Mammalian Grb2 regulates multiple steps in embryonic development and malignant transformation

The binding selectivity of the C-terminal SH3 domain of Grb2, but not its folding pathway, is dictated by its contiguous SH2 domain

The adaptor protein Grb2, or growth factor receptor-bound protein 2, possesses a pivotal role in the transmission of fundamental molecular signals in the cell. Despite lacking enzymatic activity, Grb2 functions as a dynamic assembly platform, orchestrating intracellular signals through its modular structure. This study delves into the energetic communication of Grb2 domains, focusing on the folding and binding properties of the C-SH3 domain linked to its neighboring SH2 domain. Surprisingly, while the folding and stability of C-SH3 remain robust and unaffected by SH2 presence, significant differences emerge in the binding properties when considered within the tandem context compared with isolated C-SH3. Through a double mutant cycle analysis, we highlighted a subset of residues, located at the interface with the SH2 domain and far from the binding site, finely regulating the binding of a peptide mimicking a physiological ligand of the C-SH3 domain. Our results have mechanistic implications about the mechanisms of specificity of the C-SH3 domain, indicating that the presence of the SH2 domain optimizes binding to its physiological target, and emphasizing the general importance of considering supramodular multidomain protein structures to understand the functional intricacies of protein-protein interaction domains.

GRB2 stabilizes RAD51 at reversed replication forks suppressing genomic instability and innate immunity against cancer

Growth factor receptor-bound protein 2 (GRB2) is a cytoplasmic adapter for tyrosine kinase signaling and a nuclear adapter for homology-directed-DNA repair. Here we find nuclear GRB2 protects DNA at stalled replication forks from MRE11-mediated degradation in the BRCA2 replication fork protection axis. Mechanistically, GRB2 binds and inhibits RAD51 ATPase activity to stabilize RAD51 on stalled replication forks. In GRB2-depleted cells, PARP inhibitor (PARPi) treatment releases DNA fragments from stalled forks into the cytoplasm that activate the cGAS-STING pathway to trigger pro-inflammatory cytokine production. Moreover in a syngeneic mouse metastatic ovarian cancer model, GRB2 depletion in the context of PARPi treatment reduced tumor burden and enabled high survival consistent with immune suppression of cancer growth. Collective findings unveil GRB2 function and mechanism for fork protection in the BRCA2-RAD51-MRE11 axis and suggest GRB2 as a potential therapeutic target and an enabling predictive biomarker for patient selection for PARPi and immunotherapy combination.

GRB2 is a BECN1 interacting protein that regulates autophagy

GRB2 is an adaptor protein of HER2 (and several other tyrosine kinases), which we identified as a novel BECN1 (Beclin 1) interacting partner. GRB2 co-immunoprecipitated with BECN1 in several breast cancer cell lines and regulates autophagy through a mechanism involving the modulation of the class III PI3Kinase VPS34 activity. In ovo studies in a CAM (Chicken Chorioallantoic Membrane) model indicated that GRB2 knockdown, as well as overexpression of GRB2 loss-of-function mutants (Y52A and S86A-R88A) compromised tumor growth. These differences in tumor growth correlated with differential autophagy activity, indicating that autophagy effects might be related to the effects on tumorigenesis. Our data highlight a novel function of GRB2 as a BECN1 binding protein and a regulator of autophagy.

Transcriptional Factors Mediated Reprogramming to Pluripotency

A unique kind of pluripotent cell, i.e., Induced pluripotent stem cells (iPSCs), now being targeted for iPSC synthesis, are produced by reprogramming animal and human differentiated cells (with no change in genetic makeup for the sake of high efficacy iPSCs formation). The conversion of specific cells to iPSCs has revolutionized stem cell research by making pluripotent cells more controllable for regenerative therapy. For the past 15 years, somatic cell reprogramming to pluripotency with force expression of specified factors has been a fascinating field of biomedical study. For that technological primary viewpoint reprogramming method, a cocktail of four transcription factors (TF) has required: Kruppel-like factor 4 (KLF4), four-octamer binding protein 34 (OCT3/4), MYC and SOX2 (together referred to as OSKM) and host cells. IPS cells have great potential for future tissue replacement treatments because of their ability to self-renew and specialize in all adult cell types, although factor-mediated reprogramming mechanisms are still poorly understood medically. This technique has dramatically improved performance and efficiency, making it more useful in drug discovery, disease remodeling, and regenerative medicine. Moreover, in these four TF cocktails, more than 30 reprogramming combinations were proposed, but for reprogramming effectiveness, only a few numbers have been demonstrated for the somatic cells of humans and mice. Stoichiometry, a combination of reprogramming agents and chromatin remodeling compounds, impacts kinetics, quality, and efficiency in stem cell research.

Role of Fibroblast Growth Factor Receptor 2 (FGFR2) in Corneal Stromal Thinning

Purpose

To determine the role of fibroblast growth factor receptor 2 (FGFR2)-mediated signaling in keratocytes during corneal development, a keratocyte-specific FGFR2-knockout (named FGFR2cKO) mouse model was generated, and its phenotypic characteristics were determined.

Methods

A FGFR2cKO mouse model was generated by the following method: FGFR2 flox mice were crossed with the inducible keratocyte specific-Cre mice (Kera-rtTA/tet-O-Cre). Both male and female FGFR2cKO- and control mice (1 to 3-months-old) were analyzed for changes in corneal topography and pachymetry maps using the optical coherence tomography (OCT) method. The comparative TUNEL assay and immunohistochemical analyses were performed using corneas of FGFR2cKO and control mice to determine apoptotic cells, and expression of collagen-1 and fibronectin. Transmission electron microscopic analysis was conducted to determine collagen structures and their diameters in corneas of FGFR2cKO and control mice.

Results

OCT-analyses of corneas of FGFR2cKO mice (n = 24) showed localized central thinning and an increased corneal steepness compared to control mice (n = 23). FGFR2cKO mice further showed a decreased expression in collagen-1, decreased collagen diameters, acute corneal hydrops, an increased fibronectin expression, and an increased number of TUNEL-positive cells suggesting altered collagen structures and keratocytes' apoptosis in the corneas of FGFR2cKO mice compared to control mice.

Conclusions

The FGFR2cKO mice showed several corneal phenotypes (as described above in the results) that are also exhibited by the human keratoconus corneas. The results suggested that the FGFR2cKO mouse model serves to elucidate not only the yet unknown role of FGFR2-mediated signaling in corneal physiology but also serves as a model to determine molecular mechanism of human keratoconus development.

