Phosphorylation of signal transducer and activator of transcription 3 in soft tissue leiomyosarcoma is associated with a better prognosis

Ulipristal acetate, a selective progesterone receptor modulator, induces cell death via inhibition of STAT3/CCL2 signaling pathway in uterine sarcoma

Ulipristal acetate (UPA) is a selective progesterone receptor modulator and is used for the treatment of uterine leiomyoma (a benign tumor). Uterine sarcoma which is highly malignant cancer with a poor prognosis is clinically resembled with uterine leiomyoma. There has been no experimental research on the effect of UPA on uterine sarcoma. In this study, we examined the efficacy of UPA in uterine sarcoma with in vitro and in vivo animal models. Cytotoxicity of UPA was determined in uterine sarcoma cell lines (MES-SA, SK-UT-1, and SK-LMS-1). Apoptotic genes and signaling pathways affected by UPA were analyzed by complementary DNA (cDNA) microarray of uterine sarcoma cell lines and western blot, respectively. An in vivo efficacy of UPA was examined with uterine sarcoma cell line- and patient-derived xenograft (PDX) mice models. UPA inhibited cell growth in uterine sarcoma cell lines and primary culture cells from a PDX mouse (PDX-C). cDNA microarray analysis revealed that CCL2 was highly down-regulated by UPA. Phosphorylation and the total expression of STAT3 were inhibited by UPA. UPA also inhibited CCL2 and STAT3 in PDX-C. The inhibitory effect of UPA had not changed in the overexpression of PR and treatment of progesterone. In vivo efficacy studies with cell line-derived xenografts and a PDX model with leiomyosarcoma, a typical uterine sarcoma, demonstrated that UPA significantly decreased tumor growth. UPA had significant anti-tumor effects in uterine sarcoma through the inhibition of STAT3/CCL2 signaling pathway and might be a potential therapeutic agent to treat this disease.

Malignancy-associated immune responses: Lessons from human inborn errors of immunity

It is widely understood that cancer is a significant cause of morbidity and mortality worldwide. Despite numerous available treatments, prognosis for many remains poor, thus, the development of novel therapies remains essential. Given the incredible success of many immunotherapies in this field, the important contribution of the immune system to the control, and elimination, of malignancy is clear. While many immunotherapies target higher-order pathways, for example, through promoting T-cell activation via immune checkpoint blockade, the potential to target specific immunological pathways is largely not well researched. Precisely understanding how immunity can be tailored to respond to specific challenges is an exciting idea with great potential, and may trigger the development of new therapies for cancer. Inborn Errors of Immunity (IEI) are a group of rare congenital disorders caused by gene mutations that result in immune dysregulation. This heterogeneous group, spanning widespread, multisystem immunopathology to specific immune cell defects, primarily manifest in immunodeficiency symptoms. Thus, these patients are particularly susceptible to life-threatening infection, autoimmunity and malignancy, making IEI an especially complex group of diseases. While precise mechanisms of IEI-induced malignancy have not yet been fully elucidated, analysis of these conditions can highlight the importance of particular genes, and downstream immune responses, in carcinogenesis and may help inform mechanisms which can be utilised in novel immunotherapies. In this review, we examine the links between IEIs and cancer, establishing potential connections between immune dysfunction and malignancy and suggesting roles for specific immunological mechanisms involved in preventing carcinogenesis, thus, guiding essential future research focused on cancer immunotherapy and providing valuable insight into the workings of the immune system in both health and disease.

Merkel cell polyomavirus-negative Merkel cell carcinoma is associated with JAK-STAT and MEK-ERK pathway activation

