Focal Adhesions Require Catalytic Activity of Src Family Kinases To Mediate Integrin-Matrix Adhesion

Members of the Src family of tyrosine kinases function to phosphorylate focal adhesion (FA) proteins. To explore the overlapping functions of Src kinases, we have targeted Csk, a negative regulator of the Src family, to FA structures. Expression of FA-targeted Csk (FA-Csk) effectively reduced the active form (nonphosphorylated at the C-terminal regulatory tyrosine) of Src members in the cell. We found that fibroblasts expressing FA-Csk lost integrin-mediated adhesion. Activated Src (SrcY529F) as well as activation of putative Src signaling mediators (Fak, Cas, Crk/CrkL, C3G, and Rap1) blocked the effect of FA-Csk in a manner dependent on Rap1. SrcY529F also inhibited activated Ras-induced cell detachment but failed to rescue detachment caused by an activated mutant of Raf1 (Raf-BXB) that Rap1 cannot inhibit. Although normal spreading onto fibronectin was restored by the beta(1) integrin affinity-activating antibody TS2/16 in cells expressing FA-Csk or Raf-BXB, FAs were lost in these cells. On the other hand, Rap1 activation could restore FAs in cells expressing FA-Csk. Activation of the executioner caspase, caspase 3, is essential for many forms of apoptosis. While a caspase 3 inhibitor (Z-DEVD-FMK) inhibited cell detachment triggered by activation of caspase 8, this inhibitor had no effect on cell detachment caused by FA-Csk. Likewise, overexpression of an activated Akt made cells resistant to the effect of caspase 8 activation, but not to the effect of FA-Csk. It is therefore likely that the primary cause of cell rounding and detachment induced by FA-Csk involves dysfunction of FAs rather than caspase-mediated apoptosis that may result from possible loss of survival signals mediated by Src family kinases. We suggest that endogenous Src family kinases are essential for FAs through activation of Rap1 in fibroblasts.     

Mechanism of Focal Adhesion Kinase Mechanosensing

Mechanosensing at focal adhesions regulates vital cellular processes. Here, we present results from molecular dynamics (MD) and mechano-biochemical network simulations that suggest a direct role of Focal Adhesion Kinase (FAK) as a mechano-sensor. Tensile forces, propagating from the membrane through the PIP₂ binding site of the FERM domain and from the cytoskeleton-anchored FAT domain, activate FAK by unlocking its central phosphorylation site (Tyr576/577) from the autoinhibitory FERM domain. Varying loading rates, pulling directions, and membrane PIP₂ concentrations corroborate the specific opening of the FERM-kinase domain interface, due to its remarkably lower mechanical stability compared to the individual alpha-helical domains and the PIP₂-FERM link. Analyzing downstream signaling networks provides further evidence for an intrinsic mechano-signaling role of FAK in broadcasting force signals through Ras to the nucleus. This distinguishes FAK from hitherto identified focal adhesion mechano-responsive molecules, allowing a new interpretation of cell stretching experiments.     

Neuropeptide-Induced Androgen Independence in Prostate Cancer Cells: Roles of Nonreceptor Tyrosine Kinases Etk/Bmx, Src, and Focal Adhesion Kinase

