TC-PTP dephosphorylates IL-6–induced tyrosine pSTAT3 but does not affect STAT3-DNA binding. CLL cells (CLL 16 and 25) were incubated for 30 minutes, with or without 50 ng/mL IL-6. Nuclear fractions were extracted and treated with TC-PTP for 30 minutes, as described in “EMSA.” After TC-PTP treatment, nuclear extracts were analyzed by (A) Western blot analysis using antityrosine pSTAT3 and antiserine pSTAT3 to detect the corresponding proteins or (B) EMSA to detect binding of STAT3 to the biotin-labeled DNA probe, as described in “EMSA.”