Le cancer du sein triple négatif (CSTN) est le sous-type de cancer du sein le plus hétérogène et le plus défavorable. La pierre angulaire du traitement de ces tumeurs repose sur la chimiothérapie systémique, de plus en plus fréquemment administrée en néoadjuvant, puisqu’aucune thérapie ciblée n’est à ce jour validée. L'obtention d'une réponse complète histologique (RCH) constitue un marqueur pronostique favorable majeur ainsi qu'un test in vivo de la sensibilité aux médicaments anti-tumoraux. L’objectif de notre travail de thèse a donc été d’apporter des éléments de compréhension de cette hétérogénéité grâce à la dissection clinique, biologique et moléculaire de ces tumeurs. Nous avons analysé les profils d'expression géniques de ces CSTN et ainsi identifié 6 sous-types moléculaires distincts avec des biologies et des pronostics différents. Cette classification s’appuie sur une méthodologie originale basée à la fois sur des outils bioinformatiques classiques associée à l’utilisation de réseaux biologiques. L’enrichissement en gènes de l'immunité issus du compartiment stromal de la tumeur représente un déterminant majeur du pronostic de ces tumeurs : une forte expression des gènes de l'immunité est associée un pronostic significativement plus favorable. Notre principale contribution repose sur une meilleure compréhension de l’immunité et de l’infiltrat lymphocytaire (TILS) de ces CSTN. Il s’agit probablement du sous-groupe de cancers du sein le plus immunogène avec des taux de TILS pré-CNA parmi les plus élevés avec les tumeurs HER2-positives. Cet infiltrat lymphocytaire est d'ailleurs très corrélé aux gènes de notre module immunitaire pronostique dans les CSTN. La valeur prédictive et pronostique des TILS du stroma tumoral est différente selon le sous-type moléculaire de cancer du sein, suggérant une immunité complètement différente de ces tumeurs. Le taux de TILS varie également différentiellement au sein de chaque sous-groupe sous l'influence de la CNA, témoignant d'une interaction complexe entre les TILS et les traitements. Nous montrons que la cinétique des TILS sous l'effet de la CNA est un indicateur pertinent de réponse à la CNA avec une réponse d'autant plus importante qu'une décroissance du taux de TILS sera importante. Les tumeurs les plus immunogènes avec une activité immunitaire importante sont donc les tumeurs triple-négatives les plus favorables. L'un des challenge des années à venir sera donc d'identifier le plus tôt possible les CSTN les moins immunogènes susceptibles de bénéficier au mieux des immunothérapies seules ou combinées au traitement chimiothérapique afin d'activer ou de rétablir précocement une immunité déficiente. Sous une même dénomination de TILS se trouve très certainement des populations phénotypiques de lymphocytes différentes. En effet, après CNA, leur valeur pronostique est opposée entre les CSTN et les tumeurs HER2-positives: des taux élevés de TILS sont associés à un pronostic défavorable dans les tumeurs HER2-positives alors qu’ils ont une tendance à être associés à des CSTN de meilleur pronostic. Les interactions sont complexes entre les agents cytotoxiques et la tumeur et/ou son microenvironnement. L'analyse du résidu tumoral mammaire ou ganglionnaire représente un matériel sous-exploité qui pourrait permettre de mieux comprendre les mécanismes de sensibilité ou de résistance aux traitements. Au delà de la pierre angulaire que constitue l'immunité pour ces tumeurs, nos travaux identifient certains CSTN pour lesquels l'environnement hormonal, au travers de l'indice de masse corporel ou du statut ménopausique, pourrait jouer un rôle. Ainsi l'exploration du métabolome, des particularités immunitaires chez les patientes en surpoids/obèses ou l'analyse de la voie androgène-récepteur (et ses connexions avec les voies oestrogène et progestérone-récepteur) des CSTN doit aussi être explorée de manière détaillée. Ceci ouvre des perspectives de traitement possibles pour certaines patientes. / Triple negative breast cancer (TNBC) is the most heterogeneous and pejorative subtype of breast cancer. The cornerstone of the treatment of such tumors is based on systemic chemotherapy, more and more frequently administered before surgery, since no targeted therapy has been validated to date. Obtaining a pathological complete response (PCR) is a major favorable prognostic marker as well as an in vivo test of anti-tumor drug susceptibility. The objective of our thesis work was therefore to provide elements of understanding of this heterogeneity through the clinical, biological and molecular dissection of these tumors.We analyzed gene expression profiles of TNBCs and identified 6 distinct molecular subtypes with different biologies and prognoses. This classification used an original methodology based on both classical bioinformatic tools and biological networks. The enrichment of immunity genes from the stromal compartment of the tumor represents a major determinant of the prognosis of these tumors: a strong expression of the immunity genes is associated with a significantly more favorable prognosis.Our main contribution is based on a better understanding of immunity and tumor infiltrated lymphocytes (TILS) of these TNBCs. It is probably the most immunogenic subgroup of breast cancers with the highest TILs levels pre-NAC with HER2-positive tumors. TILS levels are also highly correlated with genes of our immune prognosis module. The predictive and prognostic value of stromal TILS is different according to the molecular subtype of breast cancer, suggesting a completely different immunity of these tumors. The rate of TILS also varies differentially within each subgroup under the influence of the NAC, indicating a complex interaction between TILS and treatments. We show that the kinetics of TILS levels with NAC is a