The Trophoblast Compartment Helps Maintain Embryonic Pluripotency and Delays Differentiation towards Cardiomyocytes

Normal developmental progression relies on close interactions between the embryonic and extraembryonic lineages in the pre- and peri-gastrulation stage conceptus. For example, mouse epiblast-derived FGF and NODAL signals are required to maintain a stem-like state in trophoblast cells of the extraembryonic ectoderm, while visceral endoderm signals are pivotal to pattern the anterior region of the epiblast. These developmental stages also coincide with the specification of the first heart precursors. Here, we established a robust differentiation protocol of mouse embryonic stem cells (ESCs) into cardiomyocyte-containing embryoid bodies that we used to test the impact of trophoblast on this key developmental process. Using trophoblast stem cells (TSCs) to produce trophoblast-conditioned medium (TCM), we show that TCM profoundly slows down the cardiomyocyte differentiation dynamics and specifically delays the emergence of cardiac mesoderm progenitors. TCM also strongly promotes the retention of pluripotency transcription factors, thereby sustaining the stem cell state of ESCs. By applying TCM from various mutant TSCs, we further show that those mutations that cause a trophoblast-mediated effect on early heart development in vivo alter the normal cardiomyocyte differentiation trajectory. Our approaches provide a meaningful deconstruction of the intricate crosstalk between the embryonic and the extraembryonic compartments. They demonstrate that trophoblast helps prolong a pluripotent state in embryonic cells and delays early differentiative processes, likely through production of leukemia inhibitory factor (LIF). These data expand our knowledge of the multifaceted signaling interactions among distinct compartments of the early conceptus that ensure normal embryogenesis, insights that will be of significance for the field of synthetic embryo research.

Deletion of p66Shc Dysregulates ERK and STAT3 Activity in Mouse Embryonic Stem Cells, Enhancing Their Naive-Like Self-Renewal in the Presence of Leukemia Inhibitory Factor

The ShcA adapter protein is necessary for early embryonic development. The role of ShcA in development is primarily attributed to its 52 and 46 kDa isoforms that transduce receptor tyrosine kinase signaling through the extracellular signal regulated kinase (ERK). During embryogenesis, ERK acts as the primary signaling effector, driving fate acquisition and germ layer specification. P66Shc, the largest of the ShcA isoforms, has been observed to antagonize ERK in several contexts; however, its role during embryonic development remains poorly understood. We hypothesized that p66Shc could act as a negative regulator of ERK activity during embryonic development, antagonizing early lineage commitment. To explore the role of p66Shc in stem cell self-renewal and differentiation, we created a p66Shc knockout murine embryonic stem cell (mESC) line. Deletion of p66Shc enhanced basal ERK activity, but surprisingly, instead of inducing mESC differentiation, loss of p66Shc enhanced the expression of core and naive pluripotency markers. Using pharmacologic inhibitors to interrogate potential signaling mechanisms, we discovered that p66Shc deletion permits the self-renewal of naive mESCs in the absence of conventional growth factors, by increasing their responsiveness to leukemia inhibitory factor (LIF). We discovered that loss of p66Shc enhanced not only increased ERK phosphorylation but also increased phosphorylation of Signal transducer and activator of transcription in mESCs, which may be acting to stabilize their naive-like identity, desensitizing them to ERK-mediated differentiation cues. These findings identify p66Shc as a regulator of both LIF-mediated ESC pluripotency and of signaling cascades that initiate postimplantation embryonic development and ESC commitment.

Generation of pulsatile ERK activity in mouse embryonic stem cells is regulated by Raf activity

The extracellular signal-regulated kinase (ERK) is a serine/threonine kinase that is known to regulate cellular events such as cell proliferation and differentiation. The ERK signaling pathway is activated by fibroblast growth factors, and is considered to be indispensable for the differentiation of primitive endoderm cells, not only in mouse preimplantation embryos, but also in embryonic stem cell (ESC) culture. To monitor ERK activity in living undifferentiated and differentiating ESCs, we established EKAREV-NLS-EB5 ESC lines that stably express EKAREV-NLS, a biosensor based on the principle of fluorescence resonance energy transfer. Using EKAREV-NLS-EB5, we found that ERK activity exhibited pulsatile dynamics. ESCs were classified into two groups: active cells showing high-frequency ERK pulses, and inactive cells demonstrating no detectable ERK pulses during live imaging. Pharmacological inhibition of major components in the ERK signaling pathway revealed that Raf plays an important role in determining the pattern of ERK pulses.

Biophysical models of early mammalian embryogenesis

Embryo development is a critical and fascinating stage in the life cycle of many organisms. Despite decades of research, the earliest stages of mammalian embryogenesis are still poorly understood, caused by a scarcity of high-resolution spatial and temporal data, the use of only a few model organisms, and a paucity of truly multidisciplinary approaches that combine biological research with biophysical modeling and computational simulation. Here, we explain the theoretical frameworks and biophysical processes that are best suited to modeling the early mammalian embryo, review a comprehensive list of previous models, and discuss the most promising avenues for future work.

Synthesis and Biochemical Evaluation of Monocarboxylic GRB2 SH2 Domain Inhibitors

This protocol discloses the synthesis of monocarboxylic inhibitors with a macrocyclic peptide scaffold to bind with the GRB2 SH2 domain and disrupt the protein-protein interactions (PPIs) between GRB2 and phosphotyrosine-containing proteins.

Regulation of Embryonic Stem Cell Self-Renewal

Embryonic stem cells (ESCs) are a type of cells capable of self-renewal and multi-directional differentiation. The self-renewal of ESCs is regulated by factors including signaling pathway proteins, transcription factors, epigenetic regulators, cytokines, and small molecular compounds. Similarly, non-coding RNAs, small RNAs, and microRNAs (miRNAs) also play an important role in the process. Functionally, the core transcription factors interact with helper transcription factors to activate the expression of genes that contribute to maintaining pluripotency, while suppressing the expression of differentiation-related genes. Additionally, cytokines such as leukemia suppressor factor (LIF) stimulate downstream signaling pathways and promote self-renewal of ESCs. Particularly, LIF binds to its receptor (LIFR/gp130) to trigger the downstream Jak-Stat3 signaling pathway. BMP4 activates the downstream pathway and acts in combination with Jak-Stat3 to promote pluripotency of ESCs in the absence of serum. In addition, activation of the Wnt-FDZ signaling pathway has been observed to facilitate the self-renewal of ESCs. Small molecule modulator proteins of the pathway mentioned above are widely used in in vitro culture of stem cells. Multiple epigenetic regulators are involved in the maintenance of ESCs self-renewal, making the epigenetic status of ESCs a crucial factor in this process. Similarly, non-coding RNAs and cellular energetics have been described to promote the maintenance of the ESC's self-renewal. These factors regulate the self-renewal and differentiation of ESCs by forming signaling networks. This review focused on the role of major transcription factors, signaling pathways, small molecular compounds, epigenetic regulators, non-coding RNAs, and cellular energetics in ESC's self-renewal.

