Lithium regulates keratinocyte proliferation via glycogen synthase kinase 3 and NFAT2 (nuclear factor of activated T cells 2).
Bottom Line: Inhibition of GSK-3 in keratinocytes by retroviral transduction of GSK-binding protein (an endogenous inhibitory protein) or through a highly selective pharmacological inhibitor also resulted in increased keratinocyte proliferation.Both lithium and genetic/pharmacological inhibition of GSK-3 resulted in increased nuclear localization of NFAT2 (NFATc1) and increased NFAT transcriptional activation.Finally, retroviral transduction of NFAT2 increased keratinocyte proliferation whereas siRNA-mediated knockdown of NFAT2 reduced keratinocyte proliferation and decreased epidermal thickness in an organotypic skin equivalent model.
Affiliation: Dermatological Sciences, Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK.Show MeSH
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Mentions: Having confirmed that lithium-induced keratinocyte proliferation and inhibited GSK-3β, we further investigated the role of GSK-3 in regulating keratinocyte proliferation. To investigate whether inhibition of GSK-3 by lithium accounted for the effect of lithium on keratinocyte proliferation, we overexpressed GSKBP. GSKBP is a specific GSK-3 inhibitor, which we have shown, using Tcf/LEF-dependent TOPFLASH luciferase assays, to be functionally active in human keratinocytes (data not shown). We transduced SV-k14 keratinocytes with the empty vector, pLEGFP empty vector (Fig. 2A) or with a retroviral GFP–GSKBP fusion protein, pLEGFP-GSKBP (Fig. 2B), and showed that pLEGFP-GSKBP induced significantly greater proliferation at 7 days compared to pLEGFP empty vector (Fig. 2C, P < 0.005). Transduction of human keratinocytes with pLEGFP-GSKBP for 4 days induced increased proliferation compared to empty vector control pLEGFP empty (Fig. 2D, P = 0.02). To further confirm the role of GSK-3 in regulating keratinocyte proliferation, we next investigated pharmacological inhibition of GSK-3 using a specific GSK-3 inhibitor BIO (Meijer et al., 2003) and showed that BIO induced increased proliferation of SV-k14 keratinocytes at 7 days (Fig. 2E, P < 0.005 at 5, 50, and 500 nM).
Affiliation: Dermatological Sciences, Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK.