Immunoelectron microscopic localization of the 210,000-mol wt microtubule-associated protein in cultured cells of primates

Results from ultrastructural immunocytochemistry on glutaraldehyde- fixed cells confirmed and extended findings previously obtained with immunofluorescence. A microtubule-associated protein (MAP) of 210,000 molecular weight was shown to be specifically associated with all cytoplasmic and mitotic microtubules along their entire length in primate cells. Specific labeling with the anti-MAP antibody could not be detected on any other subcellular structures, notably the centrosomes, kinetochores, microfilaments, and intermediate filaments. Treatment with the microtubule-disrupting drug, nocodazole, induced diffusion of the MAP throughout the cytoplasm. During repolymerization of microtubules following disassembly by nocodazole, the association of the MAP with the microtubules was intermediate and complete. When cells were treated with vinblastine, the tubulin paracrystals formed were heavily stained by the antibody. Neither sodium azide nor taxol affected the association of the MAP with microtubules.     

Nuclear distribution pattern of tumour-associated nonhistone protein of mol. wt 48,000.

• 1.1. As a further step toward characterizing nonhistone protein of mol. wt 48,000 which was found to be much more abundant in animal tumour cells than in normal ones [Krajewska W.M., Lipinska A., Marszatek M., Kiliańska Z., Wojtkowiak Z. and Kłyszejko-Stefanowicz L. Cell. Biochem. Funct. 8, 79–89 (1990)] its intranuclear localization in hamster liver and Kirkman-Robbins hepatoma was studied. The protein was identified by immunoblotting technique in the presence of antibodies against polypeptide of mol. wt about 48,000 from Kirkman-Robbins hepatoma.
• 2.2. Distribution of antigen with mol. wt of 48,000 in nuclear fractions representing different levels of nuclear material organization i.e. in nucleoli, nuclease-sensitive and nuclease-resistant fractions, and extensive nuclease digestion products separated by size on Bio-Gel A-50m, implied the structural role of this component.
• 3.3. Fractionation of endogenously digested nuclei into low salt extract, high salt extract and nuclear matrix revealed that in normal liver the antigen studied is associated with nuclear matrix while in hepatoma this component appeared in high salt extract.
• 4.4. These results suggest that polypeptide with mol. wt of 48,000 is a shuttling protein which may be involved in reorganization of nuclear matrix during neoplastic transformation.

     

Cellular distribution of a protein related to neuronal microtubule-associated protein MAP-2 in Leydig cells

A monoclonal antibody to neuronal microtubule-associated protein MAP-2 was produced. Immunoblotting of lysates of cultured cells revealed that the antibody, called MA-01, bound to a protein of Mr 210 kDa. Double immunofluorescence microscopy showed that the antibody stained microtubules. No fibrillar structures were observed in cells treated with Colcemid, but the antibody stained vinblastine paracrystals. In cytochalasin B-treated Leydig cells, MA-01 antibody stained star-like structures that codistributed with actin patches and with a star-like arrangement of vimentin. These observations indicate that the protein immunologically related to MAP-2 in Leydig cells could be involved in the interaction of microtubules with intermediate filaments or microfilaments.     

Widespread distribution of the major polypeptide component of MAP 1 (microtubule-associated protein 1) in the nervous system