Evaluation of NF1 and RASA1 gene expression in endometriosis

Background

Endometrios affecting 6-10% of women of reproductive ages around the globe. Important pathways, including the MAPK and PI3K / Akt pathways, have been identified in the disease. The NF1 and RASA1 genes inactivate Ras by their own GTPase activity and controlled the high activity of these pathways.

Objective

In this study, we measured NF1 and RASA1 gene expression in the endometrial tissues of patients (eutopic and ectopic tissues) compared to the control samples.

Materials and methods

In our study, tissue samples were collected from 15 patients with endometriosis and 15 healthy women. We used quantitative polymerase chain reaction (qRT-PCR) to measure the NF1 and RASA1 gene expression levels in these samples.

Results

We observed a significant decrease in the expression level of the NF1 gene in both eutopic and ectopic samples of endometriosis patients compared to control samples, while the expression of the RASA1 gene was significantly reduced only in ectopic tissues.

An efficient method of inducing differentiation of mouse embryonic stem cells into primitive endodermal cells

Primitive Endoderm (PrE) is an extraembryonic structure derived from inner cell mass (ICM) in the blastocysts. Its interaction with the epiblast is critical to sustain embryonic growth and embryonic pattern. In this study, we reported a simple and efficient method to induce the differentiation of mouse Embryonic Stem Cells (mESCs) into PrE cells. In the process of ESC monolayer adherent culture, 1 μM atRA and 10 μM CHIR inducers were used to activate RA and Wnt signaling pathways respectively. After 9 days of differentiation, the proportion of PrE cells was up to 85%. Further studies indicated that Wnt signaling pathway acted as a switch that RA induces mESCs differentiation between SMC and PrE cell. In the presence of only RA signaling, mESCs adopted the fate of smooth muscle cells (SMCs); Simultaneous activation of the Wnt signaling pathway changed the differentiation fate of mESCs into PrE cells. This efficient induction method can provide new cellular resources and models for relevant studies of PrE.

Synthesis and structural characterization of a monocarboxylic inhibitor for GRB2 SH2 domain

A monocarboxylic inhibitor was designed and synthesized to disrupt the protein-protein interaction (PPI) between GRB2 and phosphotyrosine-containing proteins. Biochemical characterizations show compound 7 binds with the Src homology 2 (SH2) domain of GRB2 and is more potent than EGFR₁₀₆₈ phosphopeptide 14-mer. X-ray crystallographic studies demonstrate compound 7 occupies the GRB2 binding site for phosphotyrosine-containing sequences and reveal key structural features for GRB2-inhibitor binding. This compound with a -1 formal charge offers a new direction for structural optimization to generate cell-permeable inhibitors for this key protein target of the aberrant Ras-MAPK signaling cascade.

GRB2 enforces homology-directed repair initiation by MRE11

DNA double-strand break (DSB) repair is initiated by MRE11 nuclease for both homology-directed repair (HDR) and alternative end joining (Alt-EJ). Here, we found that GRB2, crucial to timely proliferative RAS/MAPK pathway activation, unexpectedly forms a biophysically validated GRB2-MRE11 (GM) complex for efficient HDR initiation. GRB2-SH2 domain targets the GM complex to phosphorylated H2AX at DSBs. GRB2 K109 ubiquitination by E3 ubiquitin ligase RBBP6 releases MRE11 promoting HDR. RBBP6 depletion results in prolonged GM complex and HDR defects. GRB2 knockout increased MRE11-XRCC1 complex and Alt-EJ. Reconstitution with separation-of-function GRB2 mutant caused HDR deficiency and synthetic lethality with PARP inhibitor. Cell and cancer genome analyses suggest biomarkers of low GRB2 for noncanonical HDR deficiency and high MRE11 and GRB2 expression for worse survival in HDR-proficient patients. These findings establish GRB2's role in binding, targeting, and releasing MRE11 to promote efficient HDR over Alt-EJ DSB repair, with implications for genome stability and cancer biology.

p52Shc regulates the sustainability of ERK activation in a RAF-independent manner

p52SHC (SHC) and GRB2 are adaptor proteins involved in the RAS/MAPK (ERK) pathway mediating signals from cell-surface receptors to various cytoplasmic proteins. To further examine their roles in signal transduction, we studied the translocation of fluorescently labeled SHC and GRB2 to the cell surface, caused by the activation of ERBB receptors by heregulin (HRG). We simultaneously evaluated activated ERK translocation to the nucleus. Unexpectedly, the translocation dynamics of SHC were sustained when those of GRB2 were transient. The sustained localization of SHC positively correlated with the sustained nuclear localization of ERK, which became more transient after SHC knockdown. SHC-mediated PI3K activation was required to maintain the sustainability of the ERK translocation regulating MEK but not RAF. In cells overexpressing ERBB1, SHC translocation became transient, and the HRG-induced cell fate shifted from a differentiation to a proliferation bias. Our results indicate that SHC and GRB2 functions are not redundant but that SHC plays the critical role in the temporal regulation of ERK activation.

Principles of Self-Organization of the Mammalian Embryo

Early embryogenesis is a conserved and self-organized process. In the mammalian embryo, the potential for self-organization is manifested in its extraordinary developmental plasticity, allowing a correctly patterned embryo to arise despite experimental perturbation. The underlying mechanisms enabling such regulative development have long been a topic of study. In this Review, we summarize our current understanding of the self-organizing principles behind the regulative nature of the early mammalian embryo. We argue that geometrical constraints, feedback between mechanical and biochemical factors, and cellular heterogeneity are all required to ensure the developmental plasticity of mammalian embryo development.

