Selumetinib suppresses cell proliferation, migration and trigger apoptosis, G1 arrest in triple-negative breast cancer cells

Identification of a Group of Therapeutic Targets and Prognostic Biomarker for Triple Negative Breast Cancer

INTRODUCTION

Triple-negative breast cancer (TNBC) is a highly heterogeneous disease. Mining differentially expressed genes of TNBC is helpful to explore new therapeutic targets. This study aimed to investigate diagnostic biomarker genes in TNBC compared to normal tissue. Additionally, we explored the functions and prognostic value of these key genes as well as potential targeted drugs that could affect these genes.

METHODS

Differential gene expression analysis was conducted using the R software with data from the Gene Expression Omnibus (GEO) database. Then, the identified differentially expressed genes (DEGs) were used to construct a protein-protein interaction (PPI) network using the Search Tool for the Retrieval of Interacting Genes (STRING) database and Cytoscape software. The mRNA expression levels of key genes were analyzed using the UALCAN database with data from The Cancer Genome Atlas (TCGA). Enrichment and survival analyses were performed using R software. In addition, potential compounds showing sensitivity to key genes were identified by gene set cancer analysis (GSCA).

RESULTS

Compared with normal tissues, a total of 203 DEGs were upregulated in TNBC. These DEGs participated in various biological processes including nuclear division, microtubule binding, cell cycle, and the p53 signaling pathway. Through the PPI network analysis, ten key genes were identified, among which four genes showed significant correlation with poor progression-free interval (PFI) in patients with TNBC. Moreover, the four survival-related genes were found to act as sensitive therapeutic targets.

CONCLUSION

The identified four key genes were considered new biomarkers for diagnosis and prognosis and also potential therapeutic targets for TNBC.

Inhibition of Aurora Kinase Induces Endogenous Retroelements to Induce a Type I/III IFN Response via RIG-I

Type I IFN signaling is a crucial component of antiviral immunity that has been linked to promoting the efficacy of some chemotherapeutic drugs. We developed a reporter system in HCT116 cells that detects activation of the endogenous IFI27 locus, an IFN target gene. We screened a library of annotated compounds in these cells and discovered Aurora kinase inhibitors (AURKi) as strong hits. Type I IFN signaling was found to be the most enriched gene signature after AURKi treatment in HCT116, and this signature was also strongly enriched in other colorectal cancer cell lines. The ability of AURKi to activate IFN in HCT116 was dependent on MAVS and RIG-I, but independent of STING, whose signaling is deficient in these cells. MAVS dependence was recapitulated in other colorectal cancer lines with STING pathway deficiency, whereas in cells with intact STING signaling, the STING pathway was required for IFN induction by AURKi. AURKis were found to induce expression of endogenous retroviruses (ERV). These ERVs were distinct from those induced by the DNA methyltransferase inhibitors (DNMTi), which can induce IFN signaling via ERV induction, suggesting a novel mechanism of action. The antitumor effect of alisertib in mice was accompanied by an induction of IFN expression in HCT116 or CT26 tumors. CT26 tumor growth inhibition by alisertib was absent in NSG mice versus wildtype (WT) mice, and tumors from WT mice with alisertib treatment showed increased in CD8+ T-cell infiltration, suggesting that antitumor efficacy of AURKi depends, at least in part, on an intact immune response.

SIGNIFICANCE

Some cancers deactivate STING signaling to avoid consequences of DNA damage from aberrant cell division. The surprising activation of MAVS/RIG-I signaling by AURKi might represent a vulnerability in STING signaling deficient cancers.

