ZEB1 targets multiple malignancy-related components to promote uveal melanoma cell dedifferentiation, proliferation, invasion, and metastasis

Abstract

Purpose : ZEB1 is a zinc finger E-box binding transcription factor (TF) important for epithelial-to-mesenchymal transition (EMT), a critical cellular event for metastasis of malignant tumors of epithelium origin. However in uveal melanoma, a non-epithelium origin tumor, ZEB1^high epithelioid phenotype denotes malignancy and metastasis, instead of the mesenchymal like ZEB1^low spindle cell phenotype. How EMT and EMT-TFs participates in the phenotype switch and deciding malignancy is unclear.

Methods : Two human uveal melanoma cells were studied. C918 is ZEB1^high epithelioid cell line while OCM1 is ZEB1^low spindle cell line. We knocked down ZEB1 in C918 and overexpressed ZEB1 in OCM1 to investigate how ZEB1 is involved in regulation of EMT, proliferation, migration, invasion, differentiation, and metastasis by western blot, qPCR and chromatin precipitation assay. Comparisons between cell lines were assessed using a Student’s t-test. We also analyzed gene expression profiling of two cohorts of human primary uveal melanomas and correlation of ZEB1 expression with metastasis by Kaplan-Meier survival curves.

Results : Change in ZEB1 expression has no influence on uveal melanoma cell morphology. ZEB1 binds and thereby represses cyclin-dependent kinase (CDK) inhibitors and differentiation regulators including MITF and BAP1, but transactivates extracellular matrix degradation enzymes such as MMPs and PLAU to strengthen cell dedifferentiation, proliferation, and invasion for uveal melanoma progression. Gene expression profiling of two large cohorts of human primary uveal melanomas clearly shows that high expression of ZEB1 significantly predisposes the tumor to metastasis.

Conclusions : EMT itself does not propel tumor progression per se in uveal melanomas, the EMT-TF ZEB1 exert its tumorigenic effects by initiating cell de-differentiation, promoting cell proliferation, facilitating cell migration, local invasion and distant dissemination.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.