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PubMed2004

Subcellular localization of aflatoxin biosynthetic enzymes Nor-1, Ver-1, and OmtA in time-dependent fractionated colonies of Aspergillus parasiticus.

The biosynthesis of aflatoxin in Aspergillus parasiticus is a complex process that involves the activities of at least 18 pathway enzymes. The distribution of these enzymes within fungal colonies and fungal cells is not clearly understood. The objective of this study was to investigate the distribution and subcellular location of Nor-1, Ver-1, and OmtA, which represent early, middle, and late enzymatic activities, respectively, in the aflatoxin biosynthetic pathway. The distribution of these three enzymes within A. parasiticus SU-1 was analyzed in time-fractionated, 72-h fungal colonies (fraction 1, 48-72 h; fraction 2, 24-48 h; fraction 3, 0-24 h). Western blot analysis and immunofluorescence microscopy demonstrated the highest abundance of Nor-1, Ver-1, and OmtA in colony fraction 2. Fungal tissues in this fraction were analyzed by immunoelectron microscopy. Nor-1 and Ver-1 were primarily localized to the cytoplasm, suggesting that they are cytosolic enzymes. OmtA was also detected in the cytoplasm. However, in cells located near the basal (substrate) surface of the colony, OmtA was predominantly detected in organelles tentatively identified as vacuoles. The role of this organelle in toxin biosynthesis is unclear. The relative distribution of OmtA to the cytoplasm or to vacuole-like organelles may depend on the age and/or physiological condition of the fungal cells.

Aflatoxins↗
PubMed2001

Induction and subcellular localization of protein kinase C isozymes following renal ischemia.

BACKGROUND: We have previously reported that the expression of the receptor for activated C kinase (RACK1) is induced post-ischemia/preperfusion injury to the kidney, and activation of protein kinase C (PKC) protects renal cells from hypoxic injury. This study was done to determine whether the induced expression of RACK1 is accompanied by changes in the level of expression and subcellular distribution of PKC isozymes. METHODS: Ischemia/reperfusion injury resulting in acute renal failure was induced by 60 minutes of bilateral renal artery clamping in rats. The expression levels and translocation of various PKC isozymes between soluble and particulate fractions in whole kidney homogenates were demonstrated by immunoblot analysis. The expression pattern of the various PKC isozymes in the kidney postinjury was performed by immunohistochemistry. RESULTS: PKC alpha, beta II, and zeta were induced and translocated from the soluble fraction to the particulate fraction post-injury. Immunolocalization showed PKC alpha, beta II, and zeta expression to be induced in the proximal tubule epithelial cell (PTEC) at 0 to 30 minutes post-ischemia/reperfusion injury (IRI). At one-day postinjury, the alpha isozyme was translocated to the plasma membrane of the undamaged PTEC, while it was translocated to the nucleus in damaged PTEC. PKC beta II expression was along the basal and lateral side of the undamaged PTEC, while it was distributed in the cytoplasm of sloughed cells in the damaged PTEC. PKC zeta expression at one day was along the apical side of the damaged PTEC. At seven-days postinjury, the expressions of the alpha and zeta isozymes were localized to the plasma membrane of the regenerating PTEC and the expression of PKC beta II isozyme to certain interstitial cells. CONCLUSION: The induced expression, translocation, and the intracellular spatial distributions of the enzymes suggest that they may mediate multiple processes during IRI.

Acute Kidney Injury↗
PubMedDate not supplied

Subcellular localization of IRS-1 in cell proliferation and differentiation.

The type 1 insulin-like growth factor receptor (IGF-IR) and its docking protein, insulin receptor substrate-1 (IRS-1), play important roles in cell transformation, cell differentiation and aging. IRS-1 and other IRS proteins can, under certain conditions, localize to the nuclei of cells, where they undergo interactions with nuclear and nucleolar proteins. In this study, we confirm and extend these observations, demonstrating that IRS-1 is preferentially nuclear in growing cells. Differentiation and inhibition of ribosomal RNA synthesis cause subcellular redistribution of IRS-1 and other nuclear proteins to the cytoplasm.

Animals↗
PubMed2001

Cellular and subcellular localization of gastrointestinal glutathione peroxidase in normal and malignant human intestinal tissue.

The gastrointestinal glutathione peroxidase (GI-GPx) is believed to prevent absorption of hydroperoxides. GI-GPx is expressed in the intestine together with the other three glutathione peroxidase isoenzymes, raising the question of the physiological role of the different GPx types. We therefore studied the cellular and subcellular distribution of GI-GPx in normal and malignant tissue obtained from patients with colorectal cancer or familial polyposis by immunohistochemistry. In healthy ileum epithelium GI-GPx was preferentially enriched in Paneth cells. In unaffected crypts of colon and rectum, it decreased gradually from the ground to the luminal surface. In crypt ground, GI-GPx was uniformly distributed, whereas in cells at the luminal surface it was concentrated in structures capping the nuclei at the apical pole. In colorectal cancer, GI-GPx expression depended on the stage of malignant transformation. In early stages, GI-GPx was increased and pronouncedly associated with the vesicular structures. In progressed stages of malignancy, structures disintegrated and GI-GPx distribution became more diffuse. These observations support the hypothesis that GI-GPx, apart from being a barrier against hydroperoxide absorption, might be involved in cell growth and differentiation.

