Factor Receptor Protein Tyrosine Kinase Research Articles

MiR133b-mediated inhibition of EGFR-PTK pathway promotes rAAV2 transduction by facilitating intracellular trafficking and augmenting second-strand synthesis.

Recombinant adeno-associated virus (rAAV) is an extremely attractive vector in the in vivo delivery of gene therapy as it is safe and its genome is simple. However, challenges including low permissiveness to specific cells and restricted tissue specificity have hindered its clinical application. Based on the previous studies, epidermal growth factor receptor-protein tyrosine kinase (EGFR-PTK) negatively regulated rAAV transduction, and EGFR-positive cells were hardly permissive to rAAV transduction. We constructed a novel rAAV-miRNA133b vector, which co-expressed miRNA133b and transgene, and investigated its in vivo and in vitro transduction efficiency. Confocal microscopy, live-cell imaging, pharmacological reagents and labelled virion tracking were used to analyse the effect of miRNA133b on rAAV2 transduction and the underlying mechanisms. The results demonstrated that miRNA133b could promote rAAV2 transduction and the effects were limited to EGFR-positive cells. The increased transduction was found to be a direct result of decreased rAAV particles degradation in the cytoplasm and enhanced second-strand synthesis. ss-rAAV2-miRNA133b vector specifically increased rAAV2 transduction in EGFR-positive cells or tissues, while ss-rAAV2-Fluc-miRNA133b exerted an antitumor effect. rAAV-miRNA133b vector might emerge as a promising platform for delivering various transgene to treat EGFR-positive cell-related diseases, such as non-small-cell lung cancer.

Futibatinib (Lytgobi) for cholangiocarcinoma

STRUCTURE: Futibatinib (brand name LytgobiTM) is a small molecule kinase inhibitor with the molecular formula C22H22N6O3 and a molecular mass of 418.45 g/mole. The drug is a pyrazolo[3,4-d]pyrimidine derivative with an attached α,β-unsaturated amide warhead, also called a Michael acceptor, that forms a covalent bond with a cysteine residue in the fibroblast growth factor receptor (FGFR) protein-tyrosine kinase glycine-rich loop.

A Concise Synthesis of Triazole Analogues of Lavendustin A via Click Chemistry Approach and Preliminary Evaluation of Their Antiparasitic Activity Against Trypanosoma cruzi

AbstractLavendustin A is a natural product isolated from the actinobacteria Streptomyces griseolavendus that presents a potent inhibitory activity on the Epidermal Growth Factor Receptor Protein Tyrosine Kinase (EGFR PTK). In addition, some of its analogues have also shown potent inhibitory activity against the polymerization of tubulin to microtubules, a pivotal process for the cell mitosis. From strategic structural modifications, two useful unprecedented alkynes bearing lavendustin A pharmacophoric subunit were rapidly accessed. Next, a set of novel triazole analogues of lavendustin A were synthesized in good yields employing CuI‐catalyzed azide‐alkyne cycloadditions (CuAAC) under mild conditions. Furthermore, preliminary evaluation of their biological activity against the epimastigote stage of Trypanosoma cruzi points towards promising trypanocidal properties.

Exploration of potential EGFR inhibitors: a combination of pharmacophore-based virtual screening, atom-based 3D-QSAR and molecular docking analysis

Epidermal growth factor receptor (EGFR) protein tyrosine kinases are over expressed in several human cancers and considered as a promising target for developing novel anticancer drugs. In this study, the ligand-based pharmacophore mapping and atom-based 3D-QSAR approach was carried out on a series of 40 novel pyrrolo[3, 2-d]pyrimidine derivatives acting as EGFR inhibitors. The best pharmacophore hypothesis AAADRR.295 was selected and an atom-based 3D-QSAR model was generated by applying partial least-squares algorithm. The developed model was validated and used as a 3D query in sequential virtual screening study to filter five chemical databases. The obtained compounds were further filtered according to Lipinski rule of five and fitness score. Subsequently, a multistep molecular docking study was employed on the retrieved hits and finally, 12 compounds were prioritized as potential leads against EGFR, which exhibited high docking scores, correlated binding mode to experimentally proven compounds and constructive drug-like properties. The results of this study provide detailed structural insights and emphasize the important binding features of these compounds, which may assists in the design and development of novel EGFR inhibitors.

