Gene methylation and silencing of SOCS 3 in mantle cell lymphoma

Summary The significance of loss of SOCS 3, a negative regulator of signalling pathways including those of STAT 3 and NF ‐κ B , was examined in mantle cell lymphoma ( MCL ). The protein expression and gene methylation status of SOCS 3 were detected using immunohistochemistry/ W estern blots and methylation‐specific polymerase chain reaction, respectively. To evaluate its functional importance, SOCS 3 was restored in two SOCS 3‐negative MCL cell lines using a lentiviral vector. Loss of SOCS 3 protein expression was found in 3/4 MCL cell lines and 18/33 (54·5%) tumours. SOCS3 was found consistently methylated in cell lines (3/4) and tumours (7/7) negative for SOCS 3, and was unmethylated in all SOCS 3‐positive cell line (1/1) and tumours (5/5) examined. Treatment of all three SOCS 3‐negative cell lines with 2′‐deoxy‐5‐azacytidine restored SOCS 3 expression. SOCS 3 is biologically important in MCL , as lentiviral transfer of SOCS 3 in SOCS 3‐negative cell lines increased their apoptotic activity, downregulated nuclear factor ( NF ) ‐κ B‐p65, cyclin D 1 ( CCND1 ), BCL 2 and BCL‐XL (BCL2L1), and substantially dampened interleukin 10‐induced STAT 3 activation. In 19 patients aged ≤69 years at time of diagnosis, we found that those that carried SOCS 3‐negative tumours showed a trend toward a worse outcome ( P  = 0·1, log‐rank).