Adenomatous Polyposis Coli↗
PubMed1997

Subcellular localization of myosin-V in the B16 melanoma cells, a wild-type cell line for the dilute gene.

The discovery that the dilute gene encodes a class V myosin led to the hypothesis that this molecular motor is involved in melanosome transport and/or dendrite outgrowth in mammalian melanocytes. The present studies were undertaken to gain insight into the subcellular distribution of myosin-V in the melanoma cell line B16-F10, which is wild-type for the dilute gene. Immunofluorescence studies showed some degree of superimposed labeling of myosin-V with melanosomes that predominated at the cell periphery. A subcellular fraction highly enriched in melanosomes was also enriched in myosin-V based on Western blot analysis. Immunoelectron microscopy showed myosin-V labeling associated with melanosomes and other organelles. The stimulation of B16 cells with the alpha-melanocyte-stimulating hormone led to a significant increase in myosin-V expression. This is the first evidence that a cAMP signaling pathway might regulate the dilute gene expression. Immunofluorescence also showed an intense labeling of myosin-V independent of melanosomes that was observed within the dendrites and at the perinuclear region. Although the results presented herein are consistent with the hypothesis that myosin-V might act as a motor for melanosome translocation, they also suggest a broader cytoplasmic function for myosin-V, acting on other types of organelles or in cytoskeletal dynamics.

Animals↗
PubMed2000

Torsin A and its torsion dystonia-associated mutant forms are lumenal glycoproteins that exhibit distinct subcellular localizations.

Early-onset torsion dystonia is an autosomal dominant hyperkinetic movement disorder that has recently been linked to a 3-base pair deletion in the DYT1 gene. The DYT1 gene encodes a 332-amino acid protein, torsin A, that bears low but significant homology to the Hsp100/Clp family of ATPase chaperones. The deletion in DYT1 associated with torsion dystonia results in the loss of one of a pair of glutamic acid residues residing near the C terminus of torsin A (DeltaE-torsin A). At present, little is known about the expression, subcellular distribution, and/or function of either the torsin A or DeltaE-torsin A protein. When transfected into mammalian cells, both torsin A and DeltaE-torsin A were found to behave as lumenally oriented glycoproteins. Immunofluorescence studies revealed that torsin A localized to a diffuse network of intracellular membranes displaying significant co-immunoreactivity for the endoplasmic reticulum resident protein BiP, whereas DeltaE-torsin A resided in large spheroid intracellular structures exclusive of BiP immunoreactivity. These results initially suggested that DeltaE-torsin A might exist as insoluble aggregates. However, both torsin A and DeltaE-torsin A were readily solubilized by nonionic detergents, were similarly accessible to proteases, and displayed equivalent migration patterns on sucrose gradients. Collectively, these data support that both the wild type and torsion dystonia-associated forms of torsin A are properly folded, lumenal proteins of similar oligomeric states. The potential relationship between the altered subcellular distribution of DeltaE-torsin A and the disease-inducing phenotype of the protein is discussed.

Animals↗
PubMed2003

Distinct subcellular localizations of Nox1 and Nox4 in vascular smooth muscle cells.

OBJECTIVE: Reactive oxygen species (ROS) that act as signaling molecules in vascular smooth muscle cells (VSMC) and contribute to growth, hypertrophy, and migration in atherogenesis are produced by multi-subunit NAD(P)H oxidases. Nox1 and Nox4, two homologues to the phagocytic NAD(P)H subunit gp91phox, both generate ROS in VSMC but differ in their response to growth factors. We hypothesize that the opposing functions of Nox1 and Nox4 are reflected in their differential subcellular locations. METHODS AND RESULTS: We used immunofluorescence to visualize the NAD(P)H subunits Nox1, Nox4, and p22phox in cultured rat and human VSMC. Optical sectioning using confocal microscopy showed that Nox1 is co-localized with caveolin in punctate patches on the surface and along the cellular margins, whereas Nox4 is co-localized with vinculin in focal adhesions. These immunocytochemical distributions are supported by membrane fractionation experiments. Interestingly, p22phox, a membrane subunit that interacts with the Nox proteins, is found in surface labeling and in focal adhesions in patterns similar to Nox1 and Nox4, respectively. CONCLUSIONS: The differential roles of Nox1 and Nox4 in VSMC may be correlated with their differential compartmentalization in specific signaling domains in the membrane and focal adhesions.

Animals↗