JAK/STAT3 Pathway Is Involved in Survival of Neurons in Response to Insulin-like Growth Factor and Negatively Regulated by Suppressor of Cytokine Signaling-3

Abstract

Janus kinases (JAK) and signal transducers and activator of transcription (STAT) proteins are activated in response to many cytokines and growth factors and are well studied in the immune system. This study was conducted to examine the role of the JAK/STAT pathway in neurons in response to tumor necrosis factor-␣ (TNF␣) and insulin-like growth factor-1 (IGF-1), which play a major role during neurodegeneration, and to study their effect on expression of suppressors of cytokine signaling 3 (SOCS-3), belonging to the novel family of feedback regulators of cytokine and growth factor activities. In this report, we showed that TNF␣ is inhibitory to the survival of primary cortical neurons at higher doses and that IGF-1 can rescue TNF␣-stimulated cell death. We showed that the JAK/ STAT pathway is involved in this rescue as tyrphostin AG490, a specific inhibitor of JAK/STAT, completely inhibits cell survival in response to IGF-1. STAT3 gets tyrosine-phosphorylated and translocated to the nucleus in response to IGF-1. Northern blot, semi-quantitative reverse transcription-PCR, and real time PCR experiments demonstrated that the JAK/STAT pathway also up-regulated SOCS-3 mainly in response to IGF-1. SOCS-3 associated with the IGF receptor and blocked further STAT3 activation. To our knowledge, this is the first report that demonstrated the importance of the JAK/STAT pathway and the role of SOCS-3 in the survival of neurons in response to IGF-1. We have subsequently shown that SOCS-3 overexpression, on one hand, leads to neuroblastoma cell death and on the other hand leads to primary cell differentiation, indicating the involvement of SOCS-3 in cell survival and differentiation.

IGF‐1 stimulated upregulation of cyclin D1 is mediated via STAT5 signaling pathway in neuronal cells

“…IGF-1 has been shown to regulate cyclins, CDK protein expression, and retinoblastoma (Rb) protein phosphorylation in breast cancer cell lines (11). Our previous studies have shown that IGF-1 was a potent survival and rescue factor for dying neurons mediated by JAK/STAT, PI3kinase as well as JNK kinase pathway (12,13). However, the specific target genes involved in IGF-1 mediated cell survival in neuronal cells are not clear.…”

“…Cortices were dissected in Neural Basal Medium supplemented with B27, glutamine, Glutamax, penstrep, and growth factors bFGF and mEGF and 5 Â 10 6 cells were seeded in T-25 flasks and were grown at 37 C in a humidified atmosphere with 5% CO 2 (Thermo Scientific) to obtain neurospheres. Neurospheres were confirmed with the appropriate neural stem cell markers (14) and IGF-1 was used at 20 ng/ml as previously described (12). The cells were serum starved overnight prior to all stimulation experiments.…”

“…Timed mated Sprague Dawley (Charles River, Sulzfeld, Germany) rats were bred and culled as done previously (12). Neocortical tissues were dissected from embryonic day 18 rat brains.…”

“…SH-SY5Y human neuroblastoma cells were cultured in DMEM medium with high glucose, 10% fetal bovine serum in CO 2 incubator as per protocol (12). TNF-a was used at 50 ng/ml in SH-SY5Y cells and IGF-1 was used at 50 ng/ml (13).…”

Insulin-like growth factor-I protects cells from ER stress-induced apoptosis via enhancement of the adaptive capacity of endoplasmic reticulum

“…Moreover, in primary cortical neurons, the JAK/STAT pathway mediates IGF-I-dependent cell survival, and the tyrphostin AG490, a specific JAK inhibitor, abrogates the antiapoptotic effect of IGF-I. 33 The G-protein/adenylyl cyclase/PKA pathway may underlie the IGF-I-mediated antiapoptotic activity as well. It has been shown that in certain cell types, including NIH/3T3 fibroblasts, the IGF-IR is coupled with certain types of Gproteins and receptor activation leads to a biologically significant dissociation of G-protein subunits.…”