Alteration of SOCS Is a Possible Pathogenetic Mechanism of Myeloproliferative Neoplasm

Abstract 4121

The activation of the JAK/STAT pathway caused by the JAK2 gene mutations is an important pathogenetic mechanism of myeloproliferative neoplasm(MPN). Recently, many evidences suggest that there are factors besides the mutations of JAK2 gene participate in the pathogenesis of MPN. Suppressors of cytokine signaling (SOCS) proteins are potent inhibitors of JAK/STAT pathway, therefore we hypothesized that the down regulation of SOCS protein system may be a possible pathogenetic mechanism of MPN through the activation of the JAK/STAT pathway. In order to testify our hypothesis, we investigated mutated points, the expression and methylation status of the SOCS1, SOCS2 and SOCS3 gene in 100 MPN patients(44 polycythemia vera (PV), 38 essential thrombocythemia (ET) and 18 idiopathic myelofibrosis(MF)). We obtained some interesting results: (1) By using DNA sequence analysis, two mutations of SOCS3 were identified with in the coding region in 1 of PV patients and 1 of ET patients (2%), respectively, and both of these 2 patients are with JAK2V617F mutation.(wide type ACG, coding Threonine, alterering to mutant type AAG, coding Lysine). Furthermore, three types of nonsense mutations were identified in SOCS3:Firstly,38 (38%) mutations of SOCS3 were identified with in the coding region in 19 of PV patients,17 of ET patients and 2 of MF respectively, (wide type CCC, coding Proline, alterering to mutant type CCA, coding Proline); Secondly, 44 (44%) mutations of SOCS3 were identified with in the coding region in 21 of PV patients,18 of ET patients and 5 of MF respectively, (wide type GTA, coding Valine, alterering to mutant type GTG, coding Valine); At last, 35 (35%) mutations of SOCS3 were identified with in the coding region in 13 of PV patients,20 of ET patients and 2 of MF respectively, (wide type GAT, coding Aspartic acid, alterering to mutant type GAC, coding Aspartic acid).Five nonsense mutations were found in SOCS2: 2 of PV patients,3 of ET patients, (wide type AAT, coding Asparagine, alterering to mutant type AAC, coding Asparagine). On the contrary, the presence of JAK2V617F mutation did not affect the nonsense mutations of SOCS2 or SOCS3. (2) By using Methylation Specific PCR (MSP), SOCS1 hypermethylation was identified in 27 patients. Hypermethylation of the SOCS2 promoter was identified in 9 of 100 (9%) patients. Hypermethylation of the SOCS3 promoter was identified in 35 of 100 (35%) patients. There was no hypermethylation of the SOCS1, SOCS2 and SOCS3 gene in 173 normal controls. (3) By using semi-quantitative PCR, the RNA expression levels of SOCS1, SOCS2 and SOCS3 were also investigated. We observed hypermethylated patients had lower SOCS1 or SOCS3 mRNA levels than unmethylated MPN samples, also observed that among patients with unmethylated SOCS1 and SOCS3, mRNA expression was higher from patients carrying the JAK2V617F mutation as compared with JAK2 wild type patients. On the contrary, the presence of JAK2V617F mutation did not affect the expression of SOCS1 or SOCS3 mRNA in methylated patients. Moreover, SOCS3 transcript levels were highest in patients with polycythemia vera and other JAK2 V617F negative myeloproliferative neoplasm. (4) According to SOCS1, SOCS3 methylation was not significantly correlated with survival or other clinical variables. In conclusion, SOCS1 and SOCS3 hypermethylation can activate the JAK/STATsignaling pathway in alternative or together with JAK2 mutations. These alterations might represent a potential therapeutic target.