MicroRNA-Based Discovery of Biomarkers, Therapeutic Targets, and Repositioning Drugs for Breast Cancer

Breast cancer treatment can be improved with biomarkers for early detection and individualized therapy. A set of 86 microRNAs (miRNAs) were identified to separate breast cancer tumors from normal breast tissues (n = 52) with an overall accuracy of 90.4%. Six miRNAs had concordant expression in both tumors and breast cancer patient blood samples compared with the normal control samples. Twelve miRNAs showed concordant expression in tumors vs. normal breast tissues and patient survival (n = 1093), with seven as potential tumor suppressors and five as potential oncomiRs. From experimentally validated target genes of these 86 miRNAs, pan-sensitive and pan-resistant genes with concordant mRNA and protein expression associated with in-vitro drug response to 19 NCCN-recommended breast cancer drugs were selected. Combined with in-vitro proliferation assays using CRISPR-Cas9/RNAi and patient survival analysis, MEK inhibitors PD19830 and BRD-K12244279, pilocarpine, and tremorine were discovered as potential new drug options for treating breast cancer. Multi-omics biomarkers of response to the discovered drugs were identified using human breast cancer cell lines. This study presented an artificial intelligence pipeline of miRNA-based discovery of biomarkers, therapeutic targets, and repositioning drugs that can be applied to many cancer types.

ERK activation modulates invasiveness and Reactive Oxygen Species (ROS) production in triple negative breast cancer cell lines

Triple negative breast cancer (TNBC) is the breast cancer subtype with the worst prognosis and still lacks a targeted therapy. In this study, we found increased ERK phosphorylation in TNBC cell lines and an important role for ERK in sustaining the migration of TNBC cells. Although ROS have been suggested to have an important role in sustaining MAPK signaling, antioxidant treatment increased ERK phosphorylation, probably suggesting increased invasive potential. Interestingly, treatment with PD0325901 (PD), a MEK inhibitor, decreased ROS levels in TNBC cells and decreased mitochondrial fragmentation in the MDAMB231 cell line. Our data supports an important role for MEK/ERK in TNBC, sustaining cellular migration, regulating mitochondrial dynamics and ROS production in this breast cancer subtype.

Effects of thiostrepton alone or in combination with selumetinib on triple-negative breast cancer metastasis

OBJECTIVE

FoxM1 transcription factor contributes to tumor metastasis and poor prognosis in many cancers including triple-negative breast cancer (TNBC). In this study, we examined the effects of FoxM1 inhibitor Thiostrepton (THIO) alone or in combination with MEK inhibitor Selumetinib (SEL) on metastatic parameters in vitro and in vivo.

METHODS

Cell viability was determined by MTT assay. Immunoblotting and immunohistochemistry was used to assess metastasis-related protein expressions in 4T1 cells and its allograft tumor model in BALB/c mice. In vivo uPA activity was determined by enzymatic methods.

RESULTS

Both inhibitors were effective on the expressions of FoxM1, ERK, p-ERK, Twist, E-cadherin, and Vimentin alone or in combination in vitro. THIO significantly decreased 4T1 cell migration and changed the cell morphology from mesenchymal-like to epithelial-like structure. THIO was more effective than in combination with SEL in terms of metastatic protein expressions in vivo. THIO alone significantly inhibited mean tumor growth, decreased lung metastasis rate and tumor foci, however, no significant changes in these parameters were observed in the combined group. Immunohistochemically, FoxM1 expression intensity was decreased with THIO and its combination with SEL in the tumors.

CONCLUSIONS

This study suggests that inhibiting FoxM1 as a single target is more effective than combined treatment with MEK in theTNBC allograft model. The therapeutic efficacy of THIO should be investigated with further studies on appropriate drug delivery systems.

