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Biomedical subjects

I Babic

Publications and source records attributed to I Babic.

7 recordsLinked to original sources
PubMed2006

SUMO modification of Sam68 enhances its ability to repress cyclin D1 expression and inhibits its ability to induce apoptosis.

Sam68 (Src associated in mitosis; 68 kDa) is an RNA-binding protein and substrate of Src family kinases. It is thought to play a role in cell cycle progression. Overexpression of Sam68 in fibroblasts was reported to have two separable functions dependent on its ability to bind RNA--cell cycle arrest or the induction of apoptosis. Post-translational modification with SUMO (small ubiquitin-like modifier) is common to many transcription factors and can regulate protein localization, stability and function. Here we show Sam68 to be modified by SUMO, and demonstrate that the SUMO E3 ligase (PIAS1) (protein inhibitor of activated STAT1) can enhance Sam68 sumoylation. Lysine 96, the first lysine in the amino-terminal region of Sam68, was found to be the major SUMO acceptor site. Mutation of the SUMO acceptor lysine to arginine enhanced the ability of Sam68 to induce apoptosis but inhibited its ability to act as a transcriptional inhibitor of cyclin D1 expression. A SUMO-1 Sam68 fusion protein, on the other hand, inhibited the ability of Sam68 to induce apoptosis but was a strong repressor of cyclin D1 expression. Thus, SUMO may be an important regulator of Sam68 function in cell cycle progression.

Adaptor Proteins, Signal Transducing↗
PubMed2000

SHPS-1 induces aggregation of Ba/F3 pro-B cells via an interaction with CD47.

SHPS-1 (SH2-domain bearing protein tyrosine phosphatase (SHP) substrate-1), a member of the inhibitory-receptor superfamily that is abundantly expressed in macrophages and neural tissue, appears to regulate intracellular signaling events downstream of receptor protein-tyrosine kinases and integrin-extracellular matrix molecule interactions. To investigate the function of SHPS-1 in a hematopoietic cell line, SHPS-1 was expressed in Ba/F3 cells, an IL-3-dependent pro-B-cell line that lacks endogenous SHPS-1 protein. Interestingly, expression of either SHPS-1, or a mutant lacking the intracellular domain of SHPS-1 (DeltaCT SHPS-1), resulted in the rapid formation of macroscopic Ba/F3 cell aggregates. As the integrin-associated protein/CD47 was shown to be a SHPS-1 ligand in neural cells, we investigated whether CD47 played a role in the aggregation of SHPS-1-expressing Ba/F3 cells. In support of this idea, aggregate formation was inhibited by an anti-CD47 Ab. Furthermore, erythrocytes from control, but not from CD47-deficient mice, were able to form rosettes on SHPS-1-expressing Ba/F3 cells. Because erythrocytes do not express integrins, this result suggested that SHPS-1-CD47 interactions can take place in the absence of a CD47-integrin association. We also present evidence that the amino-terminal Ig domain of SHPS-1 mediates the interaction with CD47. Although SHPS-1-CD47 binding likely triggers bidirectional intracellular signaling processes, these results demonstrate that this interaction can also mediate cell-cell adhesion.

Animals↗
PubMed1997

The Src homology 2 (SH2) domain of SH2-containing inositol phosphatase (SHIP) is essential for tyrosine phosphorylation of SHIP, its association with Shc, and its induction of apoptosis.

In this study we have investigated the role that the Src homology 2 domain (SH2) of the 145-kDa 5-phosphatase, SH2-containing inositol phosphatase (SHIP), plays in three of the properties that have been associated with this protein following cytokine stimulation: its association with Shc, its tyrosine phosphorylation, and its inhibition of hemopoietic cell growth. In vitro studies using this SH2 domain revealed that it was capable of binding directly to the Tyr(P)317 motif of Shc with a KD of approximately 290 nM, in keeping with other specific SH2/Tyr(P) interactions. In vivo analysis revealed the SH2 and NPXpY motifs of SHIP acted together, with the Tyr(P)317 and phosphotyrosine binding (PTB) domains of Shc, respectively, to ensure a high affinity SHIP.Shc complex. Expression of cDNAs encoding hemagglutinin-tagged wild type and SH2-inactivated forms of SHIP in the murine hemopoietic cell line DA-ER revealed that wild type SHIP becomes both tyrosine-phosphorylated and associated with Shc following interleukin-3 stimulation, as expected, but the SH2-inactivated SHIPs do neither. Moreover, while the growth rates of parental DA-ER cells and cells expressing these various SHIP constructs are identical, the wild type SHIP-expressing cells die, via programmed cell death, far more rapidly than parental cells. Cells expressing SH2-inactivated SHIPs, on the other hand, show either a reduced or no effect on apoptosis. These results suggest that the SH2 domain of SHIP is required not only for the tyrosine phosphorylation of SHIP and Shc association following cytokine stimulation but also for its induction of apoptosis.

