SOX2 Expression in Melanoma Is Related to Tumorigenic Growth
AC Laga, CY Lai, Q Zhan, SJ Huang, EF Velazquez, MY Hsu, GF Murphy. Brigham and Women's Hospital, Harvard Medical School, Boston, MA
Background: SOX2 is a gene located on chromosome 3q26.33 that encodes for a transcription factor important for embryonic neural crest stem cell pluripotency. Laser capture microdissection and genomic screening of stem cell-rich microdomains within the basal layer of squamous epithelium disclosed significant expression of SOX2. Immunohistochemistry confirmed SOX2 expression within rare basal cells that co-expressed microphtalmia transcription factor (MITF), but not mature melanocytic markers. This stimulated the hypothesis that SOX2 expression may be linked to melanocytic tumors.
Design: Human melanocytic nevi (n=40), vertical growth phase melanomas (n=151), and experimental xenografts derived from A2058 and SK-MEL-5 melanoma cell lines, expressing high and low levels of endogenous SOX2, respectively, were evaluated by immunohistochemistry. Stable SOX2-knockdown (KD) clones were generated in A2058 melanoma cells using a lentiviral shRNA approach. SOX2-KD efficiency was assessed by Western Blotting and mRNA levels of SOX2 and TIE1, a marker of melanoma cell plasticity and angiogenesis, were quantified using real time RT-PCR. Xenograft tumor volume was determined using the following formula: (maximal dimension x minimal dimension)²/2. Statistical analysis was performed using ANOVA following log-transformation of data.
Results: Nuclear positivity for SOX2 was detected in 42% of melanomas compared to 15% of nevi, and SOX2 expression correlated with Breslow thickness. A2058-derived xenograft tumors achieved significantly greater mean estimated volumes than those derived from SKMEL5 cells (p<.05). Monolayer culture showed similar growth kinetics for SOX2 KD and control cells, but in vivo tumorigenicity assays revealed significantly diminished tumor growth in SOX2-KD tumors compared to controls (p<.05). SOX2-KD-derived tumors showed fewer TIE1-positive, CD31-negative patterned networks as compared to controls, a finding confimed by real time RT-PCR.
Conclusions: Human melanoma cells express the embryonic neural crest transcription factor, SOX2. SOX2 gene and protein expression correlate with melanoma growth in a xenograft model relevant to human disease. This effect may relate in part to a decrease in TIE1 gene and protein expression, suggesting a potential relationship between pluripotency and plasticity by melanoma cell subpopulations.
Monday, March 22, 2010 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 70, Monday Morning