The Challenges and Strategies of Antisense Oligonucleotide Drug Delivery

Antisense oligonucleotides (ASOs) are used to selectively inhibit the translation of disease-associated genes via Ribonuclease H (RNaseH)-mediated cleavage or steric hindrance. They are being developed as a novel and promising class of drugs targeting a wide range of diseases. Despite the great potential and numerous ASO drugs in preclinical research and clinical trials, there are many limitations to this technology. In this review we will focus on the challenges of ASO delivery and the strategies adopted to improve their stability in the bloodstream, delivery to target sites, and cellular uptake. Focusing on liposomal delivery, we will specifically describe liposome-incorporated growth factor receptor-bound protein-2 (Grb2) antisense oligodeoxynucleotide BP1001. BP1001 is unique because it is uncharged and is essentially non-toxic, as demonstrated in preclinical and clinical studies. Additionally, its enhanced biodistribution makes it an attractive therapeutic modality for hematologic malignancies as well as solid tumors. A detailed understanding of the obstacles that ASOs face prior to reaching their targets and continued advances in methods to overcome them will allow us to harness ASOs’ full potential in precision medicine.

The adaptor protein Grb2b is an essential modulator for lympho-venous sprout formation in the zebrafish trunk

Vegfc/Vegfr3 signaling is critical for lymphangiogenesis, the sprouting of lymphatic vessels. In zebrafish, cells sprouting from the posterior cardinal vein can either form lymphatic precursor cells or contribute to intersegmental vein formation. Both, the Vegfc-dependent differential induction of Prox1a in sprouting cells as well as a Notch-mediated pre-pattern within intersegmental vessels have been associated with the regulation of secondary sprout behavior. However, how exactly a differential lymphatic versus venous sprout cell behavior is achieved is not fully understood. Here, we characterize a zebrafish mutant in the adaptor protein Grb2b, and demonstrate through genetic interaction studies that Grb2b acts within the Vegfr3 pathway. Mutant embryos exhibit phenotypes that are consistent with reduced Vegfr3 signaling outputs prior to the sprouting of endothelial cells from the vein. During secondary sprouting stages, loss of grb2b leads to defective cell behaviors resulting in a loss of parachordal lymphangioblasts, while only partially affecting the number of intersegmental veins. A second GRB2 zebrafish ortholog, grb2a, contributes to the development of lymphatic structures in the meninges and in the head, but not in the trunk. Our results illustrate an essential role of Grb2b in vivo for cell migration to the horizontal myoseptum and for the correct formation of the lymphatic vasculature, while being less critically required in intersegmental vein formation. Thus, there appear to be higher requirements for Grb2b and therefore Vegfr3 downstream signaling levels in lymphatic versus vein precursor-generating sprouts.

Pluripotent stem cells in the research for extraembryonic cell differentiation

Mouse embryonic stem cells (mESCs) are pluripotent stem cell populations derived from the preimplantation embryo and are used to study the differentiation of many types of somatic and germ cells in developing embryos. They are also used to study cell lineages of extraembryonic tissues, such as the trophectoderm (TE) and the primitive endoderm (PrE). mESC cultures are suitable systems for reproducing cellular and molecular events occurring during the differentiation of these cell types, such as changes in gene expression patterns, signaling events, and genome rearrangements although the consistency between the results obtained using mESCs and those of in vivo studies on embryos should be carefully taken into account. Since TE and PrE cells can be induced from mESCs in vitro, mESC cultures are useful systems to study differentiation of these cell lineages during development, if used appropriately. In addition, human pluripotent stem cells (hPSCs), such as human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs), are capable of generating extraembryonic lineages in vitro and are promising tools to study the differentiation of these lineages in the human embryo.

Dynamic conversion of cell sorting patterns in aggregates of embryonic stem cells with differential adhesive affinity

BACKGROUND

Mammalian early development comprises the proliferation, differentiation, and self-assembly of the embryonic cells. The classic experiment undertaken by Townes and Holtfreter demonstrated the ability of dissociated embryonic cells to sort and self-organize spontaneously into the original tissue patterns. Here, we further explored the principles and mechanisms underlying the phenomenon of spontaneous tissue organization by studying aggregation and sorting of mouse embryonic stem (ES) cells with differential adhesive affinity in culture.

RESULTS

As observed previously, in aggregates of wild-type and E-cadherin-deficient ES cells, the cell assemblies exhibited an initial sorting pattern showing wild-type cells engulfed by less adhesive E-cadherin-deficient ES cells, which fits the pattern predicted by the differential adhesive hypothesis proposed by Malcom Steinberg. However, in further study of more mature cell aggregates, the initial sorting pattern reversed, with the highly adhesive wild-type ES cells forming an outer shell enveloping the less adhesive E-cadherin-deficient cells, contradicting Steinberg's sorting principle. The outer wild-type cells of the more mature aggregates did not differentiate into endoderm, which is known to be able to sort to the exterior from previous studies. In contrast to the naive aggregates, the mature aggregates presented polarized, highly adhesive cells at the outer layer. The surface polarity was observed as an actin cap contiguously spanning across the apical surface of multiple adjacent cells, though independent of the formation of tight junctions.

CONCLUSIONS

Our experimental findings suggest that the force of differential adhesive affinity can be overcome by even subtle polarity generated from strong bilateral ligation of highly adhesive cells in determining cell sorting patterns.

KPNA2-Associated Immune Analyses Highlight the Dysregulation and Prognostic Effects of GRB2, NRAS, and Their RNA-Binding Proteins in Hepatocellular Carcinoma

Karyopherin α2 (KPNA2) was reported to be overexpressed and have unfavorable prognostic effects in many malignancies including hepatocellular carcinoma (HCC). Although its contributions to inflammatory response were reported in many studies, its specific associations with immune infiltrations and immune pathways during cancer progression were unclear. Here, we aimed to identify new markers for HCC diagnosis and prognosis through KPNA2-associated immune analyses. RNA-seq expression data of HCC datasets were downloaded from The Cancer Genome Atlas and International Cancer Genome Consortium. The gene expressions were counts per million normalized. The infiltrations of 24 kinds of immune cells in the samples were evaluated with ImmuCellAI (Immune Cell Abundance Identifier). The Spearman correlations of the immune infiltrations with KPNA2 expression were investigated, and the specific positive correlation of B-cell infiltration with KPNA2 expression in HCC tumors was identified. Fifteen genes in KEGG (Kyoto Encyclopedia of Genes and Genomes) B-cell receptor signaling pathway presented significant correlations with KPNA2 expression in HCC. Among them, GRB2 and NRAS were indicated to be independent unfavorable prognostic factors for HCC overall survival. Clinical Proteomic Tumor Analysis Consortium HCC dataset was investigated to validate the results at protein level. The upregulation and unfavorable prognostic effects of KPNA2 and GRB2 were confirmed, whereas, unlike its mRNA form, NRAS protein was presented to be downregulated and have favorable prognostic effects. Through receiver operating characteristic curve analysis, the diagnostic potential of the three proteins was shown. The RNA-binding proteins (RBPs) of KPNA2, NRAS, and GRB2, downloaded via The Encyclopedia of RNA Interactomes, were investigated for their clinical significance in HCC at protein level. An eight-RBP signature with independent prognostic value and dysregulations in HCC was identified. All the RBPs were significantly correlated with MKI67 expression and at least one of KPNA2, GRB2, and NRAS at protein level in HCC, indicating their roles in HCC progression and the regulation of the three proteins. We concluded that KPNA2, GRB2, NRAS, and their RBPs might have coordinating roles in HCC immunoregulation and progression. They might be new markers for HCC diagnosis and prognosis predication and new targets for HCC immunotherapy.