We prepared a monoclonal antibody to microtubule-associated protein 1 (MAP 1), one of the two major high molecular weight MAP found in microtubules isolated from brain tissue. We found that MAP 1 can be resolved by SDS PAGE into three electrophoretic bands, which we have designated MAP 1A, MAP 1B, and MAP 1C in order of increasing electrophoretic mobility. Our antibody recognized exclusively MAP 1A, the most abundant and largest MAP 1 polypeptide. To determine the distribution of MAP 1A in nervous system tissues and cells, we examined tissue sections from rat brain and spinal cord, as well as primary cultures of newborn rat brain by immunofluorescence microscopy. Anti-MAP 1A stained white matter and gray matter regions, while a polyclonal anti-MAP 2 antibody previously prepared in this laboratory stained only gray matter. This confirmed our earlier biochemical results, which indicated that MAP 1 is more uniformly distributed in brain tissue than MAP 2 (Vallee, R.B., 1982, J. Cell Biol., 92:435-442). To determine the identity of cells and cellular processes immunoreactive with anti-MAP 1A, we examined a variety of brain and spinal cord regions. Fibrous staining of white matter by anti-MAP 1A was generally observed. This was due in part to immunoreactivity of axons, as judged by examination of axonal fiber tracts in the cerebral cortex and of large myelinated axons in the spinal cord and in spinal nerve roots. Cells with the morphology of oligodendrocytes were brightly labeled in white matter. Intense staining of Purkinje cell dendrites in the cerebellar cortex and of the apical dendrites of pyramidal cells in the cerebral cortex was observed. By double-labeling with antibodies to MAP 1A and MAP 2, the presence of both MAP in identical dendrites and neuronal perikarya was found. In primary brain cell cultures anti-MAP 2 stained predominantly cells of neuronal morphology. In contrast, anti-MAP 1A stained nearly all cells. Included among these were neurons, oligodendrocytes and astrocytes as determined by double-labeling with anti-MAP 1A in combination with antibody to MAP 2, myelin basic protein or glial fibrillary acidic protein, respectively. These results indicate that in contrast to MAP 2, which is specifically enriched in dendrites and perikarya of neurons, MAP 1A is widely distributed in the nervous system.     

Comparison of a major heat-stable microtubule-associated protein in HeLa cells and 190-kDa microtubule-associated protein in bovine adrenal cortex

A heat-stable microtubule-associated protein (MAP) with a molecular weight of 190,000, termed 190-kDa MAP, has been purified from bovine adrenal cortex (Murofushi, H. et al. (1986) J. Cell Biol. 103, 1911-1919). Immunoblotting experiments using an antibody against this MAP revealed that several kinds of culture cells derived from human tissues contain proteins with an apparent molecular weight of 180,000 reacting with the antibody. Indirect immunofluorescence microscopic observation of HeLa cells showed that the immunoreactive protein co-exists with microtubules, indicating that the protein is one of the HeLa MAPs. A heat-stable MAP with a molecular weight of 180,000, termed here HeLa 180-kDa MAP, was purified by the taxol-dependent procedure (Vallee, R.B. (1982) J. Cell Biol. 92, 435-442) and successive co-polymerization with brain tubulin. This protein was the most abundant MAP in HeLa cells, suggesting that the MAP is identical to the major HeLa MAP previously reported by Bulinski and Borisy (Bulinski, J.C. & Borisy, G.G. (1980) J. Biol. Chem. 255, 11570-11576) and Weatherbee et al. [1980) Biochemistry 19, 4116-4123). It was shown that, like bovine adrenal 190-kDa MAP, yet distinct from brain MAP2 and tau, purified HeLa 180-kDa MAP does not interact with actin filaments. This common characteristic of the two MAPs along with the same heat-stability strongly suggests that they are members of the same group of MAPs. The fact that HeLa 180-kDa MAP reacts with an antibody against bovine adrenal 190-kDa MAP means that they share common epitopes, in other words, common local amino acid sequences. However, the limited proteolytic patterns of the two MAPs with S. aureus V8 protease and chymotrypsin were distinct from each other, suggesting the presence of large differences in the overall primary structures between bovine adrenal 190-kDa MAP and HeLa 180-kDa MAP.     

