The term "BRCAness" is used to describe breast-cancer patients who lack a germline mutation in BRCA1 or BRCA2, yet who are believed to express characteristics similar to patients who do have a germline mutation in BRCA1 or BRCA2. Although it is hypothesized that BRCAness is related to deficiency in the homologous recombination repair (HRR) pathways, relatively little is understood about what drives BRCAness or what criteria should be used to assign patients to this category. We hypothesized that patients whose tumor carries a genomic or epigenomic aberration in BRCA1 or BRCA2 should be classified under the BRCAness category and that these tumors would exhibit downstream effects (additional mutations or gene-expression changes) similar to patients with germline BRCA1/2 mutations. To better understand BRCAness, we examined similarities and differences in gene-expression profiles and somatic-mutation "signatures" among 1054 breast-cancer patients from The Cancer Genome Atlas. First, we categorized patients into three categories: those who carried a germline BRCA1/2 mutation, those whose tumor carried a genomic aberration or DNA hypermethylation in BRCA1/2 (the BRCAness group), and those who fell into neither of the first two groups. Upon evaluating the gene-expression data in context of the PAM50 subtypes, we did not observe significant similarity between the germline BRCA1/2 and BRCAness groups, but we did observe enrichment within the basal subtype, especially for BRCAness tumors with hypermethylation of BRCA1/2. However, the gene-expression profiles were fairly heterogeneous; for example, BRCA1 patients differed significantly from BRCA2 patients. In agreement with prior findings, certain mutational signatures—especially "Signature 3"—were enriched for patients with germline BRCA1/2 mutations as well as for BRCAness patients. Furthermore, we observed significant similarity between germline BRCA1/2 patients and patients with germline mutations in PALB2, RAD51B, and RAD51C, genes that are key parts of the HRR pathway and that interact with BRCA1/2. Our findings suggest that the BRCAness category does have biological and clinical relevance but that the criteria for including patients in this category should be carefully defined, potentially including BRCA1/2 hypermethylation and homozygous deletions as well as germline mutations in PALB2, RAD51B, and RAD51C.

The term "BRCAness" is used to describe breast-cancer patients who lack a germline mutation in BRCA1 or BRCA2, yet who are believed to express characteristics similar to patients who do have a germline mutation in BRCA1 or BRCA2. Although it is hypothesized that BRCAness is related to deficiency in the homologous recombination repair (HRR) pathways, relatively little is understood about what drives BRCAness or what criteria should be used to assign patients to this category. We hypothesized that patients whose tumor carries a genomic or epigenomic aberration in BRCA1 or BRCA2 should be classified under the BRCAness category and that these tumors would exhibit downstream effects (additional mutations or gene-expression changes) similar to patients with germline BRCA1/2 mutations. To better understand BRCAness, we examined similarities and differences in gene-expression profiles and somatic-mutation "signatures" among 1054 breast-cancer patients from The Cancer Genome Atlas. First, we categorized patients into three categories: those who carried a germline BRCA1/2 mutation, those whose tumor carried a genomic aberration or DNA hypermethylation in BRCA1/2 (the BRCAness group), and those who fell into neither of the first two groups. Upon evaluating the gene-expression data in context of the PAM50 subtypes, we did not observe significant similarity between the germline BRCA1/2 and BRCAness groups, but we did observe enrichment within the basal subtype, especially for BRCAness tumors with hypermethylation of BRCA1/2. However, the gene-expression profiles were fairly heterogeneous; for example, BRCA1 patients differed significantly from BRCA2 patients. In agreement with prior findings, certain mutational signatures—especially "Signature 3"—were enriched for patients with germline BRCA1/2 mutations as well as for BRCAness patients. Furthermore, we observed significant similarity between germline BRCA1/2 patients and patients with germline mutations in PALB2, RAD51B, and RAD51C, genes that are key parts of the HRR pathway and that interact with BRCA1/2. Our findings suggest that the BRCAness category does have biological and clinical relevance but that the criteria for including patients in this category should be carefully defined, potentially including BRCA1/2 hypermethylation and homozygous deletions as well as germline mutations in PALB2, RAD51B, and RAD51C.

