Positive selection of human cells lacking several transformation parameters from an SV40-transformed culture by means of parvovirus H-1

Neoplastic transformation-associated stimulation of the in vitro resolution of concatemer junction fragments from minute virus of mice DNA

Minute virus of mice (MVM) shows an oncotropic behavior reflected by its ability to amplify its genome more efficiently in a number of transformed versus normal cells. In vivo and in vitro studies revealed that the major effect of cell transformation on MVM DNA replication occurs at the level of double-stranded replicative-form amplification. In particular, resolution of MVM DNA concatemers into monomers was found to be highly sensitive to neoplastic transformation.

Antineoplastic activity of parvoviruses

The family of Parvoviridae is composed of small, nuclear-replicating viruses that are without envelope and contain an essentially single-stranded, linear DNA genome. Certain parvoviruses proved to have the remarkable capacity to prevent the formation of spontaneous as well as virtually- and chemically-induced tumors in laboratory animals. Established tumor cells serve as targets for the antineoplastic activity of parvoviruses, since the growth of preformed cancer cells transplanted in recipient animals can also be inhibited by these viruses. Furthermore, epidemiological studies in humans have revealed a correlation between serological evidence of parvoviral infection and a lower incidence of certain cancers. The parvoviral life-cycle appears to depend on cellular factors that are expressed as a function of proliferation and differentiation. This subordination may account for the oncotropism of parvoviruses in vivo and for the specificity of their interactions with (pre-)neoplastic cells under appropriate culture conditions. Thus, certain parvoviruses were found to preferentially lyse initiated or stably transformed cells in vitro, as a possible result of the stimulation of the production and/or activity of cytotoxic viral proteins. Parvoviruses can also have a cytostatic effect and cause the reversion of transformation traits, parallel to the down-modulation of the expression of defined genes, in particular oncogenes. Such direct disturbance of neoplastic cells or their precursors may participate in the oncosuppressive activity of parvoviruses, although indirect viral effects mediated by host defense mechanisms also deserve to be considered. Altogether, these properties suggest the possible use of parvoviruses as probes to investigate the process of malignant transformation.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-dependent induction of resistance to terminal differentiation in x-irradiated cultures of normal human keratinocytes

Epidermal cell clones able to proliferate under conditions that cause normal human foreskin keratinocytes (NHK) to terminally differentiate were obtained in a dose-dependent fashion after repeated x-irradiation. No terminal differentiation-resistant (TDR) clones were detected unless the total x-ray dose was split in several fractions given at protracted intervals. The x-ray-induced TDR cells were aneuploid and differed from growing NHK with regard to expression of specific protein markers of differentiation. One of the isolated TDR clones escaped senescence but failed to form tumors in nude mice. Altogether, these data indicate that NHK cultures can be used to quantitate phenotypic changes associated with neoplastic transformation of normal human epithelial cells upon exposure to defined regimens of physicochemical treatments.

Identification of a transformation-sensitive nuclear protein from normal human fibroblasts that specifically interacts with minute virus of mice DNA and correlates with cell resistance to the parvovirus

Normal human fibroblasts (MRC-5, KMS-6) were compared to transformed derivatives induced by SV40 (MRC-5V1) or gamma rays (KMST-6) for the expression of nuclear proteins that interact with the genome of minute virus of mice (MVMp), using the southwestern blot technique. A protein of 100-104 kDa apparent molecular weight was found to form a specific complex with MVMp DNA and to have an especially high affinity for the 3' terminal portion of the viral genome. This protein (p102) was differentially expressed by normal and transformed cells, i.e., its availability or DNA binding activity (or both) was much reduced in the transformants. A high level of p102 cosegregated with resistance to MVMp in cell hybrids between normal human and transformed mouse fibroblasts. Taken altogether these data suggest that the p102 protein may be a candidate for a transformation-sensitive cellular marker and for a negative regulator of parvovirus replication.