Fas Ligand Reduces Viability in Primary Melanoma Short-Term Cell Cultures More than in Metastatic Melanoma Short-Term Cell Cultures

Down-regulation of mcl-1 by small interfering RNA sensitizes resistant melanoma cells to fas-mediated apoptosis

Resistance of malignant melanoma cells to Fas-mediated apoptosis is among the mechanisms by which they escape immune surveillance. However, the mechanisms contributing to their resistance are not completely understood, and it is still unclear whether antiapoptotic Bcl-2-related family proteins play a role in this resistance. In this study, we report that treatment of Fas-resistant melanoma cell lines with cycloheximide, a general inhibitor of de novo protein synthesis, sensitizes them to anti-Fas monoclonal antibody (mAb)-induced apoptosis. The cycloheximide-induced sensitization to Fas-induced apoptosis is associated with a rapid down-regulation of Mcl-1 protein levels, but not that of Bcl-2 or Bcl-xL. Targeting Mcl-1 in these melanoma cell lines with specific small interfering RNA was sufficient to sensitize them to both anti-Fas mAb-induced apoptosis and activation of caspase-9. Furthermore, ectopic expression of Mcl-1 in a Fas-sensitive melanoma cell line rescues the cells from Fas-mediated apoptosis. Our results further show that the expression of Mcl-1 in melanoma cells is regulated by the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) and not by phosphatidylinositol 3-kinase/AKT signaling pathway. Inhibition of ERK signaling with the mitogen-activated protein/ERK kinase-1 inhibitor or by expressing a dominant negative form of mitogen-activated protein/ERK kinase-1 also sensitizes resistant melanoma cells to anti-Fas mAb-induced apoptosis. Thus, our study identifies mitogen-activated protein kinase/ERK/Mcl-1 as an important survival signaling pathway in the resistance of melanoma cells to Fas-mediated apoptosis and suggests that its targeting may contribute to the elimination of melanoma tumors by the immune system.

Overcoming apoptosis deficiency of melanoma-hope for new therapeutic approaches

The increased incidence of malignant melanoma in the last decades, its high mortality and pronounced therapy resistance pose an enormous challenge. Important therapeutic targets for melanoma are the induction of apoptosis and suppression of survival pathways. Preclinical studies have demonstrated the efficacy of pro-apoptotic Bcl-2 proteins and of death receptor ligands to trigger apoptosis in melanoma cells. In the clinical setting, BH3 domain mimics and death receptor agonists are therefore considered as promising, specific novel treatments to add to the conventional pro-apoptotic strategies such as chemo- or radiotherapy. However, constitutively activated survival pathways, in particular the mitogen-activated protein kinases, protein kinase B/Akt and nuclear factor (NF)-kappaB, all may work in concert to prevent effective therapy. Thus, selective biologicals developed with the aim to inhibit pro-survival signaling are currently tested in melanoma. For highly therapy-resistant tumors such as melanoma, development of novel drug combinations will be essential, and combinations of survival inhibitors and pro-apoptotic mediators appear most promising. The challenge of the near future will be to make a rational choice of the multiple possible combinations and protocols. This review gives a critical overview of proteins involved in melanoma chemoresistance, which are targets for current drug development leading to the best choice for future trials.

Fas/Fas ligand gene polymorphism in patients with papillary thyroid cancer in the Turkish population

OBJECTIVE

Fas ligand (FasL) is an apoptotic agent and a member of tumor necrosis factor (TNF) family. FasL exists in cytotoxic T lymphocyte (CTL) and natural killer (NK) cells, and it is increased in tumor cell membrane. On the contrary, CTL and NK are bound to Fas on the surfaces of cell membrane; this triggers apoptosis in cytotoxic cells and leads to their death. This system plays an important role in eliminating viral infections and cancer cells. Malfunction of this system results in the development and spread of the malignancy. This study aims at evaluating the influence of Fas and FasL gene polymorphism in papillary thyroid cancer (PTC) in the Turkish population.

RESEARCH DESIGN AND METHODS

Forty-five patients with PTC and 100 healthy controls were included in this study. The diagnosis of PTC was confirmed by histopathologic examination after surgery. The evaluation of genotype for Fas 670 A/G and FasL 843 C/T gene polymorphism was performed using the PCR-restriction fragment length polymorphism (RFLP) method.

RESULTS

The evaluation of Fas/FasL genotype and gene allele frequency did not show statistically significant differences between the patient and control group (p>0.05). In addition, the univariate analysis did not reveal a statistically significant relationship between the size of the nodule and the Fas/FasL gene polymorphism in patients with PTC.

CONCLUSIONS

As in other types of malignancy, genetic factors in the pathogenesis of PTC may also show changes in different populations. Fas/FasL gene polymorphysms are possible that different mechanisms function in apoptosis balance in PTC development.

Expression of Fas ligand (CD95L) in primary malignant melanoma and melanoma metastases is associated with overall survival

BACKGROUND

There is increasing evidence that the Fas/Fas ligand (FasL) system is involved in tumor-mediated immune suppression. The purpose of this study was to investigate the effect of Fas (CD95) as well as FasL (CD95L) expression in primary malignant melanoma and melanoma metastases on overall survival (OS).

PATIENTS AND METHODS

19 patients with metastatic malignant melanoma who were treated with different dacarbazine (DTIC)-based chemotherapy regimens were included in this study. From each patient, primary melanoma biopsies and biopsies from metastases were histologically evaluated. Immunohistology was performed with antibodies to Fas/CD95 and FasL/CD95L. Differences in OS were plotted using the Kaplan-Meier method and compared by the log rank test.

RESULTS

Fas/CD95 and FasL/CD95L expression was detected in 73.7 and 63.2% of primary melanomas, respectively. In metastases, expression of both Fas/CD95 (63.2%) and FasL/CD95L (47.4%) was markedly decreased. Presence of FasL/ CD95L expression in primary melanoma resulted in significantly (p = 0.024) prolonged OS compared with FasL/CD95L-negative high-risk primary melanomas. In contrast, loss of FasL/CD95L expression in melanoma metastases resected before chemotherapy was associated with significantly prolonged median survival (p = 0.0139).

CONCLUSION

Presence of FasL/CD95L expression in primary malignant melanoma and the loss of FasL/ CD95L expression in metastases seem to be positive prognostic factors.