Case records of the Massachusetts General Hospital. Weekly clinicopathological exercises. Case 26-2004. A 56-year-old woman with cough and a lung nodule

Ubiquitin-Conjugating Enzymes in Cancer

The ubiquitin-mediated degradation system is responsible for controlling various tumor-promoting processes, including DNA repair, cell cycle arrest, cell proliferation, apoptosis, angiogenesis, migration and invasion, metastasis, and drug resistance. The conjugation of ubiquitin to a target protein is mediated sequentially by the E1 (activating)‒E2 (conjugating)‒E3 (ligating) enzyme cascade. Thus, E2 enzymes act as the central players in the ubiquitination system, modulating various pathophysiological processes in the tumor microenvironment. In this review, we summarize the types and functions of E2s in various types of cancer and discuss the possibility of E2s as targets of anticancer therapeutic strategies.

USP14 Inhibition Regulates Tumorigenesis by Inducing Autophagy in Lung Cancer In Vitro

The ubiquitin–proteasome system is an essential regulator of several cellular pathways involving oncogenes. Deubiquitination negatively regulates target proteins or substrates linked to both hereditary and sporadic forms of cancer. The deubiquitinating enzyme ubiquitin-specific protease 14 (USP14) is associated with proteasomes where it trims the ubiquitin chain on the substrate. Here, we found that USP14 is highly expressed in patients with lung cancer. We also demonstrated that USP14 inhibitors (IU1-47 and siRNA-USP14) significantly decreased cell proliferation, migration, and invasion in lung cancer. Remarkably, we found that USP14 negatively regulates lung tumorigenesis not only through apoptosis but also through the autophagy pathway. Our findings suggest that USP14 plays a crucial role in lung tumorigenesis and that USP14 inhibitors are potent drugs in lung cancer treatment.

Association of Uba6-Specific-E2 (USE1) With Lung Tumorigenesis

Background

The UBA6-specific E2 conjugating enzyme 1 (USE1) ubiquitin enzyme cascade is a poorly characterized arm of the ubiquitin-proteasome system. We investigated whether the UBA6-USE1 enzyme cascade plays a role in lung cancer tumorigenesis.

Methods

USE1 expression was assessed in tumor-normal paired samples from 106 lung cancer patients by immunoblot. USE1 was stably overexpressed and knocked down in lung cancer cell lines to evaluate cell proliferation, colony formation, and invasion. Xenograft models were used to determine the effects of USE1 on tumor growth (n = 7). Proteomics analysis was used to identify proteins interacting with USE1. The USE1 gene was sequenced in lung cancer patients, and missense mutations of USE1 were generated to evaluate its function. All statistical tests were two-sided.

Results

USE1 proteins were frequently overexpressed in lung cancer patients (92.5%) Stable overexpression of USE1 increased cell proliferation ( P = .002), migration ( P < .001), and invasion ( P < .001), whereas knockdown of USE1 reduced cell proliferation ( P < .001), migration ( P = .003), and invasion in lung cancer cells and xenograft models ( P < .001). USE1 was found to have a conserved D-box domain, and the level of the protein was regulated by the anaphase-promoting complex. Several missense mutations in USE1 identified in patients prolong the stability of the protein.

Conclusions

USE1 proteins are frequently overexpressed in lung cancer, and missense mutations in USE1 prolong the half-life of the protein, promoting tumor formation. Our findings reveal novel roles for USE1 in lung cancer and the possible use of USE1 as a novel biomarker and therapeutic target for lung cancer treatment.

Electroneutral composite polymersomes self-assembled by amphiphilic polyphosphazenes for effective miR-200c in vivo delivery to inhibit drug resistant lung cancer

MiR-200c has been confirmed to display remarkable effects on proliferation inhibition and apoptosis induction of certain cancer cells, but the main challenge for its successful translation into the clinic remains its effective delivery to the action site in vivo. In this study, a novel composite polyphosphazene vesicle system composed of amphiphilic [NP(PEG)0.3(EAB)1.7]n (PEEP) and weakly cationic [NP(PEG)0.5(DPA)1.5]n (PEDP) was prepared via a very simple dialysis method. The loading of miR-200c was accomplished with high efficiency by taking advantage of the combination effect of physical encapsulation and electrostatic interaction between vectors and miR-200c. The resultant miR-200c-loaded PEEP-PEDP polymersome (Nano-ED-200c) displayed suitable particle size, electric neutrality, excellent Ribonuclease stability and hemocompatibility. We also evaluated its subsequent miR-200c function in paclitaxel resistance human lung cancer (A549/T) cells in culture and tumor xenografts in nude mice. The results showed that Nano-ED-200c could achieve a higher miR-200c level and the enhanced antitumor efficacy with 68% tumor inhibition ratio at a very low dose of 1.0 mg/kg than PEEP nanoparticle, PEDP nanoparticle, even than Lipo2000. All these evidences indicated that this miR-200c delivery via polyphosphazene vesicles could act as a potential new therapeutic option for paclitaxel resistant human lung cancer.

Probing homodimer formation of epidermal growth factor receptor by selective crosslinking

Ligand binding promotes conformational rearrangement of the epidermal growth factor receptor (EGFR) leading to receptor autophosphorylation and downstream signaling. However, transient interactions between unstimulated EGFR molecules on the cell surface are not fully understood. In this report, we describe the investigation of homodimer formation of EGFR by means of an SNAP-tag based selective crosslinking approach (S-CROSS). EGFR homodimers were selectively captured in living cells and utilized for analysis of protein receptor interactions on the plasma membrane and ligand-induced activation. We showed that EGFR forms homodimers in unstimulated cells with efficiencies similar to those seen in cells treated with the epidermal growth factor ligand (EGF) supporting the existence of constitutive transient receptor-receptor interactions. EGFR crosslinked homodimers displayed a substantially increase in kinase activation upon ligand stimulation. Interestingly, in unstimulated cells the levels of spontaneous phosphorylation were found to correlate with the yields of the crosslinked homodimers species. In addition, we demonstrated that this crosslinking approach can be applied to interrogate the effect of small molecule inhibitors on receptor dimerization and kinase activity. Our crosslinking assay provides a new tool to dissect ligand-independent dimerization and activation mechanisms of receptor tyrosine kinases, many of which are important anticancer drug targets.