SOS GEFs in health and disease

SOS1 and SOS2 are the most universal and widely expressed family of guanine exchange factors (GEFs) capable or activating RAS or RAC1 proteins in metazoan cells. SOS proteins contain a sequence of modular domains that are responsible for different intramolecular and intermolecular interactions modulating mechanisms of self-inhibition, allosteric activation and intracellular homeostasis. Despite their homology, analyses of SOS1/2-KO mice demonstrate functional prevalence of SOS1 over SOS2 in cellular processes including proliferation, migration, inflammation or maintenance of intracellular redox homeostasis, although some functional redundancy cannot be excluded, particularly at the organismal level. Specific SOS1 gain-of-function mutations have been identified in inherited RASopathies and various sporadic human cancers. SOS1 depletion reduces tumorigenesis mediated by RAS or RAC1 in mouse models and is associated with increased intracellular oxidative stress and mitochondrial dysfunction. Since WT RAS is essential for development of RAS-mutant tumors, the SOS GEFs may be considered as relevant biomarkers or therapy targets in RAS-dependent cancers. Inhibitors blocking SOS expression, intrinsic GEF activity, or productive SOS protein-protein interactions with cellular regulators and/or RAS/RAC targets have been recently developed and shown preclinical and clinical effectiveness blocking aberrant RAS signaling in RAS-driven and RTK-driven tumors.

[Formula: see text]H, [Formula: see text]C and [Formula: see text]N assignments of human Grb2 free of ligands

Growth factor receptor-bound 2 (Grb2) is an important link in the receptor tyrosine kinase signaling cascades. It is involved in crucial processes, both physiological (mainly embryogenesis) and pathological (different types of cancer). Several binding partners of all three domains (SH3-SH2-SH3) of this adaptor protein are well described, such as ErbB family members for the SH2 domain and Sos for the SH3 domains. How the different domains interact with each other, both structurally and functionally, is still unclear. These interactions could be essential for regulation processes, and therefore are of great interest. Although a lot of structural data on Grb2 exist, they describe either individual domains, ligand-bound conformations, or frozen pictures of the protein captured by crystallography. Here we report the assignment of backbone and of [Formula: see text] chemical shifts of full-length, apo-Grb2 in solution. In addition to the assigned conformation corresponding to three well-folded domains, a set of peaks compatible with the presence of an unfolded conformation of the N-terminal SH3 domain is observed. This assignment paves the way for future studies of inter-domain interactions and dynamics that have to be taken into account when studying the regulation of Grb2 interactions and signaling pathways.

Phosphoproteomics identifies a bimodal EPHA2 receptor switch that promotes embryonic stem cell differentiation

Embryonic Stem Cell (ESC) differentiation requires complex cell signalling network dynamics, although the key molecular events remain poorly understood. Here, we use phosphoproteomics to identify an FGF4-mediated phosphorylation switch centred upon the key Ephrin receptor EPHA2 in differentiating ESCs. We show that EPHA2 maintains pluripotency and restrains commitment by antagonising ERK1/2 signalling. Upon ESC differentiation, FGF4 utilises a bimodal strategy to disable EPHA2, which is accompanied by transcriptional induction of EFN ligands. Mechanistically, FGF4-ERK1/2-RSK signalling inhibits EPHA2 via Ser/Thr phosphorylation, whilst FGF4-ERK1/2 disrupts a core pluripotency transcriptional circuit required for Epha2 gene expression. This system also operates in mouse and human embryos, where EPHA receptors are enriched in pluripotent cells whilst surrounding lineage-specified trophectoderm expresses EFNA ligands. Our data provide insight into function and regulation of EPH-EFN signalling in ESCs, and suggest that segregated EPH-EFN expression coordinates cell fate with compartmentalisation during early embryonic development.

Phosphotyrosine isosteres: past, present and future

Tyrosine phosphorylation is a critical component of signal transduction for multicellular organisms, particularly for pathways that regulate cell proliferation and differentiation. While tyrosine kinase inhibitors have become FDA-approved drugs, inhibitors of the other important components of these signaling pathways have been harder to develop. Specifically, direct phosphotyrosine (pTyr) isosteres have been aggressively pursued as inhibitors of Src homology 2 (SH2) domains and protein tyrosine phosphatases (PTPs). Medicinal chemists have produced many classes of peptide and small molecule inhibitors that mimic pTyr. However, balancing affinity with selectivity and cell penetration has made this an extremely difficult space for developing successful clinical candidates. This review will provide a comprehensive picture of the field of pTyr isosteres, from early beginnings to the current state and trajectory. We will also highlight the major protein targets of these medicinal chemistry efforts, the major classes of peptide and small molecule inhibitors that have been developed, and the handful of compounds which have been tested in clinical trials.

Grb2 binds to PTEN and regulates its nuclear translocation to maintain the genomic stability in DNA damage response

Growth factor receptor bound protein 2 (Grb2) is an adaptor protein critical for signal transduction and endocytosis, but its role in DNA damage response (DDR) remains unknown. Here, we report that either knockdown of Grb2 or overexpression of the mutated Grb2 promotes micronuclei formation in response to oxidative stress. Furthermore, Grb2 was demonstrated to interact with phosphatase and tensin homologue (PTEN; a tumor suppressor essential for nuclear stability), and the loss of Grb2 reduced the nuclear-localized PTEN, which was further decreased upon stimulation with hydrogen peroxide (H₂O₂). Overexpression of the T398A-mutated, nuclear-localized PTEN reduced micronuclei frequency in the cells deficient of functional Grb2 via rescuing the H₂O₂-dependent expression of Rad51, a protein essential for the homologous recombination (HR) repair process. Moreover, depletion of Grb2 markedly decreased the expression of Rad51 and its interaction with PTEN. Notably, Rad51 showed a preference to immunoprecipation with the T398A-PTEN mutant, and silencing of Rad51 alone accumulated micronuclei concurring with decreased expression of both Grb2 and PTEN. Our findings indicate that Grb2 interacts with PTEN and Rad51 to regulate genomic stability in DDR by mediating the nuclear translocation of PTEN to affect the expression of Rad51.

