Biomedical subjects

Carl B Baron

Publications and source records attributed to Carl B Baron.

3 recordsLinked to original sources

PubMed2006

Polyamines, PI(4,5)P2, and actin polymerization.

Spermine (SPM) and spermidine (SPD) activate isolated phosphatidylinositol-4-phosphate 5-kinases (PI(4)P5K), enzymes that convert phosphatidylinositol-4-phosphate to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). PI(4,5)P2 formation is known to be involved in cellular actin reorganization and motility, functions that are also influenced by polyamines. It has not been proven that endogenous polyamines can control inositol phospholipid metabolism. We evoked large decreases in SPD and putrescine (PUT) contents in HL60 cells, using the ornithine decarboxylase inhibitor, alpha-difluoromethylornithine (DFMO), which resulted in decreases in PI(4,5)P2 content per cell and inositol phosphate formation to 76.9 +/- 3.5% and 81.5 +/- 4.0% of control, respectively. Accurately reversing DFMO-evoked decreases in SPD content by incubating cells with exogenous SPD for 20 min rescued these decreases. DFMO treatment and SPD rescues also changed the ratio of total cellular PI(4,5)P2 to PIP suggesting involvement of a SPD-sensitive PI(4)P5K. PUT and SPM were not involved in DFMO-evoked changes in cellular PI(4,5)P2 contents. In DFMO-treated HL60 cells, the percent of total actin content that was filamentous was decreased to 59.1 +/- 5.8% of that measured in paired control HL60 cells, a finding that was rescued following reversal of DFMO-evoked decreases in SPD and PI(4,5)P2 contents. In slowly proliferating DMSO-differentiated HL60 cells, inositol phospholipid metabolism was uncoupled from SPD control. We conclude: in rapidly proliferating HL60 cells, but not in slowly proliferating differentiated HL60 cells, there are endogenous SPD-sensitive PI(4,5)P2 pools, probably formed via SPD-sensitive PI(4)P5K, that likely control actin polymerization.

Actins↗

PubMed2003

Smooth muscle raft-like membranes.

We developed a method for extracting raft-like, liquid-ordered membranes from the particulate fraction prepared from porcine trachealis smooth muscle. This fraction, which contains most of the plasma membrane in this tissue, was homogenized in the presence of cold 0.5% Triton X-100. After centrifugation, membranes containing high contents of sphingomyelin (SM) and cholesterol and low phosphatidylcholine (PC) contents remained in the pellet. Thirty-five millimolar octyl glucoside (OG) extracted 75% of these membranes from the Triton X-100-resistant pellet. These membranes had low buoyant densities and accounted for 28% of the particulate fraction lipid. Their lipid composition, 22% SM, 60% cholesterol, 11% phosphatidylethanolamine, 8% PC, <1% phosphatidylinositol, and coisolation with 5'-nucleotidase and caveolin-1 suggest that they are liquid-ordered membranes. We compared characteristics of OG and Triton X-100 extractions of the particulate fraction. In contrast to Triton X-100 extractions, membranes released from the particulate fraction by OG were mainly collected in low buoyant fractions at densities ranging from 1.05 to 1.11 g/ml and had phospholipid and cholesterol contents consistent with a mixture of liquid-ordered and liquid-disordered membranes. Thus, OG extraction of apparent liquid-ordered membranes from Triton X-100-resistant pellets was not due to selective extraction of these membranes. Low buoyant density appears not to be unique for liquid-ordered membranes.

5'-Nucleotidase↗

PubMed2002

Spermine increases phosphatidylinositol 4,5-bisphosphate content in permeabilized and nonpermeabilized HL60 cells.

The polyamine spermine (N,N'bis[3-aminopropyl]-1,4-butanediamine) activates phosphatidylinositol-4-phosphate 5-kinase (PtdIns(4)P5K) and phosphatidylinositol 4-kinase (PtdIns4K) in vitro. Spermine concentration increases that occur in proliferating cells were approximated in streptolysin O-permeabilized HL60 cells. When phospholipase C was activated by GTPgammaS in the presence of PITPalpha, 0.1-1.2 mM spermine evoked increases in PtdIns(4,5)P(2) contents in a dose-dependent manner to 110-170% of control and concomitantly decreased inositol phosphate formation by 10-50%. Spermine-induced increases in PtdIns(4,5)P(2) content in permeabilized cells also occurred during GTPgammaS stimulation in the absence of PITPalpha, were augmented in the presence of PITPalpha, occurred in unstimulated cells and were additive to PtdIns(4,5)P(2) formation evoked by ARF1, another activator of phosphoinositide kinases. Slowly developing spermine-evoked increases in PtdIns(4,5)P(2) contents occurred in nonpermeabilized cells that were abolished in the presence of a spermine transport inhibitor. Data are consistent with spermine at physiological concentrations evoking a PITPalpha-dependent shift in formation of PtdIns(4,5)P(2) from compartments that contained an active phospholipase C to compartments that were separated from an active PLC and from PtdIns(4,5)P(2) formed by ARF1.

ADP-Ribosylation Factor 1↗