English

Epidermal growth factor receptor (EGFR) protein tyrosine kinases (PTKs) are known for their role in cancer. Lapatinib drug have been reported to be the molecules of interest, with potent anticancer activity and they act by binding to adenosine triphosphate (ATP) site of protein kinases. ATP binding site of protein kinases provides an extensive opportunity to design newer analogs. Here we aimed to do the molecular docking studies for the potent anti-cancer drugs iressa, tarceva and capsaicin against the breast cancer treatment. The estimated free energy of binding and inhibition constant are highly differed with each drugs compared to the current market available drugs and bioactive compounds. Our results strongly suggest that the bioactive compound capsaicin activity would be comparable with the commercially available cancer drug. Further study indicates that in silico method would be an important tool for the drug design and development against cancer.   Key words: Epidermal growth factor receptor (EGFR), inhibitors, docking studies, protein tyrosine kinases (PTKs), breast cancer.

Analysis of genomic mutation and immunohistochemistry of platelet‐derived growth factor receptors in canine vascular tumours

We examined whether mutation of the platelet-derived growth factor receptor protein tyrosine kinase (PDGFR)-α and PDGFR-β genes contributes to their overexpression in canine vascular tumours. Genomic sequences of trans- or juxtamembrane regions of PDGFR-α and PDGFR-β were analysed with immunohistochemical staining and polymerase chain reaction-direct sequencing using DNA from paraffin-embedded neoplastic tissues of 27 hemangiosarcomas (HSAs) and 20 hemangiomas (HAs). Immunohistochemically, 75% of the HA cases were positive for PDGFR-α and almost most of the HA cases were negative for PDGFR-β. Of the HSA cases, 55.6% were negative for PDGFR-α and 63% were strongly positive for PDGFR-β. Among the HA cases, 1 missense mutation was detected in PDGFR-α exon 18 and 1 in PDGFR-β exon 17. Two HSA cases had missense mutations in exon 14 and 1 in exon 17 of PDGFR-β. Thus, genomic mutation of trans- or juxtamembrane regions of PDGFRs was not the main mechanism driving the activation of receptors in HSA and HA.

Design and Synthesis of a Series of Novel Bisquinazoline Glycosides as Epidermal Growth Factor Receptor Inhibitors

A new series of potential epidermal growth factor receptor inhibitors possessing bisquinazoline and saccharide moieties were designed and synthesized. The biological results demonstrated that the synthetic derivatives significantly inhibited epidermal growth factor receptor enzymatic activity in vitro. Of them, compound 14b showed the highest inhibitory rate toward epidermal growth factor receptor protein tyrosine kinase (81.36%) at a concentration of 1 μM. Further molecular simulation predicted that 14b offered its saccharide moieties hydrogen bonding to ATP-binding pocket.

Prediction of Inhibitory Activity of Epidermal Growth Factor Receptor Inhibitors Using Grid Search-Projection Pursuit Regression Method

The epidermal growth factor receptor (EGFR) protein tyrosine kinase (PTK) is an important protein target for anti-tumor drug discovery. To identify potential EGFR inhibitors, we conducted a quantitative structure–activity relationship (QSAR) study on the inhibitory activity of a series of quinazoline derivatives against EGFR tyrosine kinase. Two 2D-QSAR models were developed based on the best multi-linear regression (BMLR) and grid-search assisted projection pursuit regression (GS-PPR) methods. The results demonstrate that the inhibitory activity of quinazoline derivatives is strongly correlated with their polarizability, activation energy, mass distribution, connectivity, and branching information. Although the present investigation focused on EGFR, the approach provides a general avenue in the structure-based drug development of different protein receptor inhibitors.