The bombesin/gastrin-releasing peptide (GRP) family of neuropeptides has been implicated in various in vitro and in vivo models of human malignancies including prostate cancers. It was previously shown that bombesin and/or neurotensin (NT) acts as a survival and migratory factor(s) for androgen-independent prostate cancers. However, a role in the transition from an androgen-dependent to -refractory state has not been addressed. In this study, we investigate the biological effects and signal pathways of bombesin and NT on LNCaP, a prostate cancer cell line which requires androgen for growth. We show that both neurotrophic factors can induce LNCaP growth in the absence of androgen. Concurrent transactivation of reporter genes driven by the prostate-specific antigen promoter or a promoter carrying an androgen-responsive element (ARE) indicate that growth stimulation is accompanied by androgen receptor (AR) activation. Furthermore, neurotrophic factor-induced gene activation was also present in PC3 cells transfected with the AR but not in the parental line which lacks the AR. Given that bombesin does not directly bind to the AR and is known to engage a G-protein-coupled receptor, we investigated downstream signaling events that could possibly interact with the AR pathway. We found that three nonreceptor tyrosine kinases, focal adhesion kinase (FAK), Src, and Etk/BMX play important parts in this process. Etk/Bmx activation requires FAK and Src and is critical for neurotrophic factor-induced growth, as LNCaP cells transfected with a dominant-negative Etk/BMX fail to respond to bombesin. Etk's activation requires FAK, Src, but not phosphatidylinositol 3-kinase. Likewise, bombesin-induced AR activation is inhibited by the dominant-negative mutant of either Src or FAK. Thus, in addition to defining a new G-protein pathway, this report makes the following points regarding prostate cancer. (i) Neurotrophic factors can activate the AR, thus circumventing the normal growth inhibition caused by androgen ablation. (ii) Tyrosine kinases are involved in neurotrophic factor-mediated AR activation and, as such, may serve as targets of future therapeutics, to be used in conjunction with current antihormone and antineuropeptide therapies.     

Subcellular Localization and Ser-137 Phosphorylation Regulate Tumor-suppressive Activity of Profilin-1

The actin-binding protein profilin-1 (Pfn1) inhibits tumor growth and yet is also required for cell proliferation and survival, an apparent paradox. We previously identified Ser-137 of Pfn1 as a phosphorylation site within the poly-l-proline (PLP) binding pocket. Here we confirm that Ser-137 phosphorylation disrupts Pfn1 binding to its PLP-containing ligands with little effect on actin binding. We find in mouse xenografts of breast cancer cells that mimicking Ser-137 phosphorylation abolishes cell cycle arrest and apoptotic sensitization by Pfn1 and confers a growth advantage to tumors. This indicates a previously unrecognized role of PLP binding in Pfn1 antitumor effects. Spatial restriction of Pfn1 to the nucleus or cytoplasm indicates that inhibition of tumor cell growth by Pfn1 requires its nuclear localization, and this activity is abolished by a phosphomimetic mutation on Ser-137. In contrast, cytoplasmic Pfn1 lacks inhibitory effects on tumor cell growth but rescues morphological and proliferative defects of PFN1 null mouse chondrocytes. These results help reconcile seemingly opposed cellular effects of Pfn1, provide new insights into the antitumor mechanism of Pfn1, and implicate Ser-137 phosphorylation as a potential therapeutic target for breast cancer.     

LKB1 Represses Focal Adhesion Kinase (FAK) Signaling via a FAK-LKB1 Complex to Regulate FAK Site Maturation and Directional Persistence

Liver kinase β1 (LKB1, also known as STK11) is a serine/threonine kinase that has multiple cellular functions including the regulation of cell polarity and motility. Murine proteomic studies show that LKB1 loss causes aberrant adhesion signaling; however, the mechanistic underpinnings of this relationship are unknown. We show that cells stably depleted of LKB1 or its co-activator STRADα have increased phosphorylation of focal adhesion kinase (FAK) at Tyr³⁹⁷/Tyr⁸⁶¹ and enhanced adhesion to fibronectin. LKB1 associates in a complex with FAK and LKB1 accumulation at the cellular leading edge is mutually excluded from regions of activated Tyr³⁹⁷-FAK. LKB1-compromised cells lack directional persistence compared with wild-type cells, but this is restored through subsequent pharmacological FAK inhibition or depletion, showing that cell directionality is mediated through LKB1-FAK signaling. Live cell confocal imaging reveals that LKB1-compromised cells lack normal FAK site maturation and turnover, suggesting that defects in adhesion and directional persistence are caused by aberrant adhesion dynamics. Furthermore, re-expression of full-length wild-type or the LKB1 N-terminal domain repressed FAK activity, whereas the kinase domain or C-terminal domain alone did not, indicating that FAK suppression is potentially regulated through the LKB1 N-terminal domain. Based upon these results, we conclude that LKB1 serves as a FAK repressor to stabilize focal adhesion sites, and when LKB1 function is compromised, aberrant FAK signaling ensues, resulting in rapid FAK site maturation and poor directional persistence.     