Widespread cellular distribution of MAP-1A (microtubule-associated protein 1A) in the mitotic spindle and on interphase microtubules

In the accompanying paper (Bloom, G.S., T.A. Schoenfeld, and R.B. Vallee, 1983, J. Cell Biol. 98:320-330), we reported that microtubule-associated protein 1 (MAP 1) from brain comprises multiple protein species, and that the principal component, MAP 1A, can be detected in both neuronal and glial cells by immunofluorescence microscopy using a monoclonal antibody. In the present study, we sought to determine the cellular and subcellular distribution of MAP 1A in commonly used cultured cell systems. For this purpose we used immunofluorescence microscopy and immunoblot analysis with anti-MAP 1A to examine 18 types of mammalian cell cultures. MAP 1A was detected in every culture system examined. Included among these were cells of mouse, rat, Chinese hamster, Syrian hamster, Potoroo (marsupial), and human origin derived from a broad variety of tissues and organs. Anti-MAP 1A consistently labeled mitotic spindles and stained cytoplasmic fibers during interphase in most of the cultures. These fibers were identified as microtubules by co-localization with tubulin in double-labeling experiments, by their disappearance in response to colchicine or vinblastine, and by their reorganization in response to taxol. The anti-MAP 1A stained microtubules in a punctate manner, raising the possibility that MAP 1A is located along microtubules at discrete foci that might represent sites of interaction between microtubules and other organelles. Verification that MAP 1A was, indeed, the reactive material in immunofluorescence microscopy was obtained from immunoblots. Anti-MAP 1A stained a band at the position of MAP 1A in all cultures examined. These results establish that MAP 1A, a major MAP from brain, is widely distributed among cultured mammalian cells both within and outside of the nervous system.     

Quantitation of microtubule-associated protein MAP-1B in brain and other tissues

1. The presence of microtubule-associated protein MAP-1B in all mammalian tissues tested, as well as in brain, has been demonstrated by immunoblotting using a monospecific polyclonal antibody. 2. The expression of brain MAP-1B is developmentally controlled, as it is less abundant in adult than in newborn rat brain, where it is a major microtubule assembly promoting factor. 3. The level of MAP-1B in tissues other than brain is lower than it is in brain; but the relative ratios of MAP-1B to tubulin are very similar in all tissues, thus differing from the observed for MAP-2 or tau. 4. The amount of MAP-1B in non-nervous tissues seems not to be under developmental control. 5. These results are consistent with a role for MAP-1B in the assembly of microtubules in most cells.     

Phosphorylation of an acidic mol. wt. 80 000 cellular protein in a cell-free system and intact Swiss 3T3 cells: a specific marker of protein kinase C activity.

Activation of the endogenous Ca2+-activated phospholipid-dependent protein kinase (protein kinase C) by Ca2+, phosphatidylserine (PS) and phorbol dibutyrate (PBt2) in detergent-solubilized extracts of Swiss 3T3 cells resulted in a very rapid increase (detectable within seconds) in the phosphorylation of an 80 000 mol. wt. protein (termed 80 K). Neither cyclic AMP nor Ca2+ had any effect on 80 K phosphorylation. The 80 K phosphoproteins generated after activation of protein kinase C, both in cell-free conditions and in intact fibroblasts, are identical as judged by one and two-dimensional polyacrylamide slab gel electrophoresis and peptide mapping. Prolonged treatment of cells with phorbol esters causes a selective decrease in protein kinase C activity and prevents the stimulation of 80 K phosphorylation in intact fibroblasts. We now show that extracts from PBt2-treated cultures fail to stimulate 80 K phosphorylation after the addition of the protein kinase C activators. This effect was due to the lack of protein kinase C activity since the addition of exogenous protein kinase C from mouse brain stimulated 80 K phosphorylation in both control and PBt2-treated preparations. The 80 K phosphoprotein generated by activation of endogenous and exogenous protein kinase C yielded similar phosphopeptide fragments after peptide mapping by limited proteolysis. We conclude that the detection of changes in the phosphorylation of 80 K provides a useful approach to ascertain which extracellular ligands activate protein kinase C in intact cells.     

