Secretogranin II influences the assembly and function of MHC class I in melanoma.

Melanoma is the deadliest form of skin cancer showing rising incidence over the past years. New insights into the mechanisms of melanoma progression contributed to the development of novel treatment options, such as immunotherapies. However, acquiring resistance to treatment poses a big problem to therapy success. Therefore, understanding the mechanisms underlying resistance could improve therapy efficacy. Correlating expression levels in tissue samples of primary melanoma and metastases revealed that secretogranin 2 (SCG2) is highly expressed in advanced melanoma patients with poor overall survival (OS) rates. By conducting transcriptional analysis between SCG2-overexpressing (OE) and control melanoma cells, we detected a downregulation of components of the antigen presenting machinery (APM), which is important for the assembly of the MHC class I complex. Flow cytometry analysis revealed a downregulation of surface MHC class I expression on melanoma cells that showed resistance towards the cytotoxic activity of melanoma-specific T cells. IFNγ treatment partially reversed these effects. Based on our findings, we suggest that SCG2 might stimulate mechanisms of immune evasion and therefore be associated with resistance to checkpoint blockade and adoptive immunotherapy.

ADCK2 Knockdown Affects the Migration of Melanoma Cells via MYL6.

BACKGROUND: ADCK2 is a member of the AarF domain-containing kinase family, which consists of five members, and has been shown to play a role in CoQ metabolism. However, ADCKs have also been connected to cancer cell survival, proliferation and motility. In this study, we investigated the role of ADCK2 in melanoma. METHODS: The effect of ADCK2 on melanoma cell motility was evaluated by a scratch assay and a transwell invasion assay upon siRNA-mediated knockdown or stable overexpression of ADCK2. RESULTS: We found that high levels of intratumoral ADCK2 and MYL6 are associated with a higher survival rate in melanoma patients. Knocking down ADCK2 resulted in enhanced cell migration of melanoma cells. Moreover, ADCK2-knockdown cells adopted a more dedifferentiated phenotype. A gene expression array revealed that the expression of ADCK2 correlated with the expressions of MYL6 and RAB2A. Knocking down MYL6 in ADCK2-overexpressing cells could abrogate the effect of ADCK2 overexpression and thus confirm the functional connection between ADCK2 and MYL6. CONCLUSION: ADCK2 affects melanoma cell motility, most probably via MYL6. Our results allow the conclusion that ADCK2 could act as a tumor suppressor in melanoma.

FOXD1 promotes dedifferentiation and targeted therapy resistance in melanoma by regulating the expression of connective tissue growth factor.

Metastatic melanoma is an aggressive skin cancer and associated with a poor prognosis. In clinical terms, targeted therapy is one of the most important treatments for patients with BRAFV600E -mutated advanced melanoma. However, the development of resistance to this treatment compromises its therapeutic success. We previously demonstrated that forkhead box D1 (FOXD1) regulates melanoma migration and invasion. Here, we found that FOXD1 was highly expressed in melanoma cells and was associated with a poor survival of patients with metastatic melanoma. Upregulation of FOXD1 expression enhanced melanoma cells' resistance to vemurafenib (BRAF inhibitor [BRAFi]) or vemurafenib and cobimetinib (MEK inhibitor) combination treatment whereas loss of FOXD1 increased the sensitivity to treatment. By comparing gene expression levels between FOXD1 knockdown (KD) and overexpressing (OE) cells, we identified the connective tissue growth factor (CTGF) as a downstream factor of FOXD1. Chromatin immunoprecipitation and luciferase assay demonstrated the direct binding of FOXD1 to the CTGF promoter. Similar to FOXD1, knockdown of CTGF increased the sensitivity of BRAFi-resistant cells to vemurafenib. FOXD1 KD cells treated with recombinant CTGF protein were less sensitive towards vemurafenib compared to untreated FOXD1 KD cells. Based on these findings, we conclude that FOXD1 might be a promising new diagnostic marker and a therapeutic target for the treatment of targeted therapy resistant melanoma.

HER3-Receptor-Mediated STAT3 Activation Plays a Central Role in Adaptive Resistance toward Vemurafenib in Melanoma.

