Natural Killer Cells in the Malignant Niche of Multiple Myeloma

Natural killer (NK) cells represent a subset of CD3- CD7+ CD56+/dim lymphocytes with cytotoxic and suppressor activity against virus-infected cells and cancer cells. The overall potential of NK cells has brought them to the spotlight of targeted immunotherapy in solid and hematological malignancies, including multiple myeloma (MM). Nonetheless, NK cells are subjected to a variety of cancer defense mechanisms, leading to impaired maturation, chemotaxis, target recognition, and killing. This review aims to summarize the available and most current knowledge about cancer-related impairment of NK cell function occurring in MM.

Restoring p53 Function in Head and Neck Squamous Cell Carcinoma to Improve Treatments

TP53 mutation is one of the most frequent genetic alterations in head and neck squamous cell carcinoma (HNSCC) and results in an accumulation of p53 protein in tumor cells. This makes p53 an attractive target to improve HNSCC therapy by restoring the tumor suppressor activity of this protein. Therapeutic strategies targeting p53 in HNSCC can be divided into three categories related to three subtypes encompassing WT p53, mutated p53 and HPV-positive HNSCC. First, compounds targeting degradation or direct inhibition of WT p53, such as PM2, RITA, nutlin-3 and CH1iB, achieve p53 reactivation by affecting p53 inhibitors such as MDM2 and MDMX/4 or by preventing the breakdown of p53 by inhibiting the proteasomal complex. Second, compounds that directly affect mutated p53 by binding it and restoring the WT conformation and transcriptional activity (PRIMA-1, APR-246, COTI-2, CP-31398). Third, treatments that specifically affect HPV+ cancer cells by targeting the viral enzymes E6/E7 which are responsible for the breakdown of p53 such as Ad-E6/E7-As and bortezomib. In this review, we describe and discuss p53 regulation and its targeting in combination with existing therapies for HNSCC through a new classification of such cancers based on p53 mutation status and HPV infection.

Wnt Inhibitory Factor 1 Binds to and Inhibits the Activity of Sonic Hedgehog

The hedgehog (Hh) and Wnt pathways, crucial for the embryonic development and stem cell proliferation of Metazoa, have long been known to have similarities that argue for their common evolutionary origin. A surprising additional similarity of the two pathways came with the discovery that WIF1 proteins are involved in the regulation of both the Wnt and Hh pathways. Originally, WIF1 (Wnt Inhibitory Factor 1) was identified as a Wnt antagonist of vertebrates, but subsequent studies have shown that in Drosophila, the WIF1 ortholog serves primarily to control the distribution of Hh. In the present, work we have characterized the interaction of the human WIF1 protein with human sonic hedgehog (Shh) using Surface Plasmon Resonance spectroscopy and reporter assays monitoring the signaling activity of human Shh. Our studies have shown that human WIF1 protein binds human Shh with high affinity and inhibits its signaling activity efficiently. Our observation that the human WIF1 protein is a potent antagonist of human Shh suggests that the known tumor suppressor activity of WIF1 may not be ascribed only to its role as a Wnt inhibitor.

Polycomb Group Ring Finger Protein 6 suppresses Myc-induced lymphomagenesis

Max is an obligate dimerization partner for the Myc transcription factors and for several repressors, such as Mnt, Mxd1-4 and Mga, collectively thought to antagonize Myc function in transcription and oncogenesis. Mga, in particular, is part of the variant Polycomb group repressive complex PRC1.6. Here, we show that ablation of the distinct PRC1.6 subunit Pcgf6 – but not Mga – accelerates Myc-induced lymphomagenesis in Eµ-myc transgenic mice. Unexpectedly, however, Pcgf6 loss shows no significant impact on transcriptional profiles, in neither pre-tumoral B-cells, nor lymphomas. Altogether, these data unravel an unforeseen, Mga- and PRC1.6-independent tumor suppressor activity of Pcgf6.