Merkel cell polyomavirus (MCPyV) is monoclonally integrated into the genomes of approximately 80% of Merkel cell carcinomas (MCCs). While the presence of MCPyV affects the clinicopathological features of MCC, the molecular mechanisms of MCC pathogenesis after MCPyV infection are unclear. This study investigates the association between MCPyV infection and activation of the MEK-ERK and JAK-STAT signaling pathways in MCC to identify new molecular targets for MCC treatment. The clinicopathological characteristics of 30 MCPyV-positive and 20 MCPyV-negative MCC cases were analyzed. The phosphorylation status of MEK, ERK, JAK, and STAT was determined by immunohistochemical analysis. The activation status of the MEK-ERK and JAK-STAT pathways and the effects of a JAK inhibitor (ruxolitinib) was analyzed in MCC cell lines. Immunohistochemically, the expression of pJAK2 (P = .038) and pERK1/2 (P = .019) was significantly higher in MCPyV-negative than in MCPyV-positive MCCs. Male gender (hazard ratio [HR] 2.882, P = .039), older age (HR 1.137, P < .001), negative MCPyV status (HR 0.324, P = .013), and advanced cancer stage (HR 2.672, P = .041) were identified as unfavorable prognostic factors; however, the phosphorylation states of JAK2, STAT3, MEK1/2, and ERK1/2 were unrelated to the prognosis. The inhibition of cell proliferation by ruxolitinib was greater in MCPyV-negative MCC cell lines than in an MCPyV-positive MCC cell line. The expression of pERK1/2 and pMEK was higher in MCPyV-negative than in MCPyV-positive cell lines. These results suggest that activation of the JAK2 and MEK-ERK pathways was more prevalent in MCPyV-negative than in MCPyV-positive MCC and the JAK inhibitor ruxolitinib inhibited MEK-ERK pathway activation. Consequently, the JAK-STAT and MEK-ERK signaling pathways may be potential targets for MCPyV-negative MCC treatment.

PLCG2 as a potential indicator of tumor microenvironment remodeling in soft tissue sarcoma

The tumor microenvironment (TME) plays an important role in the occurrence and development of soft tissue sarcoma (STS). A number of studies have shown that to inhibit tumor growth, the TME can be remodeled into an environment unsuitable for tumor proliferation. However, a lack of understanding exists regarding the dynamic regulation of TME.In this study, we used CIBERSORT and ESTIMATE calculation methods from the Cancer Genome Atlas (TCGA) database to calculate the proportion of tumor infiltrating immune cells (TICs) and the number of immune and stromal components in 263 STS samples. Differential expression genes (DEGs) shared by Immune Score and Stromal Score were obtained via difference analysis. Univariate Cox regression analysis and construction of protein-protein interaction (PPI) networks were applied to the DEGs.Through intersection analysis of univariate COX and PPI, PLCG2 was determined as the indicator. Further analysis showed that PLCG2 expression was positively correlated with the survival of STS patients. Gene set enrichment analysis (GSEA) showed that genes in the highly expressed PLCG2 group were enriched in immune-related activities. In the low-expression PLCG2 group, genes were enriched in the E2F, G2M, and MYC pathways. Difference analysis and correlation analysis showed that CD8+ T cells, gamma delta T cells, monocytes, and M1 macrophages were positively correlated with PLCG2 expression, indicating that PLCG2 may represent the immune status of TME.Therefore, the level of PLCG2 may aid in determining the prognosis of STS patients, especially the status of TME. These data provide additional insights into the remodeling of TME.

Cross-talk between Janus kinase-signal transducer and activator of transcription pathway and transforming growth factor beta pathways and increased collagen1A1 production in uterine leiomyoma cells

OBJECTIVE

To characterize the potential interaction between interleukin-6 (IL6), Janus kinase (JAK)-signal transducer and activator of transcription (STAT)-3 (JAK/STAT3) pathway, and Transforming growth factor beta (TGFβ)-3 , and to determine whether such cross-talk was a contributing factor in the dysregulation of type I collagen production in leiomyomas.

DESIGN

Laboratory study.

SETTING

University research laboratory.

PATIENTS

None.

INTERVENTIONS

Exposure of leiomyoma and myometrial cell lines to IL6 and STAT3 activators/inhibitors. Western immunoblot analysis and immunohistochemistry.

MAIN OUTCOME MEASURES

Expression of STAT3, pSTAT3, SOCS3, COL1A1, and TGFb3.

RESULTS

We observed that IL6 increased pSTAT3 as well as collagen1A1 in uterine leiomyoma cells. Direct activation of the JAK/STAT3 pathway increased collagen1A1 production in leiomyoma cells, whereas inhibition of the pathway significantly decreased collagen1A1 production. We further observed that modulation of the JAK/STAT3 pathway also increased the expression of TGFβ3 protein. Leiomyoma cells exposed to TGFβ3 demonstrated a significant decrease in pSTAT3 protein. Myometrial cells demonstrated a less sensitive response to STAT3 modulation and collagen production.

