Dysregulated expression of COOH-terminally truncated Stat5 and loss of IL2-inducible Stat5-dependent gene expression in Sezary Syndrome.
Sezary Syndrome (SzS) is a leukemic variant of cutaneous T-cell lymphoma characterized by the accumulation of clonal neoplastic CD4+ T cells. The signal transducers and activators of transcription (STAT) family members, Stat5a and Stat5b, play an important role in regulating T-cell activation. Recent studies have shown that inappropriate activation of STATs occurs frequently in a wide variety of human cancers. Here we examine the functional status of Stat5 proteins in SzS as compared with healthy donors. Western blotting demonstrates that in cytoplasmic extracts of unstimulated T cells from healthy controls two isoforms of Stat5, full-length and a COOH-terminal truncated isoform, termed Stat5(t), are present. However, bandshift assays demonstrate that only Stat5(t) translocates to the nucleus and binds DNA on IL-2 stimulation. In contrast, preactivated T cells express only full-length Stat5, which is functionally activated on IL-2 stimulation. Analysis of Stat5 protein isoforms from five of five SzS patients revealed predominant aberrant expression of Stat5(t) in preactivated peripheral blood mononuclear cell. Furthermore, patients showed preferential IL-2-induced DNA binding of Stat5(t). Consistent with the inappropriate activation of Stat5(t) in SzS patients, real-time PCR revealed that IL-2-induced mRNA expression of the Stat5 target genes, Bcl-2, PIM-1, and CISH were markedly reduced. These data indicate that functional Stat5 isoform expression is regulated by T-cell activation status and that dysregulated expression of Stat5(t) in malignant T cells in SzS can suppress Stat5-dependent gene expression. Thus, aberrant expression of Stat5(t) may be one mechanism that contributes to the cellular transformation of T cells in this disease.
Mitchell
Tracey J
TJ
Skin Cancer Unit, St. Johns Institute of Dermatology, Division of Skin Sciences, Kings College London, St. Thomas Hospital, London, United Kingdom.
Whittaker
Sean J
SJ
John
Susan
S
D000328:Adult; D002467:Cell Nucleus / Q000378:metabolism; D004273:DNA, Neoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000097:blood / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology*; D007963:Leukocytes, Mononuclear / Q000378:metabolism / Q000502:physiology; D008894:Milk Proteins; D050799:STAT5 Transcription Factor; D012751:Sezary Syndrome / Q000097:blood* / Q000235:genetics; D015534:Trans-Activators / Q000096:biosynthesis* / Q000097:blood / Q000235:genetics; D025521:Tumor Suppressor Proteins
D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D007376:Interleukin-2; D008894:Milk Proteins; D050799:STAT5 Transcription Factor; C494092:STAT5A protein, human; C494095:STAT5B protein, human; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins