Thymic targets for Abelson murine leukemia virus are early gamma/delta T lymphocytes

Molecular analysis has shown that the majority of Abelson murine leukemia virus (Ab-MuLV)-induced primary thymomas represent transformed gamma/delta thymocytes. Many of these thymomas are of monoclonal origin as judged by provirus integration pattern and contain rearranged genes encoding T-cell receptor (TCR) gamma and delta chains but germ-line immunoglobulin heavy-chain genes. Some of the monoclonal tumors contain multiple rearranged alleles encoding TCR gamma, delta, and beta chains. Further, one Ab-MuLV thymoma cell line contained germ-line-configuration TCR gamma- and delta-chain genes, which became rearranged after in vitro propagation. Clones of this cell line were observed to rearrange these genes after intrathymic passage. Also, some subclones of this cell line underwent rearrangement of their immunoglobulin heavy-chain genes in culture. These observations suggest that the thymic targets for Ab-MuLV transformation are early gamma/delta thymocytes, some of which continue to rearrange their TCR gamma- and delta-chain genes.

Abelson murine leukemia virus induces platelet-derived growth factor-independent fibroblast growth: correlation with kinase activity and dissociation from full morphologic transformation

Abelson murine leukemia virus (A-MuLV) encodes a single protein product, a tyrosine-specific protein kinase, whose activity is necessary for cell transformation by this retrovirus. Using a defined medium culture system, we demonstrate that transformation of NIH 3T3 fibroblasts by A-MuLV abrogates their normal requirement for platelet-derived growth factor (PDGF) for cell growth. Analysis of constructed insertional mutant viruses revealed an absolute correlation between A-MuLV-encoded tyrosine kinase activity and PDGF-independent fibroblast growth. Sequences of the provirus not required for kinase activity appeared unnecessary for abrogating the fibroblast requirement for PDGF. Conversely, sequences required for kinase activity appeared necessary, suggesting that induction of PDGF-independent fibroblast growth, like cell transformation, is a function of this tyrosine kinase. Fibroblasts transformed by a partially transformation-defective mutant demonstrated incomplete morphological transformation but were still independent of PDGF for growth. Thus, the processes of full morphological transformation and growth factor independence can be partially dissociated.

Blast colonies containing hemopoietic progenitor cells can give rise to Abelson virus (A-MuLV)-transformed cell lines

We have established an in vitro system with which to examine the ability of Abelson murine leukemia virus (A-MuLV) to infect early hemopoietic progenitor cells. Blast cell colonies containing less than 100 cells were shown to contain up to 85% of cells with secondary hemopoietic colony-forming ability. Infection of cells from these blast colonies resulted in generation of transformed mast cell lines when a feeder was provided. Morphological examination of cells taken from infected cultures at various times postinfection indicated a progression of cellular differentiation to the mast cell lineage. Southern analysis on early subclones of transformed cells from two wells, using a v-abl specific probe, indicated a unique pattern of viral integration amongst subclones, suggesting that all subclones had derived from a single cell in each well. Similar results were observed with helper-free Abelson virus obtained by transfecting psi 2 cells with P160 A-MuLV proviral DNA. These data indicate that hemopoietic progenitor cells can be infected by A-MuLV and subsequently in our in vitro culture condition give rise to transformed mast cell lines.

Partial maturation and light chain restriction of Abelson virus-transformed B cell precursors

The induction of partial maturation in an in vitro derived Abelson virus-transformed murine lymphoid cell subline (ABC-1/AT1) is described. Pre-B (cytoplasmic, mu chain-positive) lymphocytes were induced from presumptive B cell precursors by prostaglandin E1, butyric acid, lipopolysaccharide and interferon. Maturation was independent of alterations in cellular growth rate and could be achieved in the absence of cell division. The AT1 subline was found to be restricted to the expression of a single light chain type (lambda) indicating a possible B cell lineage-committed precursor as the target for viral transformation.