concanavalin-a and herbimycin

We have used the two-electrode voltage clamp technique and the patch clamp technique to investigate the regulation of ROMK1 channels by protein-tyrosine phosphatase (PTP) and protein-tyrosine kinase (PTK) in oocytes coexpressing ROMK1 and cSrc. Western blot analysis detected the presence of the endogenous PTP-1D isoform in the oocytes. Addition of phenylarsine oxide (PAO), an inhibitor of PTP, reversibly reduced K(+) current by 55% in oocytes coinjected with ROMK1 and cSrc. In contrast, PAO had no significant effect on K(+) current in oocytes injected with ROMK1 alone. Moreover, application of herbimycin A, an inhibitor of PTK, increased K(+) current by 120% and completely abolished the effect of PAO in oocytes coexpressing ROMK1 and cSrc. The effects of herbimycin A and PAO were absent in oocytes expressing the ROMK1 mutant R1Y337A in which the tyrosine residue at position 337 was mutated to alanine. However, addition of exogenous cSrc had no significant effect on the activity of ROMK1 channels in inside-out patches. Moreover, the effect of PAO was completely abolished by treatment of oocytes with 20% sucrose and 250 microg/ml concanavalin A, agents that inhibit the endocytosis of ROMK1 channels. Furthermore, the effect of herbimycin A is absent in the oocytes pretreated with either colchicine, an inhibitor of microtubules, or taxol, an agent that freezes microtubules. We conclude that PTP and PTK play an important role in regulating ROMK1 channels. Inhibiting PTP increases the internalization of ROMK1 channels, whereas blocking PTK stimulates the insertion of ROMK1 channels.

Topics: Alanine; Animals; Benzoquinones; Blotting, Western; Colchicine; Concanavalin A; Enzyme Inhibitors; Lactams, Macrocyclic; Microscopy, Fluorescence; Microtubules; Models, Biological; Mutation; Oocytes; Paclitaxel; Patch-Clamp Techniques; Potassium; Potassium Channels; Potassium Channels, Inwardly Rectifying; Protein Tyrosine Phosphatases; Protein-Tyrosine Kinases; Quinones; Rifabutin; RNA, Complementary; Sucrose; Time Factors; Tyrosine; Xenopus

Previous studies have demonstrated that an increase in the activity of protein-tyrosine kinase (PTK) is involved in the down-regulation of the activity of apical small conductance K(+) (SK) channels in the cortical collecting duct (CCD) from rats on a K(+)-deficient diet (). We used the patch clamp technique to investigate the role of protein-tyrosine phosphatase (PTP) in the regulation of the activity of SK channels in the CCD from rats on a high K(+) diet. Western blot analysis indicated that PTP-1D is expressed in the renal cortex. Application of 1 microm phenylarsine oxide (PAO) or 1 mm benzylphosphonic acid, agents that inhibit PTP, reversibly reduced channel activity by 95%. Pretreatment of CCDs with PAO for 30 min decreased the mean NP(o) reversibly from control value 3.20 to 0.40. Addition of 1 microm herbimycin A, an inhibitor of PTK, had no significant effect on channel activity in the CCDs from rats on a high K(+) diet. However, herbimycin A abolished the inhibitory effect of PAO, indicating that the effect of PAO is the result of interaction between PTK and PTP. Addition of brefeldin A, an agent that blocks protein trafficking from Golgi complex to the membrane, had no effect on channel activity. Moreover, application of colchicine, a microtubule inhibitor, or paclitaxel, a microtubule stabilizer, had no effect on channel activity. In contrast, PAO still reduced channel activity in the presence of brefeldin A, colchicine, or paclitaxel. Furthermore, the effect of PAO on channel activity was absent when the tubules were bathed in 16% sucrose-containing bath solution or treated with concanavalin A. We conclude that PTP is involved in the regulation of the activity of SK channels and that inhibition of PTP may facilitate the internalization of the SK channels.

Topics: Animals; Arsenicals; Benzoquinones; Brefeldin A; Colchicine; Concanavalin A; Diet; Enzyme Inhibitors; Female; Intracellular Signaling Peptides and Proteins; Kidney Tubules, Collecting; Lactams, Macrocyclic; Male; Paclitaxel; Patch-Clamp Techniques; Potassium; Potassium Channels; Potassium Channels, Calcium-Activated; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Protein Tyrosine Phosphatase, Non-Receptor Type 6; Protein Tyrosine Phosphatases; Quinones; Rats; Rats, Sprague-Dawley; Rifabutin; Small-Conductance Calcium-Activated Potassium Channels

We established IL-2-dependent T cells from an adult T-cell leukaemia (ATL) patient whose leukaemic cells changed from CD4 single-positive in the initial phase to double-negative (CD4- CD8-) at the time of exacerbation. The cells termed SO-4 were of ATL cell origin and showed the double-negative TCR alpha beta/CD3+ T-cell phenotype. SO-4 cells acquired CD4 antigen expression following stimulation with concanavalin A (ConA) or immobilized anti-CD3 antibody. The induction was inhibited by herbimycin A, an inhibitor of protein tyrosine kinase (PTK) activity. No CD4 mRNA was detectable in unstimulated SO-4 cells but a 3.0 kb signal specific for CD4 mRNA was detected after stimulation. These findings indicate that SO-4 cells return to their original phenotype (CD4 single-positive) by stimulation involving PTK. The results indicate that there is a pathway of phenotypic cycling between CD4 single-positive and double-negative T cells.

Topics: Benzoquinones; Blotting, Northern; Blotting, Southern; CD3 Complex; CD4 Antigens; CD8 Antigens; Concanavalin A; Female; Gene Expression; Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; Humans; Interleukin-2; Lactams, Macrocyclic; Leukemia, T-Cell; Middle Aged; Protein-Tyrosine Kinases; Quinones; Receptors, Antigen, T-Cell, alpha-beta; Rifabutin; RNA, Messenger; T-Lymphocyte Subsets; Tumor Cells, Cultured