Induction of apoptosis by extracellular ubiquitin in human hematopoietic cells: possible involvement of STAT3 degradation by proteasome pathway in interleukin 6-dependent hematopoietic cells

STAT3 Contributes to Radioresistance in Cancer

Radiotherapy has been used in the clinic for more than one century and it is recognized as one of the main methods in the treatment of malignant tumors. Signal Transducers and Activators of Transcription 3 (STAT3) is reported to be upregulated in many tumor types, and it is believed to be involved in the tumorigenesis, development and malignant behaviors of tumors. Previous studies also found that STAT3 contributes to chemo-resistance of various tumor types. Recently, many studies reported that STAT3 is involved in the response of tumor cells to radiotherapy. But until now, the role of the STAT3 in radioresistance has not been systematically demonstrated. In this study, we will review the radioresistance induced by STAT3 and relative solutions will be discussed.

Fludarabine as an Adjuvant Improves Newcastle Disease Virus-Mediated Antitumor Immunity in Hepatocellular Carcinoma

In addition to direct oncolysis, oncolytic viruses (OVs) also induce antitumor immunity, also called viro-immunotherapy. Limited viral replication and immune-negative feedback are the major hurdles to effective viro-immunotherapy. In this study, we found that use of an adjuvant of fludarabine, a chemotherapeutic drug for chronic myeloid leukemia, increased the replication of Newcastle disease virus (NDV) by targeting signal transducer and activator of transcription 1 (STAT1), which led to enhanced oncolysis of hepatocellular carcinoma (HCC) cells. Moreover, fludarabine accelerated ubiquitin-proteasomal degradation by enhancing ubiquitylation rather than proteasomal activity. This resulted in accelerated degradation of phosphorylated STAT3 and indoleamine 2, 3-dioxygenase 1 (IDO1), whose expression was induced by NDV infection. In addition, fludarabine significantly increased the NDV-induced infiltration of NK cells and decreased the number of NDV-induced myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment. The aforementioned effects of fludarabine significantly improved NDV-mediated antitumor immunity and prolonged survival in mouse model of HCC. Our findings indicate the utility of fludarabine as an adjuvant for oncolytic anticancer viro-immunotherapy.

Serum ubiquitin via CXC chemokine receptor 4 triggered cyclooxygenase-1 ubiquitination possibly involved in the pathogenesis of aspirin resistance

Extracellular ubiquitin (Ub) with platelet aggregation property was found higher in acute myocardial infarction (AMI) patients. Here we detected the platelet functions and serum Ub levels in 250 AMI patients and 50 healthy volunteers before and after aspirin treatment. The influence of serum Ub on platelet functions was determined in vitro. We found that 47 out of 250 AMI patients showed aspirin resistance (AR) and 203 showed aspirin sensitivity (AS). During hospitalization, AR group had higher serum Ub levels than the AS group or the healthy group, and the serum Ub levels was related to the rates of thrombosis events. The patients with higher serum Ub levels showed that the platelets had more ubiquitinated platelets, higher contents of ubiquitinated proteins and ubiquitinated cyclooxygenase-1 (COX-1). The levels of ubiquitinated COX-1 in the platelets was inversely correlated with acetylated COX-1, the separated ubiquitinated COX-1 activity was approximately twofold or fourfold higher than the total COX-1(ubiquitinated COX-1 and COX-1) or COX-1. In vitro, we found that extracellular Ub, via the CXC chemokine receptor 4 (CXCR4) pathway, facilitated COX-1 to be ubiquitined and prevented aspirin to acetylate its target. Platelets had higher levels of ubiquitinated COX-1 showing poor response to aspirin. Such results were not detected in Ub-free serum or ovalbumin incubated platelets. Serum Ub, via the CXCR4 pathway, facilitated COX-1 to be ubiquitined and activated the platelets possibly involved in the pathogenesis of AR.

Luteolin promotes degradation in signal transducer and activator of transcription 3 in human hepatoma cells: an implication for the antitumor potential of flavonoids

