Cutaneous melanoma is the cancer with the fastest rate of increase in incidence, whereas most rates for other cancers are decreasing. Particularly, metastatic melanoma is very lethal and among the most drug resistant malignancies. Understanding the molecular and biochemical basis of melanomagenesis and progression is essential for developing novel and active targeted therapeutics.
Apurinic/apyrimidinic endonuclease/Redox factor-1 (APE/Ref-1) is a multifunctional protein that plays an important role in both DNA damage repair and cellular response to oxidative stress and is remarkably elevated in melanoma compared to normal melanocytes. Our previous studies demonstrated that the knockdown of APE/Ref-1 sensitized melanoma cells to chemo-treatment and significantly reduced metastatic potential. Our studies on JB6 cells showed that in combination with reactive oxygen species (ROS), APE/Ref-1 facilitated malignant transformation as evidence of increased colony formations in soft agar. However, limited progress has been made toward understanding the detailed mechanisms of APE/Ref-1 in melanomagenesis and progression.
E-cadherin/Snail signaling pathway plays an important role in epithelial-mesenchymal transition. Decreased E-cadherin expression has been well-documented to accompany the vertical growth phase and have been associated with elevated invasion potential. Our studies have showed that depletion of APE/Ref-1 resulted in recovery of E-cadherin expression in metastatic melanoma cells. Detected by RT-PCR, the E-cadherin level was increased to ~8 folds of control in APE/Ref-1 depleted melanoma cells. Snail, which represses transcription of E-cadherin, was found overexpressed in human melanoma. Depletion of APE/Ref-1 was also shown to inhibit Snail expression levels. Notably, Immuno-precipitation analysis demonstrated direct association between APE/Ref-1 and SNAIL protein in all tested human melanoma cell lines, which is dynamically changed with distinct stages. The APE/Ref-1/Snail complex was significantly increased in late stage of primary melanoma cells (vertical growth phase) compare to early stage and metastatic melanoma cells, which may contribute to the loss of E-cadherin and allow melanoma cells to escape from keratinocyte growth control.
Current studies are underway to ascertain whether APE/Ref-1 nuclear translocation plus Snail expression serves as a determinant of malignant transformation and melanoma progression, especially in patients with primary melanoma of Breslow depth (1-5mm).