Tel induces a G1 arrest and suppresses Ras-induced transformation L Van Rompaey 1 , M Potter 1 , C Adams 1 and G Grosveld* ,1 1 Department of Genetics, St. Jude Children's Research Hospital, Memphis, Tennessee, TN 38105, USA The Tel gene is a major target of translocations in leukemia and loss of heterozygosity is regularly observed for the non-translocated allele, thus supporting the notion that Tel is a tumor suppressor. Most tumor suppressors in¯uence cellular proliferation, dierentiation and cell death and thereby prevent oncogenic transformation and genetic instability. We found that overexpression of Tel retards proliferation of many cell types, primary cells and immortalized cells, by inducing a G1 arrest. Tel's block of cellular proliferation is rescued by high seeding densities. Furthermore, Tel suppressed Ras-mediated colony growth in soft agar and tumor formation in nude mice. The Pointed and DNA binding (DB) domains of Tel were required for all Tel-induced phenotypes. Oncogene (2000) 19, 5244 ± 5250. Keywords: Tel; transformation; tumor suppressor Introduction Tel/ETV6 is a member of the ets family of transcrip- tion factors. It was discovered as part of a fusion protein, resulting from a t(5;12) in a case of myeloid leukemia (Golub et al., 1994). It is now known to be a frequent target of chromosome translocations in leukemia: FISH analyses revealed involvement of Tel in over 30 dierent chromosomal rearrangements and over 10 dierent fusions have been cloned (Rowley, 1999). Tel is also involved in translocations in solid tumors, as exempli®ed by the Tel-NTRK3 fusion protein, resulting from a t(12;15) (Knezevich et al., 1998a). Three types of Tel translocations resulting in in-frame fusions can be discerned: (1) fusion of the N- terminal half of Tel containing the Pointed (PNT) domain to tyrosine kinase moieties of PDGFR, ABL, JAK2, NTRK3 and ARG (Cazzaniga et al., 1999; Eguchi et al., 1999; Golub et al., 1994, 1996a; Iijima et al., 2000; Knezevich et al., 1998b; Lacronique et al., 1997; Papadopoulos et al., 1995; Peeters et al., 1997a); (2) fusion of N- or C-terminal parts of Tel to parts of the transcription factors MN1, AML1, MDS1/EVI-1, BTL, CDX2 (Buijs et al., 1995; Chase et al., 1999; Cools et al., 1999; Golub et al., 1995; Peeters et al., 1997b; Romana et al., 1995); and (3) fusions in which Tel is not fused to tyrosine kinases or transcription factors, such as Tel/ACS2 and Tel/STL (Suto et al., 1997; Yagasaki et al., 1999). In the latter two cases, open reading frames are very short. Circumstantial evidence points to a role of Tel as a putative tumor suppressor in one or more cell types. The most compelling data derive from patients suering from preB-ALL that is characterized by a t(12;21). One Tel allele fuses to the AML1 transcription factor whereas the second allele often undergoes deletion (Romana et al., 1995; Shurtle et al., 1995; Stegmaier et al., 1995; Takeuchi et al., 1997). Loss of heterozygosity (LOH) for Tel was also reported in other Tel translocations such as the Tel- ABL, Tel-NTRK3, Tel-JAK2/Tel-MDS1/EVI1, Tel- STL and Tel-ACS2 (Eguchi et al., 1999; Golub et al., 1996b; Knezevich et al., 1998a, b; Peeters et al., 1997b; Suto et al., 1997; Yagasaki et al., 1999). Furthermore the 12p13 locus that contains the genes for Tel and p27 KIP1 is often deleted in leukemia (Hoglund et al., 1996; Sato et al., 1995; Wlodarska et al., 1996). But the Tel and p27 KIP1 genes are not targeted in all cases, leaving the possibility that yet other critical tumor suppressor genes may be located in that region (Baens et al., 1999; La Starza et al., 1999; Sato et al., 1997; Stegmaier et al., 1996). No clear physiological role has been de®ned for Tel, although gene ablation and biochemical experiments have provided the ®rst clues. The study of mice lacking Tel revealed non-redundant roles for Tel in angiogenic development, maintenance of selected neuronal and mesenchymal populations and in homing of the hematopoietic system from the fetal liver to the bone marrow (Wang et al., 1997, 1998). Tel is a phospho- protein expressed in most cell types as two isoforms (Poirel et al., 1997). These derive from initiation of translation at alternative start codons, Met1 and Met43. Tel contains three putative MAPK phosphor- ylation sites of which one (Ser22) is located between the ®rst two methionines. Ser22 is the only MAPK site that is conserved between Tel and Tel2, the closest Tel- homolog (Potter et al., 2000) and thus is possibly involved in regulating the activity of Tel and/or Tel2. Several proteins have been shown to interact with Tel: Tel, Tel2, Fli-1 and UBC9 interact through the PNT domain (Chakrabarti and Nucifora, 1999; Jousset et al., 1997; Kwiatkowski et al., 1998; Potter et al., 2000). Furthermore Tel is a transcriptional repressor, see- mingly by the recruitment of the co-repressors mSin3A, SMRT and N-CoR (Chakrabarti and Nucifora, 1999; Fenrick et al., 1999; Lopez et al., 1999). Lopez et al. (1999) delineated two autonomous repression domains in the central region of Tel and showed that the PNT domain is essential for the repression activity. Results Data derived from clinical studies indicate that Tel might have a tumor suppressor function in speci®c cell types. LOH of Tel is most consistently associated with Oncogene (2000) 19, 5244 ± 5250 ã 2000 Macmillan Publishers Ltd All rights reserved 0950 ± 9232/00 $15.00 www.nature.com/onc *Correspondence: G Grosveld Received 12 July 2000; revised 29 August 2000; accepted 31 August 2000