TGF-beta1 causes epithelial-mesenchymal transition in HaCaT derivatives, but induces expression of COX-2 and migration only in benign, not in malignant keratinocytes.

BACKGROUND: Transforming growth factor beta (TGF-beta) acts as a tumor promoter by inducing epithelial-mesenchymal transition (EMT), which leads to a motile phenotype, enabling invasion and metastasis of cancer cells. Cancer-related inflammation, mediated by prostaglandins, has been proposed as a critical mechanism in conversion of benign cells to malignant.

OBJECTIVE: Induction of cyclooxygenase 2 (COX-2), producer of prostaglandins, is thought to be a prerequisite for TGF-beta-induced EMT in benign cells. We used HaCaT derivatives, representative of skin cancer progression, to investigate TGF-beta1 mediated EMT response, and the role of COX-2 in it.

METHODS: Effect of TGF-beta1 was investigated by analyzing cell proliferation, morphology and protein expression. Chemotaxis and scratch-wound assays were used to study migration.

RESULTS: TGF-beta1 caused proliferation arrest of benign and malignant HaCaT cells, and changed the epithelial morphology of benign and low-grade malignant cells, but not metastatic cells, to mesenchymal spindle-shape. Epithelial junction proteins ZO-1 and E-cadherin were downregulated in all cell lines in response to TGF-beta1, but mesenchymal markers were not induced, suggesting a partial EMT response. COX-2 and migration were induced only in benign HaCaT derivatives. Malignant derivatives did not induce COX-2 in response to TGF-beta 1 treatment, thus emphasizing the role of inflammation in EMT response of benign cells.

CONCLUSIONS: TGF-beta1 operates via distinct mechanisms in inducing EMT and metastasis, and supporting this we show that TGF-beta1 induces COX-2 and promotes the migration of benign cells, but does not further augment the migration of malignant cells, indicating their resistance to TGF-beta1 in the context of motility.