Na(+) absorption is a vital process present in all living organisms. We have reported previously that lysophosphatidic acid (LPA) acutely stimulates Na(+) and fluid absorption in human intestinal epithelial cells and mouse intestine by stimulation of Na(+)/H(+) exchanger 3 (NHE3) via LPA(5) receptor. In the current study, we investigated the mechanism of NHE3 activation by LPA(5) in Caco-2bbe cells. LPA(5)-dependent activation of NHE3 was blocked by mitogen-activated protein kinase kinase (MEK) inhibitor PD98059 and U0126, but not by phosphatidylinositol 3-kinase inhibitor LY294002 or phospholipase C-β inhibitor U73122. We found that LPA(5) transactivated the epidermal growth factor receptor (EGFR) and that inhibition of EGFR blocked LPA(5)-dependent activation of NHE3, suggesting an obligatory role of EGFR in the NHE3 regulation. Confocal immunofluorescence and surface biotinylation analyses showed that LPA(5) was located mostly in the apical membrane. EGFR, on the other hand, showed higher expression in the basolateral membrane. However, inhibition of apical EGFR, but not basolateral EGFR, abrogated LPA-induced regulation of MEK and NHE3, indicating that LPA(5) selectively activates apical EGFR. Furthermore, transactivation of EGFR independently activated the MEK-ERK pathway and proline-rich tyrosine kinase 2 (Pyk2). Similarly to MEK inhibition, knockdown of Pyk2 blocked activation of NHE3 by LPA. Furthermore, we showed that RhoA and Rho-associated kinase (ROCK) are involved in activation of Pyk2. Interestingly, LPA(5) did not directly activate RhoA but was required for transactivation of EGFR. Together, these results unveil a pivotal role of apical EGFR in NHE3 regulation by LPA and show that the RhoA-ROCK-Pyk2 and MEK-ERK pathways converge onto NHE3.

Tumors of the exocrine pancreas have a poor prognosis. Several proteins are overexpressed in this cancer type, including the MET tyrosine kinase receptor and the transcription factor PAX6. In this report, we find that PAX6(5a), an alternately spliced variant form of PAX6, is expressed in pancreatic carcinoma cell lines at higher levels than the canonical PAX6 protein. Both protein forms of PAX6 bind directly to an enhancer element in the MET promoter and activate the expression of the MET gene. In addition, inhibition of PAX6 transcripts leads to a decline in cell growth and survival, differentiation, and a concurrent reduction of MET protein expression. These data support a model for a neoplastic pathway, where expression of a transcription factor from development activates the MET receptor, a protein that has been directly linked to protumorigenic processes of resisting apoptosis, tumor growth, invasion, and metastasis.Pancreatic cancer is an aggressive and deadly disease, with an average median survival of less than a year (1). Several genetic pathways have been identified as being active in the progression of this tumor, including signaling through MET (MET tyrosine kinase receptor protein). The MET gene encodes a tyrosine kinase receptor for the ligand hepatocyte growth factor/scatter factor. The MET gene produces a partially glycosylated 170-kDa precursor protein. This precursor is glycosylated further and cleaved into a 50-kDa ␣ chain and a 140-kDa ␤ chain to create a mature receptor (2). The MET receptor is essential for normal development and plays a role in cell migration, growth, survival, differentiation, angiogenesis, and tube formation/ branching morphogenesis (reviewed in Ref.3). MET has also been implicated in cancer progression and is directly involved in metastasis, resistance to apoptosis, and tumor growth.MET is expressed in the developing pancreatic bud of the embryo and marks candidate stem/progenitor cells in the embryonic and adult pancreas (4 -6). MET expression is expressed at very low levels in normal adult differentiated pancreatic cells (7). MET is overexpressed in pancreatic cancer cells and has been linked to the aggressiveness of this tumor in terms of growth, invasion, and metastasis (7-10).Although mutations in the MET locus have been identified, overexpression of MET occurs mainly due to aberrant transcriptional regulation (3). The MET gene is regulated by several transcription factors that can either activate or repress expression. Activators include HIF1 (hypoxia-induced factor 1) in response to oxygen deficiency (11), ETS1 (12), Sp1 (13), AP1 (14), Smads downstream of transforming growth factor-␤ signaling (13), and the p53 protein (15) The transcription factor PAX3 can also activate MET expression during the embryonic development of muscle cells (23). PAX3 belongs to the PAX gene family, and most of what is known about these related proteins is their role during development. Only recently has the expression of PAX proteins in adult stem cells and in disease been discovered...

