Activation of Rac1-PI3K/Akt is required for epidermal growth factor-induced PAK1 activation and cell migration in MDA-MB-231 breast cancer cells

Macropinocytosis mediates resistance to loss of glutamine transport in triple-negative breast cancer

Triple-negative breast cancer (TNBC) metabolism and cell growth uniquely rely on glutamine uptake by the transporter ASCT2. Despite previous data reporting cell growth inhibition after ASCT2 knockdown, we here show that ASCT2 CRISPR knockout is tolerated by TNBC cell lines. Despite the loss of a glutamine transporter and low rate of glutamine uptake, intracellular glutamine steady-state levels were increased in ASCT2 knockout compared to control cells. Proteomics analysis revealed upregulation of macropinocytosis, reduction in glutamine efflux and increased glutamine synthesis in ASCT2 knockout cells. Deletion of ASCT2 in the TNBC cell line HCC1806 induced a strong increase in macropinocytosis across five ASCT2 knockout clones, compared to a modest increase in ASCT2 knockdown. In contrast, ASCT2 knockout impaired cell proliferation in the non-macropinocytic HCC1569 breast cancer cells. These data identify macropinocytosis as a critical secondary glutamine acquisition pathway in TNBC and a novel resistance mechanism to strategies targeting glutamine uptake alone. Despite this adaptation, TNBC cells continue to rely on glutamine metabolism for their growth, providing a rationale for targeting of more downstream glutamine metabolism components.

PlexinA1 promotes gastric cancer migration through preventing MICAL1 protein ubiquitin/proteasome-mediated degradation in a Rac1-dependent manner

Metastasis promotes the development of tumors and is a significant cause of gastric cancer death. For metastasis to proceed, tumor cells must become mobile by modulating their cytoskeleton. MICAL1 (Molecule Interacting with CasL1) is known as an actin cytoskeleton regulator, but the mechanisms by which it drives gastric cancer cell migration are still unclear. Analysis of gastric cancer tissues revealed that MICAL1 expression is dramatically upregulated in stomach adenocarcinoma (STAD) samples as compared to noncancerous stomach tissues. Patients with high MICAL1 expression had shorter overall survival (OS), post-progression survival (PPS) and first-progression survival (FPS) compared with patients with low MICAL1 expression. RNAi-mediated silencing of MICAL1 inhibited the expression of Vimentin, a protein involved in epithelial-mesenchymal transition. This effect correlates with a significant reduction in gastric cancer cell migration. MICAL1 overexpression reversed these preventive effects. Immunoprecipitation experiments and immunofluorescence assays revealed that PlexinA1 forms a complex with MICAL1. Importantly, specific inhibition of PlexinA1 blocked the Rac1 activation and ROS production, which, in turn, impaired MICAL1 protein stability by accelerating MICAL1 ubiquitin/proteasome-dependent degradation. Overexpression of PlexinA1 enhanced Rac1 activation, ROS production, MICAL1 and Vimentin expressions, and favored cell migration. In conclusion, this study identified MICAL1 as an important facilitator of gastric cancer cell migration, at least in part, by affecting Vimentin expression and PlexinA1 promotes gastric cancer cell migration by binding to and suppressing MICAL1 degradation in a Rac1/ROS-dependent manner.

Targetable leukemia dependency on noncanonical PI3Kγ signaling

Phosphoinositide 3-kinase gamma (PI3Kγ) is implicated as a target to repolarize tumor-associated macrophages and promote anti-tumor immune responses in solid cancers. However, cancer cell-intrinsic roles of PI3Kγ are unclear. Here, by integrating unbiased genome-wide CRISPR interference screening with functional analyses across acute leukemias, we define a selective dependency on the PI3Kγ complex in a high-risk subset that includes myeloid, lymphoid, and dendritic lineages. This dependency is characterized by innate inflammatory signaling and activation of phosphoinositide 3-kinase regulatory subunit 5 ( PIK3R5 ), which encodes a regulatory subunit of PI3Kγ and stabilizes the active enzymatic complex. Mechanistically, we identify p21 (RAC1) activated kinase 1 (PAK1) as a noncanonical substrate of PI3Kγ that mediates this cell-intrinsic dependency independently of Akt kinase. PI3Kγ inhibition dephosphorylates PAK1, activates a transcriptional network of NFκB-related tumor suppressor genes, and impairs mitochondrial oxidative phosphorylation. We find that treatment with the selective PI3Kγ inhibitor eganelisib is effective in leukemias with activated PIK3R5 , either at baseline or by exogenous inflammatory stimulation. Notably, the combination of eganelisib and cytarabine prolongs survival over either agent alone, even in patient-derived leukemia xenografts with low baseline PIK3R5 expression, as residual leukemia cells after cytarabine treatment have elevated G protein-coupled purinergic receptor activity and PAK1 phosphorylation. Taken together, our study reveals a targetable dependency on PI3Kγ/PAK1 signaling that is amenable to near-term evaluation in patients with acute leukemia.

Integrins and Actions of Androgen in Breast Cancer

Androgen has been shown to regulate male physiological activities and cancer proliferation. It is used to antagonize estrogen-induced proliferative effects in breast cancer cells. However, evidence indicates that androgen can stimulate cancer cell growth in estrogen receptor (ER)-positive and ER-negative breast cancer cells via different types of receptors and different mechanisms. Androgen-induced cancer growth and metastasis link with different types of integrins. Integrin αvβ3 is predominantly expressed and activated in cancer cells and rapidly dividing endothelial cells. Programmed death-ligand 1 (PD-L1) also plays a vital role in cancer growth. The part of integrins in action with androgen in cancer cells is not fully mechanically understood. To clarify the interactions between androgen and integrin αvβ3, we carried out molecular modeling to explain the potential interactions of androgen with integrin αvβ3. The androgen-regulated mechanisms on PD-L1 and its effects were also addressed.

Role of microRNAs in regulation of doxorubicin and paclitaxel responses in lung tumor cells

Lung cancer as the leading cause of cancer related mortality is always one of the main global health challenges. Despite the recent progresses in therapeutic methods, the mortality rate is still significantly high among lung cancer patients. A wide range of therapeutic methods including chemotherapy, radiotherapy, and surgery are used to treat lung cancer. Doxorubicin (DOX) and Paclitaxel (TXL) are widely used as the first-line chemotherapeutic drugs in lung cancer. However, there is a significant high percentage of DOX/TXL resistance in lung cancer patients, which leads to tumor recurrence and metastasis. Considering, the side effects of these drugs in normal tissues, it is required to clarify the molecular mechanisms of DOX/TXL resistance to introduce the efficient prognostic and therapeutic markers in lung cancer. MicroRNAs (miRNAs) have key roles in regulation of different pathophysiological processes including cell division, apoptosis, migration, and drug resistance. MiRNA deregulations are widely associated with chemo resistance in various cancers. Therefore, considering the importance of miRNAs in chemotherapy response, in the present review, we discussed the role of miRNAs in regulation of DOX/TXL response in lung cancer patients. It has been reported that miRNAs mainly induced DOX/TXL sensitivity in lung tumor cells by the regulation of signaling pathways, autophagy, transcription factors, and apoptosis. This review can be an effective step in introducing miRNAs as the non-invasive prognostic markers to predict DOX/TXL response in lung cancer patients.

