Propagation of rat parvovirus in thymic lymphoma cell line C58(NT)d and subsequent appearance of a resistant cell clone after lytic infection

Abstract

Rat parvovirus (RPV) is nonpathogenic in rats but causes persistent lymphocytotropic infection. We found that RPV was propagated in rat thymic lymphoma cell line C58(NT)D and induced apoptosis. Interestingly, a resistant subclone, C58(NT)D/R, from surviving cells after lytic infection had differentiated phenotypic modifications, such as increased cell adherence, resistance to apoptosis, and suppressed tumorigenicity.

FIG. 1

Cytotoxicity and apoptosis induction of RPV in C58(NT)D cells. (A) Kinetics of cell survival in the RPV-infected (●) and the mock-infected (■) C58(NT)D cells. (B) Infectivity titers of the infected C58(NT)D cells (multiplicity of infection, 2). CPE in the infected cells (C) and the mock-infected control (D) at 4 days p.i. (E) DNA fragmentation in the RPV-infected cells (∗) and mock-infected cells (unmarked lanes). M, marker. (F) Western blot analysis showing Bcl-2 and β-actin as a control in the infected and the mock-infected cells.

FIG. 2

Persistent infection of RPV in C58(NT)D cells and an appearance of resistant cells. (A) Cell growth ratio of the RPV-infected C58(NT)D cells (●) compared to uninfected cells (■) at serial cell passages. (B) Infective titers of cell fluids at the indicated cell passages. Cells with a positive reaction to the viral antigen by IFA assay were progressively decreased at the 4th (C), 8th (D), and 10th (E) passages, and finally disappeared at the 12th passage (F) or later. The cells at the 12th passage (H) showed enhanced cell adherence compared to the parental C58(NT)D cells (G). One of the resistant cell clones, C58(NT)D/R (J), was observed by SEM and compared to the C58(NT)D cells (I). Bar = 1 μm.

FIG. 3

Resistance of C58(NT)D/R cells to irradiation-induced apoptosis. C58(NT)D/R cells and parental C58(NT)D cells were irradiated with 6 Gy (○ and ●) or 8 Gy (▵ and ▴) of X rays, and DNA fragmentation was assayed as an indicator of apoptotic change by using the cell death detection kit enzyme-linked immunosorbent assay (Boeringer).

FIG. 4

Tumorigenicity of C58(NT)D and C58(NT)D/R cells in nude mice. (A) Tumor incidence in nude mice inoculated with C58(NT)D (thick line) and C58(NT)D/R (thin line) is indicated (n = 8). (B) Tumor size was calculated by averaging the diameters of the tumor areas in the tumor-bearing nude mice inoculated with C58(NT)D and C58(NT)D/R and is indicated as mean ± standard error (error bars). Photographs of examples of tumors in C58(NT)D (C)- and C58(NT)D/R (D)-inoculated mice are shown.