A Preferential Role for STAT5, not Constitutively Active STAT3, in Promoting Survival of a Human Lymphoid Tumor

Abstract

STATs are believed to play key roles in normal and abnormal cell function. In the present work, we investigated the role of STATs in an IL-2-responsive human lymphoblastic lymphoma-derived cell line, YT. Only STAT3 was found constitutively tyrosine phosphorylated, but not other STATs. Hyperactive STAT3 was not attributable to a pre-existing intermediate affinity IL-2R complex and/or hyperactive Jak activity. Depletion of STAT3 protein expression reduced tumor cell viability with protracted kinetics (72–96 h), while TUNEL assays demonstrated cell death occurred via apoptosis. Interestingly, depletion of STAT5 in this same tumor induced more pronounced cell death compared with STAT3 depletion (24 h). Although IL-2 was able to rescue STAT3-depleted cells from death, it could not compensate for the loss of STAT5. To determine the prosurvival function of STAT3 vs STAT5 within the same tumor model, genes were profiled in STAT3- or STAT5-depleted YT cells by apoptosis-specific microarrays. Several differentially expressed genes were identified. Interestingly, those genes involved in NF-κB regulation, such as TNFR-associated factors 2 and 5 and B cell leukemia/lymphoma 10, were readily decreased upon STAT5, but not STAT3, depletion as validated by quantitative RT-PCR. These results suggest that STAT5 and, to a lesser extent, hyperactive STAT3 provide preferential and critical cell survival signals for certain human lymphoid tumors, indicating that nonhyperactive STATs should be considered as therapeutic targets for abrogating tumorigenesis.

Protein Phosphatase 2A Regulates Interleukin-2 Receptor Complex Formation and JAK3/STAT5 Activation

“…Electrophoretic Mobility Shift Assay-Nuclear extracts were prepared and assays conducted as previously published (26). Oligonucleotide sequences corresponding to the ␤-casein gene promoter for STAT5 (5Ј-AGATTTCTAGGAATTCAATCC-3Ј) were obtained from Santa Cruz Biotechnology.…”

Forskolin-inducible cAMP Pathway Negatively Regulates T-cell Proliferation by Uncoupling the Interleukin-2 Receptor Complex

“…Stat5 has been shown to be critical for T-cell expansion and survival in this signaling cascade by targeting G 1 /S transition and anti-apoptotic genes (34,39,40). To determine whether Fsk-cAMPi-activated pathways disrupted IL-2 activation of Stat5, its tyrosine phosphorylation status was examined by Western blot.…”

“…Nuclear Extract and Electrophoretic Mobility Shift AssaysNuclear extracts were prepared from MT-2 cell pellets as reported previously (34). Oligonucleotide sequences corresponding to the ␤-casein promoter (5Ј-AGATTTCTAG-GAATTCAATCC-3Ј) were purchased from Santa Cruz Biotechnology.…”

Survival Factors from Activated Accessory Cells and their Role in Triggering Autoimmune Diseases

“…1). Recently, data have revealed a critical role of STAT5 in cell survival [100][101][102]. The anti-apoptotic effect of IL-15 is evident in its promoting intracellular expression of antiapoptotic molecules upon binding to its receptor, including the cell-survival related signaling molecules Akt and PI3K [103] and Bcl-2 [61,65,98].…”