TA strategy for rapid and efficient site-directed mutagenesis.

A simple, rapid, and efficient site-directed mutagenesis method using TA strategy with synthetic mutagenic oligonucleotides is described. Briefly, a 3' A-overhang vector was prepared by polymerase chain reaction (PCR) using a classical Taq polymerase with terminal transferase activity, a reverse vector primer starting the complement nucleotide prior to the 5' end adenosine of the target, and a forward vector primer starting the nucleotide posterior to the 3' end thymidine. The 3' T-overhang mutagenic double-strand oligonucleotide was synthesized and cloned directly into the PCR-amplified 3' A-overhang vector. Thus, direct ligation of synthetic mutagenic oligonucleotides and PCR-amplified vector via TA sticky ends provides us with simple, rapid, and efficient site-directed mutagenesis.

Reactive oxygen generated by NADPH oxidase 1 (Nox1) contributes to cell invasion by regulating matrix metalloprotease-9 production and cell migration.

A mediating role of the reactive oxygen species-generating enzyme Nox1 has been suggested for Ras oncogene transformation phenotypes including anchorage-independent cell growth, augmented angiogenesis, and tumorigenesis. However, little is known about whether Nox1 signaling regulates cell invasiveness. Here, we report that the cell invasion activity was augmented in K-Ras-transformed normal rat kidney cells and attenuated by transfection of Nox1 small interference RNAs (siRNAs) into the cells. Diphenyleneiodonium (DPI) or Nox1 siRNAs blocked up-regulation of matrix metalloprotease-9 at both protein and mRNA levels in K-Ras-transformed normal rat kidney cells. Furthermore, DPI and Nox1 siRNAs inhibited the activation of IKKalpha kinase and the degradation of IkappaB alpha, suppressing the NFkappaB-dependent matrix metalloprotease-9 promoter activity. Additionally, epidermal growth factor-stimulated migration of CaCO-2 cells was abolished by DPI and Nox1 siRNAs, indicating the requirement of Nox1 activity for the motogenic effect of epidermal growth factor. This Nox1 action was mediated by down-regulation of the Rho activity through the low molecular weight protein-tyrosine phosphatase-p190RhoGAP-dependent mechanism. Taken together, our findings define a mediating role of Nox1-generated reactive oxygen species in cell invasion processes, most notably metalloprotease production and cell motile activity.

A possible biochemical link between NADPH oxidase (Nox) 1 redox-signalling and ERp72.

Emerging evidence indicates that Nox (NADPH oxidase) 1-generated ROS (reactive oxygen species) play critical regulatory roles in various cellular processes, yet little is known of direct targets for the oxidase. In the present study we show that one of the proteins selectively oxidized in response to Nox1-generated ROS was ERp72 (endoplasmic reticulum protein 72 kDa) with TRX (thioredoxin) homology domains. Oxidation of ERp72 by Nox1 resulted in an inhibition of its reductase activity. EGF treatment of cells stimulated the Nox1 activity and the activated Nox1 subsequently mediated EGF-induced suppression of the ERp72 reductase activity. Co-immunoprecipitation, GST (glutathione transferase) pulldown assays and mutational analysis, indicated that Nox1 associates with ERp72, which involves its N-terminus encompassing a Ca(2+)-binding site and the first TRX-like motif. Furthermore, confocal microscopy showed co-localization between Nox1 and ERp72 at the plasma membrane. These results suggest that Nox1 functionally associates with ERp72, regulating redox-sensitive signalling pathways in a cellular context.

A reducing and denaturing step maximizes the immunoprecipitations of m-calpain and I-2(PP2A)/SET: an approach toward antibodies that do not work well in immunoprecipitation.

Immunoprecipitation is an elegant method to isolate a specific protein of interest from a complex protein mixture such as cell lysate. We tried to increase the efficiency of m-calpain immunoprecipitation with anti-m-calpain antibodies directed toward denatured antigens that only work for immunoblotting and immunohistochemistry. We found that a reducing and denaturing step prior to immunoprecipitation greatly potentiates the efficiency of the immunoreaction. This improved method is also applicable for the immunoprecipitation of oncoprotein I-2(PP2A)/SET with antibodies directed toward a synthetic peptide that only work for immunoblotting. Thus, our improved method provides a way to maximize immunoprecipitation when using antibodies that do not work well under conventional immunoprecipitation conditions. Furthermore, the improved method is also suitable for decreasing the contaminating proteins during immunoprecipitation.

