H. Zinszner et al., A NOVEL EFFECTOR DOMAIN FROM THE RNA-BINDING PROTEIN TLS OR EWS IS REQUIRED FOR ONCOGENIC TRANSFORMATION BY CHOP, Genes & development, 8(21), 1994, pp. 2513-2526
In human myxoid liposarcoma, a chromosomal rearrangement leads to fusi
on of the growth-arresting and DNA-damage inducible transcription fact
or CHOP (GADD153) to a peptide fragment encoded by the TLS gene. We ha
ve found that wild-type TLS and a closely related sarcoma-associated p
rotein, EWS, are both abundant nuclear proteins that associate in vivo
with products of RNA polymerase II transcription. This association le
ads to the formation of a ternary complex with other heterogeneous RNA
-binding proteins (hnRNPs), such as Al and C1/C2. An NIH-3T3-based tra
nsformation assay was used to study the oncogenic role of the sarcoma-
associated domain of these RNA-binding proteins. Transduction of the T
LS-CHOP oncogene into cells by means of a retroviral expression vector
leads to loss of contact inhibition, acquisition of the ability to gr
ow as colonies in soft agar, and tumor formation in nude mice. Mutatio
ns that interfere with the function of the leucine zipper dimerization
domain or the adjacent basic region of CHOP abolish transformation. T
he essential role of the TLS component was revealed by the inability o
f truncated forms to fully transform cells. Domain swap between TLS- a
nd EWS associated oncogenes demonstrated that the component contribute
d by the RNA-binding proteins are functionally interchangeable, wherea
s the transcription factor component specifies tumor phenotype. The sa
rcoma-associated component of TLS and EWS contribute a strong transcri
ptional activation domain to the fusion proteins; however, transformin
g activity cannot be fully substituted by fusion of CHOP to other stro
ng trans-activators. The juxtaposition of a novel effector domain from
sarcoma-associated RNA-binding proteins to the targeting domain of tr
anscription factors such as CHOP leads to the creation of a potent onc
ogene.