relevant indicator of response to NAC with a response that is all the more important that a decrease in the TILS rate will be important. The most immunogenic tumors with an important immune activity are therefore the most favorable triple-negative tumors. One of the challenges of the coming years will therefore be to identify, as soon as possible, the least immunogenic TNBC that can best benefit from immunotherapies alone or in combination with chemotherapeutic treatment in order to activate or restore early a deficient immunity.Under the same denomination of TILS there are probably different phenotypic populations of lymphocytes. Indeed, after CNA, their prognostic value is opposite between the TNBC and the HER2-positive tumors: high levels of TILS are associated with an unfavorable prognosis in HER2-positive tumors whereas they have a tendency to be associated with a better prognosis for TNBC tumors. The interactions are complex between cytotoxic agents and the tumor and / or its microenvironment. The analysis of the breast or axillary lymph node residual disease represents an underutilized material that could lead to a better understanding of the mechanisms of sensitivity or resistance to treatment.Beyond the key role immunity for these tumors, our work identifies some TNBCs for which the hormonal environment, through the body mass index or the menopausal status, could play a role. Thus, the exploration of the metabolome, immune features in overweight / obese patients or the analysis of the androgen-receptor pathway (and its connections with the estrogen and progesterone-receptor pathways) of the TNBC must also be explored. This opens up possible treatment perspectives for some patients.

Indiana University-Purdue University Indianapolis (IUPUI) / Triple-negative breast cancers (TNBCs) are pathologically defined by the absence of estrogen, progesterone, and HER2 receptors. Compared to other breast cancers, TNBC has a relatively high mortality. In addition, TNBC patients are more likely to relapse in the first few years after treatment, and experiencing a shorter median time from recurrence to death. Detecting the presence of tumor in patients who are technically “disease-free” after neoadjuvant chemotherapy and surgery as early as possible might be able to predict recurrence of patients, and then provide timely intervention for additional therapy. To this end, I applied the analysis of “liquid biopsies” for early detection of minimal residual disease (MRD) on early-stage TNBC patients using next-generation sequencing. For the first part of this study, I focused on detecting circulating tumor DNA (ctDNA) from TNBC patients after neoadjuvant chemotherapy and surgery. First, patient-specific somatic mutations were identified by sequencing primary tumors. From these data, 82% of the patients had at least one TP53 mutation, followed by 16% of the patients having at least one PIK3CA mutation. Next, I sequenced matched plasma samples collected after surgery to identify ctDNA with the same mutations. I observed that by detecting corresponding ctDNA I was able to predict rapid recurrence, but not distant recurrence. To increase the sensitivity of MRD detection, in the second part I developed a strategy to co-detect ctDNA along with circulating tumor RNA (ctRNA). An advantage of ctRNA is its active release into the circulation from living cancer cells. Preliminary data showed that more mutant molecules were identified after incorporating ctRNA with ctDNA detection in a metastatic breast cancer setting. A validation study in early-stage TNBC is in progress. In summary, my study suggests that co-detection of ctDNA and ctRNA could be a potential solution for the early detection of disease recurrence. / 2021-08-05

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Triple-negative breast cancers (TNBCs) are negative for the expression of estrogen (ER), progesterone (PR), and HER-2 receptors. TNBC accounts for 15% of all breast cancers and results in disproportionally higher mortality compared to ER & HER2-positive tumours. Moreover, there is a paucity of therapies for this subtype of breast cancer resulting primarily from an inadequate understanding of the transcriptional differences that differentiate TNBC from normal breast. To this end, we embarked on a comprehensive examination of the transcriptomes of TNBCs and normal breast tissues using next-generation whole transcriptome sequencing (RNA-Seq). By comparing RNA-seq data from these tissues, we report the presence of differentially expressed coding and non-coding genes, novel transcribed regions, and mutations not previously reported in breast cancer. From these data we have identified two major themes. First, BRCA1 mutations are well known to be associated with development of TNBC. From these data we have identified many genes that work in concert with BRCA1 that are dysregulated suggesting a role of BRCA1 associated genes with sporadic TNBC. In addition, we observe a mutational profile in genes also associated with BRCA1 and DNA repair that lend more evidence to its role. Second, we demonstrate that using microdissected normal epithelium maybe an optimal comparator when searching for novel therapeutic targets for TNBC. Previous studies have used other controls such as reduction mammoplasties, adjacent normal tissue, or other breast cancer subtypes, which may be sub-optimal and have lead to identifying ineffective therapeutic targets. Our data suggests that the comparison of microdissected ductal epithelium to TNBC can identify potential therapeutic targets that may lead to be better clinical efficacy. In summation, with these data, we provide a detailed transcriptional landscape of TNBC and normal breast that we believe will lead to a better understanding of this complex disease.

