Lysosomal transmembrane protein LAPTM4B promotes autophagy and tolerance to metabolic stress in cancer cells

LAPTM4B counteracts ferroptosis via suppressing the ubiquitin-proteasome degradation of SLC7A11 in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a leading cause of cancer-related deaths worldwide, necessitating the identification of novel therapeutic targets. Lysosome Associated Protein Transmembrane 4B (LAPTM4B) is involved in biological processes critical to cancer progression, such as regulation of solute carrier transporter proteins and metabolic pathways, including mTORC1. However, the metabolic processes governed by LAPTM4B and its role in oncogenesis remain unknown. In this study, we conducted unbiased metabolomic screens to uncover the metabolic landscape regulated by LAPTM4B. We observed common metabolic changes in several knockout cell models suggesting of a role for LAPTM4B in suppressing ferroptosis. Through a series of cell-based assays and animal experiments, we demonstrate that LAPTM4B protects tumor cells from erastin-induced ferroptosis both in vitro and in vivo. Mechanistically, LAPTM4B suppresses ferroptosis by inhibiting NEDD4L/ZRANB1 mediated ubiquitination and subsequent proteasomal degradation of the cystine-glutamate antiporter SLC7A11. Furthermore, metabolomic profiling of cancer cells revealed that LAPTM4B knockout leads to a significant enrichment of ferroptosis and associated metabolic alterations. By integrating results from cellular assays, patient tissue samples, an animal model, and cancer databases, this study highlights the clinical relevance of the LAPTM4B-SLC7A11-ferroptosis signaling axis in NSCLC progression and identifies it as a potential target for the development of cancer therapeutics.

KPT330 promotes the sensitivity of glioblastoma to olaparib by retaining SQSTM1 in the nucleus and disrupting lysosomal function

ABBREVIATIONS

AO: acridine orange; ATM: ATM serine/threonine kinase; CHEK1: checkpoint kinase 1; CHEK2: checkpoint kinase 2; CI: combination index; DMSO: dimethyl sulfoxide; DSBs: double-strand breaks; GBM: glioblastoma; HR: homologous recombination; H2AX: H2A.X variant histone; IHC: immunohistochemistry; LAPTM4B: lysosomal protein transmembrane 4 beta; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; PARP: poly(ADP-ribose) polymerase; RAD51: RAD51 recombinase; SQSTM1: sequestosome 1; SSBs: single-strand breaks; RNF168: ring finger protein 168; XPO1: exportin 1.

Construction and validation of a prognostic nine-gene signature associated with radiosensitivity in head and neck squamous cell carcinoma

Background

Radiotherapy is an effective treatment for head and neck squamous cell carcinoma (HNSCC), however how to predict the prognosis is not clear.

Methods

Here we collected 262 radiosensitivity-associated genes, screened and constructed a prognostic nine-gene risk model through univariate COX, lasso regression, stepwise regression and multivariate COX analysis for transcriptome and clinical information of HNSCC patients obtained from the cancer genome atlas (TCGA) and gene expression omnibus (GEO) databases.

Results

The reliability and robustness of the risk model were verified by receiver operating characteristic (ROC) curves, risk maps, and Kaplan-Meier (KM) curves analysis. Differences in immune cell infiltration and immune-related pathway enrichment between high-risk and low-risk subgroups were determined by multiple immune infiltration analyses. Meanwhile, the mutation map and the responses to immunotherapy were also differentiated by the prognostic nine-gene signature associated with radiosensitivity. These nine genes expression in HNSCC was verified in the Human Protein Atlas (HPA) database. After that, these nine genes expression was verified to be related to radiation resistance through in-vitro cell experiments.