Thiol-dependent aminopeptidase (350,000 mol wt) as a marker of epidermal contamination in sweat

L-Leucine 2-naphthylamide (Leu-NA) hydrolytic activity is increased 20-fold in eccrine sweat collected by simple scraping (SS) compared with sweat collected over the white petrolatum (Vaseline) barrier (clean sweat, CS) [Am. J. Physiol. 250 (Regulatory Integrative Comp. Physiol. 19): R691-R698, 1986]. Sephadex G-200 chromatography of SS but not that of CS showed a single peak of Leu-NA hydrolytic activity (at pH 8) at 350,000 mol wt. An enzyme with similar molecular weight was eluted from tape-stripped stratum corneum and from stripped skin in situ. Anion-exchange FPLC of the 350,000 fractions yielded a single Leu-NA hydrolase peak at pH 8 (pool IV), which also showed hydrolytic activity for benzoyl-L-arginine-2-naphthylamide (BANA). Both Leu-NA and BANA hydrolytic activities of pool IV were thiol dependent, inhibited by heavy metals, and activated by ethylenediaminetetraacetic acid. The pool IV enzyme also hydrolyzed L-lysine- and L-arginine-2-naphthylamide. The most prominent BANA hydrolase activity was seen in both SS and CS at pH 5.0 at 33,000, which was not associated with Leu-NA hydrolytic activity. Diethylaminoethyl cellulose chromatography of the 33,000 fractions yielded three peaks of BANA hydrolytic activity in SS but only one in CS, suggesting that this thiol-dependent BANA hydrolyzing enzyme in CS may be of sweat gland origin. We conclude that the 350,000 thiol-dependent Leu-NA-hydrolyzing aminopeptidase is one of the most prominent epidermal contaminants and thus is a useful marker of epidermal contamination in sweat samples.     

Widespread phylogenetic distribution of a protein methyltransferase that modifies L-isoaspartyl residues.

Protein L-isoaspartyl methyltransferase is implicated in the repair or degradation of age-damaged proteins that contain atypical, L-isoaspartyl residues. The enzyme has previously been demonstrated in a variety of vertebrates and in the bacterium S. typhimurium (O'Connor, C.M. and Clarke, S. (1985) Biochem. Biophys. Res. Commun. 132, 1144-1150). We report here that the enzyme is present in a mollusc (great slug), a crustacean (pill woodlouse), a fungus (mushroom), and a plant (wheat germ). Using mushroom as an example, we show that the enzyme activity may, in some instances, require a partial purification before its presence is clearly detectable. Our findings significantly extend the known phylogenetic distribution of this enzyme and suggest that it may play an indispensable role in protein metabolism.     

Widespread cellular distribution of aldehyde oxidase in human tissues found by immunohistochemistry staining

Aldehyde oxidase (EC 1.2.3.1) is a xenobiotic metabolizing enzyme that catalyzes a variety of organic aldehydes and N-heterocyclic compounds. However, its precise pathophysiological function in humans, other than its xenobiotic metabolism, remains unknown. In order to gain a better understanding of the role of this enzyme, it is important to know its exact localization in human tissues. In this study, we investigated the distribution of aldehyde oxidase at the cellular level in a variety of human tissues by immunohistochemistry. The enzyme was found to be widespread in respiratory, digestive, urogenital, and endocrine tissues, though we also observed a cell-specific localization in the various tissues studied. In the respiratory system, it was particularly abundant in epithelial cells from the trachea and bronchium, as well as alveolar cells. In the digestive system, aldehyde oxidase was observed in surface epithelia of the small and large intestines, in addition to hepatic cells. Furthermore, the proximal, distal, and collecting tubules of the kidney were immunostained with various intensities, while glomerulus tissues were not. In epididymus and prostate tissues, staining was observed in the ductuli epididymidis and glandular epithelia. Moreover, the adrenal gland, cortex, and notably the zona reticularis, showed strong immunostaining. This prevalent tissue distribution of aldehyde oxidase in humans suggests some additional pathophysiological functions besides xenobiotic metabolism. Accordingly, some possible roles are discussed.     