3D QSAR Studies on a Series of 4-Anilino Quinazoline Derivatives as Tyrosine Kinase (EGFR) Inhibitor: The k-Nearest Neighbor Molecular Field Analysis Approach

Epidermal growth factor receptor (EGFR) protein tyrosine kinases (PTKs) are known for its role in cancer. Quinazoline have been reported to be the molecules of interest, with potent anticancer activity and they act by binding to ATP site of protein kinases. ATP binding site of protein kinases provides an extensive opportunity to design newer analogs. With this background, we report an attempt to discern the structural and physicochemical requirements for inhibition of EGFR tyrosine kinase. The k-Nearest Neighbor Molecular Field Analysis (kNN-MFA), a three dimensional quantitative structure activity relationship (3D- QSAR) method has been used in the present case to study the correlation between the molecular properties and the tyrosine kinase (EGFR) inhibitory activities on a series of quinazoline derivatives using SW, SA and GA variable selection method. kNN-MFA calculations for both electrostatic and steric field were carried out. The master grid maps derived from the best model has been used to display the contribution of electrostatic potential and steric field. The statistical results by SW variable selection method has shown significant correlation coefficient r2 (q2) of 0.9141, r2 for external test set (pred_r2) 0.8033, coefficient of correlation of predicted data set (pred_r2se) of 0.7845, and k nearest neighbor of 2.Therefore, this study not only casts light on binding mechanism between EGFR and its inhibitors, but also provides hints for the design of new EGFR inhibitors with observable structural diversity.

2D QSAR Studies on a Series of Quinazoline Derivatives as Tyrosine Kinase (EGFR) Inhibitor: An Approach to Design Anticancer Agents

Epidermal growth factor receptor (EGFR) protein tyrosine kinases (PTKs) are known for its role in cancer. QSAR studies were performed on a set of 137 analogs of quinazoline using MDS vlife science QSAR plus module by using Multiple Linear Regression (MLR), Principal Component Regression (PCR) and Partial Least Squares (PLS) Regression methods. Among these, MLR method has shown a very promising result as compared to other two methods and a QSAR model was generated by a training set of 100 molecules with correlation coefficient (r2) of 0.884, significant cross validated correlation coefficient (q2) of 0.800, F test of 39.5149, r2 for external test set (pred_r2) 0.5902, coefficient of correlation of predicted data set (pred_r2se) 0.7438 and degree of freedom 83. In the selected descriptors, alignment independent descriptors T_2_C_5 (11.74%) and T_2_O_7 (-11.27%) are the most important descriptors in predicting EGFR inhibitory activity. Electron withdrawing group at anilino quinazolines enhances the activity as evident by positive value of T_F_Cl_4 (2.07%). In addition, for quinazoline substituents, estate contribution descriptors, SaaCHE – index and Ssss NE-index have a large deactivating effect. Keywords: Quinazoline, Tyrosine kinase (EGFR), Multiple Linear Regression (MLR), Principal Component Regression (PCR), Partial Least Squares (PLS)

ChemInform Abstract: Nitrostyrene Derivatives of Adenosine 5′-Glutarates as Selective Inhibitors of the Epidermal Growth Factor Receptor Protein Tyrosine Kinase.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Protein tyrosine phosphatases in glioma biology

