Biomedical subjects

Y Kam

Publications and source records attributed to Y Kam.

6 recordsLinked to original sources

PubMed2001

A comparative study of quantitative structure activity relationship methods based on antitumor diarylsulfonylureas.

A series of 28 diarylsulfonylureas with antitumor activity was subjected to a three-dimensional quantitative activity relationship (3D-QSAR) study. Three different QSAR methods, comparative molecular field analysis (CoMFA), hologram QSAR (HQSAR) and comparative molecular similarity indices analysis (CoMSIA), were compared in terms of their potential for predictability. All three QSAR-based models had good predictability and yielded q(2) values 0.74, 0.63 and 0.72, respectively. The CoMFA model provided the highest q(2) and r(2) values, which implied the significance of correlation of steric and electrostatic fields with biological activities. The number of components was 3-4 for all three QSAR methods. The quality of HQSAR or CoMSIA was slightly lower than that of CoNFA in terms of q(2) and r(2) values. HQSAR does not require the generation of a three-dimensional structure of molecules and CoMSIA does not require molecular superposition, therefore they are faster than CoMFA in data processing.

Alkanes↗

PubMed2001

Factors affecting prostacyclin receptor agonist efficacy in different cell types.

Octimibate and related nonprostanoid prostacyclin mimetics are partial agonists displaying highly tissue-specific responses. Octimibate demonstrated considerably greater efficacy for stimulation of adenylyl cyclase activity in Chinese hamster ovary cells transiently expressing mouse prostacyclin receptors (mIP-CHO cells) when compared to human SK-N-SH neuroblastoma cells, which endogenously express prostacyclin (IP) receptors. Pretreatment of both cell types with pertussis toxin (PTx) failed to influence IP agonist efficacy or potency, indicating a lack of involvement of an agonist-stimulated inhibitory G(i)-coupled pathway. Although stimulation of mIP-CHO cells with the full agonist cicaprost increased both [3H]cyclic AMP and [3H]inositol phosphate ([3H]IP) accumulation (pEC(50) values of 8.35 and 6.82, respectively), IP receptor signalling through G(q) in SK-N-SH cells was absent. Inhibition of protein kinase C (PKC) in mIP-CHO cells increased [3H]IP accumulation but had no effect on [3H]cyclic AMP accumulation. Therefore, the poor coupling of the IP receptor in SK-N-SH cells to G(q) is unlikely to explain the relatively low efficacy of octimibate for stimulating adenylyl cyclase in these cells. Furthermore, protein kinase A (PKA) inhibition appears to enhance IP receptor signalling through both G(s) and G(q) in mIP-CHO cells.

Acetates↗

PubMed2001

Phospholipase D activity is required for actin stress fiber formation in fibroblasts.

Phospholipase D (PLD) is a ubiquitously expressed enzyme of ill-defined function. In order to explore its cellular actions, we inactivated the rat PLD1 (rPLD1) isozyme by tagging its C terminus with a V5 epitope (rPLD1-V5). This was stably expressed in Rat-2 fibroblasts to see if it acted as a dominant-negative mutant for PLD activity. Three clones that expressed rPLD1-V5 were selected (Rat2V16, Rat2V25, and Rat2V29). Another clone (Rat2V20) that lost expression of rPLD1-V5 was also obtained. In the three clones expressing rPLD1-V5, PLD activity stimulated by phorbol myristate acetate (PMA) or lysophosphatidic acid (LPA) was reduced by ~50%, while the PLD activity of Rat2V20 cells was normal. Changes in the actin cytoskeleton in response to LPA or PMA were examined in these clones. All three clones expressing rPLD1-V5 failed to form actin stress fibers after treatment with LPA. However, Rat2V20 cells formed stress fibers in response to LPA to the same extent as wild-type Rat-2 cells. In contrast, there was no significant change in membrane ruffling induced by PMA in the cells expressing rPLD1-V5. Since Rho is an activator both of rPLD1 and stress fiber formation, the activation of Rho was monitored in wild-type Rat-2 cells and Rat2V25 cells, but no significant difference was detected. The phosphorylation of vimentin mediated by Rho-kinase was also intact in Rat2V25 cells. Rat2V25 cells also showed normal vinculin-containing focal adhesions. However, the translocation of alpha-actinin to the cytoplasm and to the detergent-insoluble fraction in Rat2V25 cells was reduced. These results indicate that PLD activity is required for LPA-induced rearrangement of the actin cytoskeleton to form stress fibers and that PLD might be involved in the cross-linking of actin filaments mediated by alpha-actinin.

