L. Feuerer, S. Lamm, I. Henz, Melanie Kappelmann-Fenzl, S. Haferkamp, S. Meierjohann, C. Hellerbrand, S. Kuphal, A. Bosserhoff
Role of MIA (melanoma inhibitory activity) in melanocyte senescence
Pigment Cell & Melanoma Research, no. First Published: 06 June 2019
The protein MIA is known to be expressed in melanoma and to support melanoma progression. Interestingly, previous studies also observed the expression of MIA in nevi. Concentrating on these findings, we revealed that MIA expression is correlated with a senescent state in melanocytes. Induction of replicative or oncogene‐induced senescence resulted in increased MIA expression in vitro. Notably, MIA‐knockdown in senescent melanocytes reduced the percentage of senescence‐associated beta‐Gal‐positive cells and enhanced proliferation. Using the melanoma mouse model Tg(Grm1), MIA‐deficient mice supported the impact of MIA on senescence by showing a significantly earlier tumor onset compared to controls. In melanocytes, MIA‐knockdown led to a downregulation of the cell cycle inhibitor p21 in vitro and in vivo. In contrast, after induction of hTERT in human melanoma cells, p21 regulation by MIA was lost. In summary, our data show for the first time that MIA is a regulator of cellular senescence in human and murine melanocytes.
B. Spangler, Melanie Kappelmann-Fenzl, B. Schittek, S. Meierjohann, L. Vardimon, A. Bosserhoff, S. Kuphal
ETS‐1/RhoC signaling regulates the transcription factor c‐Jun in melanoma
International Journal of Cancer, vol. 130, no. 12, pp. 2801-2811
Recently, we discovered that the loss of E‐cadherin induces c‐Jun protein expression, which is a member of the AP‐1 transcription factor family and a key player in the processes of cell proliferation and tumor development and also found in elevated levels in melanomas. Notably, the mRNA level of c‐Jun was not affected, suggesting that c‐Jun is regulated at post‐transcriptional level. Here, we present data that suggest that the dynamic cytoskeletal network, linked to E‐cadherin, is involved in the regulation of the c‐Jun protein and transcriptional activity. In a signaling cascade, the loss of E‐cadherin activates the transcriptional regulator ETS‐1 and consequently leads to the induction of RhoC expression that stabilizes c‐Jun in melanoma. The link between RhoC and c‐Jun seems to be indirect via the cytoskeleton. We conclude that the loss of E‐cadherin mediated cell‐adhesion induces c‐Jun protein expression in a multistep process, offering several possibilities for therapeutic intervention.