The oncoprotein I-2PP2A/SET negatively regulates the MEK/ERK pathway and cell proliferation.

I-2PP2A/SET, the translocation breakpoint-encoded protein expressed in acute undifferentiated leukemia, was identified as an inhibitor of protein phosphatase 2A (PP2A). Induction of exogenous I-2PP2A/SET at a ratio of 1:1 to the endogenous protein resulted in suppression of cell proliferation. In contrast, siRNA-mediated depletion of I-2PP2A/SET resulted in enhanced cell proliferation. Depletion of I-2PP2A/SET was accompanied with a decrease in the number of cells in G1 and an increase in cells in S phase. To examine the mode of action by which I-2PP2A/SET suppresses cell proliferation, we determined the effect of over-expressed I-2PP2A/SET on ERK activation. I-2PP2A/SET suppressed activation of ERK following EGF stimulation but did not affect activation levels of stress kinases, JNK and p38. By contrast, knocking down I-2PP2A/SET by siRNA resulted in enhancement of ERK and MEK activations, suggesting that I-2PP2A/SET negatively regulates MEK/ERK. These data suggest that I-2PP2A/SET negatively regulates cell growth by inhibiting the G1/S transition and inhibiting the MEK/ERK pathway stimulated by external stimuli. These data demonstrate that I-2PP2A/SET potentially functions as a tumor suppressor.

Expression of LUN gene that encodes a novel RING finger protein is correlated with development and progression of non-small cell lung cancer.

LUN is a novel RING finger protein that is highly expressed in the lung and might be a transcriptional regulator of E-cadherin [J. Biol. Chem. 276 (2001) 14004]. It might be possible that LUN plays important roles in the development and progression of lung cancer through regulating expression of E-cadherin, but no clinical study on LUN expression has been reported. In the present study, we quantitatively examined gene expression of the LUN in surgical specimens resected from non-small cell lung cancer (NSCLC) patients. In normal lung tissues, the LUN gene expression was down-regulated in smokers (the mean LUN/GAPDH ratios, 0.222 for non-smokers and 0.144 for smokers; P = 0.030). In addition, the mean LUN/GAPDH ratio in lung cancer tissues was significantly lower than that in normal lung tissues (0.072 versus 0.162; P < 0.001). In addition, the LUN gene expression was slightly down-regulated along with progression of primary tumors, and strongly down-regulated along with nodal metastases (the mean LUN/GAPDH ratios, 0.091 for pN0, 0.073 for pN1, and 0.034 for pN2 diseases; P = 0.001). These results suggested that LUN might play important roles in inhibition of nodal metastases as well as in suppression of smoking-related oncogenesis in NSCLC.

Regulation of amphiphysin1 by mitogen-activated protein kinase: its significance in nerve growth factor receptor-mediated endocytosis.

Amphiphysin1, which can simultaneously bind to dynamin1 and the clathrin adaptor AP-2, is essential for dynamin1 recruitment during receptor-mediated endocytosis, but little is known about its regulatory mechanism. Here, we purified a 120-kDa mitogen-activated protein kinase (MAPK) substrate protein from porcine brains and identified the protein as amphiphysin1. Serine phosphorylation of amphiphysin1 was rapidly induced by nerve growth factor (NGF) in PC12 cells, and the induction was blocked by a MAPK inhibitor. Furthermore, when phosphorylated by MAPK in vitro or by NGF treatment in vivo, amphiphysin1 failed to bind to AP-2, but its association with dynamin1 was unaffected. Consistent with this, mutation of consensus MAPK phosphorylation sites increased amphiphysin1 binding to AP-2 and their intracellular colocalization. Thus, we propose that MAPK phosphorylation of amphiphysin1 controls NGF receptor/TrkA-mediated endocytosis by terminating the amphiphysin1-AP-2 interaction. This perhaps helps to regulate the availability of amphiphysin1-dynamin1 complexes for binding to the endocytic vesicle.