Identification of Lethal Inhibitors and Inhibitor Combinations for Mono-Driver versus Multi-Driver Triple-Negative Breast Cancer Cells

There are no signaling-based targeted therapies for triple-negative breast cancer. The development of targeted cancer therapy relies on identifying oncogenic signaling drivers, understanding their contributions to oncogenesis and developing inhibitors to block such drivers. In this study, we determine that DU-4475 is a mono-driver cancer cell line relying on BRAF and the mitogen-activated protein kinase pathway for viability and proliferation. It is fully and lethally inhibited by BRAF or Mek inhibitors at low nM concentrations, but it is resistant to inhibitors targeting other signaling pathways. The inhibitory lethality caused by blocking Mek or BRAF is through apoptosis. In contrast, MDA-MB-231 is a multi-driver triple-negative breast cancer cell line dependent on both Src and the KRAS-activated mitogen-activated kinase pathway for proliferation and viability. Blocking each pathway alone only partially inhibits cell proliferation without killing them, but the combination of dasatinib, an Src inhibitor, and trametinib, a Mek inhibitor, achieves synthetic lethality. The combination is highly potent, with an IC50 of 8.2 nM each, and strikingly synergistic, with a combination index of less than 0.003 for 70% inhibition. The synthetic lethality of the drug combination is achieved by apoptosis. These results reveal a crucial difference between mono-driver and multi-driver cancer cells and suggest that pharmacological synthetic lethality may provide a basis for effectively inhibiting multi-driver cancers.

Statistics and network-based approaches to identify molecular mechanisms that drive the progression of breast cancer

Breast cancer (BC) is one of the most malignant tumors and the leading cause of cancer-related death in women worldwide. So, an in-depth investigation on the molecular mechanisms of BC progression is required for diagnosis, prognosis and therapies. In this study, we identified 127 common differentially expressed genes (cDEGs) between BC and control samples by analyzing five gene expression profiles with NCBI accession numbers GSE139038, GSE62931, GSE45827, GSE42568 and GSE54002, based-on two statistical methods LIMMA and SAM. Then we constructed protein-protein interaction (PPI) network of cDEGs through the STRING database and selected top-ranked 7 cDEGs (BUB1, ASPM, TTK, CCNA2, CENPF, RFC4, and CCNB1) as a set of key genes (KGs) by cytoHubba plugin in Cytoscape. Several BC-causing crucial biological processes, molecular functions, cellular components, and pathways were significantly enriched by the estimated cDEGs including at-least one KGs. The multivariate survival analysis showed that the proposed KGs have a strong prognosis power of BC. Moreover, we detected some transcriptional and post-transcriptional regulators of KGs by their regulatory network analysis. Finally, we suggested KGs-guided three repurposable candidate-drugs (Trametinib, selumetinib, and RDEA119) for BC treatment by using the GSCALite online web tool and validated them through molecular docking analysis, and found their strong binding affinities. Therefore, the findings of this study might be useful resources for BC diagnosis, prognosis and therapies.

Selumetinib: a selective MEK1 inhibitor for solid tumor treatment

Cancer incidence is rapidly growing. Solid tumors are responsible for a majority of cancers. Recently, molecular-targeted agents have played a significant role in cancer treatment. Ras-Raf-MEK-ERK signaling pathway, is a substantial element in the survival, propagation, and drug resistance of human cancers. MEK is a specific part of the so-called cascade, and ERK proteins are its sole target. Furthermore, their downstream position in the Ras-ERK cascade, is noteworthy to direct their function in patients with upstream mutated genes. MEK1 mutations are responsible for initiating several solid tumors. Selumetinib (AZD6244) is a second-generation, selective, potent, and non-ATP competitive allosteric MEK1 inhibitor. The efficacy of selumetinib in various solid tumors such as colorectal cancer, lung cancer, neurofibroma, and melanoma is investigated. The present paper provides an overview of the MAPK cascade, the role of selumetinib as a MEK1/2 inhibitor, and the related findings of clinical trials for solid tumor treatment.

Molecular Targets of Triple-Negative Breast Cancer: Where Do We Stand?

Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer. Due to its heterogeneity and lack of hormone receptor expression, this subtype is more likely to metastasize and resist treatment attempts than are other forms of breast cancer. Due to the absence of targetable receptors, chemotherapy and breast conserving surgery have been the predominant treatment options for patients. However, resistance to chemotherapy and local recurrence of the tumors is frequent. Emerging immunotherapies have begun to change treatment plans for patients diagnosed with TNBC. In this review, we discuss the various immune pathways identified in TNBC and the role they play as targets for new potential treatment choices. Various therapeutic options that inhibit key pathways in cellular growth cycles, DNA repair mechanisms, epithelial mesenchymal transition, and immunosuppression have been shown to improve survival in patients with this disease. With promising results thus far, continued studies of immunotherapy and neoadjuvant therapy options for TNBC are likely to alter the treatment course for these diagnoses in the future.

β2-AR blockade potentiates MEK1/2 inhibitor effect on HNSCC by regulating the Nrf2-mediated defense mechanism

The β2-Adrenergic receptor (β2-AR) is a G protein-coupled receptor (GPCR), involved in the development of many cancers, among which HNSCC. In this contest, β2-AR signaling interacts with different pathways, such as PI3K and MAPK, commonly activated by TK receptors. For this reason, TK blockade is one of the most adopted therapeutic strategies in HNSCC patients. In our study we investigated the effects of the β2-AR blocking in HNSCC cell lines, using the selective inhibitor ICI118,551 (ICI), in combination with the MAPK inhibitor U0126. We found that ICI leads to the blocking of p38 and NF-kB oncogenic pathways, strongly affecting also the ERK and PI3K pathways. Cotreatment with U0126 displays a synergic effect on cell viability and pathway alteration. Interestingly, we found that the β2-AR blockade affects Nrf2-Keap1 stability and its nuclear translocation leading to a drastic ROS increase and oxidative stress. Our results are confirmed by a TCGA dataset analysis, showing that NFE2L2 gene is commonly overexpressed in HNSC, and correlated with a lower survival rate. In our system, the PI3K pathway inhibition culminated in the blocking of pro-survival autophagy, a mechanism normally adopted by cancer cells to became less responsive to the therapies. The mTOR expression, commonly upregulated in HNSC, was reduced in patients with disease-recurrence. It is well known that mTOR has a strong autophagy inhibition effect, therefore its downregulation promoted pro-survival autophagy, with a related increase recurrence rate. Our findings highlight for the first time the key role of β2-AR and related pathway in HNSCC cell proliferation and drug resistance, proposing it as a valuable therapeutic molecular target.

Application of a Biphasic Mathematical Model of Cancer Cell Drug Response for Formulating Potent and Synergistic Targeted Drug Combinations to Triple Negative Breast Cancer Cells

Triple negative breast cancer is a collection of heterogeneous breast cancers that are immunohistochemically negative for estrogen receptor, progesterone receptor, and ErbB2 (due to deletion or lack of amplification). No dominant proliferative driver has been identified for this type of cancer, and effective targeted therapy is lacking. In this study, we hypothesized that triple negative breast cancer cells are multi-driver cancer cells, and evaluated a biphasic mathematical model for identifying potent and synergistic drug combinations for multi-driver cancer cells. The responses of two triple negative breast cancer cell lines, MDA-MB-231 and MDA-MB-468, to a panel of targeted therapy drugs were determined over a broad range of concentrations. The analyses of the drug responses by the biphasic mathematical model revealed that both cell lines were indeed dependent on multiple drivers, and inhibitors of individual drivers caused a biphasic response: a target-specific partial inhibition at low nM concentrations, and an off-target toxicity at μM concentrations. We further demonstrated that combinations of drugs, targeting each driver, cause potent, synergistic, and cell-specific cell killing. Immunoblotting analysis of the effects of the individual drugs and drug combinations on the signaling pathways supports the above conclusion. These results support a multi-driver proliferation hypothesis for these triple negative breast cancer cells, and demonstrate the applicability of the biphasic mathematical model for identifying effective and synergistic targeted drug combinations for triple negative breast cancer cells.