CONCLUSION

Cross-talk between the TGFβ pathway and JAK/STAT3 pathway contributes to the fibrotic nature of uterine leiomyomas.

Association of PD-L1 and IDO1 expression with JAK-STAT pathway activation in soft-tissue leiomyosarcoma

PURPOSE

Therapies targeting the immune checkpoint molecules programmed death ligand 1 (PD-L1) and indoleamine 2,3-dioxygenase 1 (IDO1) have been explored in various malignant tumours. In this study, we examined the relationship between PDL-1, IDO1 and JAK2 expression and the roles of these signal pathways in soft tissue leiomyosarcoma (LMS).

METHODS

The next-generation sequencing data of 53 patients with LMS were obtained from an online public database and were used to assess PD-L1, IDO1 and JAK2 gene amplification and mRNA expression. Then, we determined the relationship between JAK-STAT pathway activation and PD-L1 and IDO1 expression in a LMS cell line. In addition, immunohistochemical staining of 69 cases of LMS was performed for PD-L1, IDO1, TDO2 and phosphorylated JAK2 (pJAK2).

RESULTS

Comprehensive gene expression analysis using microarray and RNA-Seq data revealed that PD-L1 and IDO1 mRNA expression positively correlated with JAK2 and STAT1 mRNA expression. Two of the 53 cases exhibited PD-L1 and JAK2 gene amplification; however, they were not related to their gene expression. LMS cell line analysis revealed that IFN-γ supplementation induced IDO1 and PD-L1 expression; these effects were suppressed by JAK inhibition. Immunohistochemical analysis of the resected specimens revealed that TDO2 expression positively correlated with pJAK2 (P = 0.0490) and IDO1 expression (P < 0.0001). PD-L1-positive specimens tended to express pJAK2; however, the relationship did not reach statistical significance (P = 0.1477).

CONCLUSION

The results suggest the possible feasibility of the combined inhibition of PD-1/PD-L1 or IDO1 with IFN-γ-JAK-STAT pathway inhibition to treat soft tissue LMS.

Clinicopathological Significance and Antitumor Effect of MPHOSPH1 in Testicular Germ Cell Tumor

MPHOSPH1, which is one of the kinesin superfamily proteins, has been reported to play an essential role in the carcinogenesis and progression of several kinds of cancers. MPHOSPH1 has also been suggested to be involved in STAT3 phosphorylation in hepatocellular carcinoma. However, the biological behavior of MPHOSPH1 in testicular germ cell tumors (TGCTs) is unclear at present. The purposes of this study were to investigate the correlation between the expression of MPHOSPH1 and clinicopathological factors and to examine the efficacy of MPHOSPH1 target therapy in TGCTs. We investigated 75 formalin-fixed paraffin-embedded TGCT samples, containing a total of 86 germ cell tumor components, by immunohistochemistry and 12 frozen samples by Western blotting. Moreover, we carried out in vitro studies to clarify the antitumor effect of MPHOSPH1 knockdown in embryonal carcinoma cell lines, NEC8 and NEC14, using small interference RNA (siRNA). A significantly high expression of MPHOSPH1 was recognized in embryonal carcinoma and yolk sac tumor components compared to the seminoma component (p<0.001, respectively). Clinically, non-seminoma cases are known to have worse prognosis than pure-seminoma cases. Interestingly, high MPHOSPH1 expression was associated with distant metastasis (p=0.001), and thus with advanced-stage disease in this study. High expression of MPHOSPH1 interacted with high expression of phosphorylated STAT3 (p=0.01). The in vitro experiments demonstrated that MPHOSPH1 interruption by siRNA resulted in a significant reduction of cell migration, invasion, proliferation and colony formation in both embryonal carcinoma cell lines (p<0.001, respectively). In conclusion, MPHOSPH1 may be a potential treatment option for TGCTs, and its expression may be a novel biomarker of poor prognosis.

