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Functional expression of the Na/K pump is controlled via a cyclosporin A-sensitive signalling pathway in activated
I I Marakhova1, A E Ivanova, F V Toropova
1Institute of Cytology, Russian Academy of Sciences, St. Petersburg. iim@mail.cytspb.rssi.ru
Abstract:
An immunosuppressant cyclosporin A (CsA) inhibits T-cell proliferation by blocking the nuclear factor of activated T-cells (NFAT) required for expression of the interleukin-2 (IL-2) gene. This work has demonstrated for the first time that in human blood lymphocytes (HBLs) activated by phytohemagglutinin (PHA), CsA at anti-proliferative doses inhibits the late sustained increase in ouabain-sensitive Rb(K) influxes, which accompanies the growth phase of G0/G1/S transition. CsA affects neither the initial, transient activation of the pump in response to PHA nor the ouabain-resistant ion fluxes during cell cycle progression. When the HBLs were rendered competent to proliferate by phorbol 12,13-dibutyrate ester and ionomycin in the presence of CsA, the exogenous IL-2 did not bypass the initial inhibitory effect of CsA on the long-term pump enhancement. When applied after the competence induction, CsA produced no effect on the sustained increase in ouabain-sensitive Rb influxes during the IL-2-induced progression phase. These results indicate that in activated HBLs, (1) IL-2 is involved in functional expression of the Na/K pump during cell transition from quiescence to proliferation, (2) the cell cycle-associated upregulation of the pump is related to a CsA-sensitive signalling pathway.
Insights
Cyclosporin A (CsA) inhibits T-cell proliferation by blocking interleukin-2 (IL-2) gene expression. This study reveals CsA disrupts the Na/K pump
Area of Science:
- Immunology and Cell Biology
- Molecular and Cellular Physiology
Background:
- Cyclosporin A (CsA) is an immunosuppressant that inhibits T-cell proliferation by blocking NFAT activation and subsequent IL-2 gene expression.
- The Na/K pump plays a role in cell proliferation, but its regulation during T-cell activation and the effect of CsA on this process are not fully understood.
Purpose of the Study:
- To investigate the effect of CsA on the Na/K pump activity during the cell cycle progression of phytohemagglutinin (PHA)-activated human blood lymphocytes (HBLs).
- To elucidate the role of interleukin-2 (IL-2) in regulating Na/K pump function during T-cell activation and proliferation.
Main Methods:
- Human blood lymphocytes (HBLs) were activated with phytohemagglutinin (PHA).
- The effects of Cyclosporin A (CsA) on ouabain-sensitive Rb(K) influxes (Na/K pump activity) were measured during cell cycle progression.
- Experiments involved using phorbol 12,13-dibutyrate ester, ionomycin, and exogenous IL-2 to modulate T-cell activation and proliferation.
Main Results:
- CsA, at anti-proliferative doses, inhibits the late sustained increase in ouabain-sensitive Rb(K) influxes during the G0/G1/S transition in PHA-activated HBLs.
- CsA does not affect the initial PHA-induced activation of the Na/K pump or ouabain-resistant ion fluxes during cell cycle progression.
- Exogenous IL-2 did not overcome CsA's initial inhibitory effect on pump enhancement, but CsA did not affect IL-2-induced pump activity when applied after competence induction.
Conclusions:
- Interleukin-2 (IL-2) is involved in the functional expression of the Na/K pump during the transition of activated HBLs from quiescence to proliferation.
- The cell cycle-associated upregulation of the Na/K pump is linked to a Cyclosporin A (CsA)-sensitive signaling pathway in activated human lymphocytes.