Alterations in SV40 DNA integration patterns are associated with acquisition of the invasive phenotype in hamster brain tumors.

A panel of cell lines that represents a reproducible, easily manipulated experimental system which discriminates between the minimally and diffusely invasive phenotypes of brain tumors has been developed. A population of SV40-transformed glial cells derived from newborn hamster cerebral cortex (Cx) has been sequentially passaged in newborn hamsters by intracerebral inoculation followed by in vitro culture, and after each passage progressively more invasive cell lines have been established. To study the molecular basis for the observed phenotypic characteristics associated with invasiveness, cloned cells were isolated from the first (Cx4T1-derived) and third Passage (Cx4T3-derived) cells lines. After injection into hamster brain, these cloned cells produce tumors that were either minimally invasive (Cx4T1-derived) or diffusely invasive (Cx4T3-derived) into normal brain tissue. In our initial attempt to identify and characterize the cellular and molecular factors that modulate the invasive phenotype, restriction endonuclease generated SV40 DNA-containing fragment patterns of DNA from each parental cell line and each of the clonal variants were determined by Southern transfer-hybridization. The results suggest the cell lines are composed of a limited number of tumorigenic subpopulations, each of which contain characteristic arrangements of integrated SV40 DNA with repeated in vivo/in vitro passage the avvangement of intecyvated SV40 changed. Analysis of DNA from minimally and diffusely invasive cloned cells indicated strong similarities of integrated SV40 DNA arrangement to their parental cells with the greatest similarities in cells exhibiting comparable invasive phenotypes. A striking difference was seen, however, in comparisons of SV40 DNA-containing fragment patterns of DNA extracted from clones which induced marginally versus diffusely invasive tumors. These differences suggest that the invasive cells were selected from a distinct minority subpopulation or that they may have arisen as a consequence of a more dynamic process of genetic rearrangement. This cell system appears to mimic the phenotypic and genetic heterogeneity observed in human tumors of glial origin and should prove valuable in defining the biochemical and molecular basis of tumor cell invasion.