Gliomas are a diverse group of brain tumors of glial origin. Most are characterized by diffuse infiltrative growth in the surrounding brain. In combination with their refractive nature to chemotherapy this makes it almost impossible to cure patients using combinations of conventional therapeutic strategies. The drastically increased knowledge about the molecular underpinnings of gliomas during the last decade has elicited high expectations for a more rational and effective therapy for these tumors. Most studies on the molecular pathways involved in glioma biology thus far had a strong focus on growth factor receptor protein tyrosine kinase (PTK) and phosphatidylinositol phosphatase signaling pathways. Except for the tumor suppressor PTEN, much less attention has been paid to the PTK counterparts, the protein tyrosine phosphatase (PTP) superfamily, in gliomas. PTPs are instrumental in the reversible phosphorylation of tyrosine residues and have emerged as important regulators of signaling pathways that are linked to various developmental and disease-related processes. Here, we provide an overview of the current knowledge on PTP involvement in gliomagenesis. So far, the data point to the potential implication of receptor-type (RPTPδ, DEP1, RPTPμ, RPTPζ) and intracellular (PTP1B, TCPTP, SHP2, PTPN13) classical PTPs, dual-specific PTPs (MKP-1, VHP, PRL-3, KAP, PTEN) and the CDC25B and CDC25C PTPs in glioma biology. Like PTKs, these PTPs may represent promising targets for the development of novel diagnostic and therapeutic strategies in the treatment of high-grade gliomas.

Tyrosine-phosphorylation of AAV2 vectors and its consequences on viral intracellular trafficking and transgene expression

We have documented that epidermal growth factor receptor protein tyrosine kinase (EGFR-PTK) signaling negatively affects intracellular trafficking and transduction efficiency of recombinant adeno-associated virus 2 (AAV2) vectors. Specifically, inhibition of EGFR-PTK signaling leads to decreased ubiquitination of AAV2 capsid proteins, which in turn, facilitates viral nuclear transport by limiting proteasome-mediated degradation of AAV2 vectors. In the present studies, we observed that AAV capsids can indeed be phosphorylated at tyrosine residues by EGFR-PTK in in vitro phosphorylation assays and that phosphorylated AAV capsids retain their structural integrity. However, although phosphorylated AAV vectors enter cells as efficiently as their unphosphorylated counterparts, their transduction efficiency is significantly reduced. This reduction is not due to impaired viral second-strand DNA synthesis since transduction efficiency of both single-stranded AAV (ssAAV) and self-complementary AAV (scAAV) vectors is decreased by ∼ 68% and ∼ 74%, respectively. We also observed that intracellular trafficking of tyrosine-phosphorylated AAV vectors from cytoplasm to nucleus is significantly decreased, which results from ubiquitination of AAV capsids followed by proteasome-mediated degradation, although downstream consequences of capsid ubiquitination may also be affected by tyrosine-phosphorylation. These studies provide new insights into the role of tyrosine-phosphorylation of AAV capsids in various steps in the virus life cycle, which has implications in the optimal use of recombinant AAV vectors in human gene therapy.

Synthesis, Antiproliferative Activity, and Structure–Activity Relationships of 3‐Aryl‐1H‐quinolin‐4‐ones

The antiproliferative activities of 36 3-aryl-1H-quinolin-4-ones were determined against two cancer cell lines (Hep G2 and KB) in vitro. The results indicate that most of these compounds show good cytotoxic activity against human cancer cell lines, but no cytotoxicity against a human normal cell line (L02). The positive control compounds genistein and 5-fluorouracil show no selectivity at inhibiting the growth of the above three cell lines. Generally, compounds that bear a halogen atom at the 8 position and a methoxy group at the 3' position exhibited remarkable cytotoxicity toward human cancer cell lines. Electron-withdrawing substituents at the 6 position decrease the antiproliferative activity significantly. We also put forward a pharmacophore model for 3-aryl-4-quinolinones binding with epidermal growth factor receptor protein tyrosine kinases (EGFR PTK). Out of the 36 synthetic compounds, 34 are reported for the first time.