Conclusions

All results showed that the nine-gene signature associated with radiosensitivity is a potential prognostic indicator for HNSCC patients after radiotherapy and provides potential gene targets for enhancing the efficacy of radiotherapy.

miR-137-LAPTM4B regulates cytoskeleton organization and cancer metastasis via the RhoA-LIMK-Cofilin pathway in osteosarcoma

Osteosarcoma (OS) is a rare malignant bone tumor but is one leading cause of cancer mortality in childhood and adolescence. Cancer metastasis accounts for the primary reason for treatment failure in OS patients. The dynamic organization of the cytoskeleton is fundamental for cell motility, migration, and cancer metastasis. Lysosome Associated Protein Transmembrane 4B (LAPTM4B) is an oncogene participating in various biological progress central to cancer biogenesis. However, the potential roles of LAPTM4B in OS and the related mechanisms remain unknown. Here, we established the elevated LAPTM4B expression in OS, and it is essential in regulating stress fiber organization through RhoA-LIMK-cofilin signaling pathway. In terms of mechanism, our data revealed that LAPTM4B promotes RhoA protein stability by suppressing the ubiquitin-mediated proteasome degradation pathway. Moreover, our data show that miR-137, rather than gene copy number and methylation status, contributes to the upregulation of LAPTM4B in OS. We report that miR-137 is capable of regulating stress fiber arrangement, OS cell migration, and metastasis via targeting LAPTM4B. Combining results from cells, patients' tissue samples, the animal model, and cancer databases, this study further suggests that the miR-137-LAPTM4B axis represents a clinically relevant pathway in OS progression and a viable target for novel therapeutics.

Autophagy and Breast Cancer: Connected in Growth, Progression, and Therapy

Despite an increase in the incidence of breast cancer worldwide, overall prognosis has been consistently improving owing to the development of multiple targeted therapies and novel combination regimens including endocrine therapies, aromatase inhibitors, Her2-targeted therapies, and cdk4/6 inhibitors. Immunotherapy is also being actively examined for some breast cancer subtypes. This overall positive outlook is marred by the development of resistance or reduced efficacy of the drug combinations, but the underlying mechanisms are somewhat unclear. It is interesting to note that cancer cells quickly adapt and evade most therapies by activating autophagy, a catabolic process designed to recycle damaged cellular components and provide energy. In this review, we discuss the role of autophagy and autophagy-associated proteins in breast cancer growth, drug sensitivity, tumor dormancy, stemness, and recurrence. We further explore how autophagy intersects and reduces the efficacy of endocrine therapies, targeted therapies, radiotherapy, chemotherapies as well as immunotherapy via modulating various intermediate proteins, miRs, and lncRNAs. Lastly, the potential application of autophagy inhibitors and bioactive molecules to improve the anticancer effects of drugs by circumventing the cytoprotective autophagy is discussed.

Autophagy-related gene LAPTM4B promotes the progression of renal clear cell carcinoma and is associated with immunity

Renal cell carcinoma (RCC) is a common urologic disease. Currently, surgery is the primary treatment for renal cancer; immunotherapy is not as effective a treatment strategy as expected. Hence, understanding the mechanism in the tumor immune microenvironment (TME) and exploring novel immunotherapeutic targets are considered important. Recent studies have demonstrated that autophagy could affect the immune environment of renal cell carcinoma and induce proliferation and apoptosis of cancer cells. By comparing lysosomal genes and regulating autophagy genes, we identified the LAPTM4B gene to be related to RCC autophagy. By analyzing the TCGA-KIRC cohort using bioinformatics, we found M2 macrophages associated with tumor metastasis to be significantly increased in the immune microenvironment of patients with high expression of LAPTM4B. GO/KEGG/GSEA/GSVA results showed significant differences in tumor autophagy- and metastasis-related pathways. Single-cell sequencing was used to compare the expression of LAPTM4B in different cell types and obtain the differences in lysosomal and autophagy pathway activities in different ccRCC cells. Subsequently, we confirmed the differential expression of LAPTM4B in renal cell carcinoma of different Fuhrman grades using western blotting. Downregulation of LAPTM4B expression significantly reduced the proliferation of renal cell carcinoma cells and promoted cell apoptosis through cell experiments. Overall, our study demonstrated that the autophagy-related gene LAPTM4B plays a critical role in the TME of RCC, and suggested that LAPTM4B is a potential therapeutic target for RCC immunotherapy.