Inhibition of cytoplasmic EZH2 induces antitumor activity through stabilization of the DLC1 tumor suppressor protein

AbstractmRNA expression of the DLC1 tumor suppressor gene is downregulated in many lung cancers and their derived cell lines, with DLC1 protein levels being low or absent. Although the role of increased EZH2 methyltransferase in cancer is usually attributed to its histone methylation, we unexpectedly observed that post-translational destabilization of DLC1 protein is common and attributable to its methylation by cytoplasmic EZH2, leading to CUL-4A ubiquitin-dependent proteasomal degradation of DLC1. Furthermore, siRNA knockdown of KRAS in several lines increases DLC1 protein, associated with a drastic reduction in cytoplasmic EZH2. Pharmacologic inhibition of EZH2, CUL-4A, or the proteasome can increase the steady-state level of DLC1 protein, whose tumor suppressor activity is further increased by AKT and/or SRC kinase inhibitors, which reverse the direct phosphorylation of DLC1 by these kinases. These rational drug combinations induce potent tumor growth inhibition, with markers of apoptosis and senescence, that is highly dependent on DLC1 protein.

TNFR2 Antagonist and Agonist: A Potential Therapeutics in Cancer Immunotherapy

Tumor necrosis factor receptor 2 or TNFR2 is considered as an appealing target protein due its limited frequency to Tregs which are highly immunosuppressive and its presence on human malignancies. Numerous studies have revealed that TNFR2 is primarily found on MDSCs (myeloid derived suppressor cells) and CD+Foxp3+ regulatory T cell (Tregs). It has a great importance in the proliferation and functional activity of Tregs and MDSCs. To treat malignancies and diseases like autoimmune disorder, the suppressor activity of TNFR2 must be eliminated by downregulation or upregulation. Therefore, at the molecular level, advances in comprehension of TNFR2's complex structure and its binding to TNF have opened the door to structure-guided drug development. Two key obstacles of cancer treatment are the dearth of Treg-specific inhibitors and the lack of widely applicable ways to directly target tumors via frequently expressed surface oncogenes. Many researchers have discovered potential antagonist and agonist of TNFR2 which were successful in the inhibition of Tregs proliferation, reduction of soluble TNFR2 secretion from normal cells and in the expansion of T effector cells. The representation of the data in the following review article elucidates the clinically administrated TNFR2 antagonist and agonist in the treatment of cancers.

Chromosome 1q amplification perturbs a ceRNA network to promote melanoma metastasis

Deregulated gene expression through epigenetic, transcriptional, and copy number alterations is a major driver of melanoma progression and metastasis. In addition to serving as blueprints for translation, some mRNAs post-transcriptionally regulate gene expression by competitively sequestering miRNAs they share with other targets. Here we report that such mRNAs, termed competitive endogenous RNAs (ceRNAs), contribute to melanoma progression and metastasis. ceRNA predictions identified multiple candidate genes on chromosome 1q, which is recurrently amplified in melanoma. Genetic studies reveal that three of these mRNAs, CEP170, NUCKS1, and ZC3H11A, promote melanoma migration, invasion, and metastasis in a protein coding-independent and miRNA binding site-dependent manner. Interestingly, CEP170, NUCKS1, and ZC3H11A cooperate to elicit oncogenic effects by collectively impairing the tumor suppressor activity of 8 miRNAs on several pro-metastatic target genes. Finally, this complex chromosome 1q ceRNA network is evident in other cancer types, suggesting ceRNA network deregulation is a common driver of cancer progression.

Merlin Tumor Suppressor Function is Regulated by PIP2-Mediated Dimerization

Neurofibromatosis Type 2 is an inherited disease characterized by Schwann cell tumors of cranial and peripheral nerves. The NF2 gene encodes Merlin, which contains an N-terminal FERM domain, a central alpha-helical region and a C-terminal domain that binds to the FERM domain. Changes in the intermolecular FERM-CTD interaction allow Merlin to transition between an open, FERM accessible conformation and a closed, FERM-inaccessible conformation, modulating Merlin activity. These conformational transitions are regulated by both phosphorylation and phosphoinositide binding. Merlin has been shown to dimerize but the role of dimerization in Merlin function is unclear. We used a nanobody based binding assay and found that Merlin dimerizes via a FERM-FERM interaction in a parallel orientation that requires an uncovered N-terminus and the first 18 amino acids of the FERM domain. Patient derived and structural mutants show that dimerization controls interactions with specific binding partners, including HIPPO pathway components, and correlates with tumor suppressor activity. Dimerization requires an open conformation, is inhibited by phosphorylation at serine 518 and is enhanced by PIP2 binding. The discovery that active, open conformation Merlin is a dimer represents a new paradigm for Merlin function with implications for the development of therapies designed to compensate for Merlin loss.