STAT5 Phosphorylation in Malignant Melanoma Is Important for Survival and Is Mediated Through SRC and JAK1 Kinases

Abstract

Altered signaling pathways are key regulators of cellular functions in tumor cells. Constitutive activation of signal transducer and activator of transcription (STAT)3 and -5 may be involved in tumor formation and progression. We have investigated the role of STAT5 in cutaneous melanoma metastases using various RNA and protein techniques. In melanoma specimens, Stat5b transcripts were upregulated approximately 3.8-fold. In 13 of 21 (62%) human melanoma metastases, STAT5 was phosphorylated in comparison to normal human melanocytes and benign nevi. The STAT5 target gene Bcl-2 was frequently upregulated. The investigation of the underlying mechanism revealed specific STAT5 activation by recombinant human epidermal growth factor (rEGF). rEGF-induced activation of STAT5 occurred in vitro through the non-receptor tyrosine kinases transforming gene (src) of Rous Sarcoma virus and Janus kinase 1. Inhibition of Stat5b expression by small interfering RNA strongly reduced the expression of Bcl-2 and led to decreased cell viability and increased apoptosis in the melanoma cell lines A375 and BLM. Transfection with dominant-negative Stat5b caused enhanced cell death and G1 arrest in A375 cells. Our study identifies phosphorylated STAT5 in melanoma and shows regulation through rEGF; STAT5 may thus act as a survival factor for growth of human melanoma and may represent a potential target for molecular therapy.

Apoptosis-associated tyrosine kinase 1 inhibits growth and migration and promotes apoptosis in melanoma

“…19 Other data also support an important role of SRC in melanoma cell growth and migration. [20][21][22][23] According to these observations, we proposed that SRC might mediate AATK functions in melanoma cells. Therefore, we examined total protein levels and SRC activation levels in COLO829 and MeWo cells by western blot analysis.…”

c-Src tyrosine kinase co-associates with and phosphorylates signal transducer and activator of transcription 5b which mediates the proliferation of normal human B lymphocytes

“…These early findings have led to an interest in STATS as downstream transducers in Src family kinasemediated tumorigenesis [26]. Recent interest has focused upon a role for c-Src in the regulation of STAT5b in transformation and certain malignancies [27][28][29][30]. Thus, there appears to be a direct relationship between c-Src and STATs, in particular STAT5b, whereby c-Src is able to phosphorylate and activate STATs and this then drives transformation and proliferation of cells.…”

“…squamous carcinoma, human breast cancer cell [24,[27][28][29][30]), particularly following epidermal growth factor stimulation. Therefore, we addressed whether a relationship between c-Src and STAT5b exists in CD40-stimulated human B lymphocytes.…”

The importance of Src signaling in sarcoma

“…Interactions between the Src pathway and Signal Transducer and Activator of Transcription (STAT) 5, STAT3, N-cadherin and basic fibroblast growth factor receptors and β-catenin have been reported in melanoma cells (36,37). It may also be of value to understand the effect of Src inhibition on a number of the environment-sensing and growth-promoting pathways known to be aberrant in cancer cells, including the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR), Ras/mitogen-activated protein kinase (MAPK), platelet-derived growth factor (PDGF), Erb1/Erb2 and vascular endothelial growth factor (VEGF) pathways (38)(39)(40).…”