequently detected in cancer. Investigation into the mechanism underlying the enhanced gene expression determined that FHIT loss is associated with decreased levels of the transcriptional repressor Bach1. In this manner, we propose that loss of Fhit supports an antioxidant program that is pivotal in establishing and maintaining carcinogenic transformation.

This thesis is comprised of two parts. In the first part we study the influence of four frequently disputed genes on the susceptibility for developing prostate cancer, and in the second part we attempt to establish a basic understanding of the molecular genetic events in penile cancer. In a prostate cancer cohort we have investigated the relation of prostate cancer risk and single nucleotide polymorphisms (SNPs) in four different genes coding for the androgen receptor (AR), the vitamin D receptor (VDR), insulin (INS) and insulin receptor substrate 1 (IRS1). Despite strong biological indications of an involvement of these genes in prostate carcinogenesis, the results from different studies are contradictory and inconclusive. The action of the AR varies between individuals in part owing to a repetitive CAG sequence (polyglutamine) in the first exon of the AR gene. The results presented in this thesis show that in our cohort of prostate cancer patients the average number of repeats is 20.1, which is significantly (p<0.001) fewer repeats compared to healthy control individuals, where the average is 22.5 repeats. We find a 4.94 fold (p=0.00003) increased risk of developing prostate cancer associated with having short repeat lengths (≤19 repeats), compared with long repeats (≥23 repeats). In paper I we also study the TaqI polymorphism in the VDR gene, and find that it does not modify the risk of prostate cancer. In the INS gene we study the +1127 PstI polymorphism and find no overall effect on the risk of prostate cancer. However, we do find that the CC genotype is associated with low grade disease defined as having a Gleason score ≤6 (OR=1.46; p=0.018). In the IRS1 gene we study the G972R polymorphism and observe that the R allele is significantly associated with a 2.44 fold increased prostate cancer risk (p=0.010). The knowledge of molecular genetic events in penile cancer is very scarce and to date very few genes have been identified to be involved in penile carcinogenesis. We chose therefore to analyse the penile cancer samples using genome-wide high-density SNP arrays. We find major regions of frequent copy number gain in chromosome arms 3q, 5p and 8q, and slightly less frequent in 1p, 16q and 20q. The chromosomal regions of most frequent copy number losses are 3p, 4q, 11p and 13q. We suggest four candidate genes residing in these areas, the PIK3CA gene (3q26.32), the hTERT gene (5p15.33), the MYC gene (8q24.21) and the FHIT gene (3p14.2). The mutational status of the PIK3CA and PTEN genes in the PI3K/AKT pathway and the HRAS, KRAS, NRAS and BRAF genes in the RAS/MAPK pathway was assessed in the penile cancer samples. We find the PIK3CA, HRAS and KRAS genes to be mutated in 29%, 7% and 3% of the cases, respectively. All mutations are mutually exclusive. In total the PI3K/AKT and RAS/MAPK pathways were found to be activated through mutation or amplification in 64% of the cases, indicating the significance of these pathways in the aetiology of penile cancer.

No description available.

No description available.