Rac1 promotes the reprogramming of glucose metabolism and the growth of colon cancer cells through upregulating SOX9

Metabolic reprogramming is the survival rule of tumor cells, and tumor cells can meet their high metabolic requirements by changing the energy metabolism mode. Metabolic reprogramming of tumor cells is an important biochemical basis of tumor malignant phenotypes. Ras-related C3 botulinum toxin substrate 1 (Rac1) is abnormally expressed in a variety of tumors and plays an important role in the proliferation, invasion, and migration of tumor cells. However, the role of Rac1 in tumor metabolic reprogramming is still unclear. Herein, we revealed that Rac1 was highly expressed in colon cancer tissues and cell lines. Rac1 promotes the proliferation, migration, and invasion of colon cancer cells by upregulating SOX9, which as a transcription factor can directly bind to the promoters of HK2 and G6PD genes and regulate their transcriptional activity. Rac1 upregulates the expression of SOX9 through the PI3K/AKT signaling pathway. Moreover, Rac1 can promote glycolysis and the activation of the pentose phosphate pathway in colon cancer cells by mediating the axis of SOX9/HK2/G6PD. These findings reveal novel regulatory axes involving Rac1/SOX9/HK2/G6PD in the development and progression of colon cancer, providing novel promising therapeutic targets.

A ROS/Akt/NF-κB Signaling Cascade Mediates Epidermal Growth Factor-Induced Epithelial-Mesenchymal Transition and Invasion in Human Breast Cancer Cells

BACKGROUND

As one of the most widely used anti-diabetic drugs for type II diabetes, metformin has been shown to exhibit anti-cancer activity in recent years. Epidermal growth factor (EGF) and its receptor, EGFR, play important roles in cancer metastasis in various tumors, including breast cancer. Epithelial-mesenchymal transition (EMT) is a critical process for cancer invasion and metastasis. In this study, we use EGF as a metastatic inducer to investigate the effect of metformin on cancer cell migration, invasion and EMT.

METHODS

Human breast cancer MCF-7 cells were exposed to EGF with or without metformin or N-acetyl cysteine (NAC). The effects of metformin on breast cancer cell proliferation were analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The production of reactive oxygen species (ROS) was tested using 2,7-dichlorodihydrofluorecein diacetate (DCFH-DA). The migratory and invasive abilities of tumor cells were analyzed using wound healing assay and transwell invasion assay, respectively. The expressions of E-cadherin, N-cadherin and Snail were tested using real-time quantitative polymerase chain reaction (qRT-PCR) and western blotting at mRNA and protein levels. The activation of protein kinase B (Akt) and nuclear factor kappa B (NF-κB) were measured by western blotting.

RESULTS

Our results showed that metformin inhibited breast cancer cell proliferation in a dose-dependent manner with or without EGF. EGF-induced alterations in cell morphology that are characteristic of EMT were reversed by metformin. Metformin also inhibited the EGF-modulated expression of E-cadherin, N-cadherin and Snail and further suppressed cell invasion and migration. In addition, metformin suppressed EGF-induced phosphorylation of Akt and NF-κB. ROS is involved in EGF-induced cancer invasion and activation of phosphatidylinositol 3-kinase (PI3K)/Akt/NF-κB pathway.

CONCLUSION

Taken together, these data indicate that metformin suppresses EGF-induced breast cancer cell migration, invasion and EMT through the inhibition of the PI3K/Akt/NF-κB pathway. These results provide a novel mechanism to explain the role of metformin as a potent anti-metastatic agent in breast cancer cells.

Pan-cancer gene expression analysis: Identification of deregulated autophagy genes and drugs to target them

Identifying suitable deregulated targets in autophagy pathway is essential for developing autophagy modulating cancer therapies. With this aim, we systematically analyzed the expression levels of genes that contribute to the execution of autophagy in 21 cancers. Deregulated genes for 21 cancers were analyzed using the level 3 mRNA data from TCGAbiolinks. A total of 574 autophagy genes were mapped to the deregulated genes across 21 cancers. PPI network, cluster analysis, gene enrichment, gene ontology, KEGG pathway, patient survival, protein expression and cMap analysis were performed. Among the autophagy genes, 260 were upregulated, and 43 were downregulated across pan-cancer. The upregulated autophagy genes - CDKN2A and BIRC5 - were the most frequent signatures in cancers and could be universal cancer biomarkers. Significant involvement of autophagy process was found in 8 cancers (CHOL, HNSC, GBM, KICH, KIRC, KIRP, LIHC and SARC). Fifteen autophagy hub genes (ATP6V0C, BIRC5, HDAC1, IL4, ITGB1, ITGB4, MAPK3, mTOR, cMYC, PTK2, SRC, TCIRG1, TP63, TP73 and ULK1) were found to be linked with patients survival and also expressed in cancer patients tissue samples, making them as potential drug targets for these cancers. The deregulated autophagy genes were further used to identify drugs Losartan, BMS-345541, Embelin, Abexinostat, Panobinostat, Vorinostat, PD-184352, PP-1, XMD-1150, Triplotide, Doxorubicin and Ouabain, which could target one or more autophagy hub genes. Overall, our findings shed light on the most frequent cancer-associated autophagy genes, potential autophagy targets and molecules for cancer treatment. These findings can accelerate autophagy modulation in cancer therapy.