Targeting the IL-6/JAK/STAT3 signalling axis in cancer

The IL-6/JAK/STAT3 pathway is aberrantly hyperactivated in many types of cancer, and such hyperactivation is generally associated with a poor clinical prognosis. In the tumour microenvironment, IL-6/JAK/STAT3 signalling acts to drive the proliferation, survival, invasiveness, and metastasis of tumour cells, while strongly suppressing the antitumour immune response. Thus, treatments that target the IL-6/JAK/STAT3 pathway in patients with cancer are poised to provide therapeutic benefit by directly inhibiting tumour cell growth and by stimulating antitumour immunity. Agents targeting IL-6, the IL-6 receptor, or JAKs have already received FDA approval for the treatment of inflammatory conditions or myeloproliferative neoplasms and for the management of certain adverse effects of chimeric antigen receptor T cells, and are being further evaluated in patients with haematopoietic malignancies and in those with solid tumours. Novel inhibitors of the IL-6/JAK/STAT3 pathway, including STAT3-selective inhibitors, are currently in development. Herein, we review the role of IL-6/JAK/STAT3 signalling in the tumour microenvironment and the status of preclinical and clinical investigations of agents targeting this pathway. We also discuss the potential of combining IL-6/JAK/STAT3 inhibitors with currently approved therapeutic agents directed against immune-checkpoint inhibitors.

Hdac7 promotes lung tumorigenesis by inhibiting Stat3 activation

Background

Lung cancer is the leading cause of cancer death worldwide. However, the molecular mechanisms underlying lung cancer development have not been fully understood. The functions of histone deacetylases (HDACs), a class of total eighteen proteins (HDAC1–11 and SIRT1–7 in mammals) that deacetylate histones and non-histone proteins, in cancers are largely unknown.

Methods

Hdac7^+/−/K-Ras mice and HDAC7-depleted human lung cancer cell lines were used as models for studying the function of Hdac7 gene in lung cancer. Kaplan-Meier survival analysis was performed to explore the relationship between HDAC7 expression and prognosis of human lung cancers. Recombinant lentivirus-mediated in vivo gene expression or knockdown, Western blotting, and pull-down assay were applied to investigate the underlying molecular mechanism by which Hdac7 promotes lung tumorigenesis.

Results

The number and burden of lung tumor were dramatically reduced in Hdac7^+/−/K-Ras mice compared to control K-Ras mice. Also, in Hdac7^+/−/K-Ras mice, cell proliferation was significantly inhibited and apoptosis in lung tumors was greatly enhanced. Similarly, cell proliferation and anchorage-independent growth of human lung cancer cell lines expressing shHDAC7 were also significantly suppressed and apoptosis was dramatically elevated respectively. Mechanistic study revealed that Hdac7 mutation in mouse lung tumors or HDAC7 depletion in human tumor cell lines resulted in significantly enhanced acetylation and tyrosine-phosphorylation of Stat3 and HDAC7 protein directly interacted with and deacetylateed STAT3. The Hdac7 mutant-mediated inhibitory effects on lung tumorigenesis in mice and cell proliferation/soft agar colony formation of human lung cancer cell lines were respectively reversed by expressing dnStat3. Finally, the high HDAC7 mRNA level was found to be correlated with poor prognosis of human lung cancer patients.

Conclusion

Our study suggests that Hdac7 promotes lung tumorigenesis by inhibiting Stat3 activation via deacetylating Stat3 and may shed a light on the design of new therapeutic strategies for human lung cancer.

Electronic supplementary material

The online version of this article (10.1186/s12943-017-0736-2) contains supplementary material, which is available to authorized users.

The prognostic values of signal transducers activators of transcription family in ovarian cancer

Signal transducer and activator of transcription (STAT), a family of latent cytoplasmic transcription factors, are composed of seven identified members (STAT1, STAT2, STAT3, STAT4, STAT5a, STAT5b, STAT6). STATs are associated with several biological processes such as cell proliferation, invasion, and metastasis in various cancer types. In addition, the STAT family has been well studied as a prognostic predictor for a considerable number of solid tumors. However, the prognostic value of the STAT family in ovarian cancer patients remains unclear. In our present study, we intend to access the prognostic roles of the STAT family in ovarian carcinoma through the ‘Kaplan–Meier plotter’ (KM plotter) online database, which collected gene expression data and survival information (overall survival (OS)) from a total of 1582 ovarian cancer patients. Our results show that high mRNA expression of STAT1, STAT4, STAT5a, STAT5b, and STAT6, are correlated to a better OS of ovarian cancer patients, especially the high level of STAT1 and STAT4 are significantly related to a favorable OS for serous ovarian cancer patients. We further accessed the prognostic roles of individual STATs in other clinicopathological features, such as pathological grades, clinical stages, and TP53 mutation, and found that these genes indicate a favorable prognosis especially for late stage, poor differentiation, and TP53 mutated ovarian cancer patients. In conclusion, these results suggest that the STAT family plays a significant prognostic role in ovarian carcinoma and individual STATs, except STAT2 and STAT3, may act as favorable prognostic markers in ovarian cancer.