Actinin↗

PubMed1999

Gating connexin 43 channels reconstituted in lipid vesicles by mitogen-activated protein kinase phosphorylation.

The regulation of gap junctional permeability by phosphorylation was examined in a model system in which connexin 43 (Cx43) gap junction hemichannels were reconstituted in lipid vesicles. Cx43 was immunoaffinity-purified from rat brain, and Cx43 channels were reconstituted into unilamellar phospholipid liposomes. The activities of the reconstituted channels were measured by monitoring liposome permeability. Liposomes containing the Cx43 protein were fractionated on the basis of permeability to sucrose using sedimentation in an iso-osmolar density gradient. The gradient allowed separation of the sucrose-permeable and -impermeable liposomes. Liposomes that were permeable to sucrose were also permeable to the communicating dye molecule lucifer yellow. Permeability, and therefore activity of the reconstituted Cx43 channels, were directly dependent on the state of Cx43 phosphorylation. The permeability of liposomes containing Cx43 channels was increased by treatment of liposomes with calf intestinal phosphatase. Moreover, liposomes formed with Cx43 that had been dephosphorylated by calf intestinal phosphatase treatment showed increased permeability to sucrose. The role of phosphorylation in the gating mechanism of Cx43 channels was supported further by the observation that phosphorylation of Cx43 by mitogen-activated protein kinase reversibly reduced the permeability of liposomes containing dephosphorylated Cx43. Our results show a direct correlation between gap junctional permeability and the phosphorylation state of Cx43.

Amino Acid Sequence↗

PubMed1998

Transfer of second messengers through gap junction connexin 43 channels reconstituted in liposomes.

Gap junction channels reconstituted in liposomes provide a pathway for the transfer of second messengers. Gap junction channels were formed in the artificial unilamellar liposomes using immunoaffinity-purified connexin 43 gap junction protein from rat brain. Sucrose-permeable and -impermeable liposomes were separated on the basis of sucrose permeability in the iso-osmolar sucrose density gradient. The liposomes permeable to sucrose were also permeable to a communicating dye molecule, Lucifer yellow. In the present study, we examined the transfer of second messengers through the connexin 43 channels reconstituted in liposomes and first report the direct evidence that the gap junction channels are permeable to second messengers including adenosine 3',5'-cyclic phosphate and inositol 1,4,5-trisphosphate.

Animals↗

PubMed1996

Inhibition of the phosphorylation of a myristoylated alanine-rich C kinase substrate by methyl methanesulfonate in cultured NIH 3T3 cells.

The effect of methyl methanesulfonate (MMS) on the phosphorylation of an acidic 80-kDa myristoylated alanine-rich C kinase substrate (MARCKS) protein was investigated in NIH 3T3 fibroblasts. An alkylating agent, MMS inhibited protein kinase C activity and the phosphorylation of MARCKS. MMS treatment also lowered the cellular amounts of second messengers of inositol-1,4,5-trisphosphate and diacylglycerol. Data suggest that MMS decreased the phosphorylation of phospholipase C, a protein whose activity is influenced by its phosphorylation state. We present here the first report that MMS intervenes in a signal cascade by inhibiting the phosphorylation of phospholipase C, which in turn leads to the inactivation of protein kinase C and the subsequent inhibition of MARCKS phosphorylation.

3T3 Cells↗