The Role Of SHP-2in CD4~+T Cell During Melanoma Progression

Protein tyrosine phosphorylation or dephosphorylation is essential for cell proliferation, differentiation and development. SHP-2, a ubiquitously expressed Src homology2(SH2) domain-containing protein tyrosine phosphatase (PTP), plays a critical role in physiology and disease. Previous studies indicate a complex role of SHP-2in regulating T-cell response. Specially its negative role in the immune system attracts much attentionSHP-2negatively regulates Jak/STAT3signal pathway, and recruiting of SHP-2to the cytoplasmic tail of PD-1mediates PD-1induced immunsuppression. Jak/STAT signal has been shown to promote tumorgenesis and tumor progression while PD-1correlates with impaired effector cell function and tumor immune escape. Thus it’s very important to understand the role of SHP-2during tumor progression.In the first chapter of this study, we investigated the expression of pSHP-2in CD4+T cell isolated from tumor and tumor-draining lymph node during tumor progression. Our study demonstrated the level of phosphorylation SHP-2gradually decreased with tumor progression, accompany by increased STAT3phosphorylation. Analysis of mouse serum revealed increased IL-6during melanoma progression, indicating that IL-6/STAT3signal pathway is activated during melanoma progression. A comparison of immune cells (CD45.2+) present in the tumor and tumor-draining lymph node showed a slight decrease in CD4+T and CD8+T cell populations, while tumor associated macrophage (TAM) was not enriched. A significant increase in myeloid derived suppressive cells (MDSC) was observed during melanoma progression. We also found increased expression of CTLA-4and PD-1on tumor infilting-CD4+and CD8+T cells. Analysis of CD4+T cell function reveals a slight increase in IFN-y production at the early stage. However, during melanoma progression, IFN-y production was significantly decreased.In the second chapter, we further investigated the effects of SHP-2ablation in CD4+T cell on melanoma growth and metastasis. The results revealed that the growth of transplanted B16-BL6and B16-F10was significantly inhibited in SHP-2conditional knockout mice in the first two weeks after tumor transplanted. However, after that inhibition of tumor growth was reversed. Analysis of tumor tissues showed decreased necris and apoptosis and increased proliferation in SHP-2conditional knockout mice. Besides, ablation of SHP-2didn’t improve the survival rate. Further studies showed increased lung metastasis and liver metastasis in SHP-2knockout mice, indicating SHP-2ablation promotes melanoma metastasis.In the third chapter, we compared cytokines and immune cell populations (CD4+T, CD8+T, TAM, MDSC) in B16-BL6bearing SHP-2f/f and SHP-2-/-mice. Some inflammatory cytokines (IL-6, TNF-α, and IL-10) in serum and tumor supernatant were both increased in SHP-2conditional knockout mice. Analysis of tumor tissues revealed increased STAT3phosphorylation in SHP-2knockout mice. A comparison of immune cells (CD45.2+) present in lymph node, spleen and tumor showed that SHP-2ablation had no influence on the quantity and function of immune cell populations (CD4+T, CD8+T and TAM). However, a significantly increase in MDSC was observed in SHP-2knockout mice and expression of Arg-1, which corrected with MDSC function was also increased.In the last chapter, we investigated the role of IL-6and MDSC during melanoma progression. In experiments examining the tumor promoting function of MDSC from SHP-2f/f and SHP-2-/-mice, results showed that coinjection of MDSC purified from B16-BL6bearing SHP-2-/-mice significantly increased tumor growth, indicating that the tumor promoting activity of MDSC from SHP-2-/-mice is much high compared with MDSC from SHP-2f/f mice. We further found that administration of anti-IL-6mAb significantly inhibited melanoma growth in mice, suggesting that SHP-2conditional ablation induced tumor progression is at least in part mediated by IL-6. Besides, Neutralization of IL-6inhibits MDSC accumulation in SHP-2-/-mice. These results indicated that increased IL-6altered MDSC homeostasis and promoted melanoma growth during melanoma progression.In summary, we for the first time indicated that phosphorylation of SHP-2in mouse CD4+T cell was decreased during melanoma progression, which was associated with increased IL-6. Increased IL-6altered MDSC homeostasis and promoted melanoma growth and metastasis during melanoma progression. Our study showed that SHP-2may regulate cytokines that impacts MDSC expansion and function, contributing to melanoma progression and indicated that SHP-2may be a potential therapeutic target to help restore immunohomeostasis and improve therapeutic responses in patients with melanoma.