Abstract Heat shock protein 47 (HSP47) plays an essential role in correcting protein folding, and abnormal protein folding is closely related to tumorigenesis. However, the relationship between HSP47 and cancer immune response is poorly studied. Herein, HSP47 was found to be frequently overexpressed in human osteosarcomas. In animal models, HSP47 inhibition resulted in enhanced immune cell infiltration and function. Transcriptome data revealed that HSP47 negatively regulated CD155, a ligand of TIGIT. Immune checkpoint blockade therapy targeting the novel immune checkpoint molecule TIGIT is effective in limited patients. Further investigations are urgently needed to harness a robust response of this treatment. TIGIT antibody and HSP47-targeted therapy significantly inhibited the progression of osteosarcoma in mice and consequently prolonged survival. Mechanistically, inhibition of HSP47 attenuated TRAF2 protein ubiquitination and subsequently facilitated NF-κB-mediated CD155 transcription in HSP47-overexpressed osteosarcomas. Similarly, CD155 expression was significantly weakened in TRAF2-inhibited osteosarcoma cells. Collectively, our data revealed that targeting HSP47 could reinforce the expression of CD155 and therefore enhance the efficacy of anti-TIGIT treatment, providing a promising strategy for cancer immunotherapy.

Adoptive cellular therapy is a promising strategy for cancer treatment. However, the effectiveness of this therapy is limited by its intricate and immunosuppressive tumor microenvironment. In this study, a targeted therapeutic strategy for macrophage loading of drugs is presented to enhance anti-tumor efficacy of macrophages. K7M2-target peptide (KTP) is used to modify macrophages to enhance their affinity for tumors. Pexidartinib-loaded ZIF-8 nanoparticles (P@ZIF-8) are loaded into macrophages to synergistically alleviate the immunosuppressive tumor microenvironment synergistically. Thus, the M1 macrophages decorated with KTP carried P@ZIF-8 and are named P@ZIF/M1-KTP. The tumor volumes in the P@ZIF/M1-KTP group are significantly smaller than those in the other groups, indicating that P@ZIF/M1-KTP exhibited enhanced anti-tumor efficacy. Mechanistically, an increased ratio of CD4+ T cells and a decreased ratio of MDSCs in the tumor tissues after treatment with P@ZIF/M1-KTP indicated that it can alleviate the immunosuppressive tumor microenvironment. RNA-seq further confirms the enhanced immune cell function. Consequently, P@ZIF/M1-KTP has great potential as a novel adoptive cellular therapeutic strategy for tumors.

The mannose-6-phosphate (M6P) biosynthetic pathway for lysosome biogenesis has been studied for decades and is considered a well-understood topic. However, whether this pathway is regulated remains an open question. In a genome-wide CRISPR/Cas9 knockout screen, we discover TMEM251 as the first regulator of the M6P modification. Deleting TMEM251 causes mistargeting of most lysosomal enzymes due to their loss of M6P modification and accumulation of numerous undigested materials. We further demonstrate that TMEM251 localizes to the Golgi and is required for the cleavage and activity of GNPT, the enzyme that catalyzes M6P modification. In zebrafish, TMEM251 deletion leads to severe developmental defects including heart edema and skeletal dysplasia, which phenocopies Mucolipidosis Type II. Our discovery provides a mechanism for the newly discovered human disease caused by TMEM251 mutations. We name TMEM251 as GNPTAB cleavage and activity factor (GCAF) and its related disease as Mucolipidosis Type V.

The lysosome (or vacuole in fungi and plants) is an essential organelle for nutrient sensing and cellular homeostasis. In response to environmental stresses such as starvation, the yeast vacuole can adjust its membrane composition by selectively internalizing membrane proteins into the lumen for degradation. Regarding the selective internalization mechanism, two competing models have been proposed. One model suggests that the ESCRT machinery is responsible for the sorting. In contrast, the ESCRT-independent intralumenal fragment (ILF) pathway proposes that the fragment generated by homotypic vacuole fusion is responsible for the sorting. Here, we applied a microfluidics-based imaging method to capture the complete degradation process in vivo. Combining live-cell imaging with a synchronized ubiquitination system, we demonstrated that ILF cargoes are not degraded through intralumenal fragments. Instead, ESCRTs function on the vacuole membrane to sort them into the lumen for degradation. We further discussed challenges in reconstituting vacuole membrane protein degradation.

The lysosome is an essential organelle to recycle cellular materials and maintain nutrient homeostasis, but the mechanism to down-regulate its membrane proteins is poorly understood. In this study, we performed a cycloheximide (CHX) chase assay to measure the half-lives of approximately 30 human lysosomal membrane proteins (LMPs) and identified RNF152 and LAPTM4A as short-lived membrane proteins. The degradation of both proteins is ubiquitin dependent. RNF152 is a transmembrane E3 ligase that ubiquitinates itself, whereas LAPTM4A uses its carboxyl-terminal PY motifs to recruit NEDD4-1 for ubiquitination. After ubiquitination, they are internalized into the lysosome lumen by the endosomal sorting complexes required for transport (ESCRT) machinery for degradation. Strikingly, when ectopically expressed in budding yeast, human RNF152 is still degraded by the vacuole (yeast lysosome) in an ESCRT-dependent manner. Thus, our study uncovered a conserved mechanism to down-regulate lysosome membrane proteins.

The lysosome is an essential organelle to recycle cellular materials and maintain nutrient homeostasis, but the mechanism to down-regulate lysosomal membrane proteins is poorly understood. In this study, we developed a cycloheximide chase assay to measure the half-lives of ~30 human lysosomal membrane proteins, and identified RNF152 as a short-lived protein. The degradation of RNF152 depends on ubiquitin and the endosomal sorting complexes required for transport (ESCRT) machinery. Ubiquitinated RNF152 is sorted and internalized by the ESCRT machinery into the lysosomal lumen for degradation. Strikingly, when expressed in budding yeast, human RNF152 is also degraded by the vacuole (yeast lysosome) in an ESCRT-dependent manner. Thus, our study uncovered a conserved mechanism to down-regulate lysosome membrane proteins.

With a special size and structure, nanoparticles (NPs) have excellent application prospects in various fields and are widely used in the biomedicine, cosmetics and chemical industries nowadays. However, there have been some reports on the biosafety of this new type of material, pointing out its cytotoxicity in inducing apoptosis. With different physicochemical properties in size, shape, surface charge, and ligand, NPs exhibit different biocompatibilities when interacting with different cells. Therefore, a comprehensive and deep study into the proapoptotic mechanism of NPs is necessary. In the present review, we summarize the NP-triggered apoptotic signal pathways in detail and highlight some important functional molecules involved. We hope our findings and perspectives provide a new direction for the sound development of nanotechnology in the future.