Long non-coding RNA LBX2-AS1 predicts poor survival of colon cancer patients and promotes its progression via regulating miR-627-5p/RAC1/PI3K/AKT pathway

Colon cancer is one of the most prevalent malignant tumors across the world. Increasing studies have demonstrated that long non-coding RNAs (lncRNAs) take part in colon cancer development. Our study intends to explore the expression characteristics of LBX2-AS1, a novel lncRNA, in colon cancer and its underlying mechanisms. The results illustrated that LBX2-AS1 level was substantially increased in colon cancer tissues and was obviously correlated with the tumor volume and early distant metastasis of patients. Besides, overexpression of LBX2-AS1 remarkably boosted growth, proliferation, and metastasis and restrained apoptosis in colon cancer cells, whereas LBX2-AS1 knockdown produced the opposite effect. On the other hand, miR-627-5p, down-regulated in colon cancer tissues, was negatively associated with LBX2-AS1 expression. Functional experiments showed that miR-627-5p suppressed colon cancer growth. Mechanistically, LBX2-AS1, as an endogenous competitive RNA, targeted miR-627-5p and restrained its expression, while miR-627-5p targeted and negatively regulated the RAC1/PI3K/AKT axis. Collectively, this study has revealed that LBX2-AS1 is a poor prognostic factor of colon cancer and can regulate colon cancer progression by regulating the miR-627-5p/RAC1/PI3K/AKT pathway.

Carboxyl-Functionalized Carbon Nanotubes Loaded with Cisplatin Promote the Inhibition of PI3K/Akt Pathway and Suppress the Migration of Breast Cancer Cells

PI3K/Akt signaling is one of the most frequently dysregulated pathways in cancer, including triple-negative breast cancer. With considerable roles in tumor growth and proliferation, this pathway is studied as one of the main targets in controlling the therapies' efficiency. Nowadays, the development of nanoparticle-drug conjugates attracts a great deal of attention due to the advantages they provide in cancer treatment. Hence, the main purpose of this study was to design a nanoconjugate based on single-walled carbon nanotubes functionalized with carboxyl groups (SWCNT-COOH) and cisplatin (CDDP) and to explore the potential of inhibiting the PI3K/Akt signaling pathway. MDA-MB-231 cells were exposed to various doses (0.01-2 µg/mL SWCNT-COOH and 0.00632-1.26 µg/mL CDDP) of SWCNT-COOH-CDDP and free components for 24 and 48 h. In vitro biological tests revealed that SWCNT-COOH-CDDP had a high cytotoxic effect, as shown by a time-dependent decrease in cell viability and the presence of a significant number of dead cells in MDA-MB-231 cultures at higher doses. Moreover, the nanoconjugates induced the downregulation of PI3K/Akt signaling, as revealed by the decreased expression of PI3K and p-Akt in parallel with PTEN activation, the promotion of Akt protein degradation, and inhibition of tumor cell migration.

Cytoplasmic P120ctn Promotes Gefitinib Resistance in Lung Cancer Cells by Activating PAK1 and ERK Pathway

Our previous studies indicated that cytoplasmic p120ctn mediated epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKI) resistance in lung cancer. In the present study, we aim to further explore the underlying molecular mechanisms. Immunohistochemistry detected PAK1, Cdc42, and Rac1 expression in lung cancer with cytoplasmic p120ctn. Immunoblotting, protein activity analysis, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide evaluated p120ctn location, PAK1, Cdc42/Rac1, and extracellular signal-regulated kinase (ERK) activity in response to TKI treatment in HCC827 and PC9 cell lines, as well as the cell sensitivity to Gefitinib. Most non-small cell lung cancer patients with cytoplasmic p120ctn showed enhanced PAK1 and Cdc42/Rac1. When Gefitinib resistance was induced, cytoplasmic p120ctn is accompanied with increasing PAK1 and Cdc42/Rac1. Cytoplasmic p120ctn activated ERK via PAK1, while PAK1 downregulation attenuated ERK activation by cytoplasmic p120ctn. After Cdc42/Rac1 inhibition, cytoplasmic p120ctn could not activate PAK1. Cytoplasmic p120ctn activates PAK1 via Cdc42/Rac1 activation, constitutively activates ERK in the EGFR downstream signaling, and promotes EGFR-TKI resistance in lung cancer cells. The current study will aid to screen the subpopulation patients who would benefit from therapy with first-generation EGFR-TKIs.

Role of the V1G1 subunit of V-ATPase in breast cancer cell migration

V-ATPase is a large multi-subunit complex that regulates acidity of intracellular compartments and of extracellular environment. V-ATPase consists of several subunits that drive specific regulatory mechanisms. The V1G1 subunit, a component of the peripheral stalk of the pump, controls localization and activation of the pump on late endosomes and lysosomes by interacting with RILP and RAB7. Deregulation of some subunits of the pump has been related to tumor invasion and metastasis formation in breast cancer. We observed a decrease of V1G1 and RAB7 in highly invasive breast cancer cells, suggesting a key role of these proteins in controlling cancer progression. Moreover, in MDA-MB-231 cells, modulation of V1G1 affected cell migration and matrix metalloproteinase activation in vitro, processes important for tumor formation and dissemination. In these cells, characterized by high expression of EGFR, we demonstrated that V1G1 modulates EGFR stability and the EGFR downstream signaling pathways that control several factors required for cell motility, among which RAC1 and cofilin. In addition, we showed a key role of V1G1 in the biogenesis of endosomes and lysosomes. Altogether, our data describe a new molecular mechanism, controlled by V1G1, required for cell motility and that promotes breast cancer tumorigenesis.

Human Costars Family Protein ABRACL Modulates Actin Dynamics and Cell Migration and Associates with Tumorigenic Growth

Regulation of cellular actin dynamics is pivotal in driving cell motility. During cancer development, cells migrate to invade and spread; therefore, dysregulation of actin regulators is often associated with cancer progression. Here we report the role of ABRACL, a human homolog of the Dictyostelium actin regulator Costars, in migration and tumorigenic growth of cancer cells. We found a correlation between ABRACL expression and the migratory ability of cancer cells. Cell staining revealed the colocalization of ABRACL and F-actin signals at the leading edge of migrating cells. Analysis of the relative F-/G-actin contents in cells lacking or overexpressing ABRACL suggested that ABRACL promotes cellular actin distribution to the polymerized fraction. Physical interaction between ABRACL and cofilin was supported by immunofluorescence staining and proximity ligation. Additionally, ABRACL hindered cofilin-simulated pyrene F-actin fluorescence decay in vitro, indicating a functional interplay. Lastly, analysis on a colorectal cancer cohort demonstrated that high ABRACL expression was associated with distant metastasis, and further exploration showed that depletion of ABRACL expression in colon cancer cells resulted in reduced cell proliferation and tumorigenic growth. Together, results suggest that ABRACL modulates actin dynamics through its interaction with cofilin and thereby regulates cancer cell migration and participates in cancer pathogenesis.

