Protective role of c-Jun NH2-terminal kinase-associated leucine zipper protein (JLP) in curcumin-induced cancer cell death.

Previous studies have established the antitumor activity of curcumin, a major component of turmeric. Increasing evidence indicates that curcumin induces autophagy, the activation of mitogen-activated protein kinase (MAPK) intracellular signaling pathways, and reactive oxygen species (ROS)-mediated cell death. The c-Jun NH2-terminal kinase (JNK)-associated leucine zipper protein (JLP), a scaffold protein for MAPK signaling pathways, has been identified as a candidate biomarker for cancer. In this study, we explored the role of JLP in curcumin-induced cancer cell death. We found that JLP knockdown (KD) increases cell death and intracellular ROS levels. Furthermore, JLP KD impaired lysosomal accumulation around perinuclear regions, which led to the inhibition of autophagosome-lysosome fusion, and attenuated p38 MAPK activation in curcumin-treated cells. The decreases in cell viability and p38 MAPK activation were reversed by expressing wild-type JLP but not a JLP mutant lacking the p38 MAPK-binding domain. In addition, the inactivation of a key gene involved in autophagy increased sensitivity to curcumin-induced cell death. Together, these results suggest that JLP mediates the induction of autophagy by regulating lysosome positioning and p38 MAPK signaling, indicating an overall protective role in curcumin-induced ROS-mediated cancer cell death.

JLP-JNK signaling protects cancer cells from reactive oxygen species-induced cell death.

Oxidative stress, which can be caused by an overproduction of reactive oxygen species (ROS), often leads to cell death. In recent years, c-Jun NH2-terminal kinase (JNK)-associated leucine zipper protein (JLP, also known as SPAG9 or JIP4), a scaffold protein for JNK mitogen-activated protein kinase (MAPK) signaling pathways, was found to serve as a novel biomarker for cancer. However, although JNK MAPK pathways are reported to be activated in response to various stimuli, including oxidative stress, whether JLP is involved in ROS signaling remains unknown. In this study, we examined the role of JLP in hydrogen peroxide (H2O2)-induced cancer cell death, and found that JLP knockdown (KD) cells exhibit a substantially enhanced cell death response, along with increased intracellular ROS levels. This is the first demonstration of a protective role for JLP in response to cell-death stimulation. We also found that the H2O2-induced JNK activation was attenuated in JLP KD cancer cells. The decreases in cell viability and JNK activation in the JLP KD cells were almost completely reversed by expressing wild-type JLP, but not a mutant JLP lacking the JNK-binding domain. These data collectively suggest that the JLP-JNK signaling pathway counteracts ROS-induced cancer cell death.

Critical role of glioma-associated oncogene homolog 1 in maintaining invasive and mesenchymal-like properties of melanoma cells.

Cutaneous melanoma is the most aggressive form of skin cancer. This aggressiveness appears to be due to the cancer cells' ability to reversibly switch between phenotypes with non-invasive and invasive potential, and microphthalmia-associated transcription factor (MITF) is known to play a central role in this process. The transcription factor glioma-associated oncogene homolog 1 (GLI1) is a component of the canonical and noncanonical sonic hedgehog pathways. Although GLI1 has been suggested to be involved in melanoma progression, its precise role and the mechanism underlying invasion remain unclear. Here we investigated whether and how GLI1 is involved in the invasive ability of melanoma cells. Gli1 knockdown (KD) melanoma cell lines, established by using Gli1-targeting lentiviral short hairpin RNA, exhibited a markedly reduced invasion ability, but their MITF expression and activity were the same as controls. Gli1 KD melanoma cells also led to less lung metastasis in mice compared with control melanoma cells. Furthermore, the Gli1 KD melanoma cells underwent a mesenchymal-to-epithelial-like transition, accompanied by downregulation of the epithelial-to-mesenchymal transition (EMT)-inducing transcription factors (EMT-TF) Snail1, Zeb1 and Twist1, but not Snail2 or Zeb2. Collectively, these results indicate that GLI1 is important for maintaining the invasive and mesenchymal-like properties of melanoma cells independent of MITF, most likely by modulating a subset of EMT-TF. Our findings provide new insight into how heterogeneity and plasticity are achieved and regulated in melanoma.

c-Jun NH2-terminal kinase (JNK)/stress-activated protein kinase-associated protein 1 (JSAP1) attenuates curcumin-induced cell death differently from its family member, JNK-associated leucine zipper protein (JLP).

Curcumin, a major component of turmeric, is known to exhibit multiple biological functions including antitumor activity. We previously reported that the mitogen-activated protein kinase (MAPK) scaffold protein c-Jun NH2-terminal kinase (JNK)-associated leucine zipper protein (JLP) reduces curcumin-induced cell death by modulating p38 MAPK and autophagy through the regulation of lysosome positioning. In this study, we investigated the role of JNK/stress-activated protein kinase-associated protein 1 (JSAP1), a JLP family member, in curcumin-induced stress, and found that JSAP1 also attenuates curcumin-induced cell death. However, JSAP1 knockout showed no or little effect on the activation of JNK and p38 MAPKs in response to curcumin. In addition, small molecule inhibitors of JNK and p38 MAPKs did not increase curcumin-induced cell death. Furthermore, JSAP1 depletion did not impair lysosome positioning and autophagosome-lysosome fusion. Instead, we noticed substantial autolysosome accumulation accompanied by an inefficient autophagic flux in JSAP1 knockout cells. Taken together, these results indicate that JSAP1 is involved in curcumin-induced cell death differently from JLP, and may suggest that JSAP1 plays a role in autophagosome degradation and its dysfunction results in enhanced cell death. The findings of this study may contribute to the development of novel therapeutic approaches using curcumin for cancer.

Functional role of c-Jun NH2-terminal kinase-associated leucine zipper protein (JLP) in lysosome localization and autophagy.

Lysosomes are involved in many cellular functions, and in turn lysosomal dysfunction underlies a variety of diseases, including cancer and neurodegenerative diseases. Lysosomes are distributed broadly in the cytoplasm and can move throughout the cell in kinesin- and dynein-dependent manners. Although many mechanisms of lysosomal transport have been reported, how lysosomal transport is regulated has yet to be fully elucidated. In this study we analyzed c-Jun NH2-terminal kinase-associated leucine zipper protein (JLP), an adaptor of kinesin and dynein motor proteins, and found that lysosomes were localized toward the cell periphery in JLP knockdown cells, leading to the impairment of autophagosome-lysosome fusion. Furthermore, we performed rescue experiments using wild-type JLP and its various deletion mutants. The results indicated that JLP may regulate lysosome localization and autophagy through interaction of JLP with kinesin-1 heavy chain, but not with dynactin p150Glued or lysosomal transmembrane protein 55b. Our findings provide new insights into the mechanisms of lysosomal trafficking regulation. This study contributes to the understanding of how lysosomes exert their multiple functions, potentially leading to the identification of molecular targets for diseases caused by lysosomal dysfunction.