Paxillin and Focal Adhesion Kinase (FAK) Regulate Cardiac Contractility in the Zebrafish Heart

An orchestrated interplay of adaptor and signaling proteins at mechano-sensitive sites is essential to maintain cardiac contractility and when defective leads to heart failure. We recently showed that Integrin-linked Kinase (ILK), ß-Parvin and PINCH form the IPP-complex to grant tuned Protein Kinase B (PKB) signaling in the heart. Loss of one of the IPP-complex components results in destabilization of the whole complex, defective PKB signaling and finally heart failure. Two components of IPP, ILK and ß-Parvin directly bind to Paxillin; however, the impact of this direct interaction on the maintenance of heart function is not known yet. Here, we show that targeted gene inactivation of Paxillin results in progressive decrease of cardiac contractility and heart failure in zebrafish without affecting IPP-complex stability and PKB phosphorylation. However, we found that Paxillin deficiency leads to the destabilization of its known binding partner Focal Adhesion Kinase (FAK) and vice versa resulting in degradation of Vinculin and thereby heart failure. Our findings highlight an essential role of Paxillin and FAK in controlling cardiac contractility via the recruitment of Vinculin to mechano-sensitive sites in cardiomyocytes.     

Extracellular Signal-Regulated Kinase Promotes Rho-Dependent Focal Adhesion Formation by Suppressing p190A RhoGAP

Cell migration is critical for normal development and for pathological processes including cancer cell metastasis. Dynamic remodeling of focal adhesions and the actin cytoskeleton are crucial determinants of cell motility. The Rho family and the mitogen-activated protein kinase (MAPK) module consisting of MEK-extracellular signal-regulated kinase (ERK) are important regulators of these processes, but mechanisms for the integration of these signals during spreading and motility are incompletely understood. Here we show that ERK activity is required for fibronectin-stimulated Rho-GTP loading, Rho-kinase function, and the maturation of focal adhesions in spreading cells. We identify p190A RhoGAP as a major target for ERK signaling in adhesion assembly and identify roles for ERK phosphorylation of the C terminus in p190A localization and activity. These observations reveal a novel role for ERK signaling in adhesion assembly in addition to its established role in adhesion disassembly.Cell migration is a highly coordinated process essential for physiological and pathological processes (69). Signaling through Rho family GTPases (e.g., Rac, Cdc42, and Rho) is crucial for cell migration. Activated Rac and Cdc42 are involved in the production of a dominant lamellipodium and filopodia, respectively, whereas Rho-stimulated contractile forces are required for tail retraction and to maintain adhesion to the matrix (57, 58, 68). Rac- and Cdc42-dependent membrane protrusions are driven by the actin cytoskeleton and the formation of peripheral focal complexes; Rho activation stabilizes protrusions by stimulating the formation of mature focal adhesions and stress fibers. Active Rho influences cytoskeletal dynamics through effectors including the Rho kinases (ROCKs) (2, 3).Rho activity is stimulated by GEFs that promote GTP binding and attenuated by GTPase-activating proteins (GAPs) that enhance Rho''s intrinsic GTPase activity. However, due to the large number of RhoGEFs and RhoGAPs expressed in mammalian cells, the molecular mechanisms responsible for regulation of Rho activity in time and space are incompletely understood. p190A RhoGAP (hereafter p190A) is implicated in adhesion and migration signaling. p190A contains an N-terminal GTPase domain, a large middle domain juxtaposed to the C-terminal GAP domain, and a short C-terminal tail (74). The C-terminal tail of ∼50 amino acids is divergent between p190A and the closely related family member p190B (14) and thus may specify the unique functional roles for p190A and p190B revealed in gene knockout studies (10, 11, 41, 77, 78). p190A activity is dynamically regulated in response to external cues during cell adhesion and migration (5, 6, 59). Arthur et al. (5) reported that p190A activity is required for the transient decrease in RhoGTP levels seen in fibroblasts adhering to fibronectin. p190A activity is positively regulated by tyrosine phosphorylation (4, 5, 8, 17, 31, 39, 40, 42): phosphorylation at Y1105 promotes its association with p120RasGAP and subsequent recruitment to membranes or cytoskeleton (8, 17, 27, 31, 71, 75, 84). However, Y1105 phosphorylation is alone insufficient to activate p190A GAP activity (39). While the functions of p190A can be irreversibly terminated by ubiquitinylation in a cell-cycle-dependent manner (80), less is known about reversible mechanisms that negatively regulate p190A GAP activity during adhesion and motility.The integration of Rho family GTPase and extracellular signal-regulated kinase (ERK) signaling is important for cell motility (48, 50, 63, 76, 79). Several studies have demonstrated a requirement for ERK signaling in the disassembly of focal adhesions in migrating cells, in part through the activation of calpain proteases (36, 37) that can downregulate focal adhesion kinase (FAK) signaling (15), locally suppress Rho activity (52), and sever cytoskeletal linkers to focal adhesions (7, 33). Inhibition of ERK signaling increases focal adhesion size and retards disassembly of focal adhesions in adherent cells (57, 64, 85, 86). It is also recognized that ERK modulates Rho-dependent cellular processes, including membrane protrusion and migration (18, 25, 64, 86). Interestingly, ERK activated in response to acute fibronectin stimulation localizes not only to mature focal adhesions, but also to peripheral focal complexes (32, 76). Since these complexes can either mature or be turned over (12), ERK may play a distinct role in focal adhesion assembly. ERK is proposed to promote focal adhesion formation by activating myosin light chain kinase (MLCK) (21, 32, 50).Here we find that ERK activity is required for Rho activation and focal adhesion formation during adhesion to fibronectin and that p190A is an essential target of ERK signaling in this context. Inspection of the p190A C terminus reveals a number of consensus ERK sites and indeed p190A is phosphorylated by recombinant ERK only on its C terminus in vitro, and on the same C-terminal peptide in vivo. Mutation of the C-terminal ERK phosphorylation sites to alanine increases the biochemical and biological activity of p190A. Finally, inhibition of MEK or mutation of the C-terminal phosphorylation sites enhances retention of p190A in peripheral membranes during spreading on fibronectin. Our data support the conclusion that ERK phosphorylation inhibits p190A allowing increases in RhoGTP and cytoskeletal changes necessary for focal adhesion formation.     

Role of Focal Adhesion Tyrosine Kinases in GPVI-Dependent Platelet Activation and Reactive Oxygen Species Formation

Background

We have previously shown the presence of a TRAF4/p47^phox/Hic5/Pyk2 complex associated with the platelet collagen receptor, GPVI, consistent with a potential role of this complex in GPVI-dependent ROS formation. In other cell systems, NOX-dependent ROS formation is facilitated by Pyk2, which along with its closely related homologue FAK are known to be activated and phosphorylated downstream of ligand binding to GPVI.

Aims

To evaluate the relative roles of Pyk2 and FAK in GPVI-dependent ROS formation and to determine their location within the GPVI signaling pathway.

Methods and Results

Human and mouse washed platelets (from WT or Pyk2 KO mice) were pre-treated with pharmacological inhibitors targeting FAK or Pyk2 (PF-228 and Tyrphostin A9, respectively) and stimulated with the GPVI-specific agonist, CRP. FAK, but not Pyk2, was found to be essential for GPVI-dependent ROS production and aggregation. Subsequent human platelet studies with PF-228 confirmed FAK is essential for GPVI-mediated phosphatidylserine exposure, α-granule secretion (P-selectin (CD62P) surface expression) and integrin α_IIbβ₃ activation. To determine the precise location of FAK within the GPVI pathway, we analyzed the effect of PF-228 inhibition in CRP-stimulated platelets in conjunction with immunoprecipitation and pulldown analysis to show that FAK is downstream of Lyn, Spleen tyrosine kinase (Syk), PI3-K and Bruton''s tyrosine kinase (Btk) and upstream of Rac1, PLCγ2, Ca²⁺ release, PKC, Hic-5, NOX1 and α_IIbβ₃ activation.

Conclusion

Overall, these data suggest a novel role for FAK in GPVI-dependent ROS formation and platelet activation and elucidate a proximal signaling role for FAK within the GPVI pathway.     