No description available.

No description available.

No description available.

Poly-(ADP-ribsoyl) Polymerases (PARPs) are a superfamily of enzymes comprised of 17 known isoforms. PARP inhibitors (PARPi) have shown success in clinical trials for the treatment of homologous recombination-deficient cancers. Though proven effective initially, tumors treated with PARPi eventually develop resistance. Combinatorial therapeutics targeting PARP and other pathways that may re-sensitize tumors to PARP inhibition, including PI3K/AKT/mTor pathway, and cell-cycle checkpoints (such as CDKs, CHK, and Wee) are being tested. In this context, the synthetic lethality of cyclin-dependent kinase 1 (CDK1) and PARP1 is known. Evaluation of PARP1 and CDK1 pharmacophores led to the development of the tetrahydro-arylazepinone (TAAP) scaffold as a potential dual PARP1/CDK1 inhibitor. We screened a handful of TAAP analogs against PARP1 in a cell-free assay that identified the low micromolar PARP1 inhibitor 1,2,3,4-tetrahydro-5H-benzo[e][1,4]-diazepin-5-one (TBAP), which served as the lead compound. The analogous 1,2,3,4-tetrahydro-5H-pyrido[2,3-e][1,4]-diazepin-5-one (TPAP) series showed a similar bioactivity profile. Satisfyingly, the N1-benzyl TPAP analogue showed activity in the low nanomolar range. The TAAP series (i.e., 6/7-membered scaffold) unfortunately lacked CDK1 inhibitory activity. Finally, many PARPi's show poor isoform-selectivity. The development of isoform-selective PARPi can clarify the specific function of each PARP isoform and may reduce the adverse side effects shown by PARPi. A handful of TAAP analogs were screened against 13 PARP isoforms, where some compounds demonstrated exquisite PARP1/2 selectivity. Concurrently, we discovered an inhibitor for PARP11, an isoform that lacks any known synthetic ligand. Future directions are suggested towards fine-tuning the structure-activity relationship of TAAP-isoform selective PARPi as well as developing a dual PARP1/CDK1 inhibitor. / Master of Science / The aim of this work is to explore the therapeutic potential of poly-(ADP-ribosyl) polymerase inhibitors (PARPi) for the treatment of ovarian and breast cancer, specifically triple negative breast cancer. Poly-(ADP-ribsoyl) Polymerases (PARPs) are a superfamily of enzymes comprised of 17 known isoforms. Currently, there are three FDA approved PARPi - olaparib, isoforms. Further, tumors have been shown to develop resistance to PARPi. Herein, we explored the 1,2,3,4-tetrahydro-5H-aryl[1,4]diazepin-5-one scaffold as a potential PARP1/2-selective rucaparib, and niraparib; however, these PARPi demonstrate non-selectivity amongst the PARP inhibitor and its possibility for targeted pharmacology with other kinases.