Next generation of adeno-associated virus 2 vectors: Point mutations in tyrosines lead to high-efficiency transduction at lower doses

Recombinant adeno-associated virus 2 (AAV2) vectors are in use in several Phase I/II clinical trials, but relatively large vector doses are needed to achieve therapeutic benefits. Large vector doses also trigger an immune response as a significant fraction of the vectors fails to traffic efficiently to the nucleus and is targeted for degradation by the host cell proteasome machinery. We have reported that epidermal growth factor receptor protein tyrosine kinase (EGFR-PTK) signaling negatively affects transduction by AAV2 vectors by impairing nuclear transport of the vectors. We have also observed that EGFR-PTK can phosphorylate AAV2 capsids at tyrosine residues. Tyrosine-phosphorylated AAV2 vectors enter cells efficiently but fail to transduce effectively, in part because of ubiquitination of AAV capsids followed by proteasome-mediated degradation. We reasoned that mutations of the surface-exposed tyrosine residues might allow the vectors to evade phosphorylation and subsequent ubiquitination and, thus, prevent proteasome-mediated degradation. Here, we document that site-directed mutagenesis of surface-exposed tyrosine residues leads to production of vectors that transduce HeLa cells approximately 10-fold more efficiently in vitro and murine hepatocytes nearly 30-fold more efficiently in vivo at a log lower vector dose. Therapeutic levels of human Factor IX (F.IX) are also produced at an approximately 10-fold reduced vector dose. The increased transduction efficiency of tyrosine-mutant vectors is due to lack of capsid ubiquitination and improved intracellular trafficking to the nucleus. These studies have led to the development of AAV vectors that are capable of high-efficiency transduction at lower doses, which has important implications in their use in human gene therapy.

Protein Tyrosine Phosphorylation and Protein Tyrosine Nitration in Redox Signaling

Reversible phosphorylation of protein tyrosine residues by polypeptide growth factor-receptor protein tyrosine kinases is implicated in the control of fundamental cellular processes including the cell cycle, cell adhesion, and cell survival, as well as cell proliferation and differentiation. During the last decade, it has become apparent that receptor protein tyrosine kinases and the signaling pathways they activate belong to a large signaling network. Such a network can be regulated by various extracellular cues, which include cell adhesion, agonists of G protein-coupled receptors, and oxidants. It is well documented that signaling initiated by receptor protein tyrosine kinases is directly dependent on the intracellular production of oxidants, including reactive oxygen and nitrogen species. Accumulated evidence indicates that the intracellular redox environment plays a major role in the mechanisms underlying the actions of growth factors. Oxidation of cysteine thiols and nitration of tyrosine residues on signaling proteins are described as posttranslational modifications that regulate, positively or negatively, protein tyrosine phosphorylation (PTP). Early observations described the inhibition of PTP activities by oxidants, resulting in increased levels of proteins phosphorylated on tyrosine. Therefore, a redox circuitry involving the increasing production of intracellular oxidants associated with growth-factor stimulation/cell adhesion, oxidative reversible inhibition of protein tyrosine phosphatases, and the activation of protein tyrosine kinases can be delineated.

Pyruvate Dehydrogenase Complex Deficiency Caused by Ubiquitination and Proteasome-mediated Degradation of the E1β Subunit

Congenital deficiencies of the human pyruvate dehydrogenase (PDH) complex are considered to be due to loss of function mutations in one of the component enzymes. Here we describe a case of PDH deficiency associated with the PDH E1beta subunit (PDHB) gene. The clinical phenotype of the patient was consistent with reported cases of PDH deficiency. Cultured skin fibroblasts demonstrated a 55% reduction in PDH activity and markedly decreased immunoreactivity for PDHB protein, compared with healthy controls. Surprisingly, nucleotide sequence analyses of cDNAs corresponding to the patient PDH E1alpha (PDHA1) and PDHB genes revealed no pathological mutations. Moreover, the relative expression level of PDHB mRNA and the rates of transcription and translation of the PDHB gene were normal. However, PDC activity could be restored in cells from this patient following treatment with MG132, a specific proteasome inhibitor, and normal levels of E1beta could be detected in MG132-treated cells. Similar results were obtained following treatment with Tyr-phostin 23 (Tyr23), a specific inhibitor of epidermal growth factor receptor-protein-tyrosine kinase (EGFR-PTK), which also restored E1beta protein levels to those in cells from healthy subjects or from patients with PDHA1 deficiency. The index patient's cells contained a high basal level of EGFR-PTK activity that correlated with the high level of ubiquitination of cellular proteins, although the total EGFR protein levels were similar to those in cells from Elalpha-deficient subjects and healthy subjects. These data indicate that PDH deficiency in our patient involves a post-translational modification in which EGFR-PTK-mediated tyrosine phosphorylation of the E1beta protein leads to enhanced ubiquitination followed by proteasome-mediated degradation. They also provide a novel mechanism accounting for congenital deficiency of the PDH complex and perhaps other inborn errors of metabolism.