Relationship between HER2 and JAK/STAT-SOCS3 signaling pathway and clinicopathological features and prognosis of ovarian cancer

OBJECTIVE

The study aims to explore the relationship between expressions of HER2 and JAK/STAT3-SOCS3 signaling pathway and clinicopathological features and prognosis of ovarian cancer (OC).

METHODS

A total of 136 OC patients were collected. Immunohistochemistry was applied to measure the expressions of STAT3, p-STAT3, SOCS3, HER2 and p-HER2 in the tumor tissues and adjacent normal tissues. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the mRNA expressions of HER2, SOCS3 and STAT3 and western blotting was applied for protein expressions of HER2, p-HER2, SOCS3, STAT3 and p-STAT3 in the tumor tissues and adjacent normal tissues. Flow cytometry was used for the cell apoptosis in the blank, afatinib (A), ruxolitinib (R) and afatinib + ruxolitinib (A + R) groups. Follow-up was performed to explore relationship of HER2, SOCS3, and STAT3 expressions with survival time of OC patients.

RESULTS

HER2, p-HER2, STAT3, and p-STAT3 expressions were higher while SOCS3 expression was lower in the tumor tissues. The positive expressions of STAT3, HER2, p-HER2 and p-STAT3 were lower while the positive expression of SOCS3 was higher in the adjacent normal tissues. The expressions of HER2, SOCS3, and p-STAT3 were associated with clinical stage and lymph node metastasis (LNM), and STAT3 expression has correlation with histological grade and LNM. The mRNA and protein expressions of HER2, STAT3 and p-STAT3 in the tumor tissues were higher than those in the adjacent normal tissues, but SOCS3 expression was significantly decreased. The positive expressions of HER2, p-HER2 and STAT3, the negative expression of SOCS3 and pathological stages were important risk factors for the prognosis of patients with OC.

CONCLUSION

Our study showed that the expressions of HER2, STAT3, and SOCS3 are associated with the progression of OC, and higher expressions of HER2 and STAT3 and lower expression of SOCS3 predict poor prognosis of OC.

The role of phosphorylated signal transducer and activator of transcription 3 (pSTAT3) in peripheral nerve sheath tumours

AIMS

STAT3 is a pro-oncogenic transcription factor that requires phosphorylation for transcriptional activation. The aim of this study was to evaluate the role of phosphorylated STAT3 (pSTAT3) expression in neurofibromas, schwannomas, and malignant peripheral nerve sheath tumours (MPNSTs).

METHODS AND RESULTS

Twenty-six neurofibromas, 62 schwannomas and 39 MPNSTs from a formalin-fixed paraffin-embedded tissue microarray were examined. Immunohistochemical analysis was performed with an anti-pSTAT3 (Tyr705) antibody. Nuclear expression was reviewed for both intensity and percentage of tumoral labelling. Distributions of disease-specific overall survival (DSOS) and event-free survival (EFS) were estimated with the Kaplan-Meier method, and compared between two pSTAT3 groups by use of the log-rank test. MPNSTs had higher median tumoral labelling than neurofibromas (P = 0.0012) or schwannomas (P = 0.0008). Moderate to strong pSTAT3 expression (defined as at least moderate labelling in ≥50% of cells) was found more frequently in MPNSTs than in neurofibromas (P = 0.026). Among MPNSTs, pSTAT3 expression differed between primary, recurrent and metastatic disease (P = 0.063 with increased expression in recurrent and metastatic cases). pSTAT3 expression (at least moderate labelling in ≥10% of cells) in primary MPNSTs was associated with worse DSOS (P = 0.048) and trended towards being associated with worse EFS (P = 0.063). Paired specimens revealed no increase in pSTAT3 expression in the recurrences or metastases relative to the primary tumour, suggesting that pSTAT3 expression may be an early indicator of aggressive disease at disease onset.