Mechanisms of suppression of cell growth by dual inhibition of ALK and MEK in ALK-positive non-small cell lung cancer

Anaplastic lymphoma kinase (ALK) rearrangement, a key oncogenic driver in a small subset of non-small cell lung cancers, confers sensitivity to ALK tyrosine kinase inhibitors (TKIs). Crizotinib, a first generation ALK-TKI, has superiority to standard chemotherapy with longer progression-free survival and higher objective response rate. However, clinical benefit is limited by development of resistance, typically within a year of therapy. In this study the combined effect of crizotinib and the MEK inhibitor selumetinib was investigated in both crizotinib naïve (H3122) and crizotinib resistant (CR-H3122) ALK-positive lung cancer cells. Results showed that combination treatment potently inhibited the growth of both H3122 and CR-H3122 cells, resulting from increased apoptosis and decreased cell proliferation as a consequence of suppressed downstream RAS/MAPK signalling. The drug combination also elicited a greater than 3-fold increase in Bim, a mediator of apoptosis, and p27, a cyclin dependent kinase inhibitor compared to crizotinib alone. The results support the hypothesis that combining MEK inhibitors with ALK inhibitor can overcome ALK inhibitor resistance, and identifies Bim, PARP and CDK1 as druggable targets for possible triple drug therapy.

The screening of pivotal gene expression signatures and biomarkers in renal carcinoma

Renal cell carcinoma (RCC) is one of the most common malignancies in the urinary system, among which the proportion of clear cell RCC (ccRCC) is over 80%. This study aims to explore potential signaling pathways and key biomarkers that drive RCC progression. The RCC GEO Datasets GSE15641 was featured to screen differentially expressed genes (DEGs). The pathway enrichment and functional annotation of differentially expressed genes were analyzed using the Kyoto Encyclopedia of Genes and Genomes (KEGG) and the Gene Ontology (GO). We screened Hub genes from DEGs using protein-protein interaction (PPI) networks and Cytoscape software. The survival and diagnostic analysis of these hub genes was performed to evaluate their potential prognostic and diagnostic value for ccRCC. In GSE15641 dataset, 598 DEGs were captured according to screening criteria (406 up-regulated genes and 192 down-regulated genes). Meanwhile, 15 hub genes were screened out from DEGs using PPI and Cytoscape. Kaplan Meier and ROC curve analysis identified three potential prognostic and diagnostic biomarkers (TGFB1, TIMP1 and VIM) for ccRCC from 15 hub genes. Gene set enrichment analysis (GSEA) revealed that these three dysregulated genes are mainly enriched in primary immunodeficiency, ECM receptor interaction, cytokine receptor interaction and natural killer cell-mediated cytotoxicity pathway. In summary, our findings discovered pivotal gene expression signatures and signaling pathways in the progression of ccRCC. TGFB1, TIMP1 and VIM might contribute to the progression of ccRCC, which could have potential as biomarkers or therapeutic targets for ccRCC.

Halogen-Substituted Derivatives of Dictyostelium Differentiation-Inducing Factor-1 Suppress Serum-Induced Cell Migration of Human Breast Cancer MDA-MB-231 Cells in Vitro

Triple-negative breast cancer (TNBC) is highly proliferative and metastatic, and because it lacks three major molecular targets for chemotherapy (estrogen receptor, progesterone receptor, and human epidermal receptor 2), it is extremely refractory. Differentiation-inducing factor 1 (DIF-1) and DIF-3, which are chlorinated alkylphenones, are lead anticancer compounds found in the cellular slime mold Dictyostelium discoideum. Here, we examined the in vitro effects of DIF-1, DIF-3, and 25 DIF derivatives on cell proliferation and serum-induced cell migration in human MDA-MB-231 cells, a model TNBC cell line. We found that Br-DIF-1, a chlorine-to-bromine-substituted derivative of DIF-1, strongly suppressed cell migration (IC₅₀, 3.8 μM) with negligible effects on cell proliferation (IC₅₀, >20 μM). We then synthesized 18 derivatives of Br-DIF-1 and examined the in vitro effects of these derivatives on cell proliferation and serum-induced cell migration in MDA-MB-231 cells. Among the derivatives, Br-DIF-1(+1), Br-DIF-1(+2), and Br-DIF-3(+2) exhibited strong anti-cell migration activities with IC₅₀ values of 1.5, 1.0, and 3.1 μM, respectively, without affecting cell proliferation (IC₅₀, >20 μM). These results suggest that these Br-DIF derivatives are good lead compounds for the development of anti-metastatic drugs against TNBC.