L-Arginine Ameliorates Defective Autophagy in GM2 Gangliosidoses by mTOR Modulation

Aims: Tay–Sachs and Sandhoff diseases (GM2 gangliosidosis) are autosomal recessive disorders of lysosomal function that cause progressive neurodegeneration in infants and young children. Impaired hydrolysis catalysed by β-hexosaminidase A (HexA) leads to the accumulation of GM2 ganglioside in neuronal lysosomes. Despite the storage phenotype, the role of autophagy and its regulation by mTOR has yet to be explored in the neuropathogenesis. Accordingly, we investigated the effects on autophagy and lysosomal integrity using skin fibroblasts obtained from patients with Tay–Sachs and Sandhoff diseases. Results: Pathological autophagosomes with impaired autophagic flux, an abnormality confirmed by electron microscopy and biochemical studies revealing the accelerated release of mature cathepsins and HexA into the cytosol, indicating increased lysosomal permeability. GM2 fibroblasts showed diminished mTOR signalling with reduced basal mTOR activity. Accordingly, provision of a positive nutrient signal by L-arginine supplementation partially restored mTOR activity and ameliorated the cytopathological abnormalities. Innovation: Our data provide a novel molecular mechanism underlying GM2 gangliosidosis. Impaired autophagy caused by insufficient lysosomal function might represent a new therapeutic target for these diseases. Conclusions: We contend that the expression of autophagy/lysosome/mTOR-associated molecules may prove useful peripheral biomarkers for facile monitoring of treatment of GM2 gangliosidosis and neurodegenerative disorders that affect the lysosomal function and disrupt autophagy.

LAPTM4B promotes the progression of bladder cancer by stimulating cell proliferation and invasion

Bladder cancer is a highly metastatic tumor and one of the most common malignant tumors originating in the urinary system. Due to the complicated etiology and lack of significant early symptoms, the diagnosis and treatment of bladder cancer is difficult. Lysosome-associated transmembrane protein 4β (LAPTM4B) was reported to be involved in the development and progression of several types of tumor, however, its potential effect on the development and metastasis of bladder cancer is still unclear. Immunohistochemistry was performed to detect the protein expression level of LAPTM4B in bladder cancer tissues and short hairpin RNAs targeting LAPTM4B were transfected into bladder cancer cells to knockdown its expression. MTT and colony formation assays were performed to detect cell proliferation, while wound healing and Transwell invasion assays were performed to detect cell migration and invasion, respectively. In addition, tumor growth assays were performed to confirm the effects of LAPTM4B in mice. The present study demonstrated that LAPTM4B was associated with the prognosis of patients with bladder cancer. In addition, LAPTM4B was associated with clinical characteristics, including tumor stage and recurrence. The results further showed that LAPTM4B knockdown could suppress the proliferation of bladder cancer cell lines. In addition, the migration and invasion of T24 and 5637 cells was suppressed following LAPTM4B knockdown in vitro. The in vivo data confirmed that knockdown of LAPTM4B markedly inhibited tumor growth and metastasis in mice. In summary, the results from the present study provide strong evidence of the effects of LAPTM4B in bladder cancer progression.

MicroRNAs involved in drug resistance of breast cancer by regulating autophagy

Autophagy is a conserved catabolic process characterized by degradation and recycling of cytosolic components or organelles through a lysosome-dependent pathway. It has a complex and close relationship to drug resistance in breast cancer. MicroRNAs (miRNAs) are small noncoding molecules that can influence numerous cellular processes including autophagy, through the posttranscriptional regulation of gene expression. Autophagy is regulated by many proteins and pathways, some of which in turn have been found to be regulated by miRNAs. These miRNAs may affect the drug resistance of breast cancer. Drug resistance is the main cause of distant recurrence, metastasis and death in breast cancer patients. In this review, we summarize the causative relationship between autophagy and drug resistance of breast cancer. The roles of autophagy-related proteins and pathways and their associated miRNAs in drug resistance of breast cancer are also discussed.

