Epigenetic alteration of the SOCS1 gene in chronic myeloid leukaemia Ta-Chih Liu, 1 Sheng-Fung Lin, 1 Jan-Gowth Chang, 2 Ming-Yu Yang, 1 Shih-Ya Hung 1 and Chao-Sung Chang 1 1 Division of Hematology-Oncology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung, and 2 Department of Molecular Medicine, China Medical University Hospital, Taichung, Taiwan Received 24 June 2003; accepted for publication 14 August 2003 Summary. The expression of the suppressor of cytokine signalling-1 (SOCS1) protein is induced in response to sti- mulation by several cytokines. The induced SOCS1 inhibits the signalling pathway through the association with a variety of tyrosine kinase proteins. In this study, the mutation analyses, CpG island methylation status, and the expression of the SOCS1 gene in 112 chronic myeloid leukaemia (CML) samples, five leukaemia cell lines, and 30 normal controls were analysed. No genetic mutations of SOCS1 gene were noted in the CML samples. The SOCS1 gene was hypermethylated in 67% and 46% of the blastic and chronic phase CML samples respectively (P <0Æ0001). However, there was no methylation of the SOCS1 gene in normal controls or CML in molecular remission. The methylation status of the SOCS1 gene is consistent with the results of the real-time quantitative reverse transcription polymerase chain reaction and immunocytochemistry staining. Our results demonstrate that the SOCS1 gene silencing is caused by the methylation of CpG islands in CML and is reversed to an unmethylated status in molecular remission. As SOCS1 has universal activity to negatively regulate several cytokine signalling pathways, the loss of the negative regulation of cytokine signalling by the SOCS1 may play a role in the pathogenesis of CML progression. Keywords: SOCS1 gene, chronic myeloid leukaemia, methylation-specific PCR. The suppressor of cytokine signalling (SOCS) proteins are a family of negative regulators of cytokine signalling (Yoshim- ura et al, 1995; Endo et al, 1997; Naka et al, 1997; Starr et al, 1997; Krebs & Hilton, 2000, 2001). These proteins are relatively small molecules containing src homology 2 (SH2) domains. The SOCS proteins have been implicated in the negative regulation of several cytokine pathways, including the inhibition of the Janus kinase (JAK), tyrosine phosphor- ylation and nuclear translocation of the signal transducers and activators of transcription (STAT) proteins (Endo et al, 1997; Naka et al, 1997; Song & Shuai, 1998; Krebs & Hilton, 2000, 2001), interferon signalling (Song & Shuai, 1998; Alexander et al, 1999) and the suppression of steel factor- dependent proliferation (Sepulveda et al, 1999). The expres- sion of the SOCS proteins is induced in response to stimulation by these cytokines, and the induced SOCS inhibits the signalling pathway (Krebs & Hilton, 2000, 2001). Among eight SOCS proteins [SOCS1–7 and cytokine inducible SH2 (CIS)-containing protein], the most potent inhibitors of cytokine signalling are SOCS1 and SOCS3 (Nicholson et al, 1999). The SOCS1 gene is located on chromosome 16p12-p13Æ1 (Yandava et al, 1999). The genomic DNA contains two exons (Genbank accession number XP 008004), where the single-coding-exon tran- scribes a 1215-bp mRNA, which in turn encodes 211 amino acids. The SOCS1 transcript is often present in cells at low levels, and can be induced rapidly by a wide variety of cytokines, hormones, and growth factors. The SOCS1 protein inhibits the signalling of many cytokines including leukae- mia inhibitory factor (LIF), interferons, interleukin (IL)-2, IL-3, IL-4, IL-6, erythropoietin, thrombopoietin, and other cytokines (Endo et al, 1997; Naka et al, 1997; Starr et al, 1997; Song & Shuai, 1998; Nicholson et al, 1999; Krebs & Hilton, 2000, 2001). The SOSC1 protein turns off the signal transduction through direct interaction with a variety of signalling proteins including JAK kinase, growth factor receptor-bound protein-2 (Grb2), Vav, fibroblast growth factor (FGF) receptor, Kit receptor, fms-like tyrosine kinase-3 Correspondence: Ta-Chih Liu MD, Division of Hematology-Oncol- ogy, Department of Internal Medicine, Kaohsiung Medical Univer- sity Hospital, 100 Shih Chuan 1st Rd, Kaohsiung, Taiwan. E-mail: d730093@cc.kmu.edu.tw British Journal of Haematology, 2003, 123, 654–661 654 Ó 2003 Blackwell Publishing Ltd