In this study, we have investigated the underlying molecular mechanism for the potent proapoptotic effect of luteolin on human hepatoma cells both in vitro and in vivo, focusing on the signal transducer and activator of transcription 3 (STAT3)/Fas signaling. A clear apoptosis was found in the luteolin-treated HLF hepatoma cells in a time- and dosage-dependent manner. In concert with the caspase-8 activation by luteolin, an enhanced expression in functional Fas/CD95 was identified. Consistent with the increased Fas/CD95 expression, a drastic decrease in the Tyr(705) phosphorylation of STAT3, a known negative regulator of Fas/CD95 transcription, was found within 20 minutes in the luteolin-treated cells, leading to down-regulation in the target gene products of STAT3, such as cyclin D1, survivin, Bcl-xL, and vascular endothelial growth factor. Of interest, the rapid down-regulation in STAT3 was consistent with an accelerated ubiquitin-dependent degradation in the Tyr(705)-phosphorylated STAT3, but not the Ser(727)-phosphorylated one, another regulator of STAT3 activity. The expression level of Ser(727)-phosphorylated STAT3 was gradually decreased by the luteolin treatment, followed by a fast and clear down-regulation in the active forms of CDK5, which can phosphorylate STAT3 at Ser(727). An overexpression in STAT3 led to resistance to luteolin, suggesting that STAT3 was a critical target of luteolin. In nude mice with xenografted tumors using HAK-1B hepatoma cells, luteolin significantly inhibited the growth of the tumors in a dosage-dependent manner. These data suggested that luteolin targeted STAT3 through dual pathways-the ubiquitin-dependent degradation in Tyr(705)-phosphorylated STAT3 and the gradual down-regulation in Ser(727)-phosphorylated STAT3 through inactivation of CDK5, thereby triggering apoptosis via up-regulation in Fas/CD95.

TMF/ARA160 is a BC-box-containing protein that mediates the degradation of Stat3

TMF/ARA160 is a Golgi resident protein whose cellular functions have not been conclusively revealed. Herein we show that TMF/ARA160 can direct the proteasomal degradation of the key cell growth regulator - Stat3. TMF/ARA160 was dispersed in the cytoplasm of myogenic C2C12 cells that were grown under low-serum conditions. The cytoplasmic distribution of TMF/ARA160 was accompanied by its transient association with the tyrosine kinase Fer and with Stat3, which underwent proteasomal degradation under those conditions. Moreover, serum deprivation induced the association of ubiquitinated proteins, with the TMF/ARA160 complex. However, TMF/ARA160 did not bind Stat1, whose cellular levels were increased in serum-starved C2C12 cells. Amino-acid sequence analysis identified a BC-box element in TMF/ARA160 that mediated the binding of this protein to elongin C. Ectopic expression of TMF/ARA160 in serum-starved C2C12 cells drove the ubiquitination and proteasomal degradation of Stat3, an effect that was not caused by TMF/ARA160 devoid of the BC-box motif. Thus, the Golgi apparatus harbors a novel BC-box-containing protein that can direct Stat3 to proteasomal degradation. Interestingly, the level of TMF/ARA160 was significantly decreased in malignant brain tumors, implying a suppressive role of that protein in tumor progression.

Plasma proteasome level is a potential marker in patients with solid tumors and hemopoietic malignancies

BACKGROUND

Proteasomes are nonlysosomal proteolytic structures that have been implicated in cell growth and differentiation. Abnormal expression levels of proteasomes have been described in tumor cells, and proteasomes can be detected and measured in plasma. The objective of this study was to characterize differences in proteasome levels between normal, healthy donors and patients with neoplastic disease and to correlate the findings with clinical status and other biologic markers of disease spread.

METHODS

Plasma proteasome levels were measured using a sandwich enzyme-linked immunosorbent assay in normal donors (n = 73 donors) and in patients with solid tumors (n = 20 patients), acute leukemia (n = 35 patients), myeloproliferative (n = 37 patients) and myelodysplastic (n = 19 patients) syndromes, chronic lymphocytic leukemia (n = 44 patients), non-Hodgkin lymphoma (n =104 patients), Hodgkin disease (n = 14 patients), other lymphoid disorders (n = 17 patients), and multiple myeloma (n = 27 patients).

RESULTS

In the normal donors, the plasma proteasome concentration was 2356 ng/mL +/- 127 ng/mL. Patients with solid tumors exhibited a significantly higher value (7589 ng/mL +/- 2124 ng/mL), similar to the patients with myeloproliferative (4099 ng/mL +/- 498 ng/mL) and myelodysplastic (2922 ng/mL +/- 322 ng/mL) syndromes. Patients with lymphoproliferative disorders, in contrast, had significantly lower values than normal donors (1751 ng/mL +/- 107 ng/mL), except those in aggressive phase of the disease. This low level persisted in patients who were in complete remission. Proteasome levels decreased during the initial phase of treatment. Although there was a significant correlation with serum lactic dehydrogenase levels, frequent discrepancies were noted. There was no correlation with C-reactive protein or beta2-microglobulin levels, even in the group of patients with multiple myeloma.

CONCLUSIONS

The plasma proteasome level is a potential new tool for the monitoring of patients with neoplastic disease. It is not correlated solely with cell lysis and may be involved in the pathophysiology of disease progression.