Oncogene database

466

ATF1

activating transcription factor 1;ATF1;activating transcription factor 1

cAMP-dependent transcription factor ATF-1|cyclic AMP-dependent transcription factor ATF-1

12q13

protein-coding

Chromosomal fusion of the N-terminal region of the Ewings Sarcoma oncogene (EWS-activation-domain, EAD) to the DNA-binding domains of a variety of cellular transcription factors produce oncogenic proteins (EWS-fusion proteins (EFPs)) that cause distinct malignancies. In EFPs, the EAD acts as a potent transcriptional activation domain and this ability is repressed in the context of normal, non-tumorigenic, EWS. Trans-activation by the EAD is therefore a specific characteristic of EFPs and it is thought that EFPs induce tumorigenesis via improper transcriptional activation of cellular genes. Functional elements required for transcriptional activation are dispersed throughout the EAD, as are thirty-one copies of a Degenerate Hexapeptide Repeat (DHR, consensus SYGQQS). This suggests that the EAD contains a highly reiterated functional element related to DHRs. Here we show that in the context of EWS/ATF1, the EFP that causes malignant melanoma of soft parts, trans-cooperation by small regions of the EAD ( approximately 30 residues) results in potent transcriptional activation dependent on the conserved tyrosine residues present in DHRs. These findings provide the first evidence for a role of DHRs in EAD-mediated trans-activation and demonstrate that the EAD represents a novel tyrosine-dependent transcriptional activation domain.

The t(12;22)(q13;q12) chromosomal rearrangement results in an EWS/ATF1 fusion transcript and is associated with clear cell sarcoma (CCS). CCS is an uncommon tumor arising in tendons and aponeuroses of the extremities and shows evidence of melanocytic differentiation at the light microscopic, immunohistochemical, and/or ultrastructural level. Only 5 cases have been reported to arise in bone, none of which had molecular confirmation of the diagnosis. The current report describes a 7-year-old girl with a primary round cell sarcoma of the left humerus showing polyphenotypic differentiation on immunohistochemical analysis. Antibodies directed at melanocytic antigens were negative, and there was no evidence of melanocytic differentiation by light microscopy or ultrastructural analysis. Cytogenetic analysis revealed rearrangement of the EWS locus within 22q12. RT-PCR and sequence analysis revealed the presence of a fusion transcript bringing together exon 7 of EWS with exon 5 of ATF1, consistent with a type 2 transcript reported in association with CCS. However, given the lack of morphologic features usually present in CCS, a diagnosis of polyphenotypic round cell sarcoma was made. This tumor thus expands the spectrum of neoplasms associated with the t(12;22)(q13;q12) rearrangement.

Chromosomal translocations that fuse the N-terminal region of the Ewings sarcoma oncogene (EWS) to the C-terminal region (including the DNA-binding domain) of the cellular transcription factor ATF1 are associated with a tumour type termed malignant melanoma of soft parts (MMSP). It is envisioned that transformation by the EWS/ATF1 fusion protein results from aberrant transcriptional regulation of genes that are normally regulated by ATF1. To examine this hypothesis we have expressed exogenous EWS-ATF1 in JEG3 cells and tested its ability to activate several promoters that contain binding sites for ATF1. We show that EWS-ATF1 is a strong constitutive activator of some promoters tested but represses others. Significantly, the ability of particular promoters to be activated by EWS/ATF1 in JEG3 cells correlates with promoter activity in two MMSP-derived cell lines (SU-CCS-1 and DTC1). Our results therefore provide evidence that endogenous EWS/ATF1 can de-regulate transcription and that this capacity may contribute to transformation in MMSP.

Malignant Melanoma of Soft Parts (MMSP) is associated with the EWS/ATF1 fusion protein that arises due to chromosomal fusion of the Ewings Sarcoma oncogene (EWS) and the cellular transcription factor ATF1. EWS/ATF1 can activate several cAMP-inducible promoters, suggesting that cellular transformation in MMSP might involve constitutive activation of cAMP-inducible promoters. To assess this possibility we have examined the status of the cAMP-signaling pathway in the available MMSP-derived cell lines (DTC1 and Su-ccs-1) and find that both cell lines share several features. First, in contrast to previous effects observed in transient assays, three chromosomal promoters containing ATF binding sites are not constitutively activated by endogenous EWS/ATF1 in MMSP cells. Second, ALL the components that are known to be required for cAMP-inducible transcription are present. Third, phosphorylation of the cAMP-response-element-binding protein (CREB) can be efficiently induced by cAMP. Fourth, cAMP is unable to activate transcription, as assessed by a GAL4/ATF1 reporter assay and analysis of the c-fos and adenovirus early promoters. Thus, cell lines derived from MMSP have a block to cAMP-signaling that lies downstream of CREB phosphorylation. In light of the cAMP-responsiveness of almost ALL mammalian cell types, our findings suggest that the inability to respond to cAMP might be an important feature of MMSP cells.