Animals↗
PubMed1996

MutS interaction with mismatch and alkylated base containing DNA molecules detected by optical biosensor.

An optical biosensor was used to monitor interactions between the Escherichia coli DNA mismatch repair molecule MutS and various immobilized oligonucleotides. While associating poorly with single-stranded DNA, MutS was capable of rapid association/dissociation from homoduplex DNA. The interaction of MutS with oligonucleotide 30-mers containing single site mismatches demonstrated that during the dissociation phase, MutS binding was greatest to a G-G mismatch, followed by G-T > A-A > C-T, A-C. Binding to A-G, T-T and C-C mispairs was marginally higher than that seen between MutS and homoduplex DNA. The ability of MutS to interact with 30-mers containing alkylated bases was also tested. While binding to O6-methyl-G-C, or to O4-methyl-T-A base pairs was similar to that of homoduplex DNA, strong binding was seen to a O6-methyl-G-T mispair. O4-methyl-T-G, however, was poorly recognized by MutS, with relative binding affinity similar to homoduplex DNA, predicting poor in vivo recognition of O4-methyl-T-G by MutS. Interestingly, MutS demonstrated a relatively high affinity for an 1,N6-etheno-A-T containing homoduplex. Thus, in allowing rapid evaluation of interactions between such molecules, the biosensor will be useful to structure-function analyses.

Adenosine Triphosphatases↗
PubMed1996

Changes in microbial populations on fresh cut spinach.

The microbial populations found on fresh-cut spinach leaves that were stored in gas permeable bags at 10 degrees C for 12 days were examined and identified. The microorganisms consisted of mesophilic aerobic bacteria, psychrotrophic bacteria, Pseudomonadaceae, Enterobacteriaceae, Micrococcaceae, lactic acid bacteria and yeasts. Populations of mesophiles, psychrotrophs, Pseudomonadaceae and Enterobacteriaceae increased sharply during the storage period. The initial populations were 10(7), 10(6), 10(6) and 10(4) CFU.g-1 respectively. Populations reached 10(10) for the mesophiles, psychrotrophs and Pseudomonadaceae and 10(7) CFU.g-1 for Enterobacteriaceae after 12 days of storage. Micrococcaceae, lactic acid bacteria and yeasts remained constant (10(3)-10(4) CFU.g-1. The majority of the bacterial isolates were identified as Pseudomonas fluorescens, Aeromonas caviae and Staphylococcus xylosus. The yeasts, which were most frequently isolated, were classified in the genus Cryptococcus. No pathogens such as Listeria monocytogenes and Salmonella were detected. Observations with low temperature scanning electron microscopy (LTSEM) indicated that the microorganisms were not present on the surface of healthy unbroken leaves. Alternatively, they were found in areas where the cuticle was broken and could be seen infecting the internal palisade parenchyma.

Colony Count, Microbial↗
PubMed1994

Antimicrobial activity of shredded carrot extracts on food-borne bacteria and yeast.

Purified ethanolic extracts of peeled and shredded carrots showed an antimicrobial effect against a range of food-borne micro-organisms. The minimum inhibitory concentration, expressed as mg ml-1 dried carrot material used for the extraction were: Leuconostoc mesenteroides, 27; Listeria monocytogenes, > 27 < 55; Staphylococcus aureus, > 27 < 55; Pseudomonas fluorescens, > 55 < 110; Candida lambica, > 55 < 110; Escherichia coli, > 110 < 220. The antimicrobial activity was not linked to phenolic compounds but was presumably due to apolar components. Free saturated fatty acid (dodecanoic acid) and methyl esters of saturated fatty acids (of dodecanoic and pentadecanoic acids) were identified in purified active extracts of carrots by gas chromatography coupled to mass spectrometry and could be responsible for the antimicrobial activity. This effect did not seem to play a role in the resistance of shredded carrots to microbial spoilage, although the antimicrobial activity was present in fresh carrots at concentrations sufficient to inhibit spoilage bacteria.

Anti-Bacterial Agents↗