P21‑activated kinase 1 mediates angiotensin II‑induced differentiation of human atrial fibroblasts via the JNK/c‑Jun pathway

Cardiac fibrosis is a common pathophysiological condition involved in numerous types of cardiovascular disease. The renin‑angiotensin system, particularly angiotensin II (AngII), serves an important role in cardiac fibrosis and remodeling. Furthermore, p21‑activated kinase 1 (PAK1) is a highly conserved serine/threonine protein kinase, which is abundantly expressed in all regions of the heart. However, the role of PAK1 in AngII‑mediated activation of cardiac fibroblasts remains unknown. Therefore, the present study aimed to investigate the role of PAK1 in cardiac fibroblasts and its underlying mechanisms. Human cardiac fibroblasts (HCFs) were cultured and treated with PAK1 inhibitor IPA‑3 or transduced with PAK1 short hairpin (sh)RNA by lentiviral particles to silence PAK1 expression levels. Subsequently, the cell proliferation and migration abilities of the HCFs were determined. Western blot analysis was used to detect the phosphorylation status of Janus kinase (JNK) and c‑Jun. A Cell Counting Kit‑8 assay showed that PAK1 inhibition following treatment of HCFs with 5 µM IPA‑3 or PAK1‑shRNA, significantly attenuated AngII‑induced proliferation of fibroblasts. In addition, wound healing and Transwell migration assays demonstrated that inhibition of PAK1 significantly inhibited AngII‑induced cell migration. Finally, decreased PAK1 expression levels downregulated AngII‑mediated upregulation of α‑smooth muscle actin (α‑SMA), collagen I, phosphorylated (p)‑JNK and p‑c‑Jun, a downstream molecule of JNK signaling. These findings indicate that PAK1 contributes to AngII‑induced proliferation, migration and transdifferentiation of HCFs via the JNK/c‑Jun pathway.

Rho GTPases in cancer radiotherapy and metastasis

Despite treatment advances, radioresistance and metastasis markedly impair the benefits of radiotherapy to patients with malignancies. Functioning as molecular switches, Rho guanosine triphosphatases (GTPases) have well-recognized roles in regulating various downstream signaling pathways in a wide range of cancers. In recent years, accumulating evidence indicates the involvement of Rho GTPases in cancer radiotherapeutic efficacy and metastasis, as well as radiation-induced metastasis. The functions of Rho GTPases in radiotherapeutic efficacy are divergent and context-dependent; thereby, a comprehensive integration of their roles and correlated mechanisms is urgently needed. This review integrates current evidence supporting the roles of Rho GTPases in mediating radiotherapeutic efficacy and the underlying mechanisms. In addition, their correlations with metastasis and radiation-induced metastasis are discussed. Under the prudent application of Rho GTPase inhibitors based on critical evaluations of biological contexts, targeting Rho GTPases can be a promising strategy in overcoming radioresistance and simultaneously reducing the metastatic potential of tumor cells.

Y-27632 Induces Neurite Outgrowth by Activating the NOX1-Mediated AKT and PAK1 Phosphorylation Cascades in PC12 Cells

Y-27632 is known as a selective Rho-associated coiled coil-forming kinase (ROCK) inhibitor. Y-27632 has been shown to induce neurite outgrowth in several neuronal cells. However, the precise molecular mechanisms linking neurite outgrowth to Y-27632 are not completely understood. In this study, we examined the ability of Y-27632 to induce neurite outgrowth in PC12 cells and evaluated the signaling cascade. The effect of Y-27632 on the neurite outgrowth was inhibited by reactive oxygen species (ROS) scavengers such as N-acetyl cysteine (NAC) and trolox. Furthermore, Y-27632-induced neurite outgrowth was not triggered by NADPH oxidase 1 (NOX1) knockdown or diphenyleneiodonium (DPI), a NOX inhibitor. Suppression of the Rho-family GTPase Rac1, which is under the negative control of ROCK, with expression of the dominant negative Rac1 mutant (Rac1N17) prevented Y-27632-induced neurite outgrowth. Moreover, the Rac1 inhibitor NSC23766 prevented Y-27632-induced AKT and p21-activated kinase 1 (PAK1) activation. AKT inhibition with MK2206 suppressed Y-27632-induced PAK1 phosphorylation and neurite outgrowth. In conclusion, our results suggest that Rac1/NOX1-dependent ROS generation and subsequent activation of the AKT/PAK1 cascade contribute to Y-27632-induced neurite outgrowth in PC12 cells.

Identification of osteoporosis markers through bioinformatic functional analysis of serum proteome

Osteoporosis is a severe chronic skeletal disorder that increases the risks of disability and mortality; however, the mechanism of this disease and the protein markers for prognosis of osteoporosis have not been well characterized. This study aims to characterize the imbalanced serum proteostasis, the disturbed pathways, and potential serum markers in osteoporosis by using a set of bioinformatic analyses. In the present study, the large-scale proteomics datasets (PXD006464) were adopted from the Proteome Xchange database and processed with MaxQuant. The differentially expressed serum proteins were identified. The biological process and molecular function were analyzed. The protein-protein interactions and subnetwork modules were constructed. The signaling pathways were enriched. We identified 209 upregulated and 230 downregulated serum proteins. The bioinformatic analyses revealed a highly overlapped functional protein classification and the gene ontology terms between the upregulated and downregulated protein groups. Protein-protein interactions and pathway analyses showed a high enrichment in protein synthesis, inflammation, and immune response in the upregulated proteins, and cell adhesion and cytoskeleton regulation in the downregulated proteins. Our findings greatly expand the current view of the roles of serum proteins in osteoporosis and shed light on the understanding of its underlying mechanisms and the discovery of serum proteins as potential markers for the prognosis of osteoporosis.

Current trends and opportunities in targeting p21 activated kinase-1(PAK1) for therapeutic management of breast cancers

Breast cancer is the most frequently diagnosed cancer in women worldwide. Identifying reliable biomarkers and druggable molecular targets pose to be a significant quest in breast cancer research. p21-activated kinase 1 (PAK1) is a serine/threonine kinase that direct cell motility, cytoskeletal remodelling, and has been shown to function as a downstream regulator for various cancer signalling cascades that promote cell proliferation, apoptosis deregulation and hasten mitotic abnormalities, resulting in tumor formation and progression. The heterogeneity and acquired drug resistance are important factors that challenge the treatment of breast cancer. p21-activated kinase 1 signalling is crucial for activation of the Ras/RAF/MEK/ERK, PI3K/Akt/mTOR and Wnt signalling cascades which regulate cell survival, cell cycle progression, differentiation, and proliferation. A study involving proteogenomics analysis on breast cancer tissues showed the PAK1 as outlier kinase. In addition to this, few outlier molecules were identified specific to subtypes of breast cancer. A few substrates of PAK1 in breast cancer are already known. In this paper, we have discussed a similar approach called Kinase Interacting Substrate Screening (KISS) for the identification of novel oncogenic substrates of p21-activated kinase specific to subtypes of breast cancer. Such high throughput approaches are expected to accelerate the process of identifying novel drug targets and biomarkers.

