Focal adhesion kinase (FAK) regulates cell migration, proliferation, and apoptosis. FAK protein is reduced at the edge of migrating gut epithelial sheets in vitro, but it has not been characterized in restitutive gut mucosa in vivo. Here we show that FAK and activated phospho-FAK (FAK 397 ) immunoreactivity was lower in epithelial cells immediately adjacent to human gastric and colonic ulcers in vivo, but dramatically increased in epithelia near the ulcers, possibly reflecting stimulation by growth factors absent in vitro. Transforming growth factor (TGF)-␤, but not fibroblast growth factor, platelet-derived growth factor, or vascular endothelial growth factor, increased FAK levels in Caco-2 and IEC-6 cells. Epithelial immunoreactivity to TGF-␤ and phospho-Smad3 was also higher near the ulcers, varying in parallel with FAK. The TGF-␤ receptor antagonist SB431542 completely blocked TGF-␤-induced Smad2/3 and p38 activation in IEC-6 cells. SB431542 , the p38 antagonist SB203580 , and siRNA-mediated reduction of Smad2 and p38␣ prevented TGF-␤ stimulation of both FAK transcription and translation (as measured via a FAK promoter-luciferase construct). Survival and function of epithelial cells depends critically on interactions between the extracellular matrix and cell surface integrins. These interactions are mediated through focal adhesions, multicomponent juxtamembrane structures that lie at the convergence of integrin adhesion, signaling, and the cytoskeleton.1 Focal adhesion kinase (FAK) is an important nonreceptor tyrosine kinase within the focal adhesion complex.2 Originally described as being rapidly tyrosine phosphorylated on integrin-mediated cell-matrix adhesion, FAK is now known to be activated during epithelial cell motility and phosphorylated at both serine and tyrosine residues by various factors.3-5 Once localized to sites of transmembrane integrin receptor clustering, tyrosine-phosphorylated FAK plays a central role in signal transduction triggered by diverse extracellular signals 6 and represents a convergent point for synergistic interaction between signal pathways activated by growth factors and integrins.7 FAK binds to different signaling proteins via Src homology 2 (SH2) and SH3 recognition sites, acting as a scaffold and transmitting signals crucial to cell survival, motility, proliferation, and differentiation.8 FAK also regulates the cycle of focal contact formation and disassembly required for efficient cell movement and thus, mucosal restitution. 9Levels of FAK protein expression and/or activation have been correlated to phenotypic changes that affect cell differentiation and function, notably adhesion and migration, in a number of tissues. 10 -13 Targeted FAK deletion in vascular endothelial cells leads to apoptosis and aberrant cell movement whereas FAK overexpression results in increased angiogenesis.14,15 Total and activated FAK levels are also directly related to the state of differentiation in human colon cancer. 16 Induction of differentiation in dedifferentiated, rounded, detached Co...

The Golgi-associated, ␥-adaptin homologous, ADP-ribosylation factor (ARF)-interacting proteins (GGAs) are adaptors that sort receptors from the trans-Golgi network into the endosomal͞lyso-somal pathway. The GGAs and TOM1 (GAT) domains of the GGAs are responsible for their ARF-dependent localization. The 2.4-Å crystal structure of the GAT domain of human GGA1 reveals a three-helix bundle, with a long N-terminal helical extension that is not conserved in GAT domains that do not bind ARF. The ARF binding site is located in the N-terminal extension and is separate from the core three-helix bundle. An unanticipated structural similarity to the N-terminal domain of syntaxin 1a was discovered, comprising the entire three-helix bundle. A conserved binding site on helices 2 and 3 of the GAT domain three-helix bundle is predicted to interact with coiled-coil-containing proteins. We propose that the GAT domain is descended from the same ancestor as the syntaxin 1a N-terminal domain, and that both protein families share a common function in binding coiled-coil domain proteins.

Proteome studies are powerful tools to solve many different problems in metabolism, signal transduction, drug discovery, and other areas of interest in life sciences. Up to now, high-sensitive methods for protein identification after two-dimensional gel electrophoresis using mass spectrometry are available. However, the identification of post-translational modifications after two-dimensional gel electrophoresis is still an unsolved problem. In this paper, we want to give several examples for the successful identification of post-translational modifications and point mutations.

