CD133+ cell content correlates with tumour growth in melanomas from skin with chronic sun-induced damage

CD133-Dependent Activation of Phosphoinositide 3-Kinase /AKT/Mammalian Target of Rapamycin Signaling in Melanoma Progression and Drug Resistance

Melanoma frequently harbors genetic alterations in key molecules leading to the aberrant activation of PI3K and its downstream pathways. Although the role of PI3K/AKT/mTOR in melanoma progression and drug resistance is well documented, targeting the PI3K/AKT/mTOR pathway showed less efficiency in clinical trials than might have been expected, since the suppression of the PI3K/mTOR signaling pathway-induced feedback loops is mostly associated with the activation of compensatory pathways such as MAPK/MEK/ERK. Consequently, the development of intrinsic and acquired resistance can occur. As a solid tumor, melanoma is notorious for its heterogeneity. This can be expressed in the form of genetically divergent subpopulations including a small fraction of cancer stem-like cells (CSCs) and non-cancer stem cells (non-CSCs) that make the most of the tumor mass. Like other CSCs, melanoma stem-like cells (MSCs) are characterized by their unique cell surface proteins/stemness markers and aberrant signaling pathways. In addition to its function as a robust marker for stemness properties, CD133 is crucial for the maintenance of stemness properties and drug resistance. Herein, the role of CD133-dependent activation of PI3K/mTOR in the regulation of melanoma progression, drug resistance, and recurrence is reviewed.

Mechanisms of Melanoma Progression and Treatment Resistance: Role of Cancer Stem-like Cells

Melanoma is the third most common type of skin cancer, characterized by its heterogeneity and propensity to metastasize to distant organs. Melanoma is a heterogeneous tumor, composed of genetically divergent subpopulations, including a small fraction of melanoma-initiating cancer stem-like cells (CSCs) and many non-cancer stem cells (non-CSCs). CSCs are characterized by their unique surface proteins associated with aberrant signaling pathways with a causal or consequential relationship with tumor progression, drug resistance, and recurrence. Melanomas also harbor significant alterations in functional genes (BRAF, CDKN2A, NRAS, TP53, and NF1). Of these, the most common are the BRAF and NRAS oncogenes, with 50% of melanomas demonstrating the BRAF mutation (BRAFV600E). While the successful targeting of BRAFV600E does improve overall survival, the long-term efficacy of available therapeutic options is limited due to adverse side effects and reduced clinical efficacy. Additionally, drug resistance develops rapidly via mechanisms involving fast feedback re-activation of MAPK signaling pathways. This article updates information relevant to the mechanisms of melanoma progression and resistance and particularly the mechanistic role of CSCs in melanoma progression, drug resistance, and recurrence.

Suitability of CD133 as a Marker for Cancer Stem Cells in Melanoma

Objectives:

CD133 is considered a cancer stem cell (CSC) marker in various malignancies; however, its role as a biomarker of malignant melanoma remains controversial. The present study was conducted to evaluate the suitability of CD133 surface antigen as a CSC marker in melanoma.

Methods:

Human melanoma cells were fractionally separated by magnetic cell separation depending on the CD133 phenotype and transplanted into immunodeficient mice to evaluate their tumorigenic capacity. Furthermore, the time until the development of a palpable tumor and the growth rate were measured, and the final tumor volume was assessed after 8 weeks. The immunohistochemical expression of CD133 in the induced neoplasia was then compared using histomorphometry.

Results:

Notably, neoplasms were induced in all the groups (n = 48), including in the CD133-negative group. Tumors induced by unsorted cells had the largest volume (p = 0.014) but were detected significantly later in this group (p ≤ 0.001). Interestingly, all explanted tumors expressed CD133, with no significant differences among groups.

Conclusions:

In contrast to the results obtained in prior studies, the suitability of CD133 as a CSC marker could not be demonstrated. The current encouraging progress in targeted therapy for malignant melanoma highlights the need to identify more effective targets.

Morin inhibits proliferation and self-renewal of CD133+ melanoma cells by upregulating miR-216a

Melanoma is one of the most malignant skin tumors with high mortality rate. Morin has been reported to treat several cancers. However, whether or how Morin affects melanoma progression is still poorly understood. Either Morin treatment or miR-216a overexpression reduced cell viability, sphere formation ability and expressions of stem cell marker genes CD20, CD44, CD133 and Wnt-3A. MiR-216a was induced by Morin treatment in CD133⁺ melanoma cells. Melanoma xenograft model treated by Morin showed reduced tumor size, weight as well as expressions of stemness markers and Wnt-3A. Inhibition of the stemness marker gene expressions in CD133⁺ melanoma cells is mediated by downregulating Wnt-3A through miR-216a. MiR-216a and Wnt-3A may potentially serve as clinical biomarkers of melanoma, and Morin may contribute to the treatment of melanoma.

From Normal Skin to Squamous Cell Carcinoma: A Quest for Novel Biomarkers

Squamous cells carcinoma (SCC) is the second most frequent of the keratinocyte-derived malignancies after basal cell carcinoma and is associated with a significant psychosocial and economic burden for both the patient himself and society. Reported risk factors for the malignant transformation of keratinocytes and development of SCC include ultraviolet light exposure, followed by chronic scarring and inflammation, exposure to chemical compounds (arsenic, insecticides, and pesticides), and immune-suppression. Despite various available treatment methods and recent advances in noninvasive or minimal invasive diagnostic techniques, the risk recurrence and metastasis are far from being negligible, even in patients with negative histological margins and lymph nodes. Analyzing normal, dysplastic, and malignant keratinocyte proteome holds special promise for novel biomarker discovery in SCC that could be used in the future for early detection, risk assessment, tumor monitoring, and development of targeted therapeutic strategies.

Evaluation of the expressions pattern of miR-10b, 21, 200c, 373 and 520c to find the correlation between epithelial-to-mesenchymal transition and melanoma stem cell potential in isolated cancer stem cells

Small non-coding RNAs named microRNAs (miRNAs) modulate some functions and signaling pathways in skin epithelial cells and melanocytes. They also function as oncogenes or tumor suppressors in malignancies and tumor metastasis. We investigated the expression patterns of miRNAs, including miR-10b, 21, 200c, 373 and 520c, which regulate epithelial-to-mesenchymal transition (EMT) and metastasis in isolated cancer stem cells (CSCs) and non- CSCs. Six melanoma cell lines were tested for the expressions of stem cell markers. Melanoma stem cells were enriched via fluorescence-activated cell sorting (FACS) using the CD133 cell surface marker or spheroid culture. They were then characterized based on colony and sphere formation, and the expressions of stemness and EMT regulator genes and their invasion potential were assessed using real-time qRT-PCR and invasion assay. Our results indicate that cells enriched via sphere formation expressed all the stemness-related genes and had an enhanced number of colonies, spheres and invaded cells compared to cells enriched using the CD133 cell surface marker. Moreover, miRNAs controlling metastasis increased in the melanospheres. This may be related to the involvement of CSCs in the metastatic process. However, this must be further confirmed through the application of knockdown experiments. The results show that sphere formation is a useful method for enriching melanoma stem cells. Melanospheres were found to upregulate miR-10b, 21, 200c, 373 and 520c, so we suggest that they may control both metastasis and stemness potential.

Dioxin receptor regulates aldehyde dehydrogenase to block melanoma tumorigenesis and metastasis

Background

The dioxin (AhR) receptor can have oncogenic or tumor suppressor activities depending on the phenotype of the target cell. We have shown that AhR knockdown promotes melanoma primary tumorigenesis and lung metastasis in the mouse and that human metastatic melanomas had reduced AhR levels with respect to benign nevi.

Methods

Mouse melanoma B16F10 cells were engineered by retroviral transduction to stably downregulate AhR expression, Aldh1a1 expression or both. They were characterized for Aldh1a1 activity, stem cell markers and migration and invasion in vitro. Their tumorigenicity in vivo was analyzed using xenografts and lung metastasis assays as well as in vivo imaging.

Results

Depletion of aldehyde dehydrogenase 1a1 (Aldh1a1) impairs the pro-tumorigenic and pro-metastatic advantage of melanoma cells lacking AhR expression (sh-AhR). Thus, Aldh1a1 knockdown in sh-AhR cells (sh-AhR + sh-Aldh1a1) diminished their migration and invasion potentials and blocked tumor growth and metastasis to the lungs in immunocompetent AhR+/+ recipient mice. However, Aldh1a1 downmodulation in AhR-expressing B16F10 cells did not significantly affect tumor growth in vivo. Aldh1a1 knockdown reduced the high levels of CD133⁺/CD29⁺/CD44⁺ cells, melanosphere size and the expression of the pluripotency marker Sox2 in sh-AhR cells. Interestingly, Sox2 increased Aldh1a1 expression in sh-AhR but not in sh-AhR + sh-Aldh1a1 cells, suggesting that Aldh1a1 and Sox2 may be co-regulated in melanoma cells. In vivo imaging revealed that mice inoculated with AhR + Aldh1a1 knockdown cells had reduced tumor burden and enhanced survival than those receiving Aldh1a1-expressing sh-AhR cells.

Conclusions

Aldh1a1 overactivation in an AhR-deficient background enhances melanoma progression. Since AhR may antagonize the protumoral effects of Aldh1a1, the AhR^low-Aldh1a1^high phenotype could be indicative of bad outcome in melanoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0419-9) contains supplementary material, which is available to authorized users.