Selective STAT3-? or -? expression reveals spliceform-specific phosphorylation kinetics, nuclear retention and distinct gene expression outcomes.

ABSTRACT: Phosphorylation of STAT3 (signal transducer and activator of transcription 3) is critical for its nuclear import and transcriptional activity. Although a shorter STAT3? spliceform was initially described as a negative regulator of STAT3?, gene knockout studies have revealed that both forms play critical roles. We have expressed STAT3? and STAT3? at comparable levels to facilitate a direct comparison of their functional effects, and have shown their different cytokine-stimulated kinetics of phosphorylation and nuclear translocation. Notably, the sustained nuclear translocation and phosphorylation of STAT3? following cytokine exposure contrasted with a transient nuclear translocation and phosphorylation of STAT3?. Importantly, co-expression of the spliceforms revealed that STAT3? enhanced and prolonged the phosphorylation and nuclear retention of STAT3?, but a STAT3? R609L mutant, with a disrupted SH2 (Src homology 2) domain, was not tyrosine phosphorylated following cytokine stimulation and could not cross-regulate STAT3?. The physiological importance of prolonged phosphorylation and nuclear retention was indicated by transcriptome profiling of STAT3(-/-) cells expressing either STAT3? or STAT3?, revealing the complexity of genes that are up- and down-regulated by the STAT3 spliceforms, including a distinct set of STAT3?-specific genes regulated under basal conditions and after cytokine stimulation. These results highlight STAT3? as a significant transcriptional regulator in its own right, with additional actions to cross-regulate STAT3? phosphorylation and nuclear retention after cytokine stimulation.

SUBMITTER: Ng IH 

PROVIDER: S-EPMC3441131 | biostudies-literature | 2012 Oct

REPOSITORIES: biostudies-literature