An Updated Review on Implications of Autophagy and Apoptosis in Tumorigenesis: Possible Alterations in Autophagy through Engineered Nanomaterials and Their Importance in Cancer Therapy

Most commonly recognized as a catabolic pathway, autophagy is a perplexing mechanism through which a living cell can free itself of excess cytoplasmic components, i.e., organelles, by means of certain membranous vesicles or lysosomes filled with degrading enzymes. Upon exposure to external insult or internal stimuli, the cell might opt to activate such a pathway, through which it can gain control over the maintenance of intracellular components and thus sustain homeostasis by intercepting the formation of unnecessary structures or eliminating the already present dysfunctional or inutile organelles. Despite such appropriateness, autophagy might also be considered a frailty for the cell, as it has been said to have a rather complicated role in tumorigenesis. A merit in the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. In fact, several investigations on tumorigenesis have reported diminished levels of autophagic activity in tumor cells, which might result in transition to malignancy. On the contrary, autophagy has been suggested to be a seemingly favorable mechanism to progressed malignancies, as it contributes to survival of such cells. Based on the recent literature, this mechanism might also be activated upon the entry of engineered nanomaterials inside a cell, supposedly protecting the host from foreign materials. Accordingly, there is a good chance that therapeutic interventions for modulating autophagy in malignant cells using nanoparticles may sensitize cancerous cells to certain treatment modalities, e.g., radiotherapy. In this review, we will discuss the signaling pathways involved in autophagy and the significance of the mechanism itself in apoptosis and tumorigenesis while shedding light on possible alterations in autophagy through engineered nanomaterials and their potential therapeutic applications in cancer. SIGNIFICANCE STATEMENT: Autophagy has been said to have a complicated role in tumorigenesis. In the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. On the contrary, autophagy has been suggested to be a favorable mechanism to progressed malignancies. This mechanism might be affected upon the entry of nanomaterials inside a cell. Accordingly, therapeutic interventions for modulating autophagy using nanoparticles may sensitize cancerous cells to certain therapies.

CRISPR editing of the GLI1 first intron abrogates GLI1 expression and differentially alters lineage commitment

GLI1 is one of three GLI family transcription factors that mediate Sonic Hedgehog signaling, which plays a role in development and cell differentiation. GLI1 forms a positive feedback loop with GLI2 and likely with itself. To determine the impact of GLI1 and its intronic regulatory locus on this transcriptional loop and human stem cell differentiation, we deleted the region containing six GLI binding sites in the human GLI1 intron using CRISPR/Cas9 editing to produce H1 human embryonic stem cell (hESC) GLI1‐edited clones. Editing out this intronic region, without removing the entire GLI1 gene, allowed us to study the effects of this highly complex region, which binds transcription factors in a variety of cells. The roles of GLI1 in human ESC differentiation were investigated by comparing RNA sequencing, quantitative‐real time PCR (q‐rtPCR), and functional assays. Editing this region resulted in GLI1 transcriptional knockdown, delayed neural commitment, and inhibition of endodermal and mesodermal differentiation during spontaneous and directed differentiation experiments. We found a delay in the onset of early osteogenic markers, a reduction in the hematopoietic potential to form granulocyte units, and a decrease in cancer‐related gene expression. Furthermore, inhibition of GLI1 via antagonist GANT‐61 had similar in vitro effects. These results indicate that the GLI1 intronic region is critical for the feedback loop and that GLI1 has lineage‐specific effects on hESC differentiation. Our work is the first study to document the extent of GLI1 abrogation on early stages of human development and to show that GLI1 transcription can be altered in a therapeutically useful way.

Dual targeting of tumor cell energy metabolism and lysosomes as an anticancer strategy

To sustain their proliferative and metastatic capacity, tumor cells increase the activity of energy-producing pathways and lysosomal compartment, resorting to autophagolysosomal degradation when nutrients are scarce. Consequently, large fragile lysosomes and enhanced energy metabolism may serve as targets for anticancer therapy. A simultaneous induction of energy stress (by caloric restriction and inhibition of glycolysis, oxidative phosphorylation, Krebs cycle, or amino acid/fatty acid metabolism) and lysosomal stress (by lysosomotropic detergents, vacuolar ATPase inhibitors, or cationic amphiphilic drugs) is an efficient anti-cancer strategy demonstrated in a number of studies. However, the mechanisms of lysosomal/energy stress co-amplification, apart from the protective autophagy inhibition, are poorly understood. We here summarize the established and suggest potential mechanisms and candidates for anticancer therapy based on the dual targeting of lysosomes and energy metabolism.

