NSD3 in Cancer: Unraveling Methyltransferase-Dependent and Isoform-Specific Functions.

NSD3 (nuclear receptor-binding SET domain protein 3) is a member of the NSD histone methyltransferase family of proteins. In recent years, it has been identified as a potential oncogene in certain types of cancer. The NSD3 gene encodes three isoforms, the long version (NSD3L), a short version (NSD3S) and the WHISTLE isoforms. Importantly, the NSD3S isoform corresponds to the N-terminal region of the full-length protein, lacking the methyltransferase domain. The chromosomal location of NSD3 is frequently amplified across cancer types, such as breast, lung, and colon, among others. Recently, this amplification has been correlated to a chromothripsis event, that could explain the different NSD3 alterations found in cancer. The fusion proteins containing NSD3 have also been reported in leukemia (NSD3-NUP98), and in NUT (nuclear protein of the testis) midline carcinoma (NSD3-NUT). Its role as an oncogene has been described by modulating different cancer pathways through its methyltransferase activity, or the short isoform of the protein, through protein interactions. Specifically, in this review we will focus on the functions that have been characterized as methyltransferase dependent, and those that have been correlated with the expression of the NSD3S isoform. There is evidence that both the NSD3L and NSD3S isoforms are relevant for cancer progression, establishing NSD3 as a therapeutic target. However, further functional studies are needed to differentiate NSD3 oncogenic activity as dependent or independent of the catalytic domain of the protein, as well as the contribution of each isoform and its clinical significance in cancer progression.

NSD3S stabilizes MYC through hindering its interaction with FBXW7.

The MYC transcription factor plays a key role in cell growth control. Enhanced MYC protein stability has been found to promote tumorigenesis. Thus, understanding how MYC stability is controlled may have significant implications for revealing MYC-driven growth regulatory mechanisms in physiological and pathological processes. Our previous work identified the histone lysine methyltransferase nuclear receptor binding SET domain protein 3 (NSD3) as a MYC modulator. NSD3S, a noncatalytic isoform of NSD3 with oncogenic activity, appears to bind, stabilize, and activate the transcriptional activity of MYC. However, the mechanism by which NSD3S stabilizes MYC remains to be elucidated. To uncover the nature of the interaction and the underlying mechanism of MYC regulation by NSD3S, we characterized the binding interface between both proteins by narrowing the interface to a 15-amino acid region in NSD3S that is partially required for MYC regulation. Mechanistically, NSD3S binds to MYC and reduces the association of F-box and WD repeat domain containing 7 (FBXW7) with MYC, which results in suppression of FBXW7-mediated proteasomal degradation of MYC and an increase in MYC protein half-life. These results support a critical role for NSD3S in the regulation of MYC function and provide a novel mechanism for NSD3S oncogenic function through inhibition of FBXW7-mediated degradation of MYC.

The OncoPPi Portal: an integrative resource to explore and prioritize protein-protein interactions for cancer target discovery.

Motivation: As cancer genomics initiatives move toward comprehensive identification of genetic alterations in cancer, attention is now turning to understanding how interactions among these genes lead to the acquisition of tumor hallmarks. Emerging pharmacological and clinical data suggest a highly promising role of cancer-specific protein-protein interactions (PPIs) as druggable cancer targets. However, large-scale experimental identification of cancer-related PPIs remains challenging, and currently available resources to explore oncogenic PPI networks are limited. Results: Recently, we have developed a PPI high-throughput screening platform to detect PPIs between cancer-associated proteins in the context of cancer cells. Here, we present the OncoPPi Portal, an interactive web resource that allows investigators to access, manipulate and interpret a high-quality cancer-focused network of PPIs experimentally detected in cancer cell lines. To facilitate prioritization of PPIs for further biological studies, this resource combines network connectivity analysis, mutual exclusivity analysis of genomic alterations, cellular co-localization of interacting proteins and domain-domain interactions. Estimates of PPI essentiality allow users to evaluate the functional impact of PPI disruption on cancer cell proliferation. Furthermore, connecting the OncoPPi network with the approved drugs and compounds in clinical trials enables discovery of new tumor dependencies to inform strategies to interrogate undruggable targets like tumor suppressors. The OncoPPi Portal serves as a resource for the cancer research community to facilitate discovery of cancer targets and therapeutic development. Availability and implementation: The OncoPPi Portal is available at http://oncoppi.emory.edu. Contact: andrey.ivanov@emory.edu or hfu@emory.edu.

