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

Overexpression of JNK-associated leucine zipper protein induces chromosomal instability through interaction with dynein light intermediate chain 1

The c-Jun N-terminal kinase-associated leucine zipper protein (JLP), a scaffold protein of mitogen-activated protein kinase signaling pathways, is a multifunctional protein involved in a variety of cellular processes. It has been reported that JLP is overexpressed in various types of cancer and is expected to be a potential therapeutic target. However, whether and how JLP overexpression affects non-transformed cells remain unknown. Here, we aimed to investigate the effect of JLP overexpression on chromosomal stability in human non-transformed cells and the mechanisms involved. We found that aneuploidy was induced in JLP-overexpressed cells. Moreover, we established JLP-inducible cell lines and observed an increased frequency of chromosome missegregation, reduced time from nuclear envelope breakdown to anaphase onset, and decreased levels of the spindle assembly checkpoint (SAC) components at the prometaphase kinetochore in cells overexpressing the wild-type JLP. In contrast, we observed that a point mutant JLP lacking the ability to interact with dynein light intermediate chain 1 (DLIC1) failed to induce chromosomal instability. Our results suggest that overexpression of the wild-type JLP facilitates premature SAC silencing through interaction with DLIC1, leading to aneuploidy. This study provides a novel insight into the mechanism through which JLP overexpression is associated with cancer development and progression.

SPAG9 Expression Predicts Good Prognosis in Patients with Clear-Cell Renal Cell Carcinoma: A Bioinformatics Analysis with Experimental Validation

Clear-cell renal cell carcinoma (ccRCC) is the most common and aggressive type of renal-cell carcinoma (RCC). Sperm-associated antigen 9 (SPAG9) has been reported to promote the progression of a variety of tumors and is thus a potential prognostic marker. This study combined a bioinformatics analysis with an experimental validation, exploring the prognostic value of SPAG9 expression in ccRCC patients and the possible underlying mechanisms. The SPAG9 expression was associated with a poor prognosis in pan-cancer patients, but with a good prognosis and slow tumor progression in ccRCC patients. To explore the underlying mechanism, we investigated the roles of SPAG9 in ccRCC and bladder urothelial carcinoma (BLCA). The latter was chosen for comparison with ccRCC to represent the tumor types in which SPAG9 expression suggests a poor prognosis. The overexpression of SPAG9 increased the expression of autophagy-related genes in 786-O cells but not in HTB-9 cells, and SPAG9 expression was significantly correlated with a weaker inflammatory response in ccRCC but not in BLCA. Through an integrated bioinformatics analysis, we screened out seven key genes (AKT3, MAPK8, PIK3CA, PIK3R3, SOS1, SOS2, and STAT5B) in this study. The correlation between SPAG9 expression and ccRCC prognosis depends on the expression of key genes. Since most of the key genes were PI3K-AKT-pathway members, we used the PI3K agonist 740Y-P to stimulate the 786-O cells, to mimic the effect of key-gene overexpression. Compared with the Ov-SPAG9 786-O cells, the 740Y-P further increased the expression of autophagy-related genes by more than twofold. Moreover, we constructed a nomogram based on SPAG9/key genes and other clinical features, which was proven to have some predictive value. Our study found that SPAG9 expression predicted opposite clinical outcomes in pan-cancer and ccRCC patients, and we speculated that SPAG9 suppresses tumor progression by promoting autophagy and inhibiting inflammatory responses in ccRCC. We further found that some genes might cooperate with SPAG9 to promote autophagy, and that these were highly expressed in the tumor stroma and could be represented by key genes. The SPAG9-based nomogram can help to estimate the long-term prognosis of ccRCC patients, indicating that SPAG9 is a potential prognostic marker for ccRCC.

Redundant roles of extra-cellular signal-regulated kinase (ERK) 1 and 2 in the G1-S transition and etoposide-induced G2/M checkpoint in HCT116 cells

The extracellular signal-regulated kinase (ERK) 1 and 2 intracellular signaling pathways play key roles in a variety of cellular processes, such as proliferation and differentiation. Dysregulation of ERK1/2 signaling has been implicated in many diseases, including cancer. Although ERK1/2 signaling pathways have been extensively studied, controversy remains as to whether ERK1 and ERK2 have specific or redundant functions. In this study, we examined the functional roles of ERK1 and ERK2 in cell proliferation and cell cycle progression using an auxin-inducible degron system combined with gene knockout technology. We found that ERK1/2 double depletion, but not ERK1 or ERK2 depletion, substantially inhibited the proliferation of HCT116 cells during G1-S transition. We further demonstrated that ERK1/2-double-depleted cells were much more tolerant to etoposide-induced G2/M arrest than ERK1 or ERK2 single-knockout cells. Together, these results strongly suggest the functional redundancy of ERK1 and ERK2 in both the G1-S transition under physiological conditions and the DNA damage-induced G2/M checkpoint. Our findings substantially advance understanding of the ERK1/2 pathways, which could have strong implications for future pharmacological developments.

Autophagy-related signaling pathways are involved in cancer (Review)

Autophagy is a self-digestion process in cells that can maintain energy homeostasis under normal circumstances. However, misfolded proteins, damaged mitochondria and other unwanted components in cells can be decomposed and reused via autophagy in some specific cases (including hypoxic stress, low energy states or nutrient deprivation). Therefore, autophagy serves a positive role in cell survival and growth. However, excessive autophagy may lead to apoptosis. Furthermore, abnormal autophagy may lead to carcinogenesis and promote tumorigenesis in normal cells. In tumor cells, autophagy may provide the energy required for excessive proliferation, promote the growth of cancer cells, and evade apoptosis caused by certain treatments, including radiotherapy and chemotherapy, resulting in increased treatment resistance and drug resistance. On the other hand, autophagy leads to an insufficient nutrient supply in cancer cells and the destruction of energy homeostasis, thereby inducing cancer cell apoptosis. Therefore, understanding the mechanism of the double-edged sword of autophagy is crucial for the treatment of cancer. The present review summarizes the signaling pathways and key factors involved in autophagy and cancer to provide possible strategies for treating tumors.

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.

Polyphenol-Mediated Autophagy in Cancer: Evidence of In Vitro and In Vivo Studies

One of the hallmarks of cellular transformation is the altered mechanism of cell death. There are three main types of cell death, characterized by different morphological and biochemical features, namely apoptosis (type I), autophagic cell death (type II) and necrosis (type III). Autophagy, or self-eating, is a tightly regulated process involved in stress responses, and it is a lysosomal degradation process. The role of autophagy in cancer is controversial and has been associated with both the induction and the inhibition of tumor growth. Autophagy can exert tumor suppression through the degradation of oncogenic proteins, suppression of inflammation, chronic tissue damage and ultimately by preventing mutations and genetic instability. On the other hand, tumor cells activate autophagy for survival in cellular stress conditions. Thus, autophagy modulation could represent a promising therapeutic strategy for cancer. Several studies have shown that polyphenols, natural compounds found in foods and beverages of plant origin, can efficiently modulate autophagy in several types of cancer. In this review, we summarize the current knowledge on the effects of polyphenols on autophagy, highlighting the conceptual benefits or drawbacks and subtle cell-specific effects of polyphenols for envisioning future therapies employing polyphenols as chemoadjuvants.

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 p150^Glued 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.