In its simplest form, a DNA G-quadruplex is a four-stranded DNA structure that is composed of stacked guanine tetrads. G-quadruplex-forming sequences have been identified in eukaryotic telomeres, as well as in non-telomeric genomic regions, such as gene promoters, recombination sites, and DNA tandem repeats. Of particular interest are the G-quadruplex structures that form in gene promoter regions, which have emerged as potential targets for anticancer drug development. Evidence for the formation of G-quadruplex structures in living cells continues to grow. In this review, we examine recent studies on intramolecular G-quadruplex structures that form in the promoter regions of some human genes in living cells and discuss the biological implications of these structures. The identification of G-quadruplex structures in promoter regions provides us with new insights into the fundamental aspects of G-quadruplex topology and DNA sequence-structure relationships. Progress in G-quadruplex structural studies and the validation of the biological role of these structures in cells will further encourage the development of small molecules that target these structures to specifically modulate gene transcription.

Melanomas of the choroid, ciliary body, and iris of the eye are collectively known as uveal melanomas. These cancers represent 5% of all melanoma diagnoses in the United States, and their age-adjusted risk is 5 per 1 million population. These less frequent melanomas are dissimilar to their more common cutaneous melanoma relative, with differing risk factors, primary treatment, anatomic spread, molecular changes, and responses to systemic therapy. Once uveal melanoma becomes metastatic, therapy options are limited and are often extrapolated from cutaneous melanoma therapies despite the routine exclusion of patients with uveal melanoma from clinical trials. Clinical trials directed at uveal melanoma have been completed or are in progress, and data from these well designed investigations will help guide future directions in this orphan disease. Cancer 2016;122:2299-312. V C 2016 American Cancer Society.KEYWORDS: breast cancer 1-associated protein 1 (BAP1), choroidal melanoma, diagnosis, guanine nucleotide binding protein a11 (GNA11), guanine nucleotide-binding protein Q polypeptide (GNAQ), ocular melanoma, review, science, treatment, uveal melanoma. BACKGROUND AND EPIDEMIOLOGYUveal melanoma is the most common primary intraocular malignancy. The uveal tract is the pigmented layer of the globe encompassing the iris, ciliary body, and choroid (Fig. 1). The terms choroidal melanoma and ocular melanoma are alternative terms for this cancer, because most of the uveal tract is choroidal. However, the term ocular melanoma should be avoided, because it implies the inclusion of conjunctival and adnexal melanomas, which behave and are managed like cutaneous rather than uveal primaries. Approximately 1500 new cases of uveal melanoma are diagnosed in the United States each year, most commonly arising in the choroid followed by the ciliary body. Iris melanomas are the least common location for uveal melanoma (Fig. 2).1 Although the disease has no sex preference, it is more common in middle-aged Caucasians (median age at presentation, 58 years). Risk factors include the presence of a choroidal nevus, which can be observed in 7% to 8% of the Caucasian population. Certain skin conditions, such as dysplastic nevus syndrome and nevus of Ota, are also associated with uveal melanoma.2 It has been theorized by some investigators that exposure to ultraviolet radiation increases the risk of this neoplasia, but this has not been definitively proven. Whereas certain somatic mutations are associated with neoplastic growth and distant metastasis, the malignancy is not inherited in a traditional genetic fashion, although it is believed that individuals who have germline breast cancer 1 (BRCA1)-associated protein 1 (BAP1) mutations are at higher risk for uveal and cutaneous melanoma as well as mesothelioma and renal cancers.

The proximal 5′-flanking region of the human platelet-derived growth factor A (PDGF-A) promoter contains one nuclease hypersensitive element (NHE) that is critical for PDGF-A gene transcription. On the basis of circular dichroism (CD) and electrophoretic mobility shift assay (EMSA), we have shown that the guanine-rich (G-rich) strand of the DNA in this region can form stable intramolecular parallel G-quadruplexes under physiological conditions. A Taq polymerase stop assay has shown that the G-rich strand of the NHE can form two major G-quadruplex structures, which are in dynamic equilibrium and differentially stabilized by three G-quadruplex-interactive drugs. One major parallel G-quadruplex structure of the G-rich strand DNA of NHE was identified by CD and dimethyl sulfate (DMS) footprinting. Surprisingly, CD spectroscopy shows a stable parallel G-quadruplex structure formed within the duplex DNA of the NHE at temperatures up to 100°C. This structure has been characterized by DMS footprinting in the double-stranded DNA of the NHE. In transfection experiments, 10 μM TMPyP4 reduced the activity of the basal promoter of PDGF-A ∼40%, relative to the control. On the basis of these results, we have established that ligand-mediated stabilization of G-quadruplex structures within the PDGF-A NHE can silence PDGF-A expression.

Hypoxia is not only a prominent contributor to the heterogeneity of solid tumors but also a crucial stressor in the microenvironment to drive adaptations for tumors to evade immunosurveillance. Herein, we discuss the potential role of hypoxia within the microenvironment contributing to immune resistance and immune suppression of tumor cells. We outline recent discoveries of hypoxia-driven adaptive mechanisms that diminish immune cell response via skewing the expression of important immune checkpoint molecules (e.g., cluster of differentiation 47, programmed death ligand 1, and human leukocyte antigen G), altered metabolism and metabolites, and pH regulation. Importantly, inhibition of hypoxic stress-relevant pathways can collectively enhance T-cell-mediated tumor cell killing. Furthermore, we discuss how manipulation of hypoxia stress may pose a promising new strategy for a combinational therapeutic intervention to enhance immunotherapy of solid tumors.

Our findings reveal a new regulatory pathway of YY1/HDACs/miR-155/HBP1 in macrophage-derived foam cell formation during early atherogenesis and suggest that miR-155 is a potential therapeutic target for atherosclerosis.