Molecular characterization and expression analysis of protein enhancer of sevenless 2B from Artemia sinica at early embryonic development and during immune response to bacterial stimulation

Protein enhancer of sevenless 2B, E(sev)2B, is a key adapter protein in the Ras/MAPK signaling pathway which has been reported to be involved in innate immunity. In this study, the gene that encodes AsE(sev)2B was isolated from A. sinica. It was found to contain a 636 bp open reading frame encoding 211 amino acids with a calculated molecular mass of 24.357 kDa and a predicted isoelectric point of 5.39. The predicted protein contains a N-terminal Src homology 3 domain (SH3), a central Src homology 2 domain (SH2), and a C-terminal Src homology 3 domain (SH3). Homology analysis revealed that AsE(sev)2B shares 49%-95% identity with E(sev)2B homologs from other species. In this study, the expression pattern and location of AsE(sev)2B during different stages of embryonic development and bacterial challenge were investigated by means of real-time qPCR, Western blotting and immunohistochemistry. Results showed that the highest expression level of AsE(sev)2B was at 0 h. After challenged by Gram-positive bacteria and Gram-negative bacteria, AsE(sev)2B was remarkably upregulated at 10⁶ cellsL^-1 bacterial concentrations. These results suggested that AsE(sev)2B plays a vital role during early embryonic development and in immune responses against bacterial challenge.

Negative feedback via RSK modulates Erk-dependent progression from naïve pluripotency

Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signalling is implicated in initiation of embryonic stem (ES) cell differentiation. The pathway is subject to complex feedback regulation. Here, we examined the ERK-responsive phosphoproteome in ES cells and identified the negative regulator RSK1 as a prominent target. We used CRISPR/Cas9 to create combinatorial mutations in RSK family genes. Genotypes that included homozygous null mutations in Rps6ka1, encoding RSK1, resulted in elevated ERK phosphorylation. These RSK-depleted ES cells exhibit altered kinetics of transition into differentiation, with accelerated downregulation of naïve pluripotency factors, precocious expression of transitional epiblast markers and early onset of lineage specification. We further show that chemical inhibition of RSK increases ERK phosphorylation and expedites ES cell transition without compromising multilineage potential. These findings demonstrate that the ERK activation profile influences the dynamics of pluripotency progression and highlight the role of signalling feedback in temporal control of cell state transitions.

Single cell expression analysis of primate-specific retroviruses-derived HPAT lincRNAs in viable human blastocysts identifies embryonic cells co-expressing genetic markers of multiple lineages

Chromosome instability and aneuploidies occur very frequently in human embryos, impairing proper embryogenesis and leading to cell cycle arrest, loss of cell viability, and developmental failures in 50–80% of cleavage-stage embryos. This high frequency of cellular extinction events represents a significant experimental obstacle challenging analyses of individual cells isolated from human preimplantation embryos. We carried out single cell expression profiling of 241 individual cells recovered from 32 human embryos during the early and late stages of viable human blastocyst (VHB) differentiation. Classification of embryonic cells was performed solely based on expression patterns of human pluripotency-associated transcripts (HPAT), which represent a family of primate-specific transposable element-derived lincRNAs highly expressed in human embryonic stem cells and regulating nuclear reprogramming and pluripotency induction. We then validated our findings by analyzing transcriptomes of 1,708 individual cells recovered from more than 100 human embryos and 259 mouse cells from more than 40 mouse embryos at different stages of preimplantation embryogenesis. HPAT's expression-guided spatiotemporal reconstruction of human embryonic development inferred from single-cell expression analysis of VHB differentiation enabled identification of telomerase-positive embryonic cells co-expressing key pluripotency regulatory genes and genetic markers of three major lineages. Follow-up validation analyses confirmed the emergence in human embryos prior to lineage segregation of telomerase-positive cells co-expressing genetic markers of multiple lineages. Observations reported in this contribution support the hypothesis of a developmental pathway of creation embryonic lineages and extraembryonic tissues from telomerase-positive pre-lineage cells manifesting multi-lineage precursor phenotype.

GATA6 phosphorylation by Erk1/2 propels exit from pluripotency and commitment to primitive endoderm

The transcription factor GATA6 and the Fgf/Ras/MAPK signaling pathway are essential for the development of the primitive endoderm (PrE), one of the two lineages derived from the pluripotent inner cell mass (ICM) of mammalian blastocysts. A mutant mouse line in which Gata6-coding exons are replaced with H2BGFP (histone H2B Green Fluorescence Protein fusion protein) was developed to monitor Gata6 promoter activity. In the Gata6-H2BGFP heterozygous blastocysts, the ICM cells that initially had uniform GFP fluorescence signal at E3.5 diverged into two populations by the 64-cell stage, either as the GFP-high PrE or the GFP-low epiblasts (Epi). However in the GATA6-null blastocysts, the originally moderate GFP expression subsided in all ICM cells, indicating that the GATA6 protein is required to maintain its own promoter activity during PrE linage commitment. In embryonic stem cells, expressed GATA6 was shown to bind and activate the Gata6 promoter in PrE differentiation. Mutations of a conserved serine residue (S264) for Erk1/2 phosphorylation in GATA6 protein drastically impacted its ability to activate its own promoter. We conclude that phosphorylation of GATA6 by Erk1/2 compels exit from pluripotent state, and the phosphorylation propels a GATA6 positive feedback regulatory circuit to compel PrE differentiation. Our findings resolve the longstanding question on the dual requirements of GATA6 and Ras/MAPK pathway for PrE commitment of the pluripotent ICM.