Multi-Omic Data Interpretation to Repurpose Subtype Specific Drug Candidates for Breast Cancer

Triple-negative breast cancer (TNBC), which is largely synonymous with the basal-like molecular subtype, is the 5th leading cause of cancer deaths for women in the United States. The overall prognosis for TNBC patients remains poor given that few treatment options exist; including targeted therapies (not FDA approved), and multi-agent chemotherapy as standard-of-care treatment. TNBC like other complex diseases is governed by the perturbations of the complex interaction networks thereby elucidating the underlying molecular mechanisms of this disease in the context of network principles, which have the potential to identify targets for drug development. Here, we present an integrated "omics" approach based on the use of transcriptome and interactome data to identify dynamic/active protein-protein interaction networks (PPINs) in TNBC patients. We have identified three highly connected modules, EED, DHX9, and AURKA, which are extremely activated in TNBC tumors compared to both normal tissues and other breast cancer subtypes. Based on the functional analyses, we propose that these modules are potential drivers of proliferation and, as such, should be considered candidate molecular targets for drug development or drug repositioning in TNBC. Consistent with this argument, we repurposed steroids, anti-inflammatory agents, anti-infective agents, cardiovascular agents for patients with basal-like breast cancer. Finally, we have performed essential metabolite analysis on personalized genome-scale metabolic models and found that metabolites such as sphingosine-1-phosphate and cholesterol-sulfate have utmost importance in TNBC tumor growth.

Expression and potential molecular mechanisms of miR‑204‑5p in breast cancer, based on bioinformatics and a meta‑analysis of 2,306 cases

Breast cancer (BC) is the most common cancer among women worldwide. However, there is insufficient research that focuses on the expression and molecular mechanisms of microRNA (miR)‑204‑5p in BC. In the current study, data were downloaded from the Cancer Genome Atlas (TCGA), the Gene Expression Omnibus (GEO) and the University of California Santa Cruz (UCSC) Xena databases. They were then used to undertake a meta‑analysis that leveraged the standard mean difference (SMD) and summarized receiver operating characteristic (sROC) to evaluate the expression of the precursor miR‑204 and mature miR‑204‑5p in BC. Additionally, an intersection of predicted genes, differentially expressed genes (DEGs) from the TCGA database and the GEO database were plotted to acquire desirable putative genes. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and protein‑protein interaction (PPI) network analyses were performed to assess the potential pathways and hub genes of miR‑204‑5p in BC. A decreased trend in precursor miR‑204 expression was detected in 1,077 BC tissue samples in comparison to 104 para‑carcinoma tissue samples in the TCGA database. Further, the expression of mature miR‑204‑5p was markedly downregulated in 756 BC tissue samples in comparison to 76 para‑carcinoma tissue samples in the UCSC Xena database. The outcome of the SMD from meta‑analysis also indicated that the expression of miR‑204‑5p was markedly reduced in 2,306 BC tissue samples in comparison to 367 para‑carcinoma tissue samples. Additionally, the ROC and sROC values indicated that miR‑204‑5p had a great discriminatory capacity for BC. In GO analysis, 'cell development', 'cell surface activity', and 'receptor agonist activity' were the most enriched terms; in KEGG analysis, 'endocytosis' was significantly enriched. Rac GTPase activating protein 1 (RACGAP1) was considered the hub gene in the PPI network. In conclusion, miR‑204‑5p may serve a suppressor role in the oncogenesis and advancement of BC, and miR‑204‑5p may have crucial functions in BC by targeting RACGAP1.