Myo1e modulates the recruitment of activated B cells to inguinal lymph nodes

The inclusion of lymphocytes in high endothelial venules and their migration to the lymph nodes are critical steps in the immune response. Cell migration is regulated by the actin cytoskeleton and myosins. Myo1e is a long-tailed class I myosin and is highly expressed in B cells, which have not been studied in the context of cell migration. By using intravital microscopy in an in vivo model and performing in vitro experiments, we studied the relevance of Myo1e for the adhesion and inclusion of activated B cells in high endothelial venules. We observed reduced expression of integrins and F-actin in the membrane protrusions of B lymphocytes, which might be explained by deficiencies in vesicular trafficking. Interestingly, the lack of Myo1e reduced the phosphorylation of focal adhesion kinase (FAK; also known as PTK2), AKT (also known as AKT1) and RAC-1, disturbing the FAK-PI3K-RAC-1 signaling pathway. Taken together, our results indicate a critical role of Myo1e in the mechanism of B-cell adhesion and migration.

Nakchbandi I. The Rho GTPase RAC1 in Osteoblasts Controls Their Function

The regulation of the differentiation of the bone-forming cells, the osteoblasts, is complex. Many signaling pathways converge on the master regulator of osteoblast differentiation Runx2. The role of molecules that integrate several signaling pathways such as the Rho GTPases need to be better understood. We, therefore, asked at which stage Rac1, one of the Rho GTPase, is needed for osteoblast differentiation and whether it is involved in two pathways, the anabolic response to parathyroid hormone and the stimulatory effect of fibronectin isoforms on integrins. Genetic deletion of Rac1 in preosteoblasts using the osterix promoter diminished osteoblast differentiation in vitro. This effect was however similar to the presence of the promoter by itself. We, therefore, applied a Rac1 inhibitor and confirmed a decrease in differentiation. In vivo, Rac1 deletion using the osterix promoter decreased bone mineral density as well as histomorphometric measures of osteoblast function. In contrast, deleting Rac1 in differentiating osteoblasts using the collagen α1(I) promoter had no effects. We then evaluated whether intermittent parathyroid hormone (PTH) was able to affect bone mineral density in the absence of Rac1 in preosteoblasts. The increase in bone mineral density was similar in control animals and in mice in which Rac1 was deleted using the osterix promoter. Furthermore, stimulation of integrin by integrin isoforms was able to enhance osteoblast differentiation, despite the deletion of Rac1. In summary, Rac1 in preosteoblasts is required for normal osteoblast function and bone density, but it is neither needed for PTH-mediated anabolic effects nor for integrin-mediated enhancement of differentiation.

Hyaluronic acid and epidermal growth factor improved the bovine embryo quality by regulating the DNA methylation and expression patterns of the focal adhesion pathway

Focal adhesion pathway is one of the key molecular pathways affected by suboptimal culture conditions during embryonic development. The epidermal growth factor (EGF) and hyaluronic acid (HA) are believed to be involved in the focal adhesion pathway function by regulating the adherence of the molecules to the extracellular matrix. However, regulatory and molecular mechanisms through which the EGF and HA could influence the embryo development is not clear. Therefore, this study aimed to investigate the effect of continued or stage specific supplementation of EGF and/or HA on the developmental competence and quality of bovine preimplantation embryos and the subsequent consequences on the expression and DNA methylation patterns of genes involved in the focal adhesion pathway. The results revealed that, the supplementation of EGF or HA from zygote to the blastocysts stage reduced the level of reactive oxygen species and increased hatching rate after thawing. On the other hand, HA decreased the apoptotic nuclei and increased blastocyst compared to EGF supplemented group. Gene expression and DNA methylation analysis in the resulting blastocysts indicated that, combined supplementation of EGF and HA increased the expression of genes involved in focal adhesion pathway while supplementation of EGF, HA or a combination of EGF and HA during the entire preimplantation period changed the DNA methylation patterns of genes involved in focal adhesion pathway. On the other hand, blastocysts developed in culture media supplemented with EGF + HA until the 16-cell stage exhibited higher expression level of genes involved in focal adhesion pathway compared to those supplemented after the 16-cell stage. Conversely, the DNA methylation level of candidate genes was increased in the blastocysts obtained from embryos cultured in media supplemented with EGF + HA after 16-cell stage. In conclusion, supplementation of bovine embryos with EGF and/or HA during the entire preimplantation period or in a stage specific manner altered the DNA methylation and expression patterns of candidate genes involved in the focal adhesion pathway which was in turn associated with the observed embryonic developmental competence and quality.

NEDD9 Facilitates Hypoxia-Induced Gastric Cancer Cell Migration via MICAL1 Related Rac1 Activation

Aims and Hypothesis: NEDD9 is highly expressed in gastric cancer and has a significant involvement in its pathogenesis. However, the mechanism behind hypoxia-promoted cancer cell migration and its regulation because of NEDD9 is still unknown. The aim of this study is to investigate the involvement of NEDD9 in gastric cancer cell migration under hypoxia and explore the underlying potential molecular mechanisms.

Reactive Oxygen Species and Oncoprotein Signaling-A Dangerous Liaison

SIGNIFICANCE

There is evidence to implicate reactive oxygen species (ROS) in tumorigenesis and its progression. This has been associated with the interplay between ROS and oncoproteins, resulting in enhanced cellular proliferation and survival. Recent Advances: To date, studies have investigated specific contributions of the crosstalk between ROS and signaling networks in cancer initiation and progression. These investigations have challenged the established dogma of ROS as agents of cell death by demonstrating a secondary function that fuels cell proliferation and survival. Studies have thus identified (onco)proteins (Bcl-2, STAT3/5, RAS, Rac1, and Myc) in manipulating ROS level as well as exploiting an altered redox environment to create a milieu conducive for cancer formation and progression.

CRITICAL ISSUES

Despite these advances, drug resistance and its association with an altered redox metabolism continue to pose a challenge at the mechanistic and clinical levels. Therefore, identifying specific signatures, altered protein expressions, and modifications as well as protein-protein interplay/function could not only enhance our understanding of the redox networks during cancer initiation and progression but will also provide novel targets for designing specific therapeutic strategies.