Okadaic acid activates microtubule-associated protein kinase in quiescent fibroblastic cells

Okadaic acid is a potent and specific inhibitor of protein phosphatases 1 and 2A, and is a strong tumor promoter that is not an activator of protein kinase C. Treatment of quiescent cultures of rat fibroblastic 3Y1 cells with okadaic acid induced marked activation of a kinase activity that phosphorylated microtubule-associated protein (MAP) 2 and myelin basic protein, but not histone or casein, in vitro. This activated kinase eluted at approximately 0.15 M NaCl on a DEAE-cellulose column and its apparent molecular mass was determined to be approximately 40 kDa by gel filtration. Detection of the kinase activity in polyacrylamide gels containing substrate proteins after sodium dodecyl sulfate gel electrophoresis revealed that the okadaic-acid-activated kinase activity resided mainly in two closely related polypeptides with apparent molecular mass approximately 40 kDa. The characteristics of this kinase were indistinguishable from those of the mitogen-activated MAP kinase in the same cells. The okadaic-acid-activated MAP kinase was deactivated by protein phosphatase 2A treatment in vitro. These results suggest that MAP kinase is negatively regulated by protein phosphatases 1 and/or 2A in quiescent cells and therefore can be activated by inhibiting these protein phosphatases. Interestingly, the okadaic-acid-induced activation of MAP kinase was transient and epidermal-growth-factor-induced activation was also transient, even in the presence of okadaic acid. These data may imply that protein phosphatases 1 and 2A are not involved in the deactivation of MAP kinase in cells.     

Mitogen-activated-protein-kinase-catalyzed phosphorylation of microtubule-associated proteins, microtubule-associated protein 2 and microtubule-associated protein 4, induces an alteration in their function.

Mitogen-activated protein kinase (MAPK), a serine/threonine-specific protein kinase which is generally activated by stimulation with various growth factors and phorbol esters, utilizes microtubule-associated protein (MAP) 2 as a good substrate in vitro. We have found that MAPK-catalyzed phosphorylation of MAP2 resulted in a significant loss in its ability to induce tubulin polymerization. The chymotryptic fragments, containing a microtubule-binding domain of MAP2, were phosphorylated by MAPK and the ability of the fragments to induce tubulin polymerization was also greatly decreased by the phosphorylation, suggesting that phosphorylation of the microtubule-binding domain is important for functional alteration of MAP2. In addition to MAP2, a 190-kDa heat-stable MAP (MAP4) found in various tissues and cells, was a good substrate for MAPK in vitro. Phosphorylation of MAP4 inactivated tubulin polymerization. We examined the effect of phosphorylation of MAP2 and MAP4 on the dynamics of microtubules nucleated by purified centrosomes in vitro. The data showed that MAPK-catalyzed phosphorylation of MAP2 and MAP4 reduced their ability to increase the apparent elongation rate and the number of microtubules nucleated by the centrosome. Thus, MAPK is capable of phosphorylating MAPs and negatively regulating their microtubule-stabilizing function.     

Neuronal microtubule-associated protein 2D is a dual a-kinase anchoring protein expressed in rat ovarian granulosa cells

A-kinase anchoring proteins (AKAPs) function to target protein kinase A (PKA) to specific locations within the cell. AKAPs are functionally identified by their ability to bind the type II regulatory subunits (RII) of PKA in an in vitro overlay assay. We previously showed that follicle-stimulating hormone (FSH) induces the expression of an 80-kDa AKAP (AKAP 80) in ovarian granulosa cells as they mature from a preantral to a preovulatory phenotype. In this report, we identify AKAP 80 as microtubule-associated protein 2D (MAP2D), a low molecular weight splice variant of the neuronal MAP2 protein. MAP2D is induced in granulosa cells by dexamethasone and by FSH in a time-dependent manner that mimics that of AKAP 80, and immunoprecipitation of MAP2D depletes extracts of AKAP 80. MAP2D is the only MAP2 protein present in ovaries and is localized to granulosa cells of preovulatory follicles and to luteal cells. MAP2D is concentrated at the Golgi apparatus along with RI and RII and, based on coimmunoprecipitation results, appears to bind both RI and RII in granulosa cells. Reduced expression of MAP2D resulting from treatment of granulosa cells with antisense oligonucleotides to MAP2 inhibited the phosphorylation of cAMP-response element-binding protein. These results suggest that this classic neuronal RII AKAP is a dual RI/RII AKAP that performs unique functions in ovarian granulosa cells that contribute to the preovulatory phenotype.     

