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Abstract
Cutaneous squamous cell carcinoma (cSCC) accounts for 25% of cutaneous malignancies diagnosed in Caucasian populations. Surgical removal in combination with radiation and chemotherapy are effective treatments for cSCC. Nevertheless, the aggressive metastatic forms of cSCC still have a relatively poor patient outcome. Studies have linked actin cytoskeletal dynamics and the Wnt/β-catenin signaling pathway as important modulators of cSCC pathogenesis. Previous studies have also shown that the actin-remodeling protein Flightless (Flii) is a negative regulator of cSCC. The aim of this study was to investigate if the functional effects of Flii on cSCC involve the Wnt/β-catenin signaling pathway. Flii knockdown was performed using siRNA in a human late stage aggressive metastatic cSCC cell line (MET-1) alongside analysis of Flii genetic murine models of 3-methylcholanthrene induced cSCC. Flii was increased in a MET-1 cSCC cell line and reducing Flii expression led to fewer PCNA positive cells and a concomitant reduction in cellular proliferation and symmetrical division. Knockdown of Flii led to decreased β-catenin and a decrease in the expression of the downstream effector of β-catenin signaling protein SOX9. 3-Methylcholanthrene (MCA)-induced cSCC in Flii overexpressing mice showed increased markers of cancer metastasis including talin and keratin-14 and a significant increase in SOX9 alongside a reduction in Flii associated protein (Flap-1). Taken together, this study demonstrates a role for Flii in regulating proteins involved in cSCC proliferation and tumor progression and suggests a potential role for Flii in aggressive metastatic cSCC.
Highlights
The incidence of cutaneous squamous cell carcinoma has been rising at an alarming rate in the last three decades, with higher numbers of aggressive metastatic tumors observed in men, the elderly and in immunosuppressed patients [1]
While the current study suggests a role for Flightless I (Flii) in regulating epithelial to mesenchymal transition of keratinocytes, to further elucidate the role of Flii in Cutaneous squamous cell carcinoma (cSCC) metastasis, use of MET-1 cell lines in future studies with murine metastasis models in immunocompromised or syngeneic mice are required
Previous studies have suggested that Flii affects cSCC growth via its effects on tumor invasion and apoptosis and studies presented here demonstrate a role for Flii in regulating proteins involved in cSCC proliferation and tumor progression mediated by Wnt/β-catenin signaling
Summary
The incidence of cutaneous squamous cell carcinoma (cSCC) has been rising at an alarming rate in the last three decades, with higher numbers of aggressive metastatic tumors observed in men, the elderly and in immunosuppressed patients [1]. Identifying new target proteins that regulate metastatic cell division, proliferation and signaling pathways critical to cancer cell progression and invasion may aid the development of therapeutic approaches to reduce the burden on aggressive metastatic cSCC in the community. Flightless I (Flii), a multifunctional actin remodeling protein with both intracellular and extracellular roles, has been shown to modulate cellular functions and signaling pathways critical in wound repair, inflammation and cancer progression [9,10,11]. Flii association with Leucine Rich Repeat Flightless Interacting Protein 1 (LRRFIP1/Flap-1) has been linked to regulation of epithelial–mesenchymal transition through regulation of the Wnt/β-catenin signaling pathway, a process strongly linked to invasion of aggressive cSCC [23,24]. Flii may regulate cancer progression through its effects on proteins involved in nuclear export and subsequent mRNA translation [20]
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