[ES] El cáncer de mama triple negativo representa el 10-20% de los casos de cáncer de mama. Este subtipo molecular se caracteriza por su gran agresividad y capacidad invasiva y se asocia a un mal pronóstico. La ausencia de receptores hormonales y de HER2 hace que la quimioterapia sea el principal tratamiento sistémico eficaz. Sin embargo, varias pacientes con cáncer de mama triple negativo recaen tras recibir quimioterapia. Por lo tanto, es crucial descifrar las características moleculares y buscar nuevas herramientas terapéuticas para este subtipo. En este sentido, los microRNAs (miRNAs) están desregulados en varios tipos de cáncer y emergen como potenciales moléculas pronósticas implicadas en procesos biológicos y en la respuesta a la quimioterapia. Esta tesis titulada "Papel de los microRNAs-449 en las características del cáncer de mama: de la regulación epigenética a la resistencia a la quimioterapia" se centra en el papel de la familia miRNA-449 (miRNA-449a, miRNA-449b-5p y miRNA-449c-5p) en la modulación de la agresividad del cáncer de mama y la respuesta a la quimioterapia. Este estudio aportó pruebas de la regulación a la baja de los miRNAs-449 en líneas celulares de cáncer de mama triple negativo y en pacientes, y sugirió la desacetilación de histonas de su región promotora como mecanismo inhibidor. En particular, se observó que las histonas desacetilasas HDAC1 y SIRT1 estaban reguladas al alza en las células de cáncer de mama triple negativo, y se sugirió su inhibición como mecanismo de inhibición. Los análisis in silico señalaron a ACSL4, una enzima activadora de ácidos grasos, como diana de miARNs-449. Esto concuerda con otros estudios que señalan una alteración del metabolismo de los lípidos como causa de la progresión del cáncer. Se observó una correlación inversa entre los miRNA-449 y la expresión de ACSL4 en líneas celulares de cáncer de mama triple negativo y en pacientes, y el ensayo de reportero de luciferasa confirmó por primera vez esta diana directa de ACSL4 por los miRNA-449a y miRNA-449b-5p. Además, la sobreexpresión del microRNA-449c-5p por sí sola también produjo una regulación a la baja de ACSL4, por lo que también se sugirió una relación indirecta a través de la modulación de moléculas desconocidas. La sobreexpresión de miRNAs-449 y la infraexpresión de ACSL4 inhibieron la proliferación celular, la migración al disminuir la capacidad de sufrir el proceso de transición epitelial-mesenquimal, y la formación de colonias al regular a la baja los marcadores de troncalidad. Estos resultados sugieren una inhibición miRNAs-449 de la agresividad del cáncer de mama a través de la regulación a la baja de ACSL4. Además, basándonos en la literatura previa y en los resultados publicados por nuestro laboratorio, se evaluó la implicación de los miRNAs-449 en la respuesta a la quimioterapia a través de esta nueva diana. Los miRNAs-449 fueron regulados a la baja en las células resistentes a la doxorrubicina. A su vez, se observó una sobreexpresión de ACSL4 en células resistentes a la doxorrubicina y en pacientes que recayeron tras un tratamiento con quimioterapia. El tratamiento posterior con doxorrubicina aumentó la expresión de miRNAs-449 pero disminuyó la de ACSL4 en las células sensibles a la doxorrubicina, pero no en las resistentes, sugiriendo así una implicación de miRNAs-449 y ACSL4 en la respuesta a la quimioterapia. En este estudio, observamos que la sobreexpresión de miRNAs-449 producía sensibilidad a la doxorrubicina a través de la regulación a la baja de ACSL4 mediante ensayos de viabilidad y apoptosis. Además, la inhibición de ACSL4 disminuyó la expresión de la bomba de extrusión de fármacos ABCG2, lo que condujo a un aumento de la acumulación de doxorrubicina en las células. La implicación del miRNAs-449 en la inhibición de la agresividad y la sensibilidad a la doxorrubicina sugiere su potencial uso como herramienta terapéutica en el cáncer de mama triple negativo. / [CA] El càncer de mama triple negatiu representa el 10-20% dels casos de càncer de mama. Aquest subtipus molecular es caracteritza per la seua gran agressivitat i capacitat invasiva i s'associa a un mal pronòstic. L'absència de receptors hormonals i d'HER2 fa que la quimioteràpia siga el principal tractament sistèmic eficaç. No obstant això, diverses pacients amb càncer de mama triple negatiu recauen després de rebre quimioteràpia. Per tant, és crucial desxifrar les característiques moleculars i buscar noves eines terapèutiques per a aquest subtipus. En aquest sentit, els microRNAs (miRNAs) estan desregulats en diversos tipus de càncer i emergeixen com a potencials molècules pronósticas implicades en processos biològics i en la resposta a la quimioteràpia. Aquesta tesi titulada "Paper dels