Les bactéries lactiques sont largement utilisées en tant que ferments dans l'industrie laitière. Leur production s’effectue généralement dans des milieux semi-définis ou complexes dans lesquels certains nutriments peuvent être apportés par des extraits de levure (EXLs). Ce projet de thèse, qui associe deux partenaires industriels, les groupes Lesaffre et Sacco, ainsi que l’INRA, s’est focalisé sur l’effet des peptides de deux EXLs (EXL1 et EXL2) sur une souche industrielle de Streptococcus thermophilus, un levain lactique d’intérêt économique majeur. L’hypothèse sous-jacente était que ces peptides pourraient avoir un double rôle de nutrition et de régulation de fonctions cellulaires pouvant présenter un intérêt technologique. Afin d’explorer cette question, une stratégie expérimentale à deux niveaux a été élaborée : i) caractérisation et suivi cinétique de la fraction peptidique des deux EXLs par spectrométrie de masse (peptidomique) durant la fermentation de S. thermophilus en bioréacteurs, et ii) suivi cinétique parallèle du transcriptome et du protéome de la bactérie. L’objectif final était de croiser ces deux niveaux d’information afin de corréler des différences de contenu peptidique avec des différences d’activation de systèmes participant aux performances globales du levain.La caractérisation et le suivi du peptidome des EXLs en cours de fermentation a nécessité un important travail de développement méthodologique ayant abouti in fine à l’élaboration d’un outil analytique complet, combinant analyse peptidomique à haut-débit des échantillons et traitement bioinformatique et statistique des données. Cet outil a permis d’identifier environ 4000 peptides différents composant les deux EXLs. Le suivi cinétique a notamment permis de préciser la spécificité du transporteur d’oligopeptides de la bactérie (Ami). En particulier, il s’est avéré qu’une charge nette positive était le facteur prévalent pour le transport des peptides chez S. thermophilus. En complément de cette approche semi-quantitative, des analyses quantitatives ont été réalisées sur des fractions peptidiques des EXLs (dosages différentiels par HPLC des acides aminés avant et après hydrolyse). Elles ont notamment permis de révéler d’importantes différences de teneurs en oligopeptides entre les deux EXLs.En parallèle, le suivi transcriptomique et protéomique réalisé durant la croissance de la bactérie a révélé deux faits marquants. Le premier fait a trait à la surexpression dans l’EXL1 d’un locus génétique régulé par un mécanisme de quorum sensing utilisant un peptide phéromone comme signal moléculaire. Le deuxième fait marquant concerne diverses voies de biosynthèse (acides aminés et purines) différentiellement affectées par les deux EXLs. L’origine de ces dynamiques pourrait être au moins pour partie le fait de différences de contenu peptidique entre les deux substrats. Notamment, certaines voies de biosynthèse pourraient avoir été modulées différentiellement sous l’action de régulateurs centraux tels que CodY, dont l’activité est corrélée au contenu peptidique du milieu, ou encore YebC, un régulateur CodY-like dont le lien fonctionnel avec CodY reste encore inconnu chez S. thermophilus. Tous ces résultats ouvrent d’intéressantes perspectives pour mieux explorer le lien entre peptides et métabolisme bactérien. A terme, cette démarche pourrait se traduire par l’identification de biomarqueurs de performances dans les EXLs, et l’élaboration à façon de produits permettant de maximiser le potentiel technologique des ferments lactiques. / Lactic acid bacteria are widely used as starters in dairy industry. They are generally produced in complex fermentation media containing a wide array of nutrients that can be provided by yeast extracts (YEs). The main goal of this thesis project, involving two industrial partners, Lesaffre and Sacco, as well as INRA, was to investigate the effect of the peptide fraction of two YEs (YE1 and YE2) on an industrial Streptococcus thermophilus strain, a major lactic acid starter. The underlying hypothesis of this whole project was that YE peptides could have a role in nutrition but also regulate cellular functions of technological relevance. In order to explore this question, a two-step strategy was elaborated: i) mass spectrometry characterization (peptidomics) of both YE peptide fractions and time course analysis of their relative abundance during the growth in bioreactors of S. thermophilus, and ii) parallel time course analysis of the strain transcriptome and proteome. The final objective was to cross these two levels of information in order to correlate differences of peptide content with differentially activated systems related to technological performances.YE peptidome characterization and kinetic analysis first required an important methodological development. It eventually resulted in a complete analytical tool that combines high throughput peptidomic analysis as well as bioinformatic and statistical data processing. This powerful tool was able to identify around 4,000 different peptides in both YEs. Then, the time course analysis also clarified the in vivo substrate specificities of the oligopeptide transport system of the bacterium (Ami). A peptide positive net charge notably turned out to be the leading factor governing peptide transport. In addition to this semi-quantitative approach, quantitative analyses were carried out on YE peptide fractions (differential HPLC analyses of amino acids before and after sample hydrolysis). They notably revealed significant differences in oligopeptides content between both YEs.Meanwhile, genome scale transcriptomic and proteomic analyses performed during the strain growth highlighted two significant events. The first one concerns the overexpression in YE1 of a quorum sensing-based genetic locus that uses a pheromone peptide as molecular signal. The second event relates to several biosynthesis pathways (amino acids and purines) that were differentially affected by both YEs. These dynamics could result from differences in peptide content between both substrates. In particular, some pathways could have been differentially modulated by central regulators such as CodY, whose activity is correlated to the medium peptide richness, or YebC, a CodY-like regulator whose functional link with CodY is still unknown in S. thermophilus. All these results open avenues for a better understanding of the interplay between peptides and bacterial metabolism. In the future, this whole approach could lead to the identification of performance biomarkers in YEs, which in turns may eventually translate into the conception of new customized products granting high technological performances to dairy starters.