CHOP

Abstract: Endoplasmic reticulum (ER) is the site of synthesis and folding of secretory proteins. Perturbations of ER homeostasis affect protein folding and cause ER stress. ER can sense the stress and respond to it through translational attenuation, upregulation of the genes for ER chaperones and related proteins, and degradation of unfolded proteins by a quality-control system. However, when the ER function is severely impaired, the organelle elicits apoptotic signals. ER stress has been implicated in a variety of common diseases such as diabetes, ischemia and neurodegenerative disorders. One of the components of the ER stress-mediated apoptosis pathway is C/EBP homologous protein (CHOP), also known as growth arrest- and DNA damage-inducible gene 153 (GADD153). Here, we summarize the current understanding of the roles of CHOP/GADD153 in ER stress-mediated apoptosis and in diseases including diabetes, brain ischemia and neurodegenerative disease.

Abstract: Background CHOP is a first-generation, combination-chemotherapy regimen consisting of cyclophosphamide, doxorubicin, vincristine, and prednisone that has cured approximately 30 percent of patients with advanced stages of intermediate-grade or high-grade non-Hodgkin's lymphoma in national cooperative-group trials. However, studies at single institutions have suggested that 55 to 65 percent of such patients might be cured by third-generation regimens such as ones consisting of low-dose methotrexate with leucovorin rescue, bleomycin, doxorubicin, cyclophosphamide, vincristine, and dexamethasone (m-BACOD); prednisone, doxorubicin, cyclophosphamide, and etoposide, followed by cytarabine, bleomycin, vincristine, and methotrexate with leucovorin rescue (ProMACE-CytaBOM); and methotrexate with leucovorin rescue, doxorubicin, cyclophosphamide, vincristine, prednisone, and bleomycin (MACOP-B). Methods To make a valid comparison of these regimens, the Southwest Oncology Group and the Eastern Cooperative Oncology Gro...

Abstract: Summary Background The role of rituximab in combination with diff erent CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone)-like chemotherapy regimens in young patients with good-prognosis diff use large-B-cell lymphoma remains to be defi ned. We aimed to compare CHOP-like chemotherapy and rituximab with CHOP-like chemotherapy alone in these patients. Methods 824 patients who were from 18 countries; aged 18–60 years; and who had no risk factors or one risk factor according to age-adjusted International Prognostic Index (IPI), stage II–IV disease, or stage I disease with bulk were enrolled. These patients were randomly assigned to six cycles of CHOP-like chemotherapy and rituximab (n=413) or to six cycles of CHOP-like chemotherapy alone (n=411). Bulky and extranodal sites received additional radiotherapy. The primary endpoint was event-free survival; secondary endpoints were response, progression under therapy, progression-free survival, overall survival, and frequency of toxic eff ects. Analyses were done by intention to treat and per protocol. This trial is registered at http://www.clinicaltrials.gov, NCT 00064116. Findings After a median follow-up of 34 months (range 0·03–61), patients assigned chemotherapy and rituximab had increased 3-year event-free survival compared with those assigned chemotherapy alone (79% [95% CI 75–83] vs 59% [54–64]; diff erence between groups 20% [13–27], log-rank p<0·0001), and had increased 3-year overall survival (93% [90–95] vs 84% [80–88]; diff erence between groups 9% [3–13], log-rank p=0·0001). Event-free survival was aff ected by treatment group, presence of bulky disease, and age-adjusted IPI: after chemotherapy and rituximab, a favourable subgroup (ie, IPI=0, no bulk) could be defi ned from a less-favourable subgroup (ie, IPI=1 or bulk, or both). Groups did not diff er in the frequency of adverse events.

Abstract: Unfolded and malfolded client proteins impose a stress on the endoplasmic reticulum (ER), which contributes to cell death in pathophysiological conditions. The transcription factor C/EBP homologous protein (CHOP) is activated by ER stress, and CHOP deletion protects against its lethal consequences. We find that CHOP directly activates GADD34, which promotes ER client protein biosynthesis by dephosphorylating phospho-Ser 51 of the alpha-subunit of translation initiation factor 2 (eIF2alpha) in stressed cells. Thus, impaired GADD34 expression reduces client protein load and ER stress in CHOP(-/-) cells exposed to perturbations that impair ER function. CHOP(-/-) and GADD34 mutant cells accumulate less high molecular weight protein complexes in their stressed ER than wild-type cells. Furthermore, mice lacking GADD34-directed eIF2alpha dephosphorylation, like CHOP(-/-) mice, are resistant to renal toxicity of the ER stress-inducing drug tunicamycin. CHOP also activates ERO1alpha, which encodes an ER oxidase. Consequently, the ER of stressed CHOP(-/-) cells is relatively hypo-oxidizing. Pharmacological and genetic manipulations that promote a hypo-oxidizing ER reduce abnormal high molecular weight protein complexes in the stressed ER and protect from the lethal consequences of ER stress. CHOP deletion thus protects cells from ER stress by decreasing ER client protein load and changing redox conditions within the organelle.