Acute leukemia viruses E26 and avian myeloblastosis virus have related transformation-specific RNA sequences but different genetic structures, gene products, and oncogenic properties

Abstract

Replication-defective acute leukemia viruses E26 and myeloblastosis virus (AMV) cause distinct leukemias although they belong to the same subgroup of oncogenic avian tumor viruses based on shared transformation-specific (onc) RNA sequences. E26 causes predominantly erythroblastosis in chicken and in quail, whereas AMV induces a myeloid leukemia. However, upon cultivation in vitro for >1 month, a majority of surviving hemopoietic cells of E26-infected animals bear myeloid markers similar to those of AMV-transformed cells. We have analyzed the genetic structure and gene products of E26 virus for a comparison with those of AMV. An E26/helper virus complex was found to contain two RNA species: a 5.7-kilobase (kb) RNA that hybridizes with cloned AMV-specific proviral DNA and hence is probably the E26 genome; and an 8.5-kb RNA that is unrelated to AMV and represents helper virus RNA. Thus, E26 RNA is smaller than 7.5-kb AMV RNA. Hybridization of size-selected poly(A)-terminating E26 RNA fragments with AMV-specific DNA indicated that the shared specific sequences are located in the 5' half of the E26 genome as opposed to a 3' location in AMV RNA. In nonproducer cells transformed in vitro by E26, a gag-related nonstructural 135,000-dalton protein (p135) was found. No gag (Pr76) or gag-pol (Prl80) precursors of essential virion proteins, which are present in AMV nonproducer cells, were observed. pl35 was also found in cultured E26 virus producing cells of several leukemic chickens, and its intracellular concentration relative to that of the essential virion proteins encoded by the helper virus correlates with the ratio of E26 to helper RNA in virions released by these cells. p135 is phosphorylated but not glycosylated; antigenically it is not related to the pol or env gene products. It appears to be coded for by a partial gag gene and by E26-specific RNA sequences, presumably including those shared with AMV. Hence, AMV and E26 appear to use different strategies for the expression of related onc sequences: AMV is thought to encode a transforming protein via a subgenomic mRNA, whereas E26 codes for a gag-related polyprotein via genomic RNA. It is speculated that differences in the oncogenic properties of E26 and AMV are due to differences in their genetic structures and gene products.

Mutagenesis of avian carcinoma virus MH2: only one of two potential transforming genes (delta gag-myc) transforms fibroblasts.

“…In parallel a chicken embryo fibroblast culture infected with MH2 (MAV-1) virus stock and a quail cell line infected with MC29 (ring-necked pheasant virus) termed Q8 (40) were labeled with [35S]methionine. Cell lysates were incubated with antiserum against the viral gag proteins (47). The immunoprecipitates were dissolved, fractionated by electrophoresis in a 7.5% polyacrylamide gel, and autoradiographed as described (47).…”

“…Cell lysates were incubated with antiserum against the viral gag proteins (47). The immunoprecipitates were dissolved, fractionated by electrophoresis in a 7.5% polyacrylamide gel, and autoradiographed as described (47). Pr 180 is the gag-pol precursor, and Pr 76 is the gag-precursor of avian retroviruses; p1O0 is the Agag-mht product of MH2 (lanes 1 and 2), and p110 is the Agag-myc gene product of MC29 (lane 3) (40).…”

The proto-oncogene c-ets is preferentially expressed in lymphoid cells.

“…(To distinguish the v-myb gene of AMV from v-mvb sequences of E26, AMV v-myb is designated v-mybA, and E26 v-myb sequences are defined as v-,nybE [4,20]. Thus, the fused oncogene of E26 is v-mybE-ets.)…”

“…Except for nine nucleotide substitutions, 533 nucleotides at the 5' end of the E26 transforming gene are identical to a region of AMV v-myb, whereas the remaining nucleotides are unique to E26 and represent the v-ets sequences (4,20). (To distinguish the v-myb gene of AMV from v-mvb sequences of E26, AMV v-myb is designated v-mybA, and E26 v-myb sequences are defined as v-,nybE [4,20].…”

ERF: Genomic organization, chromosomal localization and promoter analysis of the human and mouse genes

“…The ets family of genes was originally discovered by its homology to the avian transforming virus E26 (Nunn et al, 1984;Bister et al, 1982) and is characterized by a conserved DNA binding domain (Watson et al, 1988;Karim et al, 1990) which recognize the GGA A/T motif (Macleod et al, 1992;Wasylyk et al, 1993;Werner et al, 1995;Kodandapani et al, 1996). Ets genes have been found throughout the metazoan evolution (Lautenberger et al, 1992;Laudet et al, 1993;Degnan et al, 1993) which is suggestive of their fundamental role.…”