Downregulation of LAPTM4B Contributes to the Impairment of the Autophagic Flux via Unopposed Activation of mTORC1 Signaling During Myocardial Ischemia/Reperfusion Injury

RATIONALE

Impaired autophagic flux contributes to ischemia/reperfusion (I/R)-induced cardiomyocyte death, but the underlying molecular mechanisms remain largely unexplored.

OBJECTIVE

To determine the role of LAPTM4B (lysosomal-associated transmembrane protein 4B) in the regulation of autophagic flux and myocardial I/R injury.

METHODS AND RESULTS

LAPTM4B was expressed in murine hearts but downregulated in hearts with I/R (30 minutes/2 hours) injury and neonatal rat cardiomyocytes with hypoxia/reoxygenation (6 hours/2 hours) injury. During myocardial reperfusion, LAPTM4B-knockout (LAPTM4B^-/-) mice had a significantly increased infarct size and lactate dehydrogenase release, whereas adenovirus-mediated LAPTM4B-overexpression was cardioprotective. Concomitantly, LAPTM4B^-/- mice showed higher accumulation of the autophagy markers LC3-II (microtubule-associated protein 1A/1B-light chain 3), but not P62, in the I/R heart, whereas they did not alter chloroquine-induced further increases of LC3-II and P62 in both sham and I/R hearts. Conversely, LAPTM4B-overexpression had opposite effects. The hypoxia/reoxygenation-reduced viability of neonatal rat cardiomyocytes, ratio of autolysosomes/autophagosomes, and function of lysosomes were further decreased by LAPTM4B-knockdown but reversed by LAPTM4B-overexpression. Moreover, the LAPTM4B-overexpression-mediated benefits were abolished by knockdown of lysosome-associated membrane protein-2 (an autophagosome-lysosome fusion protein) in vivo and by the autophagy inhibitor bafilomycin A1 in vivo. In contrast, rapamycin (Rapa) successfully restored the impaired autophagic flux in LAPTM4B^-/- mice and the subsequent myocardial I/R injury. Mechanistically, LAPTM4B regulated the activity of mTORC1 (mammalian target of rapamycin complex 1) via interacting with mTOR through its EC3 (extracelluar) domain. Thus, mTORC1 was overactivated in LAPTM4B^-/- mice, leading to the repression of TFEB (transcription factor EB), a master regulator of lysosomal and autophagic genes, during myocardial I/R. The mTORC1 inhibition or TFEB-overexpression rescued the LAPTM4B^-/--induced impairment in autophagic flux and I/R injury, whereas TFEB-knockdown abolished the LAPTM4B-overexpression-mediated recovery of autophagic flux and cardioprotection.

CONCLUSIONS

The downregulation of LAPTM4B contributes to myocardial I/R-induced impairment of autophagic flux via modulation of the mTORC1/TFEB pathway. Graphic Abstract: A graphic abstract is available for this article.

Identification of Lysosome-Associated Protein Transmembrane-4 as a Novel Therapeutic Target for Osteosarcoma Treatment

OBJECTIVE

The aim of the study is to evaluate the expression of lysosome-associated protein transmembrane-4 (LAPTM4B) in human osteosarcoma tissue samples collected in our hospital, and to explore the possible correlations between the clinical pathological features of osteosarcoma patients and LAPTM4B expression.

METHODS

Immunohistochemical (IHC) assays were performed to detect the expression levels of LAPTM4B in 62 tissue samples of osteosarcoma tissues and corresponding non-tumor tissues. According to LAPTM4B staining intensity in tumor tissues, osteosarcoma patients were classified into LAPTM4B high expression and low expression groups. In addition, the potential correlations between LAPTM4B expression levels and clinical pathological features were evaluated. In addition, we detected the effects of LAPTM4B on the proliferation and invasion of esteosarcoma cells through colony formation assay and transwell assay, respectively. We further explored the potential effects of LAPTM4B on tumor growth and metastasis using in vivo animal model.