The purpose of this study was to develop the modified carbapenem inactivation method (mCIM) for the detection of carbapenemase-producing (CP-PA) and carbapenemase-producing (CP-AB) and perform a multicenter evaluation of the mCIM and Carba NP tests for these nonfermenters. Thirty and 30 isolates previously characterized by whole-genome sequencing from the CDC-FDA Antibiotic Resistance Isolate Bank were evaluated, including CP isolates (Ambler class A, B, and D), non-carbapenemase-producing (non-CP) carbapenem-resistant isolates, and carbapenem-susceptible isolates. Initial comparison of a 1-μl versus 10-μl loop inoculum for the mCIM was performed by two testing sites and showed that 10 μl was required for reliable detection of carbapenemase production among and Ten testing sites then evaluated the mCIM using a 10-μl loop inoculum. Overall, the mean sensitivity and specificity of the mCIM for detection of CP-PA across all 10 sites were 98.0% (95% confidence interval [CI], 94.3 to 99.6; range, 86.7 to 100) and 95% (95% CI, 89.8 to 97.7; range, 93.3 to 100), whereas the mean sensitivity and specificity among CP-AB were 79.8% (95% CI, 74.0 to 84.9; range, 36.3 to 95.7) and 52.9% (95% CI, 40.6 to 64.9; range, 28.6 to 100), respectively. At three sites that evaluated the performance of the Carba NP test using the same set of isolates, the mean sensitivity and specificity of the Carba NP test were 97.8% (95% CI, 88.2 to 99.9; range, 93.3 to 100) and 97.8% (95% CI, 88.2 to 99.9; range, 93.3 to 100) for and 18.8% (95% CI, 10.4 to 30.1; range, 8.7 to 26.1) and 100% (95% CI, 83.9 to 100; range, 100) for Overall, we found both the mCIM and the Carba NP test to be accurate for detection of carbapenemase production among isolates and less reliable for use with isolates.

cell line represents absorptive polarized intestinal epithelial cells that express multiple forms of Na ϩ /H ϩ exchanger (NHE) in their plasma membranes. Caco-2 cells express the major apical NHE isoform NHE3, but low NHE3 expression together with inefficient transfection often hamper intended studies. In this study, we examined whether SK-CO15 cells could be used to study NHE3 regulation. SK-CO15 cells grown on Transwell inserts developed polarized epithelial cells with microvilli. The transfection efficiency of SK-CO15 cells was markedly higher compared with Caco-2 cells, an advantage in gene transfer and knockout. SK-CO15 cells expressed NHE1, NHE2, and NHE3. NHE3 expression was significantly greater in these cells than Caco-2, and NHE3 comprised more than half of total NHE activity. Apical expression of NHE3 in SK-CO15 cells was confirmed by confocal immunofluorescence and surface biotinylation. NHE regulatory factors NHERF1 and NHERF2, which are important for regulation of NHE3 activity, were expressed in these cells. Stimulatory response of NHE3 in SK-CO15 cells was assessed by dexamethasone and lysophosphatidic acid (LPA). Treatment with dexamethasone for 24 -48 h increased NHE3 expression and activity. Similarly to Caco-2 cells, SK-CO15 cells lacked the expression of the LPA receptor LPA 5, but exogenous expression of LPA5 resulted in acute stimulation of NHE3. Forskolin acutely inhibited NHE3 activity in SK-CO15 cells, further attesting the validity of these cells. We conclude that SK-CO15 cells with the amenity for transfection and high endogenous NHE3 expression are a new and better cell model for NHE3 regulatory investigation than widely used Caco-2 cells.intestine; epithelia POLARIZED INTESTINAL EPITHELIAL cells form an interface separating the internal from external environments and maintain homeostasis between intestinal lumen and the body interior. The plasma membranes of polarized epithelial cells are divided into apical and basolateral domains with asymmetric distribution of cytoplasmic organelles by vectorial sorting mechanisms (27). Na ϩ /H ϩ exchange is a major route of Na ϩ absorption in the small intestine and colon (9). Intestinal epithelial cells express multiple forms of Na ϩ /H ϩ exchangers (NHEs; Slc9a) among which the type 3, NHE3 (Slc9a3), is the primary brush-border NHE. The functions and mechanisms of NHE3 regulation by hormones and growth factors have been investigated since its cloning in the early 1990s using several cell model systems. Among these, PS120 Chinese hamster lung fibroblasts and AP1 Chinese hamster ovarian cells provide an ideal cell system for reductionist approach to characterize NHEs (26, 28). However, the nonepithelial origins of PS120 and AP1 cells often led to question the physiological validity of the findings. Originated from human intestines, T84 and HT29 human colon carcinoma epithelial cell lines are not suitable, as these cells represent secretory crypt epithelial cells (5, 6). The Caco-2 human adenocarcinoma cell line, on the other hand, express severa...