Licochalcone D induces apoptosis and inhibits migration and invasion in human melanoma A375 cells

The aim of the present study was to determine the effects of Licochalcone D (LD) on the apoptosis and migration and invasion in human melanoma A375 cells. Cell proliferation was determined by sulforhodamine B assay. Apoptosis was assessed by Hoechst 33258 and Annexin V‑FITC/PI staining and JC‑1 assay. Total intracellular reactive oxygen species (ROS) was examined by DCFH‑DA. Wound healing and Transwell assays were used to detect migration and invasion of the cells. The activities of matrix metalloproteinase (MMP‑2 and MMP‑9) were assessed via gelatin zymography. Tumor growth in vivo was evaluated in C57BL/6 mice. RT‑PCR, qPCR, ELISA and western blot analysis were utilized to measure the mRNA and protein levels. Our results showed that LD inhibited the proliferation of A375 and SK‑MEL‑5 cells in a concentration‑dependent manner. After treatment with LD, A375 cells displayed obvious apoptotic characteristics, and the number of apoptotic cells was significantly increased. Pro‑apoptotic protein Bax, caspase‑9 and caspase‑3 were upregulated, while anti‑apoptotic protein Bcl‑2 was downregulated in the LD‑treated cells. Meanwhile, LD induced the loss of mitochondrial membrane potential (ΔΨm) and increased the level of ROS. ROS production was inhibited by the co‑treatment of LD and free radical scavenger N‑acetyl‑cysteine (NAC). Furthermore, LD also blocked A375 cell migration and invasion in vitro which was associated with the downregulation of MMP‑9 and MMP‑2. Finally, intragastric administration of LD suppressed tumor growth in the mouse xenograft model of murine melanoma B16F0 cells. These results suggest that LD may be a potential drug for human melanoma treatment by inhibiting proliferation, inducing apoptosis via the mitochondrial pathway and blocking cell migration and invasion.

Mechanisms of modulation of the Egr gene family in mammary epithelial cells of different species

In the adult female, within the estrous cycle, the mammary gland undergoes multiple rounds of growth, with increased cellular proliferation, and involution, with increased apoptosis. The increase in proliferation is elicited by endocrine (Estrogen, Progesterone), as well as locally produced (epidermal growth factor, insulin-like growth factor, etc) growth factors. Among the genes that are modulated during cellular proliferation, immediate early genes play a fundamental role, being rapidly upregulated and then downregulated within the G0/G1 phase of the cell cycle, allowing the progression to the subsequent phases. Egrs (1-4) are immediate early genes that encode for transcription factors that promote, within different cell types and depending on the strength and duration of the stimuli, several different responses like mitogenesis, differentiation, apoptosis or even anti-apoptosis. In this work we have studied the mechanisms of modulation of the Egr family, in mammary epithelial cells of different origin (bovine, canine, feline, murine). Following stimulation with growth medium, Egr mRNA expression showed a strong upregulation reaching a peak at 45-60min, that rapidly declined. Among several cytokines, particularly important for mammary morphogenesis, that we have tested (EGF, IGF-I, insulin, estrogen, progesterone), only EGF upregulated Egrs to levels close to those elicited by growth medium. In order to understand how the Egr transcription factors were regulated, we have inhibited Erk 1/2 and PI3K, molecules that drive two major intracellular signaling pathways. Inhibition of the Erk 1/2 pathway totally abolished Egr upregulation mediated by growth medium or EGF. On the other hand, the PI3K-Akt pathway played a minor role on Egr levels, with a strong inhibitory effect on cat GH2 cells only, that could be ascribed to reduced Erk phosphorylation following PI3K inhibition. Finally we showed that addition of growth medium also upregulated that the mammary luminal marker cytokeratin 18, but only in the murine NMuMG cell line. This is the first manuscript describing how the Egr transcription factors are expressed in mammary epithelial cells of domestic animals and which growth factors and signaling pathways modulate their expression.