FUTURE DIRECTIONS

Not only a heightened realization is required to unravel various gene/protein networks associated with cancer formation and progression, particularly from the redox standpoint, but there is also a need for developing more sensitive tools for assessing cancer redox metabolism in clinical settings. This review attempts to summarize our current knowledge of the crosstalk between oncoproteins and ROS in promoting cancer cell survival and proliferation and treatment strategies employed against these oncoproteins. Antioxid. Redox Signal.

Oncogenic RAC1 and NRAS drive resistance to endoplasmic reticulum stress through MEK/ERK signalling

Cancer cells are able to survive under conditions that cause endoplasmic reticulum stress (ER-stress), and can adapt to this stress by upregulating cell-survival signalling pathways and down-regulating apoptotic pathways. The cellular response to ER-stress is controlled by the unfolded protein response (UPR). Small Rho family GTPases are linked to many cell responses including cell growth and apoptosis. In this study, we investigate the function of small GTPases in cell survival under ER-stress. Using siRNA screening we identify that RAC1 promotes cell survival under ER-stress in cells with an oncogenic N92I RAC1 mutation. We uncover a novel connection between the UPR and N92I RAC1, whereby RAC1 attenuates phosphorylation of EIF2S1 under ER-stress and drives over-expression of ATF4 in basal conditions. Interestingly, the UPR connection does not drive resistance to ER-stress, as knockdown of ATF4 did not affect this. We further investigate cancer-associated kinase signalling pathways and show that RAC1 knockdown reduces the activity of AKT and ERK, and using a panel of clinically important kinase inhibitors, we uncover a role for MEK/ERK, but not AKT, in cell viability under ER-stress. A known major activator of ERK phosphorylation in cancer is oncogenic NRAS and we show that knockdown of NRAS in cells, which bear a Q61 NRAS mutation, sensitises to ER-stress. These findings highlight a novel mechanism for resistance to ER-stress through oncogenic activation of MEK/ERK signalling by small GTPases.

GTPases Rac1 and Ras Signaling from Endosomes

The endocytic compartment is not only the functional continuity of the plasma membrane but consists of a diverse collection of intracellular heterogeneous complex structures that transport, amplify, sustain, and/or sort signaling molecules. Over the years, it has become evident that early, late, and recycling endosomes represent an interconnected vesicular-tubular network able to form signaling platforms that dynamically and efficiently translate extracellular signals into biological outcome. Cell activation, differentiation, migration, death, and survival are some of the endpoints of endosomal signaling. Hence, to understand the role of the endosomal system in signal transduction in space and time, it is therefore necessary to dissect and identify the plethora of decoders that are operational in the different steps along the endocytic pathway. In this chapter, we focus on the regulation of spatiotemporal signaling in cells, considering endosomes as central platforms, in which several small GTPases proteins of the Ras superfamily, in particular Ras and Rac1, actively participate to control cellular processes like proliferation and cell mobility.

Deciphering the link between PI3K and PAK: An opportunity to target key pathways in pancreatic cancer?

The development of personalised therapies has ushered in a new and exciting era of cancer treatment for a variety of solid malignancies. Yet pancreatic ductal adenocarcinoma (PDAC) has failed to benefit from this paradigm shift, remaining notoriously refractory to targeted therapies. Chemotherapy is the cornerstone of management but can offer only modest survival benefits of a few months with 5-year survival rates rarely exceeding 3%. Despite these disappointing statistics, significant strides have been made towards understanding the complex biology of pancreatic cancer, with deep genomic sequencing identifying novel genetic aberrations and key signalling pathways. The PI3K-PDK1-AKT pathway has received great attention due to its prominence in carcinogenesis. However, efforts to target several components of this network have resulted in only a handful of drugs demonstrating any survival benefit in solid tumors; despite promising pre-clinical results. p-21 activated kinase 4 (PAK4) is a gene that is recurrently amplified or overexpressed in PDAC and both PAK4 and related family member PAK1, have been linked to aberrant RAS activity, a common feature in pancreatic cancer. As regulators of PI3K, PAKs have been highlighted as a potential prognostic marker and therapeutic target. In this review, we discuss the biology of pancreatic cancer and the close interaction between PAKs and the PI3K pathway. We also suggest proposals for future research that may see the development of effective targeted therapies that could finally improve outcomes for this disease.

Mesoporous Silica Nanoparticles as an Antitumoral-Angiogenesis Strategy

Tumors depend heavily on angiogenesis for nutrient derivation and their subsequent metastasis. Targeting tumor induced angiogenesis per se can address both tumor growth and progression simultaneously. Here, we show that we could elegantly restrict the endothelial cells angiogenic behavior through digital size control of mesoporous silica nanoparticle (MSN). This antiangiogenesis effect was derived from the particle size dependent uptake and production of intracellular reactive oxygen species (ROS) that directly interfered with p53 tumor suppressor pathway. The resulting signaling cascade wrestled back the tumoral control of endothelial cells' migration, invasion, and proliferation. Overall, a mere control over the size of a highly oxidative reactive surfaced nanoparticle could provide an alternative strategy to curb the tumor induced angiogenesis process in a conventional drug-free manner.

Reactive oxygen species and cancer paradox: To promote or to suppress?

Reactive oxygen species (ROS), a group of highly reactive ions and molecules, are increasingly being appreciated as powerful signaling molecules involved in the regulation of a variety of biological processes. Indeed, their role is continuously being delineated in a variety of pathophysiological conditions. For instance, cancer cells are shown to have increased ROS levels in comparison to their normal counterparts. This is partly due to an enhanced metabolism and mitochondrial dysfunction in cancer cells. The escalated ROS generation in cancer cells contributes to the biochemical and molecular changes necessary for the tumor initiation, promotion and progression, as well as, tumor resistance to chemotherapy. Therefore, increased ROS in cancer cells may provide a unique opportunity to eliminate cancer cells via elevating ROS to highly toxic levels intracellularly, thereby, activating various ROS-induced cell death pathways, or inhibiting cancer cell resistance to chemotherapy. Such results can be achieved by using agents that either increase ROS generation, or inhibit antioxidant defense, or even a combination of both. In fact, a large variety of anticancer drugs, and some of those currently under clinical trials, effectively kill cancer cells and overcome drug resistance via enhancing ROS generation and/or impeding the antioxidant defense mechanism. This review focuses on our current understanding of the tumor promoting (tumorigenesis, angiogenesis, invasion and metastasis, and chemoresistance) and the tumor suppressive (apoptosis, autophagy, and necroptosis) functions of ROS, and highlights the potential mechanism(s) involved. It also sheds light on a very novel and an actively growing field of ROS-dependent cell death mechanism referred to as ferroptosis.