A Site-Specific Phosphorylation of the Focal Adhesion Kinase Controls the Formation of Spheroid Cell Clusters

Human dental follicle cells (DFCs) are ectomesenchymal multipotent stem cells that form spheroid cell clusters (SCCs) under serum free medium cell culture conditions (SFM). Until today, molecular mechanisms for the formation of SCCs are unknown. In this study a quantitative phosphoproteomics approach revealed regulated phosphorylated proteins in SCCs, which were derived from DFCs after 24 and 48 h in SFM. These regulated proteins were categorized using the Kyoto encyclopedia of genes and genomes program. Here, cellular processes and signaling pathway were identified such as the focal adhesion kinase (FAK) signaling pathway. In addition to the phosphoproteomics approach we showed that a specific phosphorylation of FAK (Y397) was required for the formation of SCCs. In conclusion, this study disclosed the phosphoproteome of SCCs for the first time and showed that the FAK signaling pathway is required for the formation of SCCs.     

BCAR3 Regulates Src/p130Cas Association, Src Kinase Activity, and Breast Cancer Adhesion Signaling

The nonreceptor protein-tyrosine kinase c-Src is frequently overexpressed and/or activated in a variety of cancers, including those of the breast. Several heterologous binding partners of c-Src have been shown to regulate its catalytic activity by relieving intramolecular autoinhibitory interactions. One such protein, p130^Cas (Cas), is expressed at high levels in both breast cancer cell lines and breast tumors, providing a potential mechanism for c-Src activation in breast cancers. The Cas-binding protein BCAR3 (breast cancer antiestrogen resistance-3) is expressed at high levels in invasive breast cancer cell lines, and this molecule has previously been shown to coordinate with Cas to increase c-Src activity in COS-1 cells. In this study, we show for the first time using gain- and loss-of-function approaches that BCAR3 regulates c-Src activity in the endogenous setting of breast cancer cells. We further show that BCAR3 regulates the interaction between Cas and c-Src, both qualitatively as well as quantitatively. Finally, we present evidence that the coordinated activity of these proteins contributes to breast cancer cell adhesion signaling and spreading. Based on these data, we propose that the c-Src/Cas/BCAR3 signaling axis is a prominent regulator of c-Src activity, which in turn controls cell behaviors that lead to aggressive and invasive breast tumor phenotypes.     

黏着斑激酶与肿瘤发生、发展及预后的关系

黏着斑激酶(focal adhesion kinase,FAK)作为一种非受体蛋白酪氨酸激酶,因其与肿瘤间的密切联系而备受关注。多年研究发现,FAK在许多肿瘤中过表达,通过多条信号通路调控细胞侵袭、迁移、增殖及凋亡等,从而参与肿瘤的发生、发展进程。研究表明FAK可以作为肿瘤预后因子,是潜在的抗肿瘤治疗靶点。本文对FAK与肿瘤进程的关系作一综述,以期更好地认识FAK在肿瘤发生、发展过程中所起的作用,为相关研究者提供资料参考。     

The Src Family Kinases and Protein Kinase C Synergize to Mediate Gq-dependent Platelet Activation

The Src family kinases (SFKs) play essential roles in collagen- and von Willebrand factor (VWF)-mediated platelet activation. However, the roles of SFKs in G protein-coupled receptor-mediated platelet activation and the molecular mechanisms whereby SFKs are activated by G protein-coupled receptor stimulation are not fully understood. Here we show that the thrombin receptor protease-activated receptor 4 agonist peptide AYPGKF elicited SFK phosphorylation in P2Y₁₂ deficient platelets but stimulated minimal SFK phosphorylation in platelets lacking G_q. We have previously shown that thrombin-induced SFK phosphorylation was inhibited by the calcium chelator 5,5′-dimethyl-bis-(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (dimethyl-BAPTA). The calcium ionophore A23187 induced SFK phosphorylation in both wild-type and G_q deficient platelets. Together, these results indicate that SFK phosphorylation in response to thrombin receptor stimulation is downstream from G_q/Ca²⁺ signaling. Moreover, A23187-induced thromboxane A₂ synthesis, platelet aggregation, and secretion were inhibited by preincubation of platelets with a selective SFK inhibitor, PP2. AYPGKF-induced thromboxane A₂ production in wild-type and P2Y₁₂ deficient platelets was abolished by PP2, and AYPGKF-mediated P-selectin expression, integrin α_IIbβ₃ activation, and aggregation of P2Y₁₂ deficient platelets were partially inhibited by the PKC inhibitor Ro-31-8220, PP2, dimethyl-BAPTA, or {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002, but were abolished by Ro-31-8220 plus PP2, dimethyl-BAPTA, or {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002. These data indicate that Ca²⁺/SFKs/PI3K and PKC represent two alternative signaling pathways mediating G_q-dependent platelet activation.     

