Twist, E-Cadherin, and Uveal Melanoma Metastasis
William R Bell, Arielle Spitze, Laura Asnaghi, Michael L Coonfield, Charles G Eberhart. Johns Hopkins University School of Medicine, Baltimore, MD
Background: Metastatic spread is the main cause of death in patients suffering from uveal melanomas, but the molecular basis of tumor dissemination is only partially understood. Increased expression of proteins linked to epithelial mesenchymal transition (EMT) have been previously associated with invasion and metastasis in a number of cancers, but they have not been analyzed in uveal melanoma. We therefore examined expression of the EMT-associated protein Twist in uveal melanoma cell lines and in primary tumors. We also analyzed E-cadherin, which is frequently downregulated by Twist in metastatic carcinomas.
Design: Twist expression was analyzed using Western blots of protein extracts from four uveal melanoma cell lines (OCM1, OMM1, OM431), and by immunohistochemical analysis of a tissue microarray containing representative cores from 80 uveal melanomas. At least three intact cores were required for a tumor to be scored. We also examined E-cadherin levels using immunohistochemistry on the tissue microarray. A semiquantitative (0, 1+, 2+, 3+) scale was utilized for the immunohistochemical evaluations.
Results: Twist and N-cadherin were detected in protein extracts from all three uveal melanoma cell lines examined, while E-cadherin was present only in OCM3. Interestingly, the OCM3 cells expressing E-cadherin appeared to spread more slowly than the other two lines examined. Silencing of Twist expression with shRNA resulted in significant reduced invasion in vitro. On the tissue array, 72 cases had sufficient evaluable cores for analysis, and 27 of these (38%) had high levels (3+) of Twist. In the same 72 tumors, 18 (25%) had very low or absent (0 to 1+) expression of E-cadherin. Interestingly, 11 of the 18 tumors (61%) with low or absent E-cadherin had high levels of Twist, suggesting that Twist might repress E-cadherin expression in uveal melanoma. Statistical analysis of the immunohistochemical staining data in all 72 cases showed a trend towards a negative correlation between Twist and E-cadherin (p = 0.06, two-tailed Spearman test). Twist and E-cadherin expression did not appear to correlate with histopathological factors, metastasis, or overall survival, although clinical follow-up was only available for 25 patients with tumors represented on the array.
Conclusions: High levels of Twist protein expression are more common in uveal melanoma with low E-cadherin, suggesting a potential relationship between the two. However, OCM3 cells co-express both proteins, and the overall negative correlation on our tissue microarray was not statistically significant (p = 0.06).
Monday, March 19, 2012 11:15 AM
Platform Session: Section H, Monday Morning