Growth hormone-releasing hormone receptor antagonists inhibit human gastric cancer through downregulation of PAK1-STAT3/NF-κB signaling

Gastric cancer (GC) ranks as the fourth most frequent in incidence and second in mortality among all cancers worldwide. The development of effective treatment approaches is an urgent requirement. Growth hormone-releasing hormone (GHRH) and GHRH receptor (GHRH-R) have been found to be present in a variety of tumoral tissues and cell lines. Therefore the inhibition of GHRH-R was proposed as a promising approach for the treatment of these cancers. However, little is known about GHRH-R and the relevant therapy in human GC. By survival analyses of multiple cohorts of GC patients, we identified that increased GHRH-R in tumor specimens correlates with poor survival and is an independent predictor of patient prognosis. We next showed that MIA-602, a highly potent GHRH-R antagonist, effectively inhibited GC growth in cultured cells. Further, this inhibitory effect was verified in multiple models of human GC cell lines xenografted into nude mice. Mechanistically, GHRH-R antagonists target GHRH-R and down-regulate the p21-activated kinase 1 (PAK1)-mediated signal transducer and activator of transcription 3 (STAT3)/nuclear factor-κB (NF-κB) inflammatory pathway. Overall, our studies establish GHRH-R as a potential molecular target in human GC and suggest treatment with GHRH-R antagonist as a promising therapeutic intervention for this cancer.

MICAL1 controls cell invasive phenotype via regulating oxidative stress in breast cancer cells

Background

Molecules Interacting with CasL (MICAL1), a multidomain flavoprotein monoxygenase, is strongly involved in the mechanisms that promote cancer cell proliferation and survival. Activation of MICAL1 causes an up-regulation of reactive oxygen species (ROS) in HeLa cells. ROS can function as a signaling molecule that modulates protein phosphorylation, leading to malignant phenotypes of cancer cells such as invasion and metastasis. Herein, we tested whether MICAL1 could control cell migration and invasion through regulating ROS in breast cancer cell lines.

Methods

The effects of depletion/overexperssion of MICAL1 on cell invasion rate were measured by matrigel-based transwell assays. The contents of ROS in breast cancer cells were evaluated by CM₂-DCFHDA staining and enhanced lucigenin chemiluminescence method. RAB35 activity was assessed by pulldown assay. The relationship of RAB35 and MICAL1 was evaluated by immunofluorescence, coimmunoprecipitation, immunoblotting and co-transfection techniques. Immunoblotting assays were also used to analyze Akt phosphorylation level.

Results

In this study, we found that depletion of MICAL1 reduced cell migration and invasion as well as ROS generation. Phosphorylation of Akt was also attenuated by MICAL1 depletion. Likewise, the over-expression of MICAL1 augmented the generation of ROS, increased Akt phosphorylation, and favored invasive phenotype of breast cancer cells. Moreover, we investigated the effect of EGF signaling on MICAL1 function. We demonstrated that EGF increased RAB35 activation and activated form of RAB35 could bind to MICAL1. Silencing of RAB35 repressed ROS generation, prevented Akt phosphorylation and inhibited cell invasion in response to EGF.

Conclusions

Taken together, our results provide evidence that MICAL1 plays an essential role in the activation of ROS/Akt signaling and cell invasive phenotype and identify a novel link between RAB35 and MICAL1 in regulating breast cancer cell invasion. These findings may provide a basis for designing future therapeutic strategy for blocking breast cancer metastasis.

The Enhancement of Radiation Sensitivity in Nasopharyngeal Carcinoma Cells via Activation of the Rac1/NADPH Signaling Pathway

We reported in an earlier study that using mass spectrometry and bioinformatic analysis demonstrated Rac1 protein might be mostly mitochondrial target in the radiosensitization process of nasopharyngeal carcinoma CNE-1 cells. The goal of our current study was to reveal the relationship between Rac1/NADPH pathway and radiosensitization in CNE-1 cells using Rac1 activator, phorbol 12-myristate 13-acetate (PMA) and Rac1 inhibitor NSC23766. The Rac1-GTP expression was determined using a pulldown assay, the Rac1 location using a immunofluorescence with a laser scanning confocal microscope, the NADPH oxidase activity with NBT assay and the reactive oxygen species with DCFH-DA probe. The apoptosis rate was analyzed by flow cytometry, and the expressions of p67(phox) and NFκB-p105/p50 were analyzed by Western blot. After treatment with PMA and 2 Gy radiation (compared to the control), Rac1-GTP was activated and translocated to the cell membrane. NADPH oxidase activity, reactive oxygen species of intracellular concentration and the apoptosis rate increased significantly. The expression of p67(phox) and NFκB-p50 protein also increased. However, in the cells treated with NSC23766 alone or NSC23766 combined with 2 Gy irradiation, the results were just the opposite. Overall, these results indicate that the Rac1 protein may be the key target involved in the radiosensitization of nasopharyngeal carcinoma cells. The activated Rac1/NADPH pathway combined with radiation can increase the radiosensitivity of nasopharyngeal carcinoma cells, and the Rac1/NADPH pathway may be the signaling pathway involved in the radiosensitization process.

A microfluidic Transwell to study chemotaxis

Chemotaxis is typically studied in vitro using commercially available products such as the Transwell® in which cells migrate through a porous membrane in response to one or more clearly defined chemotactic stimuli. Despite its widespread use, the Transwell assay suffers from being largely an endpoint assay, with built-in errors due to inconsistent pore size and human sampling. In this study, we report a microfluidic chemotactic chip that provides real-time monitoring, consistent paths for cell migration, and easy on-chip staining for quantifying migration. To compare its performance with that of a traditional Transwell chamber, we investigate the chemotactic response of MDA-MB-231 1833 metastatic breast cancer cells to epidermal growth factor (EGF). The results show that while both platforms were able to detect a chemotactic response, we observed a dose-dependent response of breast cancer cells towards EGF with low non-specific migration using the microfluidic platform, whereas we observed a dose-independent response of breast cancer cells towards EGF with high levels of non-specific migration using the commercially available Transwell.The microfluidic platform also allowed EGF-dependent chemotactic responses to be observed 24h, a substantially longer window than seen with the Transwell. Thus the performance of our microfluidic platform revealed phenomena that were not detected in the Transwell under the conditions tested.

bFGF Promotes the Migration of Human Dermal Fibroblasts under Diabetic Conditions through Reactive Oxygen Species Production via the PI3K/Akt-Rac1- JNK Pathways