Syk and Src Family Kinases Regulate C-type Lectin Receptor 2 (CLEC-2)-mediated Clustering of Podoplanin and Platelet Adhesion to Lymphatic Endothelial Cells

The interaction of C-type lectin receptor 2 (CLEC-2) on platelets with Podoplanin on lymphatic endothelial cells initiates platelet signaling events that are necessary for prevention of blood-lymph mixing during development. In the present study, we show that CLEC-2 signaling via Src family and Syk tyrosine kinases promotes platelet adhesion to primary mouse lymphatic endothelial cells at low shear. Using supported lipid bilayers containing mobile Podoplanin, we further show that activation of Src and Syk in platelets promotes clustering of CLEC-2 and Podoplanin. Clusters of CLEC-2-bound Podoplanin migrate rapidly to the center of the platelet to form a single structure. Fluorescence lifetime imaging demonstrates that molecules within these clusters are within 10 nm of one another and that the clusters are disrupted by inhibition of Src and Syk family kinases. CLEC-2 clusters are also seen in platelets adhered to immobilized Podoplanin using direct stochastic optical reconstruction microscopy. These findings provide mechanistic insight by which CLEC-2 signaling promotes adhesion to Podoplanin and regulation of Podoplanin signaling, thereby contributing to lymphatic vasculature development.     

Focal Adhesion and Stress Fiber Formation Is Regulated by Tyrosine Phosphatase Activity

Tyrosine phosphorylation of cytoskeletal proteins plays an important role in the regulation of focal adhesions and stress fiber organization. In the present study we examined the role of tyrosine phosphatases in this process using p125FAK and paxillin as substrates. We show that tyrosine phosphatase activity in Swiss 3T3 cells was markedly increased when actin stress fibers were disassembled by cell detachment from the substratum, by serum starvation, or by cytochalasin D treatment. This activity was blocked by phenylarsine oxide, an inhibitor of a specific class of tyrosine phosphatases characterized by two vicinal thiol groups in the active site. Phenylarsine oxide treatment of serum-starved cells induced increased tyrosine phosphorylation of p125FAK and paxillin in a dose-dependent manner and induced assembly of focal adhesions and actin stress fibers, showing that inhibition of one or more phenylarsine oxide-sensitive tyrosine phosphatases is a sufficient stimulus for triggering focal adhesion and actin stress fiber formation in adherent cells.     

Proteomic Profiling of Endothelial Invasion Revealed Receptor for Activated C Kinase 1 (RACK1) Complexed with Vimentin to Regulate Focal Adhesion Kinase (FAK)

Angiogenesis is critical for many physiological and pathological processes. To identify molecules relevant to angiogenesis, we performed a proteomic screen comparing invading versus non-invading endothelial cells in three-dimensional collagen matrices. We found up-regulated levels of receptor for activated C kinase 1 (RACK1) and the intermediate filament protein vimentin that correlated with increased endothelial cell invasion. Because both RACK1 and vimentin have been linked to focal adhesion kinase (FAK), we investigated whether this pathway regulated invasion. RACK1 depletion reduced invasion responses, and this was associated with attenuated activation of FAK. Knockdown of vimentin significantly decreased levels of phosphorylated and total FAK. Treatment with a pharmacological inhibitor of FAK dose-dependently reduced invasion, indicating a crucial role for FAK activity during invasion. Because RACK1 and vimentin were both up-regulated with sphingosine 1-phosphate treatment, required for invasion, and regulated FAK, we tested whether they complexed together. RACK1 complexed with vimentin, and growth factors enhanced this interaction. In addition, RACK1, vimentin, and FAK formed an intermolecular complex in invading endothelial cultures in three dimensions in response to stimulation by sphingosine 1-phosphate and growth factors. Moreover, depletion of RACK1 decreased the association of vimentin and FAK, suggesting that RACK1 was required for stabilizing vimentin-FAK interactions during sprouting. Silencing of vimentin and RACK1 decreased cell adhesion and focal contact formation. Taken together, these results demonstrate that proangiogenic signals converge to enhance expression and association of RACK1 and vimentin, which regulated FAK, resulting in successful endothelial sprout formation in three-dimensional collagen matrices.     

