Etoposide induces protein kinase Cdelta- and caspase-3-dependent apoptosis in neuroblastoma cancer cells.

In this report, we reveal that etoposide inhibits the proliferation of SK-N-AS neuroblastoma cancer cells and promotes protein kinase Cdelta (PKCdelta)- and caspase-dependent apoptosis. Etoposide induces the caspase-3-dependent cleavage of PKCdelta to its active p40 fragment, and active PKCdelta triggers the processing of caspase-3 by a positive-feedback mechanism. Treatment of cells with the caspase-3-specific inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone or caspase-3-specific small interacting RNA (siRNA) prevented the etoposide-induced activation of caspase-8 and inhibited apoptosis.

TRAIL recombinant adenovirus triggers robust apoptosis in multidrug-resistant HL-60/Vinc cells preferentially through death receptor DR5.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising cancer therapeutic because of its highly selective apoptosis-inducing action on neoplastic versus normal cells. However, some cancer cells express resistance to recombinant soluble TRAIL. To overcome this problem, we used a TRAIL adenovirus (Ad5/35-TRAIL) to induce apoptosis in a drug-sensitive and multidrug-resistant variant of HL-60 leukemia cells and determined the molecular mechanisms of Ad5/35-TRAIL-induced apoptosis.

Cellular FLICE-like inhibitory protein (C-FLIP): a novel target for cancer therapy.

Cellular FLICE-like inhibitory protein (c-FLIP) has been identified as a protease-dead, procaspase-8-like regulator of death ligand-induced apoptosis, based on observations that c-FLIP impedes tumor necrosis factor-alpha (TNF-alpha), Fas-L, and TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis by binding to FADD and/or caspase-8 or -10 in a ligand-dependent fashion, which in turn prevents death-inducing signaling complex (DISC) formation and subsequent activation of the caspase cascade. c-FLIP is a family of alternatively spliced variants, and primarily exists as long (c-FLIP(L)) and short (c-FLIP(S)) splice variants in human cells. Although c-FLIP has apoptogenic activity in some cell contexts, which is currently attributed to heterodimerization with caspase-8 at the DISC, accumulating evidence indicates an anti-apoptotic role for c-FLIP in various types of human cancers.

P-glycoprotein enhances TRAIL-triggered apoptosis in multidrug resistant cancer cells by interacting with the death receptor DR5.

The death-inducing cytokine TRAIL is a promising agent for anticancer therapy since it preferentially kills cancer versus normal cells; however, some cancer cells are TRAIL-resistant. We initially explored whether overexpression of the MDR1 gene product P-glycoprotein (P-gp), which causes multidrug resistance (MDR) in cancer cells, also contributes to TRAIL-resistance. Surprisingly, our results revealed that P-gp-overexpression enhances TRAIL-induced apoptosis not only in neoplastic cells transfected with the MDR1 gene but also in MDR variants selected with cytotoxic anticancer agents.

Cellular FLICE-like inhibitory protein (c-FLIP): a novel target for Taxol-induced apoptosis.

It is known that by binding to the FAS-associated death domain (FADD) protein and/or caspases-8 and -10 at the level of the death-inducing signaling complex (DISC), cellular FLICE-like inhibitory protein (c-FLIP) can prevent apoptosis triggered by death-inducing ligands. We investigated whether the c-FLIP splice variants, c-FLIP long [c-FLIP(L)] and c-FLIP short [c-FLIP(S)], play a role in Taxol-induced apoptosis. Our results showed that low Taxol concentrations triggered caspase-8- and caspase-10-dependent apoptosis in the CCRF-HSB-2 human lymphoblastic leukemia cell line, and induced the down-regulation of c-FLIP(S) and c-FLIP(L).

Mechanism of beta 2-microglobulin-induced apoptosis in the K562 leukemia cell line, defective in major histocompatibility class 1.

Background: It has been shown that exogenous beta 2-microglobulin (beta 2m) triggers significant apoptosis in several cell lines, but the molecular mechanism of beta 2m-induced apoptosis remains to be found.

Materials And Methods: To understand the mechanism of beta 2m-induced apoptosis, we added purified human beta 2m to cultures of K562 human chronic myelocytic leukemia cells, detected apoptosis by DNA fragmentation and annexin V binding assays, measured mitochondrial membrane potential (delta psi m), and used Z-VAD-fmk, a general inhibitor of caspases, inhibitors of caspases-1 and-3, as well as Western blot analysis to detect activated caspases.

Results: beta 2m-induced apoptosis was associated with decreased delta psi m K562 cells.

Beta2-microglobulin induces caspase-dependent apoptosis in the CCRF-HSB-2 human leukemia cell line independently of the caspase-3, -8 and -9 pathways but through increased reactive oxygen species.

Exogenous beta(2)-microglobulin (beta(2)m) induces significant apoptosis in the CCRF-HSB-2 human lymphoblastic leukemia cell line as detected by DNA fragmentation, DAPI staining and annexin V binding assay. beta(2)m treatment induced the release of cytochrome c and apoptosis-inducing factor (AIF) from the mitochondria, but no change in mitochondrial membrane potential (DeltaPsim) was observed during apoptosis, suggesting that cytochrome c may be released through a mechanism independent of mitochondrial permeability transition (MPT) pore formation. Moreover, the beta(2)m-induced release of cytochrome c and AIF from the mitochondria in CCRF-HSB-2 cells was caspase-independent, since Z-VAD-fmk, a general inhibitor of caspases, did not block the release of these factors.

Proteinase-3, a serine protease which mediates doxorubicin-induced apoptosis in the HL-60 leukemia cell line, is downregulated in its doxorubicin-resistant variant.

We report here that expression of proteinase 3 (PR3), a serine protease, is down-regulated in the HL60/ADR multidrug resistant variant of the human myelogenous leukemia cell line HL-60, and that down-regulation of PR3 is associated with doxorubicin (DOX) resistance in these cells. To determine whether PR3 is involved in DOX-induced apoptosis in HL-60 cells, and whether its loss causes resistance to DOX, we inhibited PR3 expression by an anti-sense PR3 oligodeoxynucleotide and showed that inhibition of PR3 expression results in a significant reduction in DOX-induced DNA fragmentation and increased resistance to DOX-induced apoptosis. Our results revealed that PR3-mediated DOX-induced apoptosis in HL-60 cells is independent of the loss of mitochondrial membrane potential (deltapsi(m)) and activation of the caspase-8 and -9 pathways.