RESULTS

We revealed that LAPTM4B was highly expressed in human osteosarcoma tissues. We determined the significance between LAPTM4B and clinical features, including the tumor size (P = 0.004*) and the clinical stage (P = 0.035*) of osteosarcoma patients. Our results further demonstrated that ablation of LAPTM4B obviously blocked the proliferation and invasion of osteosarcoma cells in vitro and restrained tumor growth and metastasis in mice.

CONCLUSION

We investigated the potential involvement of LAPTM4B in osteosarcoma progression and confirmed LAPTM4B as a novel therapeutic target for osteosarcoma.

Shwachman-Bodian-Diamond syndrome protein desensitizes breast cancer cells to apoptosis in stiff matrices by repressing the caspase 8-mediated pathway

Certain cancer types, including breast cancer, are accompanied with stiffening of the surrounding extracellular matrix (ECM). Previous studies suggest that this stiffened matrix influences cancer cell progression, such as proliferation and invasion, both biochemically and mechanically. However, the contribution of ECM stiffness to cellular response to diverse stresses, which most cancer cells are exposed to, has not been elucidated. In this study, we demonstrate that expression of the Shwachman-Bodian-Diamond syndrome protein (SDBS) in a stiff matrix protects cells from apoptosis induced by environmental stress, including anticancer drugs. Cells cultured on stiff matrices were less apoptotic process induced by serum depletion than those cultured on the soft matrix. Interestingly, knockdown (KD) of SDBS among the apoptosis-related genes significantly increased apoptosis induced by serum depletion in cells cultured in a stiff matrix. Apoptosis of SDBS KD cells in a stiff matrix was significantly inhibited by the caspase 8 inhibitor, indicating that activation of the caspase 8 pathway by SDBS KD is critical for cancer cell apoptosis in stiff matrices. Additionally, we also found that downregulation of SDBS also effectively increased cell death induced by anticancer drugs, including paclitaxel, cisplatin, and eribulin. Taken together, our findings suggest that inhibition of SDBS enhances effective chemotherapy of malignant breast cancer cells in stiff ECM environments.

Prognostic significance of LAPTM4B and p27kip1 expression in triple-negative breast cancer

BACKGROUD

Triple-negative breast cancer (TNBC) is associated with an aggressive phenotype and poor prognosis, and the lack of druggable markers leads to the unavailability of targeted therapies. Thus, there is an urgent need to identify potential targets for triple-negative breast cancer.

OBJECTIVE

In this study, we aimed to explore the expression of LAPTM4B and p27kip1 in triple-negative breast cancer, and its clinical significance.

METHODS

We analyzed the expression and association of LAPTM4B and p27kip1 in human breast cancer databases. To analyze the role of LAPTM4B in the aggressiveness of the human triple-negative breast cancer, the expressions of LAPTM4B were knocked down in MDA-MB-231 and HCC1187 cell lines. Then, cell proliferation, migration and apoptosis were assessed in vitro. Furthermore, the immunohistochemistry examinations of LAPTM4B and p27kip1 expression were performed using surgical specimens from 188 primary triple-negative breast cancer patients.

RESULTS

Through analyses of several independent breast cancer cohorts, we found the correlation of the LAPTM4B and p27kip1 expression. Remarkably, the knockdown of LAPTM4B restored p27kip1 expression and inhibited the aggressiveness of breast cancer cells. Meanwhile, the knockdown of p27kip1 relieved the suppression of cell migration. Consistent with the analyses of human breast cancer cohorts, the immunohistochemistry results showed that the expression levels of LAPTM4B and p27kip1 were correlated in 188 triple-negative breast cancer samples (p= 0.019). We also validated that the higher LAPTM4B expression, the lower p27kip1 expression (p= 0.0001), and the LAPTM4B+/p27kip1- subgroup (p< 0.0001) were poor prognostic indicators, as well as the higher histologic grade (p= 0.0001). In the multivariate Cox regression, p27kip1 expression was considered as an independent predictor of survival (p< 0.001).

