Targeting Pan-ETS Factors Inhibits Melanoma Progression.

The failure of once promising target-specific therapeutic strategies often arises from redundancies in gene expression pathways. Even with new melanoma treatments, many patients are not responsive or develop resistance, leading to disease progression in terms of growth and metastasis. We previously discovered that the transcription factors ETS1 and PAX3 drive melanoma growth and metastasis by promoting the expression of the MET receptor. Here, we find that there are multiple ETS family members expressed in melanoma and that these factors have redundant functions. The small molecule YK-4-279, initially developed to target the ETS gene-containing translocation product EWS-FLI1, significantly inhibited cellular growth, invasion, and ETS factor function in melanoma cell lines and a clinically relevant transgenic mouse model, BrafCA;Tyr-CreERT2;Ptenf/f. One of the antitumor effects of YK-4-279 in melanoma is achieved via interference of multiple ETS family members with PAX3 and the expression of the PAX3-ETS downstream gene MET. Expression of exogenous MET provided partial rescue of the effects of YK-4-279, further supporting that MET loss is a significant contributor to the antitumor effects of the drug. This is the first study identifying multiple overlapping functions of the ETS family promoting melanoma. In addition, targeting all factors, rather than individual members, demonstrated impactful deleterious consequences in melanoma progression. Given that multiple ETS factors are known to have oncogenic functions in other malignancies, these findings have a high therapeutic impact. SIGNIFICANCE: These findings identify YK-4-279 as a promising therapeutic agent against melanoma by targeting multiple ETS family members and blocking their ability to act as transcription factors.

Suppression of Pax3-MITF-M Axis Protects from UVB-Induced Skin Pigmentation by Tetrahydroquinoline Carboxamide.

Paired box gene 3 (Pax3) and cAMP responsive element-binding protein (CREB) directly interact with the cis-acting elements on the promoter of microphthalmia-associated transcription factor isoform M (MITF-M) for transcriptional activation in the melanogenic process. Tyrosinase (Tyro) is a target gene of MITF-M, and functions as a key enzyme in melanin biosynthesis. Tetrahydroquinoline carboxamide (THQC) was previously screened as an antimelanogenic candidate. In the current study, we evaluated the antimelanogenic activity of THQC in vivo and elucidated a possible mechanism. Topical treatment with THQC mitigated ultraviolet B (UVB)-induced skin pigmentation in guinea pig with decreased messenger RNA (mRNA) and protein levels of melanogenic genes such as MITF-M and Tyro. Moreover, THQC inhibited cAMP-induced melanin production in α-melanocyte-stimulating hormone (α-MSH)- or histamine-activated B16-F0 cells, in which it suppressed the expression of the MITF-M gene at the promoter level. As a mechanism, THQC normalized the protein levels of Pax3, a transcriptional activator of the MITF-M gene, in UVB-exposed and pigmented skin, as well as in α-MSH-activated B16-F0 culture. However, THQC did not affect UVB- or α-MSH-induced phosphorylation (activation) of CREB. The results suggest that suppression of the Pax3-MITF-M axis might be a potential strategy in the treatment of skin pigmentary disorders that are at high risk under UVB radiation.

The regulation of survival and differentiation of neural stem cells by miR-124 via modulating PAX3.

MicroRNAs (miRNAs) have crucial functions in the regulation of proliferation and differentiation of neural stem cells (NSCs). MiR-124 has been reported to be implicated in neurogenesis. However, the precise function and mechanism of miR-124 still need further verification. In this study, we identified paired box 3 (PAX3) as a potential target of miR-124 using bioinformatics approaches. Next, we found PAX3 had reversed expression pattern with miR-124 as well as TUBB3 and GFAP. Dual-luciferase assay showed that miR-124 could bind to the 3'-UTR of PAX3 mRNA and restrain its expression. It was demonstrated that overexpression and knocking down of miR-124 in NSCs could promote the survival and suppress the apoptosis of NSCs. Meanwhile, miR-124 enhanced the expression of TUBB3 and GFAP via impairing PAX3 expression. Mechanistic study revealed that augmented Akt-GSK3ß signaling pathway was the driving-force for the regulatory functions of miR-124 in NSCs. In summary, this study for the first time uncovered that miR-124 could suppress PAX3 expression, which in turn regulated the differentiation of NSCs.