[Abstract unavailable

The specific 26S proteasome inhibitor bortezomib (BZ) potently induces autophagy, endoplasmic reticulum (ER) stress and apoptosis in multiple myeloma (MM) cell lines (U266, IM-9 and RPMI8226). The macrolide antibiotics including concanamycin A, erythromycin (EM), clarithromycin (CAM) and azithromycin (AZM) all blocked autophagy flux, as assessed by intracellular accumulation of LC3B-II and p62. Combined treatment of BZ and CAM or AZM enhanced cytotoxicity in MM cell lines, although treatment with either CAM or AZM alone exhibited almost no cytotoxicity. This combination also substantially enhanced aggresome formation, intracellular ubiquitinated proteins and induced the proapoptotic transcription factor CHOP (CADD153). Expression levels of the proapoptotic genes transcriptionally regulated by CHOP (BIM, BAX, DR5 and TRB3) were all enhanced by combined treatment with BZ plus CAM, compared with treatment with each reagent alone. Like the MM cell lines, the CHOP+/+ murine embryonic fibroblast (MEF) cell line exhibited enhanced cytotoxicity and upregulation of CHOP and its transcriptional targets with a combination of BZ and one of the macrolides. In contrast, CHOP−/− MEF cells exhibited resistance against BZ and almost completely canceled enhanced cytotoxicity with a combination of BZ and a macrolide. These data suggest that ER stress-mediated CHOP induction is involved in pronounced cytotoxicity. Simultaneously targeting two major intracellular protein degradation systems such as the ubiquitin-proteasome system by BZ and the autophagy-lysosome system by a macrolide antibiotic enhances ER stress-mediated apoptosis in MM cells. This result suggests the therapeutic possibility of using a macrolide antibiotic with a proteasome inhibitor for MM therapy.

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The relation between expression of cell cycle-regulator molecules and apoptosis was examined in surgical specimens and cultured human lung carcinoma cell lines. Cell-cycle regulation, a fundamental mechanism determining cell proliferation, is precisely regulated by the specific interaction of cyclins, cdks and cdk-inhibitors. 1,2 Aberrant expression of cyclins and cdks is involved in oncogenic transformation in cultured cells. 3,4 Successive clinicopathologic analyses of human malignant tumors, including carcinomas of the breast, lung, gastrointestinal tract, ovary and other sites, showed a correlation between overexpression of cell-cycle proteins and worse clinical outcome. [5][6][7][8][9] Indeed, in previous studies of human lung carcinomas and soft tissue sarcomas, we found that the expression and kinase activity of the cyclin A/cdk2 complex were novel predictors of proliferative activity and prognosis. 6,10,11 Thus, studies in both cultured cells and human tumors have consistently suggested that dysregulated expression of cyclin/cdk complexes is crucially involved in neoplastic transformation and the aggressive phenotypes of cancers.However, in the past decade, overexpression or abnormal expression of several positive regulators of the cell cycle has been closely associated with apoptosis. These proteins include c-myc, E2F1 and the HPV oncoproteins. 12-15 Several studies have implicated cell-cycle regulator molecules in apoptosis: e.g., upregulation of cyclin D1, cdk4 and/or cdc2 may be a critical event during apoptosis in neuronal cells. 16 -18 Furthermore, several reports have implicated other cell cycle-regulatory molecules, including cyclin E and cyclin B, as key factors in the apoptosis of cultured cells. 19,20 Although these reports suggested that overexpression of any cyclin or cdk could induce apoptosis, each has been shown to have individual potential functions. Previously, we demonstrated that (i) constitutive overexpression of cdk4 significantly promotes apoptosis in rat pheochromocytoma PC12 cells; 17 (ii) in contrast, constitutive overexpression of cdk2 or cdc2 promotes cell proliferation and abrogates the response to nerve growth factor; 4,21 and (iii) transient overexpression of cdk4 or cyclin D1 induces apoptosis in the presence of trophic support in neuronal, hematopoietic and human cancer cell lines. 22,23 These results overall suggest that cdk4/cyclin D1 kinase plays a specific and crucial role in inducing apoptosis in a wide spectrum of cell types. However, observations of these phenomena have been limited to cultured cells and precise pathobiologic or clinicopathologic analyses on apoptosis in surgical specimens of human tumors have not been documented. Several clinicopathologic analyses of apoptosis have examined its prognostic significance in human cancers but with somewhat mixed results. In lung carcinomas, several groups have reported that enhanced apoptosis is associated with shortened survival, 24,25 yet other studies have found no statistically significant correlation. 26 In cont...

Lung cancer is a leading cause of death worldwide, and the long-term survival rate of lung cancer patients is one of the lowest among cancers.1,2) Two major types of lung cancer have been identified: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). NSCLC, the most prevalent subtype, is relatively resistant to chemotherapy and radiation therapy. On the other hand, SCLC is initially highly sensitive to chemotherapy and radiation therapy, but shows resistance to treatment in the majority of patients.3) The high mortality in NSCLC is due to the difficulty of early diagnosis and its high potential for local invasion and distant metastasis. Although relatively effective chemotherapeutic agents have been developed, lung cancer still has a low cure rate. Furthermore, the adverse effects of chemotherapeutic compounds often hamper the quality of life of lung cancer patients. Therefore, the discovery of effective novel prophylactic, diagnostic, and therapeutic treatments for NSCLC is urgently needed."Apoptosis" has been used as a synonym for programmed cell death (PCD), and is a well-known form of PCD. Since the 1960s, various morphological forms of PCD have been recognized. Clarke classified cell death into 4 types, including type I PCD (apoptosis) and type II PCD (autophagy). 4)Numerous studies have demonstrated that most chemotherapy agents and certain naturally occurring compounds induce cell death by activating the apoptotic pathway. It is thought that apoptosis induction in tumor cells with either drugs or natural products is effective therapy for cancer and immune system diseases. On the other hand, autophagy is one of the major regulatory mechanisms in the degradation of intracellular proteins and organelles. 5,6) During autophagy, the cytosol and whole organelles become encased in double-membrane vacuoles such as autophagosomes, and subsequently fuse with lysosomes.5) Degradation of the sequestered material generates nucleotides, amino acids, and free fatty acids that are recycled for macromolecular synthesis and ATP generation.7) Although originally characterized as a survival response to nutrient deficiency, autophagy is now recognized as frequently induced in response to a variety of stressors to maintain cellular homeostasis. [8][9][10][11][12] In recent years, the importance of autophagy has been emphasized in various biological fields, including cancer. 9,[13][14][15] Furthermore, cancer cells show less autophagy than normal cells. 16,17) These findings indicate that autophagy induction is an attractive modality of anticancer therapy.b-Carboline alkaloids occur in a number of medicinal plants such as Peganum harmala, Passiflora edulis, Passiflora incarnata, and Banisteriopsis caapi.18,19) These plants have been used in traditional medicine to treat asthma, jaundice, lumbago, and other human ailments.19-21) Recently, it has been reported that certain b-carboline alkaloids and their related compounds have cytotoxic effects on cancer cells. [22][23][24] We also reported previously that harm...