Fibroblasts play a pivotal role in the process of cutaneous wound repair, whereas their migratory ability under diabetic conditions is markedly reduced. In this study, we investigated the effect of basic fibroblast growth factor (bFGF) on human dermal fibroblast migration in a high-glucose environment. bFGF significantly increased dermal fibroblast migration by increasing the percentage of fibroblasts with a high polarity index and reorganizing F-actin. A significant increase in intracellular reactive oxygen species (ROS) was observed in dermal fibroblasts under diabetic conditions following bFGF treatment. The blockage of bFGF-induced ROS production by either the ROS scavenger N-acetyl-L-cysteine (NAC) or the NADPH oxidase inhibitor diphenylene iodonium chloride (DPI) almost completely neutralized the increased migration rate of dermal fibroblasts promoted by bFGF. Akt, Rac1 and JNK were rapidly activated by bFGF in dermal fibroblasts, and bFGF-induced ROS production and promoted dermal fibroblast migration were significantly attenuated when suppressed respectively. In addition, bFGF-induced increase in ROS production was indispensable for the activation of focal adhesion kinase (FAK) and paxillin. Therefore, our data suggested that bFGF promotes the migration of human dermal fibroblasts under diabetic conditions through increased ROS production via the PI3K/Akt-Rac1-JNK pathways.

Neural differentiation of mesenchymal stem cells influences their chemotactic responses to stromal cell-derived factor-1α

Mesenchymal stem cells (MSCs) are proposed as a promising source for cell-based therapies in neural disease. Although increasing numbers of studies have been devoted to the delineation of factors involved in the migration of MSCs, the relationship between the chemotactic response and the differentiation status of these cells is still unclear. In the present study, we demonstrated that MSCs in varying neural differentiation states display various chemotactic responses to stromal cell-derived factor-1α (SDF-1α). The chemotactic responses of MSCs under different differentiation stages in response to SDF-1α were analyzed by Boyden chamber, and the results showed that cells of undifferentiation, 24-h preinduction, 5-h induction, and 18-h maintenance states displayed a stronger chemotactic response to SDF-1α, while 48-h maintenance did not. Further, we found that the phosphorylation levels of PI3K/Akt, ERK1/2, SAPK/JNK, and p38MAPK are closely related to the differentiation states of MSCs subjected to SDF-1α, and finally, inhibition of SAPK/JNK signaling significantly attenuates SDF-1α-stimulated transfilter migration of MSCs of undifferentiation, 24-h preinduction, 18-h maintenance, and 48-h maintenance, but not MSCs of 5-h induction. Meanwhile, interference with PI3K/Akt, p38MAPK, or ERK1/2 signaling prevents only cells at certain differentiation state from migrating in response to SDF-1α. Collectively, these results demonstrate that MSCs in varying neural differentiation states have different migratory capacities, thereby illuminating optimization of the therapeutic potential of MSCs to be used for neural regeneration after injury.

Melatonin suppresses hypoxia-induced migration of HUVECs via inhibition of ERK/Rac1 activation

Melatonin, a naturally-occurring hormone, possesses antioxidant properties and ameliorates vascular endothelial dysfunction. In this study, we evaluate the impact of melatonin on the migratory capability of human umbilical vein endothelial cells (HUVECs) to hypoxia and further investigate whether ERK/Rac1 signaling is involved in this process. Here, we found that melatonin inhibited hypoxia-stimulated hypoxia-inducible factor-1α (HIF-1α) expression and cell migration in a dose-dependent manner. Mechanistically, melatonin inhibited Rac1 activation and suppressed the co-localized Rac1 and F-actin on the membrane of HUVECs under hypoxic condition. In addition, the blockade of Rac1 activation with ectopic expression of an inactive mutant form of Rac1-T17N suppressed HIF-1α expression and cell migration in response to hypoxia, as well, but constitutive activation of Rac1 mutant Rac1-V12 restored HIF-1α expression, preventing the inhibition of melatonin on cell migration. Furthermore, the anti-Rac1 effect of melatonin in HUVECs appeared to be associated with its inhibition of ERK phosphorylation, but not that of the PI3k/Akt signaling pathway. Taken together, our work indicates that melatonin exerts an anti-migratory effect on hypoxic HUVECs by blocking ERK/Rac1 activation and subsequent HIF-1α upregulation.

p21-Activated protein kinases and their emerging roles in glucose homeostasis

p21-Activated protein kinases (PAKs) are centrally involved in a plethora of cellular processes and functions. Their function as effectors of small GTPases Rac1 and Cdc42 has been extensively studied during the past two decades, particularly in the realms of cell proliferation, apoptosis, and hence tumorigenesis, as well as cytoskeletal remodeling and related cellular events in health and disease. In recent years, a large number of studies have shed light onto the fundamental role of group I PAKs, most notably PAK1, in metabolic homeostasis. In skeletal muscle, PAK1 was shown to mediate the function of insulin on stimulating GLUT4 translocation and glucose uptake, while in pancreatic β-cells, PAK1 participates in insulin granule localization and vesicle release. Furthermore, we demonstrated that PAK1 mediates the cross talk between insulin and Wnt/β-catenin signaling pathways and hence regulates gut proglucagon gene expression and the production of the incretin hormone glucagon-like peptide-1 (GLP-1). The utilization of chemical inhibitors of PAK and the characterization of Pak1(-/-) mice enabled us to gain mechanistic insights as well as to assess the overall contribution of PAKs in metabolic homeostasis. This review summarizes our current understanding of PAKs, with an emphasis on the emerging roles of PAK1 in glucose homeostasis.

The role of protein kinase PAK1 in the regulation of estrogen-independent growth of breast cancer

The main goal of this work was to study the intracellular signaling pathways responsible for the development of hormone resistance and maintaining the autonomous growth of breast cancer cells. In particular, the role of PAK1 (p21-activated kinase 1), the key mitogenic signaling protein, in the development of cell resistance to estrogens was analyzed. In vitro studies were performed on cultured breast cancer cell lines: estrogen-dependent estrogen receptor (ER)-positive MCF-7 cells and estrogen-resistant ER-negative HBL-100 cells. We found that the resistant HBL-100 cells were characterized by a higher level of PAK1 and demonstrated PAK1 involvement in the maintaining of estrogen-independent cell growth. We have also shown PAK1 ability to up-regulate Snail1, one of the epithelial-mesenchymal transition proteins, and obtained experimental evidence for Snail1 importance in the regulation of cell proliferation. In general, the results obtained in this study demonstrate involvement of PAK1 and Snail1 in the formation of estrogen-independent phenotype of breast cancer cells showing the potential role of both proteins as markers of hormone resistance of breast tumors.