Widespread distribution of a unique marine protistan lineage

Unicellular eukaryotes (protists) are key components of marine food webs, yet knowledge of their diversity, distributions and respective ecologies is limited. We investigated uncultured protists using 18S rRNA gene sequencing, phylogenetic analyses, specific fluorescence in situ hybridization (FISH) probes and other methods. Because few studies have been conducted in warm water systems, we focused on two Atlantic subtropical regions, the Sargasso Sea and the Florida Current. Cold temperate waters were also sampled. Gene sequences comprising a unique eukaryotic lineage, herein termed 'biliphytes', were identified in most samples, whether from high- (30 degrees C) or from low- (5 degrees C) temperature waters. Sequences within this uncultured group have previously been retrieved from high latitudes. Phylogenetic analyses suggest biliphytes are a sister group to the cryptophytes and katablepharids, although the relationship is not statistically supported. Bootstrap-supported subclades were delineated but coherence was not obvious with respect to geography or physicochemical parameters. Unlike results from the initial publication on these organisms (therein 'picobiliphytes'), we could not detect a nucleomorph, either visually, or by targeted primers. Phycobilin-like fluorescence associated with biliphyte-specific FISH-probed cells supports the hypothesis that they are photosynthetic. Our data indicate the biliphytes are nanoplanktonic in size, averaging 4.1 +/- 1.0 x 3.5 +/- 0.8 microm (+/-SD) for one probed group, and 3.5 +/- 0.9 x 3.0 +/- 0.9 microm (+/-SD) for another. We estimate biliphytes contributed 28 (+/-6)% of the phytoplanktonic biomass in tropical eddy-influenced surface waters. Given their broad thermal and geographic distribution, understanding the role these protists play in biogeochemical cycling within different habitats is essential.     

Photoaffinity labeling of a microtubule-associated cyclic AMP-binding protein

8-Azido cyclic AMP has been used as a photoaffinity probe to identify cyclic AMP-binding proteins in microtubule preparations. Bovine brain microtubule proteins and rabbit muscle protein kinase were incubated with the photoaffinity ligand in reduced light for 15 min, without additions or with 100-fold excess unlabeled cyclic AMP or 5′-AMP. Samples were then irradiated at 254 nm at a distance of 1 cm for 5 min, in ice. After irradiation aliquots were taken for electrophoresis in one or two dimensions. Polypeptides which bound the photoaffinity label were visualized by autoradiography. The apparent molecular weights of the most prominent 8-azido ³²P-cyclic AMP-binding proteins are in the same range as those of the RII of the muscle enzyme. Following two-dimensional electrophoresis the major microtubule-associated cyclic AMP-binding proteins resolve as two spots with about the same pI (~pH 5.0) but slightly different molecular weights. Both spots are in the molecular weight range of the tubulins but they are clearly resolved from the tubulins in the first dimension. Cyclic AMP, but not 5′-AMP blocks the labeling of these proteins. There are low levels of labeling of the tubulins, the high-molecular-weight MAPs and several polypeptides with molecular weights near tubulin but with more basic pI. The photoaffinity probe has demonstrated that the major microtubule-associated cyclic AMP-binding protein of bovine brain is distinct from other RII proteins and from tubulin isomorphs.