Molecular detection and targeting of EWSR1 fusion transcripts in soft tissue tumors

Abstract

Soft tissue tumors are a heterogeneous group of tumors, traditionally classified according to morphology and histogenesis. Molecular classification divides sarcomas into two main categories: (a) sarcomas with specific genetic alterations and (b) sarcomas showing multiple complex karyotypic abnormalities without any specific pattern. Most chromosomal alterations are represented by translocations which are increasingly detected. The identification of fusion transcripts, in fact, not only support the diagnosis but also provides the basis for the development of new therapeutic strategies aimed at blocking aberrant activity of the chimeric proteins. One of the genes most susceptible to breakage/translocation in soft tissue tumors is represented by Ewing sarcoma breakpoint region 1 (EWSR1). This gene has a large number of fusion partners, mainly associated with the pathogenesis of Ewing's sarcoma but with other soft tissue tumors too. In this review, we illustrate the characteristics of this gene/protein, both in normal cellular physiology and in carcinogenesis. We describe the different fusion partners of EWSR1, the molecular pathways in which is involved and the main molecular biology techniques for the identification of fusion transcripts and for their inhibition.

Fig. 1

Schematic representation of EWS gene and protein domains with the main breakpoints illustrations

Fig. 2

Schematic representation of EWS translocation with ETS-genes family fusion partners: interaction with transcriptional complex on DNA and illustration of the main molecular pathways deregulated. Gray squares indicate the soft tissue tumors characterized by EWS/ETS translocations (ES: Ewing sarcoma; PNET: Primitive neuroectodermal tumor; RS: Rhabdomyosarcoma; DSRCT: Desmoplastic small-round-cell-tumor)

Fig. 3

Schematic representation of EWS translocation with homeobox-genes family fusion partners: interaction with transcriptional complex on DNA and illustration of the main molecular pathways deregulated. Gray squares indicate the soft tissue tumors characterized by EWS/homeodomain translocations (RS: Rhabdomyosarcoma)

Fig. 4

Schematic representation of EWS translocation with zinc finger-genes family fusion partners: interaction with transcriptional complex on DNA and illustration of the main molecular pathways deregulated. Gray squares indicate the soft tissue tumors characterized by EWS/ZN translocations (PNET: Primitive neuroectodermal tumor; DSRCS: Desmoplastic small-round-cell-sarcoma; EMCS: Extraskeletal myxoid chondrosarcomas)

Fig. 5

Schematic representation of EWS translocation with leucine-zipper-genes family fusion partners: interaction with transcriptional complex on DNA and illustration of the main molecular pathways deregulated. Gray squares indicate the soft tissue tumors characterized by EWS/leucine-zipper translocations (HCCC: Sarcomatous hepatocellular carcinoma; SCOS: Small-cell-osteo-sarcoma)

Fig. 6

Upward, a FISH assay showing the EWS locus rearrangement with a break-apart probe: a absence of translocation and b EWS rearrangement-positive tumor cells showing one fusion, one orange, and one green signal pattern. Arrows shows rearrangement signals (original magnification ×60). Under, c a Polymerase chain reaction analysis of EWS–FLI1 translocation using EWS and FLI1 primers. Reactions were subjected to electrophoresis on a 2 % agarose gel: Lane 4 shows the DNA size marker (100 bp); Lane 1–3: Beta actin controls; Lane 5: Positive sample DNA (EWS/FLI1 type I-150 bp); Lane 8: Positive sample DNA (EWS/FLI1 type II-197 bp); Lane 6,7, 9 and 10: Negative samples DNA