Design and use of constitutively active STAT5 constructs

Eos Promotes TH2 Differentiation by Interacting with and Propagating the Activity of STAT5

The Ikaros zinc-finger transcription factor Eos has largely been associated with sustaining the immunosuppressive functions of regulatory T cells. Paradoxically, Eos has more recently been implicated in promoting proinflammatory responses in the dysregulated setting of autoimmunity. However, the precise role of Eos in regulating the differentiation and function of effector CD4+ T cell subsets remains unclear. In this study, we find that Eos is a positive regulator of the differentiation of murine CD4+ TH2 cells, an effector population that has been implicated in both immunity against helminthic parasites and the induction of allergic asthma. Using murine in vitro TH2 polarization and an in vivo house dust mite asthma model, we find that EosKO T cells exhibit reduced expression of key TH2 transcription factors, effector cytokines, and cytokine receptors. Mechanistically, we find that the IL-2/STAT5 axis and its downstream TH2 gene targets are one of the most significantly downregulated pathways in Eos-deficient cells. Consistent with these observations, we find that Eos forms, to our knowledge, a novel complex with and supports the tyrosine phosphorylation of STAT5. Collectively, these data define a regulatory mechanism whereby Eos propagates STAT5 activity to facilitate TH2 cell differentiation.

STAT5a/b Deficiency Delays, but does not Prevent, Prolactin-Driven Prostate Tumorigenesis in Mice

The canonical prolactin (PRL) Signal Transducer and Activator of Transcription (STAT) 5 pathway has been suggested to contribute to human prostate tumorigenesis via an autocrine/paracrine mechanism. The probasin (Pb)-PRL transgenic mouse models this mechanism by overexpressing PRL specifically in the prostate epithelium leading to strong STAT5 activation in luminal cells. These mice exhibit hypertrophic prostates harboring various pre-neoplastic lesions that aggravate with age and accumulation of castration-resistant stem/progenitor cells. As STAT5 signaling is largely predominant over other classical PRL-triggered pathways in Pb-PRL prostates, we reasoned that Pb-Cre recombinase-driven genetic deletion of a floxed Stat5a/b locus should prevent prostate tumorigenesis in so-called Pb-PRL^ΔSTAT5 mice. Anterior and dorsal prostate lobes displayed the highest Stat5a/b deletion efficiency with no overt compensatory activation of other PRLR signaling cascade at 6 months of age; hence the development of tumor hallmarks was markedly reduced. Stat5a/b deletion also reversed the accumulation of stem/progenitor cells, indicating that STAT5 signaling regulates prostate epithelial cell hierarchy. Interestingly, ERK1/2 and AKT, but not STAT3 and androgen signaling, emerged as escape mechanisms leading to delayed tumor development in aged Pb-PRL^ΔSTAT5 mice. Unexpectedly, we found that Pb-PRL prostates spontaneously exhibited age-dependent decline of STAT5 signaling, also to the benefit of AKT and ERK1/2 signaling. As a consequence, both Pb-PRL and Pb-PRL^ΔSTAT5 mice ultimately displayed similar pathological prostate phenotypes at 18 months of age. This preclinical study provides insight on STAT5-dependent mechanisms of PRL-induced prostate tumorigenesis and alternative pathways bypassing STAT5 signaling down-regulation upon prostate neoplasia progression.

Growth hormone controls lipolysis by regulation of FSP27 expression

Growth hormone (GH) has long been known to stimulate lipolysis and insulin resistance; however, the molecular mechanisms underlying these effects are unknown. In the present study, we demonstrate that GH acutely induces lipolysis in cultured adipocytes. This effect is secondary to the reduced expression of a negative regulator of lipolysis, fat-specific protein 27 (FSP27; aka Cidec) at both the mRNA and protein levels. These effects are mimicked in vivo as transgenic overexpression of GH leads to a reduction of FSP27 expression. Mechanistically, we show GH modulation of FSP27 expression is mediated through activation of both MEK/ERK- and STAT5-dependent intracellular signaling. These two molecular pathways interact to differentially manipulate peroxisome proliferator-activated receptor gamma activity (PPARγ) on the FSP27 promoter. Furthermore, overexpression of FSP27 is sufficient to fully suppress GH-induced lipolysis and insulin resistance in cultured adipocytes. Taken together, these data decipher a molecular mechanism by which GH acutely regulates lipolysis and insulin resistance in adipocytes.

Effect of STAT5 silenced by siRNA on proliferation apoptosis and invasion of esophageal carcinoma cell line Eca-109

Background

STAT is the backward position of cytokine and growth factor receptors in the nucleus, STAT dimers could bind to DNA and induce transcription of specific target genes. Several lines of evidence support the important roles of STAT, especially STAT5, in carcinogenesis. The overexpression of STAT 5 is related to the differentiation and apoptosis of tumor cells. However, the role of STAT5 in esophageal squamous cell carcinoma remains unclear.

Methods

The siRNA vectors aiming to STAT5 gene were constructed. STAT5 siRNA was transfected into Eca-109 cells by Lipofectamine™2000. Expression of STAT5、Bcl-2 and Cyclin D1 were analyzed by Western blot and RT-PCR. Eca-109 cells proliferation was determined by MTT. Eca-109 cell cycle and apoptosis were detected by the flow cytometry. Boyden chamber was used to evaluate the invasion and metastasis capabilities of Eca-109 cells.

Results

The double strands oligonucleotide of siRNA aiming to STAT5 was successfully cloned into the pRNAT-U6.1 vector, and the target sequence coincided with the design. RT-PCR and Western blotting detection demonstrated that the expression levels of STAT5、Bcl-2 and Cyclin D1 gene were obviously decreased in Eca-109 cells transfected with STAT5 siRNA. STAT5 siRNA could suppress the proliferation of Eca-109 cells. The proportion of S and G2/M period frequency was significantly decreased (p < 0.05). The proportion of G0/G1 period frequency was significantly increased (p < 0.05). The average amount of cells penetrating Matrigel was significantly decreased (p < 0.05).

Conclusions

STAT5 silenced by siRNA could induce the apoptosis and suppress the proliferation、invasion and metastasis of esophageal carcinoma cell line Eca-109, which indicated STAT5 might be a novel therapeutic strategy for the human ESCC.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1351913072103000

Constitutively active STAT5 constructs

The transcription factor Signal Tranducer and Activator of Transcription 5 (STAT5) plays an important role in many biological processes. To study STAT5 biology, several different constructs have been designed that render STAT5 constitutively active. These constructs have now been used to generate animal models that allow for targeted expression of constitutively active STAT5 including a model where STAT5 is expressed in developing B and T cells. Herein we briefly describe the design of constitutively active STAT5 constructs and recent advances in their use.

The role of STAT5 in lymphocyte development and transformation

STAT5 plays a crucial role in B and T lymphocyte development. However, whether STAT5 primarily plays a role as a permissive factor, involved in lymphocyte survival, or an instructive factor, involved in lymphocyte differentiation, has been unclear. In addition, while STAT5 has been suggested to act as a transcriptional repressor, the mechanism by which it represses transcription was undefined. Recent reports have begun to shed new light on these roles for STAT5 in lymphocyte development, transcriptional repression, and leukemic transformation.