Inhibition of novel protein kinase Cɛ augments TRAIL-induced cell death in A549 lung cancer cells

Abstract

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has great potential for cancer treatment since it provokes cell death in most tumor cells while leaving most normal cells unscathed. Some cancers, however, show resistance to TRAIL, indicating that TRAIL alone may be insufficient for cancer therapy. Here we studied whether the apoptotic susceptibility of A549 non-small cell lung cancer cells could be modulated by inhibiting protein kinase C (PKC). We show that an inhibitor with preference for novel PKC isozymes, NPC 15437, significantly augmented TRAIL sensitivity of A549 cells, as judged by assessing cell death and mitochondrial membrane potential. Likewise, NPC 15437 also significantly potentiated the responsiveness of DAOY medulloblastoma cells to TRAIL. In contrast, an inhibitor with preference for conventional PKC isozymes, Gö6976, did not augment TRAIL sensitivity of A549 cells. To further specify the PKC isozyme responsible for TRAIL sensitization, we used a peptide inhibitor with selectivity for the novel PKC isozyme epsilon, myr-PKC-epsilon V1-2. The inhibition of PKC-epsilon resulted in a significant amplification of the cytotoxic activity of TRAIL in A549 cells. Altogether, our study provides evidence for a considerable role of PKC-epsilon in the apoptotic responsiveness of A549 lung cancer cells, and possibly other malignancies, to TRAIL.

Protein Kinase C (PKC) Isozymes and Cancer

“…The antiapoptotic functions of PKC in lung cancer cells involve the inhibition of TRAILinduced cell death [301] and mitochondrial caspase signaling [302], as well as the upregulation of antiapoptotic proteins (e.g., XIAP or Bcl-XL) through S6K2, but not S6K1 signaling [303].…”

Perspectives of Protein Kinase C (PKC) Inhibitors as Anti-Cancer Agents

“…Although PKC-has been shown to be involved also in commitment of hematopoietic progenitors along the megakaryocytic lineage [26,27], its major role in protecting normal haematopoietic cells from deprivation of serum and/or growth factors was independently confirmed by our group in a factor-dependent hematopoietic cell line [28] and, more recently, by a different group of investigators on primary hematopoietic cells [29]. The possibility that the anti-apoptotic activity of PKC-might be confined to normal hematopoietic cells was excluded by many studies, performed on a variety of different tumour cell types, which have established a strong link between PKC-and suppression of apoptosis [30][31][32][33][34][35][36][37][38][39][40], a key event in the context of cancer ( Table 1). Of particular interest, PKC-was highly expressed in glioma cell lines and high-grade gliomas, and its silencing induces apoptosis in glioma cells and primary glioma cultures [32].…”

“…anti-apoptotic/pro-metastatic head and neck squamous cell carcinoma [14] anti-apoptotic skin cancer [20][21] anti-apoptotic brain tumors [30,32] anti-apoptotic thyroid cancer [31] anti-apoptotic melanomas [33] anti-apoptotic lung cancer [36][37][38][39] anti-apoptotic ovarian carcinomas [40] anti-apoptotic/pro-metastatic breast cancer [45,119] pro-angiogenic normal endothelial cells [51][52] PKCpro-apoptotic colon cancer [18] pro-apoptotic skin cancer [22,128] pro-apoptotic prostate cancer [44] pro-apoptotic/anti-metastatic breast cancer [46][47] pro-apoptotic glioma cells [108] pro-apoptotic osteosarcomas [128] XL and X-linked inhibitor of apoptosis (XIAP) [38]. The pro-survival effect of fibroblast growth factor 2 (FGF2) in these cells involves the formation of a PKC--BRAF-S6K2 complex that presumably regulates the translation of mRNA species involved in cell-death regulation.…”

Protein Kinase CαMediates Erlotinib Resistance in Lung Cancer Cells

“…Changes in the expression levels of PKC isozymes have been associated with the progression of many types of cancers, including lung cancer, as well as with resistance to chemotherapeutic agents (Basu et al, 1996;Clark et al, 2003;Bae et al, 2007;Felber et al, 2007;Garg et al, 2014). To determine whether PKC isozymes are implicated in erlotinib resistance, we took advantage of a well characterized isogenic NSCLC cell model: the parental H1650 cell line and its erlotinib-resistant derivative H1650-M3 (Yao et al, 2010) (Fig.…”