Background: Regulation of NHE3 by ubiquitination has not been reported. Results: Human NHE3, but not non-primates NHE3s, is ubiquitinated by Nedd4-2 and undergoes internalization at an increased rate. Conclusion: Human NHE3 is uniquely regulated by ubiquitination. Significance: This study provides a new mechanism of regulating NHE3 in human that may be relevant to diseases associated with increased Na ϩ and fluid absorption.

Cross-seeding of misfolded amyloid proteins is postulated to induce cross-species infection of prion diseases. In sporadic Alzheimer's disease (AD), misfolding of 42-residue β-amyloid (Aβ) is widely considered to trigger amyloid plaque deposition. Despite increasing evidence that misfolded Aβ mimics prions, interactions of misfolded 42-residue Aβ42 with more abundant 40-residue Aβ40 in AD are elusive. This study presents in vitro evidence that a heterozygous E22G pathogenic ("Arctic") mutation of Aβ40 can enhance misfolding of Aβ via cross-seeding from wild-type (WT) Aβ42 fibril. Thioflavin T (ThT) fluorescence analysis suggested that misfolding of E22G Aβ40 was enhanced by adding 5% (w/w) WT Aβ42 fibril as "seed", whereas WT Aβ40 was unaffected by Aβ42 fibril seed. C SSNMR analysis revealed that such cross-seeding prompted formation of E22G Aβ40 fibril that structurally mimics the seed Aβ42 fibril, suggesting unexpected cross talk of Aβ isoforms that potentially promotes early onset of AD. The SSNMR approach is likely applicable to elucidate structural details of heterogeneous amyloid fibrils produced in cross-seeding for amyloids linked to neurodegenerative diseases.

Na(+)/H(+) exchange by Na(+)/H(+) exchanger 3 (NHE3) is a major route of sodium absorption in the intestine and kidney. We have shown previously that lysophosphatidic acid (LPA), a small phospholipid produced ubiquitously by all types of cells, stimulates NHE3 via LPA5 receptor. Stimulation of NHE3 activity by LPA involves LPA5 transactivating EGF receptor (EGFR) in the apical membrane. EGFR activates proline-rich tyrosine kinase 2 (Pyk2) and ERK, both of which are necessary for NHE3 regulation. However, Pyk2 and ERK are regulated by EGFR via independent pathways and appear to converge on an unidentified intermediate that ultimately targets NHE3. The p90 ribosomal S6 kinase (RSK) family of Ser/Thr protein kinases is a known effector of EGFR and ERK. Hence, we hypothesized that RSK may be the convergent effector of Pyk2 and ERK although it is not known whether Pyk2 regulates RSK. In this study, we show that Pyk2 is necessary for the maintenance of phosphoinositide-dependent kinase 1 (PDK1) autophosphorylation, and knockdown of Pyk2 or PDK1 mitigated LPA-induced phosphorylation of RSK and stimulation of NHE3 activity. Additionally, we show that RSK2, but not RSK1, is responsible for NHE3 regulation. RSK2 interacts with NHE3 at the apical membrane domain, where it phosphorylates NHE3. Alteration of S663 of NHE3 ablated LPA-induced phosphorylation of NHE3 and stimulation of the transport activity. Our study identifies RSK2 as a new kinase that regulates NHE3 activity by direct phosphorylation.

Background: Association of redox-active Cu 2ϩ with aggregated A␤ in amyloid plaques has been linked with ROS and oxidative stress in AD. Results: Cu 2ϩ /Cu ϩ -bound A␤ fibrils undergo a redox cycle reaction with ascorbate and oxygen to produce H 2 O 2 .