microRNAs-449 en les característiques del càncer de mama: de la regulació epigenètica a la resistència a la quimioteràpia" se centra en el paper de la família miRNA-449 (miRNA-449a, miRNA-449b-5p i miRNA-449c-5p) en la modulació de l'agressivitat del càncer de mama i la resposta a la quimioteràpia. Aquest estudi va aportar proves de la regulació a la baixa dels miRNAs-449 en línies cel·lulars de càncer de mama triple negatiu i en pacients, i va suggerir la *desacetilación d'histones de la seua regió promotora com a mecanisme inhibidor. En particular, es va observar que les histones desacetilasas HDAC1 i SIRT1 estaven regulades a l'alça en les cèl·lules de càncer de mama triple negatiu, i es va suggerir la seua inhibició com a mecanisme d'inhibició. Les anàlisis in silico van assenyalar a ACSL4, un enzim activador d'àcids grassos, com a diana de miARNs-449. Això concorda amb altres estudis que assenyalen una alteració del metabolisme dels lípids com a causa de la progressió del càncer. Es va observar una correlació inversa entre els miRNA-449 i l'expressió d'ACSL4 en línies cel·lulars de càncer de mama triple negatiu i en pacients, i l'assaig de reporter de luciferasa va confirmar per primera vegada aquesta diana directa d'ACSL4 pels miRNA-449a i miRNA-449b-5p. A més, la sobreexpressió del miRNA-449c-5p per si sola també va produir una regulació a la baixa d'ACSL4, per la qual cosa també es va suggerir una relació indirecta a través de la modulació de molècules desconegudes. La sobreexpressió de miRNAs-449 i la infraexpressió d'ACSL4 van inhibir la proliferació cel·lular, la migració en disminuir la capacitat de patir el procés de transició epitelial-mesenquimal, i la formació de colònies en regular a la baixa els marcadors de troncalitat. Aquests resultats suggereixen una inhibició de l'agressivitat del càncer de mama a través de la regulació a la baixa d'ACSL4. A més, basant-nos en la literatura prèvia i en els resultats publicats pel nostre laboratori, es va avaluar la implicació dels miRNAs-449 en la resposta a la quimioteràpia a través d'aquesta nova diana. Els miRNAs-449 van ser regulats a la baixa en les cèl·lules resistents a la doxorubicina. Al seu torn, es va observar una sobreexpressió d'ACSL4 en cèl·lules resistents a la doxorubicina i en pacients que van recaure després d'un tractament amb quimioteràpia. El tractament posterior amb doxorubicina va augmentar l'expressió de micRNAs-449 però va disminuir la d'ACSL4 en les cèl·lules sensibles a la doxorubicina, però no en les resistents, suggerint així una implicació dels miRNAs-449 i ACSL4 en la resposta a la quimioteràpia. En aquest estudi, observem que la sobreexpressió dels miRNAs-449 produïa sensibilitat a la doxorubicina a través de la regulació a la baixa d'ACSL4 mitjançant assajos de viabilitat i apoptosi. A més, la inhibició d'ACSL4 va disminuir l'expressió de la bomba d'extrusió de fàrmacs ABCG2, la qual cosa va conduir a un augment de l'acumulació de doxorubicina en les cèl·lules. La implicació dels miRNAs-449 en la inhibició de l'agressivitat i la sensibilitat a la doxorubicina suggereix el seu potencial ús com a eina terapèutica en el càncer de mama triple negatiu. / [EN] Triple-negative breast cancer accounts for 10-20% of breast cancer cases. This molecular subtype is characterized by its highly aggressive and invasive capacity being associated with a bad prognosis. The lack of hormone and HER2 receptors makes chemotherapy the main systemic effective treatment. However, several triple-negative breast cancer patients relapse after receiving chemotherapy. Therefore, deciphering the molecular characteristics and searching for new therapeutic tools for this subtype is crucial. In this sense, microRNAs (miRNAs) are found dysregulated in several cancer types and emerge as potential prognostic molecules involved in biological processes and chemotherapy response. This thesis entitled "Role of microRNAs-449 in breast cancer features: From epigenetic regulation to chemotherapy resistance" is focused on the role of the miRNA-449 (miRNA-449a, miRNA-449b-5p, and miRNA-449c-5p) family in the modulation of breast cancer aggressiveness and chemotherapy response. This study provided evidence of microRNAs-449 downregulation in triple-negative breast cancer cell lines and patients and suggested histone deacetylation of its promoter region as an inhibitor mechanism. Particularly, the histone deacetylases HDAC1 and SIRT1 were found upregulated in triple-negative breast cancer cells, and their genetic and chemical inhibition increased microRNAs-449 expression. In addition, a negative feedback loop modulation between miRNAs-449 and HDAC1/SIRT1 was observed, thus contributing to the homeostasis or tumoral phenotype of cells. In