CONCLUSIONS

pSTAT3 is expressed in a higher proportion of MPNSTs than neurofibromas and schwannomas. Moderate to strong pSTAT3 expression in ≥10% of cells was found to be a negative prognostic factor for DSOS among primary MPNSTs, suggesting a role of pSTAT3 in the progression of these tumours.

mTOR pathway as a potential target in a subset of human medulloblastoma

As mammalian Target of Rapamycin (mTOR) plays role in protein synthesis and metabolism, mTOR pathway activation is involved in the pathogenesis of several types of tumors. Our aim was to elucidate its role in medulloblastoma in terms of prognosis and as a therapeutic target. Members of activated mTOR complex 1 (mTORC1) pathway, phospho-mTOR (p-mTOR) and phospho-S6 (p-S6) were examined by immunohistochemistry in formalin fixed paraffin embedded samples of 40 patients with medulloblastoma, and results were compared to clinical features and survival of patients. In proliferation assays, Daoy and UW228-2 medulloblastoma cell lines were tested by rapamycin, an mTORC1 inhibitor, and NVP-BEZ235, a dual mTOR and phosphatidylinositol 3-kinase (PI3K) inhibitor, each in monotherapy and in combination with cytostatic drugs (cisplatin, etoposide). Components of mTORC1 and mTORC2 complexes were also examined in these cell lines. Neither presence of p-mTOR (32.5 %) nor p-S6 (32.5 %) correlated with age, gender or histological subtype. In 22.5 % of cases simultaneous expression of p-mTOR and p-S6 was shown. Kaplan-Meier analysis showed inferior survival of patients expressing both marker proteins, but it was not statistically significant, probably due to low case number. UW228-2 cells had greater sensitivity to mTOR inhibitors, possibly due to its higher mTORC1 specific protein expression levels, compared to Daoy cells. In both cell lines antiproliferative effect of cytostatic drugs was significantly enhanced by mTOR inhibitors (p < 0.05). Based on our in vitro and clinicopathological studies mTOR inhibitors may have a role in the future treatment of a subset of patients with medulloblastoma.

The Role of STAT3 in Thyroid Cancer

Thyroid cancer is the most common endocrine malignancy and its global incidence rates are rapidly increasing. Although the mortality of thyroid cancer is relatively low, its rate of recurrence or persistence is relatively high, contributing to incurability and morbidity of the disease. Thyroid cancer is mainly treated by surgery and radioiodine remnant ablation, which is effective only for non-metastasized primary tumors. Therefore, better understanding of the molecular targets available in this tumor is necessary. Similarly to many other tumor types, oncogenic molecular alterations in thyroid epithelium include aberrant signal transduction of the mitogen-activated protein kinase, phosphatidylinositol 3-kinase/AKT (also known as protein kinase B), NF-кB, and WNT/β-catenin pathways. However, the role of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT3) pathway, a well-known mediator of tumorigenesis in different tumor types, is relatively less understood in thyroid cancer. Intriguingly, recent studies have demonstrated that, in thyroid cancer, the JAK/STAT3 pathway may function in the context of tumor suppression rather than promoting tumorigenesis. In this review, we provide an update of STAT3 function in thyroid cancer and discuss some of the evidences that support this hypothesis.

Role of stat3 in skin carcinogenesis: insights gained from relevant mouse models

Signal transducer and activator of transcription 3 (Stat3) is a cytoplasmic protein that is activated in response to cytokines and growth factors and acts as a transcription factor. Stat3 plays critical roles in various biological activities including cell proliferation, migration, and survival. Studies using keratinocyte-specific Stat3-deficient mice have revealed that Stat3 plays an important role in skin homeostasis including keratinocyte migration, wound healing, and hair follicle growth. Use of both constitutive and inducible keratinocyte-specific Stat3-deficient mouse models has demonstrated that Stat3 is required for both the initiation and promotion stages of multistage skin carcinogenesis. Further studies using a transgenic mouse model with a gain of function mutant of Stat3 (Stat3C) expressed in the basal layer of the epidermis revealed a novel role for Stat3 in skin tumor progression. Studies using similar Stat3-deficient and gain-of-function mouse models have indicated its similar roles in ultraviolet B (UVB) radiation-mediated skin carcinogenesis. This paper summarizes the use of these various mouse models for studying the role and underlying mechanisms for the function of Stat3 in skin carcinogenesis. Given its significant role throughout the skin carcinogenesis process, Stat3 is an attractive target for skin cancer prevention and treatment.