Ubiquitin signaling and the proteasome drive human DNA-protein crosslink repair.

DNA-protein crosslinks (DPCs) are large cytotoxic DNA lesions that form following exposure to chemotherapeutic drugs and environmental chemicals. Nucleotide excision repair (NER) and homologous recombination (HR) promote survival following exposure to DPC-inducing agents. However, it is not known how cells recognize DPC lesions, or what mechanisms selectively target DPC lesions to these respective repair pathways. To address these questions, we examined DPC recognition and repair by transfecting a synthetic DPC lesion comprised of the human oxoguanine glycosylase (OGG1) protein crosslinked to double-stranded M13MP18 into human cells. In wild-type cells, this lesion is efficiently repaired, whereas cells deficient in NER can only repair this lesion if an un-damaged homologous donor is co-transfected. Transfected DPC is subject to rapid K63 polyubiquitination. In NER proficient cells, the DPC is subject to K48 polyubiquitination, and is removed via a proteasome-dependent mechanism. In NER-deficient cells, the DNA-conjugated protein is not subject to K48 polyubiquitination. Instead, the K63 tag remains attached, and is only lost when a homologous donor molecule is present. Taken together, these results support a model in which selective addition of polyubiquitin chains to DNA-crosslinked protein leads to selective recruitment of the proteasome and the cellular NER and recombinational DNA repair machinery.

Tumor models to assess immune response and tumor-microbiome interactions in colorectal cancer.

Despite significant advances over the past 2 decades in preventive screening and therapy aimed at improving patient survival, colorectal cancer (CRC) remains the second most common cause of cancer death in the United States. The average 5-year survival rate of CRC patients with positive regional lymph nodes is only 40%, while less than 5% of patients with distant metastases survive beyond 5 years. There is a critical need to develop novel therapies that can improve overall survival in patients with poor prognoses, particularly since 60% of them are diagnosed at an advanced stage. Pertinently, immune checkpoint blockade therapy has dramatically changed how we treat CRC patients with microsatellite-instable high tumors. Furthermore, accumulating evidence shows that changes in gut microbiota are associated with the regulation of host antitumor immune response and cancer progression. Appropriate animal models are essential to deciphering the complex mechanisms of host antitumor immune response and tumor-gut microbiome metabolic interactions. Here, we discuss various mouse models of colorectal cancer that are developed to address key questions on tumor immune response and tumor-microbiota interactions. These CRC models will also serve as resourceful tools for effective preclinical studies.

Caffeic acid improves locomotor activity and lessens inflammatory burden in a mouse model of rotenone-induced nigral neurodegeneration: Relevance to Parkinson's disease therapy.

BACKGROUND: Caffeic acid phenethyl ester is found in honey bee propolis. It has immunomodulatory, anti-inflammatory and anti-cancer properties. Rotenone is a pesticide commonly used for inducing experimental Parkinson's disease (PD) due to complex I inhibition and microglia activating properties. The current study examined neuroprotective effect of caffeic acid against rotenone-induced neurodegeneration in groups of seven mice. METHODS: Mice received protective doses of caffeic acid (2.5, 5 or 10 mg/kg) daily and nine injections of rotenone (1 mg kg, subcutaneously) - every 48 h. Behavioral evaluation of motor function was done by a battery of tests including open-field test, cylinder test, pole test and rotarod test; all these tests showed motor impairment. RESULTS: Assay of striatal dopamine highlighted a significant decrease and increases in inflammatory markers. In addition, histopathological assessment of substantia nigra neurons demonstrated low immunostaining for tyrosine hydroxylase (TH) in rotenone treated mice. PCR analysis highlighted upregulation for genes encoding CD11b (a microglia surface antigen), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS) and nuclear factor-κB (NFκB). Treatment with caffeic acid (5 or 10 mg/kg) amended most of rotenone-induced motor deficits, lessened microglia expression and inflammatory mediators and improved the nigral TH immunostaining. CONCLUSION: These results confirmed the anti-inflammatory activity of caffeic acid and highlighted its neuroprotective activity against rotenone-induced neurodegeneration in mice.