A Dual Role of EGFR Protein Tyrosine Kinase Signaling in Ubiquitination of AAV2 Capsids and Viral Second-strand DNA Synthesis

A 52 kd cellular protein, FK506-binding protein (FKBP52), phosphorylated at tyrosine residues by epidermal growth factor receptor protein tyrosine kinase (EGFR-PTK), inhibits adeno-associated virus 2 (AAV2) second-strand DNA synthesis and transgene expression. FKBP52 is dephosphorylated at tyrosine residues by T-cell protein tyrosine phosphatase (TC-PTP), and TC-PTP over-expression leads to improved viral second-strand DNA synthesis and improved transgene expression. In these studies, we observed that perturbation of EGFR-PTK signaling by a specific inhibitor, Tyrphostin 23 (Tyr23), augmented the transduction efficiency of the single-stranded AAV (ssAAV) vector as well as the self-complementary AAV (scAAV) vector. Similarly, tyrosine-dephosphorylation of FKBP52 by TC-PTP resulted in increased transduction by both vectors. These data suggested that EGFR-PTK signaling also affects aspects of AAV transduction other than viral second-strand DNA synthesis. We document that inhibition of EGFR-PTK signaling leads to decreased ubiquitination of AAV2 capsids which, in turn, facilitates nuclear transport by limiting proteasome-mediated degradation of AAV vectors. We also document that Tyr23-mediated increase in AAV2 transduction efficiency is not further enhanced by a specific proteasome inhibitor, MG132. Thus, EGFR-PTK signaling modulates ubiquitin (Ub)/proteasome pathway-mediated intracellular trafficking as well as FKBP52-mediated second-strand DNA synthesis of AAV2 vectors. This has implications in the optimal use of AAV vectors in gene therapy.

Activation of insulin-like growth factor type-1 receptor is required for H2O2-induced PKB phosphorylation in vascular smooth muscle cellsThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference.

Evidence accumulated in recent years has revealed a potential role for reactive oxygen species (ROS) in the pathophysiology of cardiovascular diseases. However, the precise mechanisms by which ROS contribute to the development of these diseases are not fully established. Previous work from our laboratory has indicated that exogenous hydrogen peroxide (H2O2) activates several signaling protein kinases, such as extracellular signal-regulated kinase 1 and 2 (ERK1/2) and protein kinase B (PKB) in A10 vascular smooth muscle cells (VSMC). However, the upstream elements responsible for this activation remain unclear. Although a role for epidermal growth factor receptor (EGFR) protein tyrosine kinase (PTK) in H2O2-induced ERK1/2 signaling has been suggested, the contribution of this PTK or other receptor or nonreceptor PTKs to PKB activation is not well defined in VSMC. In this study, we used pharmacological inhibitors to investigate the role of receptor and Src-family-PTKs in H2O2-induced PKB phosphorylation. AG1478, a specific inhibitor of EGFR, failed to attenuate the H2O2-induced increase in PKB Ser473 phosphorylation, whereas AG1024, an inhibitor of insulin-like growth factor type1 receptor (IGF-1R)-PTK, almost completely blocked this response. H2O2 treatment also enhanced tyrosine phosphorylation of the IGF-1Rbeta subunit, which was significantly inhibited by AG1024 pretreatment of cells. Furthermore, pharmacological inhibition of Src by PP2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazole(3,4-d) pyrimidine) decreased PKB phosphorylation. Moreover, H2O2-induced PKB phosphorylation was associated with increased tyrosine phosphorylation of c-Src and Pyk2 in an AG1024- and PP2-inhibitable manner. In conclusion, these data provide evidence of the contribution of IGF-1R-PTK in initiating H2O2-evoked PKB phosphorylation in A10 VSMC, with an intermediary role for c-Src and Pyk2 in this process.