Grb2 regulates the proliferation of hematopoietic stem and progenitors cells

Although Hematopoietic Stem and Progenitor Cell (HSPC) proliferation, survival and expansion have been shown to be supported by the cooperative action of different cytokines, little is known about the intracellular signaling pathways that are activated by cytokines upon binding to their receptors. Our study showed that Growth factor receptor-bound protein 2 (Grb2) mRNAs are preferentially expressed in HSC compared to progenitors and differentiated cells of the myeloid and erythroid lineages. Conditional deletion of Grb2 induced a rapid decline of erythroid and myeloid progenitors and a progressive decline of HSC numbers in steady state conditions. We showed that when transplanted, Grb2 deleted bone marrow cells could not reconstitute irradiated recipients. Strinkingly, Grb2 deletion did not modify HSPC quiescence, but impaired LT-HSC and progenitors ability to respond a proliferative signal induced by 5FU in vivo and by various cytokines in vitro. We showed finally that Grb2 links IL3 signaling to the ERK/MAPK proliferative pathway and that both SH2 and SH3 domains of Grb2 are crucial for IL3 signaling in progenitor cells. Our findings position Grb2 as a key adaptor that integrates various cytokines response in cycling HSPC.

MPZL1 forms a signalling complex with GRB2 adaptor and PTPN11 phosphatase in HER2-positive breast cancer cells

HER2/ErbB2 is overexpressed in a significant fraction of breast tumours and is associated with a poor prognosis. The adaptor protein GRB2 interacts directly with activated HER2 and is sufficient to transmit oncogenic signals. However, the consequence of HER2 activation on global GRB2 signalling networks is poorly characterized. We performed GRB2 affinity purification combined with mass spectrometry analysis of associated proteins in a HER2+ breast cancer model to delineate GRB2-nucleated protein interaction networks. We report the identification of the transmembrane protein MPZL1 as a new GRB2-associated protein. Our data show that the PTPN11 tyrosine phosphatase acts as a scaffold to bridge the association between GRB2 and MPZL1 in a phosphotyrosine-dependent manner. We further demonstrate that the formation of this MPZL1-PTPN11-GRB2 complex is triggered by cell attachment to fibronectin. Thus, our data support the importance of this new signalling complex in the control of cell adhesion of HER2+ breast cancer cells, a key feature of the metastatic process.

Four simple rules that are sufficient to generate the mammalian blastocyst

Early mammalian development is both highly regulative and self-organizing. It involves the interplay of cell position, predetermined gene regulatory networks, and environmental interactions to generate the physical arrangement of the blastocyst with precise timing. However, this process occurs in the absence of maternal information and in the presence of transcriptional stochasticity. How does the preimplantation embryo ensure robust, reproducible development in this context? It utilizes a versatile toolbox that includes complex intracellular networks coupled to cell-cell communication, segregation by differential adhesion, and apoptosis. Here, we ask whether a minimal set of developmental rules based on this toolbox is sufficient for successful blastocyst development, and to what extent these rules can explain mutant and experimental phenotypes. We implemented experimentally reported mechanisms for polarity, cell-cell signaling, adhesion, and apoptosis as a set of developmental rules in an agent-based in silico model of physically interacting cells. We find that this model quantitatively reproduces specific mutant phenotypes and provides an explanation for the emergence of heterogeneity without requiring any initial transcriptional variation. It also suggests that a fixed time point for the cells' competence of fibroblast growth factor (FGF)/extracellular signal-regulated kinase (ERK) sets an embryonic clock that enables certain scaling phenomena, a concept that we evaluate quantitatively by manipulating embryos in vitro. Based on these observations, we conclude that the minimal set of rules enables the embryo to experiment with stochastic gene expression and could provide the robustness necessary for the evolutionary diversification of the preimplantation gene regulatory network.

Spatiotemporal Reconstruction of the Human Blastocyst by Single-Cell Gene-Expression Analysis Informs Induction of Naive Pluripotency

Human preimplantation embryo development involves complex cellular and molecular events that lead to the establishment of three cell lineages in the blastocyst: trophectoderm, primitive endoderm, and epiblast. Owing to limited resources of biological specimens, our understanding of how the earliest lineage commitments are regulated remains narrow. Here, we examined gene expression in 241 individual cells from early and late human blastocysts to delineate dynamic gene-expression changes. We distinguished all three lineages and further developed a 3D model of the inner cell mass and trophectoderm in which individual cells were mapped into distinct expression domains. We identified in silico precursors of the epiblast and primitive endoderm lineages and revealed a role for MCRS1, TET1, and THAP11 in epiblast formation and their ability to induce naive pluripotency in vitro. Our results highlight the potential of single-cell gene-expression analysis in human preimplantation development to instruct human stem cell biology.

Distinct Requirements for FGFR1 and FGFR2 in Primitive Endoderm Development and Exit from Pluripotency

Activation of the FGF signaling pathway during preimplantation development of the mouse embryo is known to be essential for differentiation of the inner cell mass and the formation of the primitive endoderm (PrE). We now show using fluorescent reporter knockin lines that Fgfr1 is expressed in all cell populations of the blastocyst, while Fgfr2 expression becomes restricted to extraembryonic lineages, including the PrE. We further show that loss of both receptors prevents the development of the PrE and demonstrate that FGFR1 plays a more prominent role in this process than FGFR2. Finally, we document an essential role for FGFRs in embryonic stem cell (ESC) differentiation, with FGFR1 again having a greater influence than FGFR2 in ESC exit from the pluripotent state. Collectively, these results identify mechanisms through which FGF signaling regulates inner cell mass lineage restriction and cell commitment during preimplantation development.

Mechanism of SOS PR-domain autoinhibition revealed by single-molecule assays on native protein from lysate

The guanine nucleotide exchange factor (GEF) Son of Sevenless (SOS) plays a critical role in signal transduction by activating Ras. Here we introduce a single-molecule assay in which individual SOS molecules are captured from raw cell lysate using Ras-functionalized supported membrane microarrays. This enables characterization of the full-length SOS protein, which has not previously been studied in reconstitution due to difficulties in purification. Our measurements on the full-length protein reveal a distinct role of the C-terminal proline-rich (PR) domain to obstruct the engagement of allosteric Ras independently of the well-known N-terminal domain autoinhibition. This inhibitory role of the PR domain limits Grb2-independent recruitment of SOS to the membrane through binding of Ras·GTP in the SOS allosteric binding site. More generally, this assay strategy enables characterization of the functional behaviour of GEFs with single-molecule precision but without the need for purification.