Melanoma is an aggressive form of skin cancer that is often characterized by activating mutations in the Mitogen-Activated Protein (MAP) kinase pathway, causing hyperproliferation of the cancer cells. Thus, inhibitors targeting this pathway were developed. These inhibitors are initially very effective, but the occurrence of resistance eventually leads to a failure of the therapy and is the major obstacle for clinical success. Therefore, investigating the mechanisms causing resistance and discovering ways to overcome them is essential for the success of therapy. Here, we observed that treatment of melanoma cells with the B-Raf Proto-Oncogene, Serine/Threonine Kinase (BRAF) inhibitor vemurafenib caused an increased cell surface expression and activation of human epidermal growth factor receptor 3 (HER3) by shed ligands. HER3 promoted the activation of signal transducer and activator of transcription 3 (STAT3) resulting in upregulation of the STAT3 target gene SRY-Box Transcription Factor 2 (SOX2) and survival of the cancer cells. Pharmacological blocking of HER led to a diminished STAT3 activation and increased sensitivity toward vemurafenib. Moreover, HER blocking sensitized vemurafenib-resistant cells to drug treatment. We conclude that the inhibition of the STAT3 upstream regulator HER might help to overcome melanoma therapy resistance toward targeted therapies.

Fluctuating role of antimicrobial peptide hCAP18/LL­37 in oral tongue dysplasia and carcinoma.

Oral tongue squamous cell carcinoma (OTSCC), the most common cancer in the oral cavity, is aggressive and its incidence is increasing globally. Human host defense cationic antimicrobial peptide­18/antimicrobial peptide leucine­leucine­37 (hCAP18/LL­37) plays a complex role in various types of cancers. In the present study, we characterized the effects of exogenous LL­37 on three OTSCC cell lines and determined the expression of hCAP18/LL­37 in oral dysplastic and OTSCC patient samples. Our data revealed that LL­37, especially in high doses, mostly reduced the proliferation of OTSCC cells, but the effect was fluctuating. However, LL­37 stimulated the migration and invasion of OTSCC cells. The high dose of LL­37 also increased the amount of total epidermal growth factor receptor (EGFR) probably due to stabilization of the receptor to the plasma membrane. However, activation of EGFR downstream pathways was mostly decreased. Our immunohistochemical analysis showed that the hCAP18/LL­37 expression was higher in normal/mild dysplasia than in moderate/severe dysplasia and OTSCC. The hCAP18/LL­37 expression did not correlate with clinicopathological features or outcome of OTSCC patients. Our data suggest that LL­37 has a fluctuating effect on proliferation, migration and invasion of OTSCC cells, but it does not seem to play a role in the progression of OTSCC.

T-type calcium channel inhibition restores sensitivity to MAPK inhibitors in de-differentiated and adaptive melanoma cells.

BACKGROUND: Drug resistance remains as one of the major challenges in melanoma therapy. It is well known that tumour cells undergo phenotypic switching during melanoma progression, increasing melanoma plasticity and resistance to mitogen-activated protein kinase inhibitors (MAPKi). METHODS: We investigated the melanoma phenotype switching using a partial reprogramming model to de-differentiate murine melanoma cells and target melanoma therapy adaptation against MAPKi. RESULTS: Here, we show that partially reprogrammed cells are a less proliferative and more de-differentiated cell population, expressing a gene signature for stemness and suppressing melanocyte-specific markers. To investigate adaptation to MAPKi, cells were exposed to B-Raf Proto-Oncogene (BRAF) and mitogen-activated protein kinase kinase (MEK) inhibitors. De-differentiated cells became less sensitive to MAPKi, showed increased cell viability and decreased apoptosis. Furthermore, T-type calcium channels expression increased in adaptive murine cells and in human adaptive melanoma cells. Treatment with the calcium channel blocker mibefradil induced cell death, differentiation and susceptibility to MAPKi in vitro and in vivo. CONCLUSION: In summary, we show that partial reprogramming of melanoma cells induces de-differentiation and adaptation to MAPKi. Moreover, we postulated a calcium channel blocker such as mibefradil, as a potential candidate to restore sensitivity to MAPKi in adaptive melanoma cells.