silico analyses pointed out ACSL4, a fatty acid-activating enzyme, as target of miRNAs-449. This is in concordance with other studies that pointed out an altered lipid metabolism to sustain cancer progression. An inverse correlation between microRNAs-449 and ACSL4 expression was observed in triple-negative breast cancer cell lines and patients, and luciferase reporter assay confirmed this ACSL4 direct targeting by miRNA-449a and miRNA-449b-5p for the first time. Moreover, the microRNA-449c-5p overexpression alone also produced an ACSL4 downregulation, so an indirect relationship was also suggested through the modulation of unknown molecules. MiRNAs-449 overexpression and ACSL4 knockdown inhibited cell proliferation, migration by diminishing the ability to undergo the epithelial-mesenchymal transition process, and colony formation by downregulating markers of stemness. These results suggested a microRNAs-449 inhibition of breast cancer aggressiveness through ACSL4 downregulation. Furthermore, based on previous literature and published results by our laboratory, a miRNAs-449 implication in chemotherapy response was evaluated through this novel target. MiRNAs-449 were downregulated in doxorubicin-resistant cells. In turn, ACSL4 overexpression was observed in doxorubicin-resistant cells and patients who relapsed after chemotherapy-containing treatment. Subsequent doxorubicin treatment increased miRNAs-449 but decreased ACSL4 expression in doxorubicin-sensitive, but not in resistant cells, thus suggesting a miRNAs-449 and ACSL4 implication in chemotherapy response. In this study, we observed that miRNAs-449 overexpression produced doxorubicin sensitivity through ACSL4 downregulation by viability and apoptosis assay. In addition, ACSL4 inhibition decreased the drug extrusion pump ABCG2's expression, leading to an increased doxorubicin accumulation in cells. The involvement of miRNAs-449 in the inhibition of aggressiveness and sensitivity to doxorubicin suggests its potential use as a therapeutic tool in triple-negative breast cancer. / Torres Ruiz, S. (2023). Papel de la familia de microRNAs-449 y el gen CDC20B en la respuesta a tratamientos en cáncer de mama: organoides y cultivos primarios como modelos tumorales [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/198846

Doctor of Philosophy / Department of Biochemistry and Molecular Biophysics / Anna Zolkiewska / The ADAM (A Disintegrin and Metalloprotease) family of multi-domain proteins modulates a number of cellular signaling pathways in both normal and cancerous cells. ADAM12 has been shown to be a candidate cancer gene for breast cancer and its expression is up-regulated in breast tumors. The human ADAM12 transcript is alternatively spliced. One of these splice variants encodes a transmembrane ADAM12 isoform, ADAM12-L, which has been demonstrated to release cell signaling molecules from the cell surface. Another variant encodes a secreted protease, ADAM12-S, which cleaves extracellular matrix proteins and other secreted proteins. Although these variants are expressed from the same promoter, their relative expression levels are highly discordant. Here, I demonstrate variant-specific regulation of ADAM12 transcripts by microRNAs. Members of the microRNA-29 and microRNA-200 families target the unique 3’UTR of the ADAM12-L transcript and cause transcript degradation. Additionally, I show the presence of a novel ADAM12 splicing event in which 9 additional nucleotides are inserted in the region encoding the autoinhibitory pro-domain. I demonstrate that this novel variant is expressed in breast epithelial cells and breast cancer cell lines. The resulting protein isoform does not undergo proteolytic processing to activate the protease. Additionally, trafficking of the novel isoform to the cell surface is impaired and this isoform is localized to the endoplasmic reticulum. Finally, I determined a role for ADAM12-L in the progression of triple negative breast cancers (TNBCs). These tumors are lacking expression of hormone receptors and the HER2 receptor. HER2 is a member of the epidermal growth factor receptor (EGFR) family and the loss of the HER2 receptor causes tumors to rely on EGFR for propagating pro-growth signals. I show here that, in TNBC tumors, ADAM12-L expression is strongly correlated with poor patient prognosis and increased activation of EGFR. These data suggest that in TNBCs, ADAM12-L enhances tumor growth via EGFR activation. Collectively, the data presented here demonstrate (a) transcript-specific regulation of ADAM12 in breast cancer, (b) the existence of a novel splice variant and protein isoform with impaired cellular trafficking, and (c) an important role of the ADAM12-L isoform in EGFR activation in TNBC.