MAPK的细胞内定位与激活后移位机制

信号蛋白的亚细胞定位和激活后移位已成为细胞信号转导研究中的重要内容.MAPK信号通路是真核细胞中的重要信号转导系统.MAPK在细胞中有着相对固定的定位,在适宜的刺激作用下会移位入核并产生相应的生理效应.目前认为,MAPK的磷酸化状态及与其他蛋白质,如上游激酶、磷酸酶和下游底物之间的相互作用,可能在其特异性定位与激活后移位中起作用.MAPK的定位与移位机制的阐明,有助于进一步揭示MAPK的生理功能.     

人牛精浆相关蛋白的亚细胞定位及生物活性

利用红色荧光蛋白表达载体pDsRed1-N1与人睾丸中牛精浆相关蛋白基因(hbrp)重组为pDsRed1-N1/hbrp,真核表达载体pcDNA3.1-myc-his与hbrp重组为pcDNA3.1-myc-his/hbrp,分别转染HEK293细胞,建立稳定的真核表达细胞系。在荧光显微镜下观察HBRP的亚细胞定位,并用放射自显影检测该细胞系的蛋白激酶C(PKC)活性。HBRP定位在细胞膜及胞浆近膜处;HBRP对PKC活性有明显的抑制作用。从而确定了人新的精子结合蛋白HBRP在细胞内的定位,并认定了HBRP为有生物活性的功能蛋白。     

Focal Adhesion Kinase Inhibitors in Combination with Erlotinib Demonstrate Enhanced Anti-Tumor Activity in Non-Small Cell Lung Cancer

Blockade of epidermal growth factor receptor (EGFR) activity has been a primary therapeutic target for non-small cell lung cancers (NSCLC). As patients with wild-type EGFR have demonstrated only modest benefit from EGFR tyrosine kinase inhibitors (TKIs), there is a need for additional therapeutic approaches in patients with wild-type EGFR. As a key component of downstream integrin signalling and known receptor cross-talk with EGFR, we hypothesized that targeting focal adhesion kinase (FAK) activity, which has also been shown to correlate with aggressive stage in NSCLC, would lead to enhanced activity of EGFR TKIs. As such, EGFR TKI-resistant NSCLC cells (A549, H1299, H1975) were treated with the EGFR TKI erlotinib and FAK inhibitors (PF-573,228 or PF-562,271) both as single agents and in combination. We determined cell viability, apoptosis and 3-dimensional growth in vitro and assessed tumor growth in vivo. Treatment of EGFR TKI-resistant NSCLC cells with FAK inhibitor alone effectively inhibited cell viability in all cell lines tested; however, its use in combination with the EGFR TKI erlotinib was more effective at reducing cell viability than either treatment alone when tested in both 2- and 3-dimensional assays in vitro, with enhanced benefit seen in A549 cells. This increased efficacy may be due in part to the observed inhibition of Akt phosphorylation when the drugs were used in combination, where again A549 cells demonstrated the most inhibition following treatment with the drug combination. Combining erlotinib with FAK inhibitor was also potent in vivo as evidenced by reduced tumor growth in the A549 mouse xenograft model. We further ascertained that the enhanced sensitivity was irrespective of the LKB1 mutational status. In summary, we demonstrate the effectiveness of combining erlotinib and FAK inhibitors for use in known EGFR wild-type, EGFR TKI resistant cells, with the potential that a subset of cell types, which includes A549, could be particularly sensitive to this combination treatment. As such, further evaluation of this combination therapy is warranted and could prove to be an effective therapeutic approach for patients with inherent EGFR TKI-resistant NSCLC.