Human parvovirus B19 nonstructural protein (NS1) induces cell cycle arrest at G1 phase

Authors:
Morita E, Nakashima A, Asao H, Sato H and Sugamura K
In:
J Virol (2003) 77(5): 2915-2921
Cells used in publication:
UT7-EpoS1
Species: human
Tissue Origin: blood
Experiment
Human parvovirus B19 infects predominantly erythroid precursor cells, leading to inhibition of erythropoiesis. This erythroid cell damage is mediated by the viral non-structural protein 1 (NS1) through an apoptotic mechanism. The authors studied the molecular mechanism by which NS1 mediates apoptosis. UT7/Epo-S1 cells were nucleofected with an expression vector encoding NS1 or control vector without insert and treated with a mitotic inhibitor, paclitaxel, stained with PI and analysed by flow cytometry. Cells were assayed for cell growth by [3H]thymidine incorporation. The results demonstrate that NS1 induces G1 cell cycle arrest and suppresses cell growth.
Abstract
Human parvovirus B19 infects predominantly erythroid precursor cells, leading to inhibition of erythropoiesis. This erythroid cell damage is mediated by the viral nonstructural protein 1 (NS1) through an apoptotic mechanism. We previously demonstrated that B19 virus infection induces G(2) arrest in erythroid UT7/Epo-S1 cells; however, the role of NS1 in regulating cell cycle arrest is unknown. In this report, by using paclitaxel, a mitotic inhibitor, we show that B19 virus infection induces not only G(2) arrest but also G(1) arrest. Interestingly, UV-irradiated B19 virus, which has inactivated the expression of NS1, still harbors the ability to induce G(2) arrest but not G(1) arrest. Furthermore, treatment with caffeine, a G(2) checkpoint inhibitor, abrogated the B19 virus-induced G(2) arrest despite expression of NS1. These results suggest that the B19 virus-induced G(2) arrest is not mediated by NS1 expression. We also found that NS1-transfected UT7/Epo-S1 and 293T cells induced cell cycle arrest at the G(1) phase. These results indicate that NS1 expression plays a critical role in G(1) arrest induced by B19 virus. Furthermore, NS1 expression significantly increased p21/WAF1 expression, a cyclin-dependent kinase inhibitor that induces G(1) arrest. Thus, G(1) arrest mediated by NS1 may be a prerequisite for the apoptotic damage of erythroid progenitor cells upon B19 virus infection