Constitutive Expression of MC1R in HaCaT Keratinocytes Inhibits Basal and UVB‐induced TNF‐α Production

Abstract

Alpha-melanocyte stimulating hormone (alpha-MSH) binds to melanocortin-1 receptor (MC1R) on melanocytes to stimulate pigmentation and modulate various cutaneous inflammatory responses. MC1R expression is not restricted to melanocytic cells and may be induced in keratinocytes after UVB exposure. We hypothesized that MC1R signaling in keratinocytes, wherein basal conditions are barely expressed, may modulate mediators of inflammation, such as nuclear factor-kappa B (NF-kappaB) and tumor necrosis factor-alpha (TNF-alpha). Therefore, we generated HaCaT cells that stably express human MC1R or the Arg151Cys (R151C) nonfunctional variant. We demonstrate that: (1) the constitutive activity of MC1R results in elevated intracellular cAMP level, reduced NF-kappaB activity and decreased TNF-alpha transcription; (2) binding of alpha-MSH to MC1R and the subsequent increase in cAMP production do not inhibit TNFalpha-mediated NF-kappaB activation; (3) MC1R signaling is sufficient to strongly inhibit UVB-induced TNF-alpha expression and this inhibitory effect is further enhanced by alpha-MSH stimulation. Our findings suggest that the constitutive activity of the G-protein-coupled MC1R in keratinocytes may contribute to the modulation of inflammatory events and immune response induced by UV light.

Dermal Melanocortin Receptor Rebound in Diffuse Systemic Sclerosis after Anti‐TGFβ1 Antibody Therapy

“…These changes may be explained by the high level of TGFb mRNA leading to elevated TGFb protein, which suppresses POMC mRNA synthesis [18]. This, in turn, leads to decreased production of MSHs and ACTH, which ultimately then leads to decreased stimulation of MCR mRNA expression, in accordance with earlier findings on the regulation of the expression of distinct MCR subtypes [20][21][22].…”

“…This leads to activation of melanin synthesis through activation of MCRs. Keratinocytes and epidermal papillae cells express MC 1, 4 R and POMC; activation of MCRs in these cells elicits anti-inflammatory effects through the inhibition of TNFa synthesis [18]. The MC 5 R is present on human keratinocytes in culture [19], giving also this receptor a potential regulatory role in these cells.…”

MC1R expression in HaCaT keratinocytes inhibits UVA‐induced ROS production via NADPH Oxidase‐ and cAMP‐dependent mechanisms

“…Indeed, several data show that α‐MSH is involved in the regulation of apoptosis, inflammation and UV‐induced immune suppression (Lipton and Catania, 1997; Luger et al, 2003; Bohm et al, 2005). Furthermore, recent findings demonstrate that, like other GPCRs, MC1R may display agonist‐independent activity, which results in increased levels of cAMP (Sanchez‐Mas et al, 2004; Garcin et al, 2007, 2009).…”

“…In this study, we investigated the effect of MC1R signaling on UVA‐induced ROS (UVA‐ROS) production in keratinocytes that express high level of MC1R at the cell surface. For that purpose, we used the immortalized human keratinocyte cell line HaCaT (Fusenig and Boukamp, 1998), stably transfected with wild‐type human MC1R (HaCaT‐MC1R) or the non‐functional variant R 151 C (HaCaT‐R 151 C) (Garcin et al, 2007, 2009). We focused our analysis on UVA radiations since most of the mutagenic and carcinogenic effects of UVA appears to be mediated through ROS production (de Gruijl, 2000).…”

Merkel Cell Polyomavirus Small T Antigen mRNA Level Is Increased following In Vivo UV-Radiation

“…We examined the UV responsiveness of the MCPyV early promoter-luciferase reporter following transfection of HaCaT human keratinocyte cell line. UVB irradiation was performed forty hours post-transfection with a dose of 50 mJ/cm 2 and cells were harvested five hours after UVB irradiation [26], [27]. The results show that MCPyV regulatory region possess an intrinsic transcriptional activity in HaCat cells (compared to the empty vector) and that this activity was significantly induced after UVB irradiation.…”