Stat1 is phosphorylated and translocated to the nucleus in response to ATRA treatment.

U-937 cells (pCIneo control cells) were stimulated with ATRA for 36 hours and nuclear (n) and cytoplasmic (c) extracts were prepared. (A) The level of tyrosine phosphorylated Stat1 was determined by Western blot using antibodies specific for tyrosine 701 phosphorylated Stat1 (α-pStat1). (B) To confirm the nuclear translocation of Stat1, the membrane was stripped and immunoblotted with α-Stat1 antibodies. Quantitation of the bands, normalized to the uninduced cytoplasmic level, is shown in the lower panels.