8. Adeno-Associated Virus 2-Mediated Gene Transfer: A Complex Interaction between Epidermal Growth Factor Receptor Protein Tyrosine Kinase Signaling and Ubiquitin/Proteasome Pathway in Transgene Expression

The transduction efficiency of AAV vectors varies greatly in different cells and tissues in vitro and in vivo. We have documented that a cellular protein, FKBP52, inhibits the viral second-strand DNA synthesis, and consequently, transgene expression (J. Virol., 75: 9818, 2001). FKBP52 is phosphorylated at tyrosine residues by epidermal growth factor receptor protein tyrosine kinase (EGFR-PTK), which inhibits AAV second-strand DNA synthesis by greater than 90% (J. Virol. 72: 9835, 1998; J. Virol., 75: 9818, 2001). Tyrosine-phosphorylated FKBP52 is dephosphorylated by T-cell protein tyrosine phosphatase (TC-PTP), which negatively regulates EGFR-PTK signaling, and leads to a significant increase in AAV transduction (J. Virol. 77: 2741, 2003). We have documented high-efficiency transduction of hepatocytes in TC-PTP-transgenic mice (Gene Ther., 11: 1165, 2004). We have also documented that intracellular trafficking of AAV from cytosol to nucleus is improved in hematopoietic cells from TC-PTP transgenic mice (Hum. Gene Ther., 15: 1207, 2004). In the present studies, we studied the role of EGFR-PTK signaling in AAV-mediated transgene expression. Consistent with our previous studies, less than 5% of HeLa cells were transduced by single-stranded (ss) AAV-EGFP vectors, and pretreatment of cells with Tyrphostin 23 (Tyr23), a specific inhibitor of EGFR-PTK, or stable expression of TC-PTP resulted in respectively |[sim]|12-fold and |[sim]|15-fold increase in AAV transduction. Although transduction by self-complementary (sc) AAV2-EGFP vectors was |[sim]|8-fold higher compared with their ss counterparts, pretreatment with Tyr23 or stable expression of TC-PTP resulted in a further |[sim]|10-fold increase in transduction. These data suggested that Tyr23 and TC-PTP affected other aspects of EGFR-PTK signaling involved in regulating vector transduction. We next examined whether Tyr23 or TC-PTP modulated the ubiquitin/proteasome pathway, both because proteasomes have been implicated in the regulation of EGFR endocytosis, and proteasome inhibitors have been shown to augment AAV transduction. Treatment of HeLa cells with MG132, a specific inhibitor of proteasome, resulted in respectively |[sim]|6-fold and |[sim]|8-fold increase in transduction efficiency of ss and scAAV vectors, However, neither a synergistic nor an additive effect was observed following pretreatment with MG132+Tyr23 or MG132+TC-PTP with either ss or scAAV vectors in HeLa cells. Similar results were obtained with murine fibroblast cell line NIH3T3, adult mouse hepatocyte cell line H2.35, and fetal mouse hepatocyte cell line FL83B. Taken together, these data indicate that complex interactions between EGFR-PTK signaling and ubiquitin/ proteasome pathway affect various aspects of intracellular trafficking and second-strand DNA synthesis of AAV vectors. A better understanding of these interactions is likely to be important in yielding new insights in the optimal use of recombinant AAV vectors in human gene therapy.