Increasing evidence is available showing the importance of the FAK (focal adhesion kinase) protein level in the migration and homeostasis of intestinal cells. TGFβ (transforming growth factor beta) modulates FAK protein expression in a complex fashion not only by inducing the activation of p38 and Smad signaling resulting in increased fak promoter activity and increased FAK protein levels, but also by activating ERK (extracellular signal regulated kinases), p38, and the Smad pathway. We show that the blockade of ERK signaling by a specific MEK (MAPK kinase) inhibitor attenuates TGFβ–induced FAK mRNA stability and reduces FAK protein levels in rat IEC-6 intestinal epithelial cells. The mTOR (mammalian target of rapamycin)-specific inhibitor rapamycin and small interfering RNAs for mTOR and p70S6 kinase also block TGFβ–induced FAK protein synthesis. Furthermore, we have found that a TGFβ–induced increase in wound closures in monolayers of these cells is abolished in the presence ERK or mTOR inhibition. Thus, TGFβ also modulates FAK protein levels in cultured rat IEC-6 intestinal epithelial cells via ERK activation, acting at the transcriptional level to complement Smad signaling and at on the translational level via the mTOR pathway downstream of ERK, which in turn promotes intestinal epithelial cell migration.

Modulating telomere dynamics may be a useful strategy for targeting prostate cancer cells, because they generally have short telomeres. Because a plateau has been reached in the development of taxane-based treatments for prostate cancer, this study was undertaken to evaluate the relative efficacy of targeting telomeres and microtubules in taxane-sensitive, taxane-resistant, androgen-sensitive, and androgen-insensitive prostate cancer cells. Paclitaxel-and docetaxel-resistant DU145 cells were developed and their underlying adaptive responses were evaluated. Telomere dynamics and the effects of targeting telomeres with sodium meta-arsenite (KML001) (an agent undergoing early clinical trials), including combinations with paclitaxel and docetaxel, were evaluated in parental and drug-resistant cells. The studies were extended to androgensensitive LNCaP cells and androgen-insensitive LNCaP/C81 cells. Both P-glycoprotein (Pgp)-dependent and non-Pgp-dependent mechanisms of resistance were recruited within the same population of DU145 cells with selection for drug resistance. Wild-type DU145 cells have a small side population (SP) (0.4 -1.2%). The SP fraction increased with increasing drug resistance, which was correlated with enhanced expression of Pgp but not breast cancer resistance protein. Telomere dynamics remained unchanged in taxane-resistant cells, which retained sensitivity to KML001. Furthermore, KML001 targeted SP and non-SP fractions, inducing DNA damage signaling in both fractions. KML001 induced telomere erosion, decreased telomerase gene expression, and was highly synergistic with the taxanes in wild-type and drug-resistant DU145 cells. This synergism extended to androgen-sensitive and androgen-insensitive LNCaP cells under basal and androgen-deprived conditions. These studies demonstrate that KML001 plus docetaxel and KML001 plus paclitaxel represent highly synergistic drug combinations that should be explored further in the different disease states of prostate cancer.

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Human phosphatidylinositol 4-kinase, isoform PI4K92, was expressed as His 6 tagged protein in Sf9 cells reaching a level of approximately 5% of cellular protein. The enzyme can be purified nearly to homogeneity in a single step by absorption/desorption on Ni/nitriloacetic acid agarose magnetic beads. High K m values in the millimolar range for ATP and PtdIns as well as only a moderate inhibition by adenosine and a sensitivity to Wortmannin (IC 50 < 300 nm) characterize the enzyme as a type 3 PI4K. The enzyme produces PtdIns4P as product. The isolated enzyme is a phosphoprotein, additionally phosphate is incorporated by incubation with ATP/Mg or ATP/Mn. Phosphorylation sites were mapped by MALDI-MS and LC-MS/MS at the following positions: S258, T263, S266, S277, S294, T423, S496, T504. Accordingly, a stretch of 81 amino acids between the common and the C-terminal catalytic domain was designated phosphorylation domain.