Transcriptome analyses of rhesus monkey preimplantation embryos reveal a reduced capacity for DNA double-strand break repair in primate oocytes and early embryos

Preimplantation embryogenesis encompasses several critical events including genome reprogramming, zygotic genome activation (ZGA), and cell-fate commitment. The molecular basis of these processes remains obscure in primates in which there is a high rate of embryo wastage. Thus, understanding the factors involved in genome reprogramming and ZGA might help reproductive success during this susceptible period of early development and generate induced pluripotent stem cells with greater efficiency. Moreover, explaining the molecular basis responsible for embryo wastage in primates will greatly expand our knowledge of species evolution. By using RNA-seq in single and pooled oocytes and embryos, we defined the transcriptome throughout preimplantation development in rhesus monkey. In comparison to archival human and mouse data, we found that the transcriptome dynamics of monkey oocytes and embryos were very similar to those of human but very different from those of mouse. We identified several classes of maternal and zygotic genes, whose expression peaks were highly correlated with the time frames of genome reprogramming, ZGA, and cell-fate commitment, respectively. Importantly, comparison of the ZGA-related network modules among the three species revealed less robust surveillance of genomic instability in primate oocytes and embryos than in rodents, particularly in the pathways of DNA damage signaling and homology-directed DNA double-strand break repair. This study highlights the utility of monkey models to better understand the molecular basis for genome reprogramming, ZGA, and genomic stability surveillance in human early embryogenesis and may provide insights for improved homologous recombination-mediated gene editing in monkey.

Properties of embryoid bodies

Embryoid bodies (EBs) have been popular in vitro differentiation models for pluripotent stem cells for more than five decades. Initially, defined as aggregates formed by embryonal carcinoma cells, EBs gained more prominence after the derivation of karyotypically normal embryonic stem cells from early mouse blastocysts. In many cases, formation of EBs constitutes an important initial step in directed differentiation protocols aimed at generated specific cell types from undifferentiated stem cells. Indeed state-of-the-art protocols for directed differentiation of cardiomyocytes still rely on this initial EB step. Analyses of spontaneous differentiation of embryonic stem cells in EBs have yielded important insights into the molecules that direct primitive endoderm differentiation and many of the lessons we have learned about the signals and transcription factors governing this differentiation event is owed to EB models, which later were extensively validated in studies of early mouse embryos. EBs show a degree of self-organization that mimics some aspects of early embryonic development, but with important exceptions. Recent studies that employ modern signaling reporters and tracers of lineage commitment have revealed both the strengths and the weaknesses of EBs as a model of embryonic axis formation. In this review, we discuss the history, application, and future potential of EBs as an experimental model. WIREs Dev Biol 2017, 6:e259. doi: 10.1002/wdev.259 For further resources related to this article, please visit the WIREs website.

The Genetic Regulation of Cell Fate During Preimplantation Mouse Development

The adult body is estimated to contain several hundred distinct cell types, each with a specialized physiological function. Failure to maintain cell fate can lead to devastating diseases and cancer, but understanding how cell fates are assigned and maintained during animal development provides new opportunities for human health intervention. The mouse is a premier model for evaluating the genetic regulation of cell fate during development because of the wide variety of tools for measuring and manipulating gene expression levels, the ability to access embryos at desired developmental stages, and the similarities between mouse and human development, particularly during the early stages of development. During the first 3 days of mouse development, the preimplantation embryo sets aside cells that will contribute to the extraembryonic tissues. The extraembryonic tissues are essential for establishing pregnancy and ensuring normal fetal development in both mice and humans. Genetic analyses of mouse preimplantation development have permitted identification of genes that are essential for specification of the extraembryonic lineages. In this chapter, we review the tools and concepts of mouse preimplantation development. We describe genes that are essential for cell fate specification during preimplantation stages, and we describe diverse models proposed to account for the mechanisms of cell fate specification during early development.

A decade of transcription factor-mediated reprogramming to pluripotency

The past 10 years have seen great advances in our ability to manipulate cell fate, including the induction of pluripotency in vitro to generate induced pluripotent stem cells (iPSCs). This process proved to be remarkably simple from a technical perspective, only needing the host cell and a defined cocktail of transcription factors, with four factors - octamer-binding protein 3/4 (OCT3/4), SOX2, Krüppel-like factor 4 (KLF4) and MYC (collectively referred to as OSKM) - initially used. The mechanisms underlying transcription factor-mediated reprogramming are still poorly understood; however, several mechanistic insights have recently been obtained. Recent years have also brought significant progress in increasing the efficiency of this technique, making it more amenable to applications in the fields of regenerative medicine, disease modelling and drug discovery.

Fibroblast growth factor 4-induced migration of porcine trophectoderm cells is mediated via the AKT cell signaling pathway

During early pregnancy, a well-coordinated communication network between the conceptus and maternal uterus is especially crucial in pigs in which there is a protracted pre-attachment phase prior to implantation. This network is regulated by an astonishing number of molecules such as growth factors. Fibroblast growth factor 4 (FGF4) is a multipotent growth factor that elicits diverse biological actions on various types of cells and tissues. In pigs, FGF4 and its receptors are expressed in the uterine endometrium and conceptus during early pregnancy, but less is known about the FGF4-mediated regulation of conceptus growth during peri-implantation period of pregnancy. Therefore, the aims of the present study were to investigate: 1) expression of endometrial FGF4 mRNA during early pregnancy; 2) up-regulation of FGF receptor expression in porcine trophectoderm (pTr) cells in response to FGF4; and 3) FGF-induced intracellular signaling and cellular activities in pTr cells. In vitro cultured pTr cells incubated with different concentrations of recombinant FGF4 (0-50 ng/ml) responded with a dose-dependent increase in AKT phosphorylation of 2.9-fold at 20 ng/ml FGF4. Within 30 min after treatment with 20 ng/ml FGF4, the abundances of p-AKT, p-P90RSK and p-RPS6 proteins increased 2.1-, 5.2- and 3.2-fold, respectively, and then returned to basal levels by 120 min. To ensure that the stimulatory effect of FGF4 on AKT signaling was p-AKT-dependent, pTr cells were pre-incubated with an AKT inhibitor (LY294002) for 1 h prior to FGF4 treatment. 20 μM of LY294002 decreased FGF4-induced p-AKT, p-P90RSK and p-RPS6 proteins. Immunofluorescence analyses revealed that p-RPS6 proteins were abundant within the cytoplasm of FGF4-treated cells, but present at basal levels in the presence of LY294002. Furthermore, FGF4 increased migration of pTr cells and LY294002 significantly reduced this effect. Results of the present study suggest that activation of the FGF receptor(s) on trophectoderm cells by FGF4 secreted by conceptus/endometrium transduces its signal through the phosphatidylinositol 3-kinase (PI3K)/AKT pathway which is linked to migration of trophectoderm cells that is critical to development of the porcine conceptus.