The OncoPPi network of cancer-focused protein-protein interactions to inform biological insights and therapeutic strategies.

As genomics advances reveal the cancer gene landscape, a daunting task is to understand how these genes contribute to dysregulated oncogenic pathways. Integration of cancer genes into networks offers opportunities to reveal protein-protein interactions (PPIs) with functional and therapeutic significance. Here, we report the generation of a cancer-focused PPI network, termed OncoPPi, and identification of >260 cancer-associated PPIs not in other large-scale interactomes. PPI hubs reveal new regulatory mechanisms for cancer genes like MYC, STK11, RASSF1 and CDK4. As example, the NSD3 (WHSC1L1)-MYC interaction suggests a new mechanism for NSD3/BRD4 chromatin complex regulation of MYC-driven tumours. Association of undruggable tumour suppressors with drug targets informs therapeutic options. Based on OncoPPi-derived STK11-CDK4 connectivity, we observe enhanced sensitivity of STK11-silenced lung cancer cells to the FDA-approved CDK4 inhibitor palbociclib. OncoPPi is a focused PPI resource that links cancer genes into a signalling network for discovery of PPI targets and network-implicated tumour vulnerabilities for therapeutic interrogation.

Apolipoprotein A-I enhances proliferation of human endothelial progenitor cells and promotes angiogenesis through the cell surface ATP synthase.

BACKGROUND: Human endothelial progenitor cells (hEPC) correspond to a subtype of stem cells which, in the presence of angiogenic stimuli, can be mobilized from bone marrow to circulation and then recruited to the damaged endothelium, where they differentiate into mature endothelial cells. High-density lipoproteins (HDL) increase the level and functionality (proliferation, migration, differentiation, angiogenesis capacity) of circulating hEPC; however, the contribution of receptors for HDL and/or apolipoprotein A-I (apoA-I), the main HDL apolipoprotein, in these effects is still unclear. On mature endothelial cells, the cell surface F1-ATP synthase has been previously characterized as a high affinity receptor of apoA-I, whereas the scavenger receptor SR-BI mainly binds with fully lipidated HDL and displays a poor affinity for lipid-free apoA-I. Furthermore, it was shown that apoA-I binding to surface ATP synthase on mature endothelial cells promotes cell proliferation, whereas inhibits apoptosis. In this work, we aimed to determine the effect of apoA-I in the proliferation and the angiogenic capacity of early hEPC, and the contribution of the cell surface ATP synthase in these events. RESULTS: We first evidenced that early hEPC express the ATP synthase at the surface of nonpermeabilized cells, where it is not colocalized with MitoTracker, a mitochondria marker. ApoA-I (50 µg/mL) increases hEPC proliferation (+14.5%, p<0.001) and potentiates the effect of hEPC on a cellular model of angiogenesis, with an increase of +31% (p<0.01) in branch point counting and in tubule length. These effects of apoA-I were totally reversed in the presence of ATP synthase inhibitors, such as IF1 or oligomycin, whereas the inhibition of the HDL receptor, SR-BI, partially inhibits these events. CONCLUSIONS: These results provide the first evidence that surface ATP synthase is expressed on early hEPC, where it mediates apoA-I effects in hEPC proliferation and in angiogenesis. This knowledge could be helpful for future investigations focused on the regulation of the number and functionality of these cells and in the development of new therapies for the treatment of diseases, such as cardiovascular disease.