TY  - JOUR
A1  - Thiem, Alexander
A1  - Hesbacher, Sonja
A1  - Kneitz, Hermann
A1  - di Primio, Teresa
A1  - Heppt, Markus V.
A1  - Hermanns, Heike M.
A1  - Goebeler, Matthias
A1  - Meierjohann, Svenja
A1  - Houben, Roland
A1  - Schrama, David
T1  - IFN-gamma-induced PD-L1 expression in melanoma depends on p53 expression
JF  - Journal of Experimental & Clinical Cancer Research
N2  - Background
Immune checkpoint inhibition and in particular anti-PD-1 immunotherapy have revolutionized the treatment of advanced melanoma. In this regard, higher tumoral PD-L1 protein (gene name: CD274) expression is associated with better clinical response and increased survival to anti-PD-1 therapy. Moreover, there is increasing evidence that tumor suppressor proteins are involved in immune regulation and are capable of modulating the expression of immune checkpoint proteins. Here, we determined the role of p53 protein (gene name: TP53) in the regulation of PD-L1 expression in melanoma.

Methods
We analyzed publicly available mRNA and protein expression data from the cancer genome/proteome atlas and performed immunohistochemistry on tumors with known TP53 status. Constitutive and IFN-ɣ-induced PD-L1 expression upon p53 knockdown in wildtype, TP53-mutated or JAK2-overexpressing melanoma cells or in cells, in which p53 was rendered transcriptionally inactive by CRISPR/Cas9, was determined by immunoblot or flow cytometry. Similarly, PD-L1 expression was investigated after overexpression of a transcriptionally-impaired p53 (L22Q, W23S) in TP53-wt or a TP53-knockout melanoma cell line. Immunoblot was applied to analyze the IFN-ɣ signaling pathway.

Results
For TP53-mutated tumors, an increased CD274 mRNA expression and a higher frequency of PD-L1 positivity was observed. Interestingly, positive correlations of IFNG mRNA and PD-L1 protein in both TP53-wt and -mutated samples and of p53 and PD-L1 protein suggest a non-transcriptional mode of action of p53. Indeed, cell line experiments revealed a diminished IFN-ɣ-induced PD-L1 expression upon p53 knockdown in both wildtype and TP53-mutated melanoma cells, which was not the case when p53 wildtype protein was rendered transcriptionally inactive or by ectopic expression of p53\(^{L22Q,W23S}\), a transcriptionally-impaired variant, in TP53-wt cells. Accordingly, expression of p53\(^{L22Q,W23S}\) in a TP53-knockout melanoma cell line boosted IFN-ɣ-induced PD-L1 expression. The impaired PD-L1-inducibility after p53 knockdown was associated with a reduced JAK2 expression in the cells and was almost abrogated by JAK2 overexpression.

Conclusions
While having only a small impact on basal PD-L1 expression, both wildtype and mutated p53 play an important positive role for IFN-ɣ-induced PD-L1 expression in melanoma cells by supporting JAK2 expression. Future studies should address, whether p53 expression levels might influence response to anti-PD-1 immunotherapy.
KW  - Melanoma
KW  - PD-L1
KW  - CD274
KW  - p53
KW  - TP53
KW  - JAK2
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-201016
VL  - 38
ER  - 
TY  - JOUR
A1  - Grimm, Johannes
A1  - Hufnagel, Anita
A1  - Wobser, Marion
A1  - Borst, Andreas
A1  - Haferkamp, Sebastian
A1  - Houben, Roland
A1  - Meierjohann, Svenja
T1  - BRAF inhibition causes resilience of melanoma cell lines by inducing the secretion of FGF1
JF  - Oncogenesis
N2  - Approximately half of all melanoma patients harbour activating mutations in the serine/threonine kinase BRAF. This is the basis for one of the main treatment strategies for this tumor type, the targeted therapy with BRAF and MEK inhibitors. While the initial responsiveness to these drugs is high, resistance develops after several months, frequently at sites of the previously responding tumor. This indicates that tumor response is incomplete and that a certain tumor fraction survives even in drug-sensitive patients, e.g., in a therapy-induced senescence-like state. Here, we show in several melanoma cell lines that BRAF inhibition induces a secretome with stimulating effect on fibroblasts and naive melanoma cells. Several senescence-associated factors were found to be transcribed and secreted in response to BRAF or MEK inhibition, among them members of the fibroblast growth factor family. We identified the growth factor FGF1 as mediator of resilience towards BRAF inhibition, which limits the pro-apoptotic effects of the drug and activates fibroblasts to secrete HGF. FGF1 regulation was mediated by the PI3K pathway and by FRA1, a direct target gene of the MAPK pathway. When FGFR inhibitors were applied in parallel to BRAF inhibitors, resilience was broken, thus providing a rationale for combined therapeutical application.
KW  - melanoma
KW  - senescence
KW  - BRAF
KW  - tumor
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-177261
VL  - 7
IS  - 71
ER  -