Melanoma is one of the most aggressive types of tumors and exhibits high metastatic potential. Fes-related (FER) kinase is a non-receptor tyrosine kinase that has been implicated in growth and metastasis of various epithelial tumors. In this study, we have examined the role that FER kinase plays in melanoma at the molecular level. FER-depleted melanoma cells exhibit impaired Wnt/β-catenin pathway activity, as well as multiple proteomic changes, which include decreased abundance of L1-cell adhesion molecule (L1-CAM). Consistent with the pro-metastatic functions of these pathways, we demonstrate that depletion of FER kinase decreases melanoma growth and formation of distant metastases in a xenograft model. These findings indicate that FER is an important positive regulator of melanoma metastasis and a potential target for innovative therapies.

Chronic inflammatory skin disorders are frequently associated with impaired skin barrier function. Selective phosphodiesterase-4 (PDE4) inhibition constitutes an effective therapeutic strategy for the treatment of inflammatory skin diseases. We now report the pharmacological anti-inflammatory profile of DRM02, a novel pyrazolylbenzothiazole derivative with selective in vitro inhibitory activity toward PDE4 isoforms A, B and D. DRM02 treatment of cultured primary human and mouse epidermal keratinocytes interfered with pro-inflammatory cytokine production elicited by interleukin-1α and tumor necrosis factor-α. Similarly, DRM02 inhibited the production of pro-inflammatory cytokines by human peripheral blood mononuclear cells ex vivo and cultured THP-1 monocyte-like cells, with IC₅₀ values of 0.6–14 µM. These anti-inflammatory properties of DRM02 were associated with dose-dependent repression of nuclear factor-κB (NF-κB) transcriptional activity. In skin inflammation in vivo mouse models, topically applied DRM02 inhibited the acute response to phorbol ester and induced Th2-type contact hypersensitivity reactivity. Further, DRM02 also decreased cutaneous clinical changes and expression of Th17 immune pathway cytokines in a mouse model of psoriasis evoked by repeated topical imiquimod application. Thus, the overall pharmacological profiling of the PDE4 inhibitor DRM02 has revealed its potential as a topical therapy for inflammatory skin disorders and restoration of skin homeostasis.

Arrestins and integrin-linked kinase (ILK) are important scaffold proteins that regulate myriad cell functions in metazoans. β-arrestins, first identified as critical components in G-protein-coupled receptor (GPCR) signaling pathways, participate in inflammatory, immunomodulatory and tissue repair processes in GPCR-dependent and -independent manners. ILK is a central mediator of signaling cascades elicited by activation of integrins, regulating cell motility, proliferation, and mechanotransduction. In the epidermis, ILK is essential for maintenance of barrier function, hair follicle development, melanocyte colonization and regeneration after injury. In this tissue, β-arrestin 2 mitigates inflammatory processes and development of allergic dermatitis, which also is associated with loss of epidermal barrier function. However, the functional role of β-arrestin 1 in epidermal cells is poorly understood. We now report that β-arrestin 1 directly binds ILK, forming hitherto unidentified protein complexes in epidermal keratinocytes. In the absence of exogenous GPCR ligand stimulation, β-arrestin 1 and ILK are found throughout the cytoplasm in epidermal keratinocytes, and also co-localize to plasma membrane regions associated with cell protrusions. Inactivation of the genes that encode both β-arrestin 1 and 2 attenuates forward cell migration, whereas expression of ILK together with β-arrestin 1 restores cell motility. The cooperative effect of ILK and β-arrestin 1 in promoting directional cell migration may have important implications for epidermal regeneration and reestablishment of barrier function after injury.

Mechanical signals play key roles in the regulation of epidermal homeostasis and regeneration after injury. Integrins are key components of focal adhesions, and these complexes are major contributors to mechanotransduction. In keratinocytes, integrin-linked kinase (ILK) modulates essential processes for epidermal homeostasis and wound repair. However, its functions in the transduction of mechanical stimuli have remained virtually unexplored. In this study, we characterized epidermal tissues and primary keratinocytes from mice with epidermis-restricted inactivation of the Ilk gene (ILK-KO). ILK-deficient epidermis exhibits abnormalities in key components of mechanotransduction cascades, including disruptions in hemidesmosomal Collagen XVII immunoreactivity at the dermal–epidermal junction, and marked reduction in the nuclear localization of the mechanosensitive transcriptional regulator YAP. In wild-type (ILK+), but not in ILK-KO-cultured keratinocytes, exposure to cyclic bidirectional strain induced marked F-actin cytoskeletal rearrangements, characterized by the assembly of thick cortical actin bundles and stress fibers, as well as YAP nuclear translocation and transcriptional activity. Exposure to mechanical strain was additionally accompanied by differential changes in miRNA expression between ILK+ and ILK-KO cells. These findings reveal multiple and previously unappreciated key regulatory roles for ILK in epidermal keratinocyte responses to mechanical signals.