CONCLUSIONS

The overexpression of LAPTM4B and the loss of p27kip1 expression are correlated. Meanwhile, the up-regulated expression of LAPTM4B together with the down-regulated expression of p27kip1 could classified a group of breast cancer patients with poor prognosis, consequently considered as a potentially prognostic marker and candidate target for therapeutic intervention of triple-negative breast cancer.

Induction of Lysosome-associated Protein Transmembrane 4 Beta via Sulfatase 2 Enhances Autophagic Flux in Liver Cancer Cells

Autophagy has been shown to be a key cellular event controlling tumor growth in different neoplasms including hepatocellular carcinoma (HCC). Although this biological role of autophagy has been clearly established, the mechanism underlying its regulation remains elusive. Here, we demonstrate a role of sulfatase 2 (SULF2), a 6‐O‐endosulfatase modulating various growth factors and cytokine‐related signaling pathways controlling tumor cell proliferation and survival, in the regulation of autophagy in HCC cells. SULF2 increased autophagosome formation, shown by increased LC3B‐II protein and green fluorescent protein–LC3 puncta. Increased fusion between autophagosomes and lysosomes/lysosomal enzymes, higher expression of lysosomal membrane protein, and an increase in autolysosomes were also shown by western blot, immunofluorescence, and electron microscopy of SULF2‐expressing cells, indicating enhanced autophagic flux. In contrast, RNA‐interference silencing of SULF2 in Huh7 cells induced lysosomal membrane permeabilization with diffuse cytosolic staining of cathepsin D and punctate staining of galectin‐3. Analysis of the mechanism showed that inhibition of lysosome‐associated protein transmembrane 4 beta (LAPTM4B), a gene induced by SULF2, resulted in decreased autophagosome formation, decreased fusion between autophagosomes and lysosomes, and increased lysosomal membrane permeabilization. Interestingly, down‐regulation of LAPTM4B also phenocopies the knockdown of SULF2, significantly reducing cell viability and colony formation. Conclusion: Our results demonstrate a role for SULF2 in the regulation of autophagic flux that is mediated through LAPTM4B induction in HCC cells, and provide a foundation for future translational efforts targeting autophagy in liver malignancies.

LAPTM4B knockdown increases the radiosensitivity of EGFR-overexpressing radioresistant nasopharyngeal cancer cells by inhibiting autophagy

Purpose

Nasopharyngeal carcinoma (NPC) is a malignant tumor that commonly occurs in southern China and Southeast Asia. Radiation therapy is the main treatment for patients with NPC, and the radioresistance of NPC is an unresolved clinical problem. This study focuses on the mechanism of NPC radioresistance and explores therapeutic targets and research directions for increasing the radiosensitivity of radioresistant cells.

Methods

We used a gradient dose model to establish radioresistant strains of 6-10B and CNE-2 human NPC cells. Plate colony formation assays were used to verify the radioresistance of the cells. We evaluated the expression of epidermal growth factor receptor (EGFR), lysosome-associated transmembrane protein 4β (LAPTM4B), Beclin1 and the autophagy-related proteins p62, LC3I, and LC3II by Western blot and observed GFP-LC3 puncta by confocal microscopy. The interaction between proteins was verified by immunofluorescence and coimmunoprecipitation analyses. Flow cytometry was performed to detect differences related to the apoptosis of radioresistant strains.

Results

The EGFR and LAPTM4B expression levels and autophagic flux were higher in radioresistant cells than in nonradioresistant cells, suggesting that EGFR and LAPTM4B are associated with autophagy levels. We observed that EGFR and LAPTM4B interact and stabilize each other in endosomes by confocal microscopy. LAPTM4B knockdown decreased the survival fraction of radioresistant cells and increased apoptosis after exposure to radiation. Coimmunoprecipitation experiments demonstrated that LAPTM4B interacts with Beclin1, which in turn promotes the initiation of autophagy.

Conclusion

This study illustrates a relationship among EGFR, LAPTM4B and autophagy in radioresistant NPC cell lines. LAPTM4B interacts with EGFR and Beclin 1, which promotes autophagy. LAPTM4B knockdown decreases radioresistance by inhibiting autophagy. This study proposes a possible mechanism for NPC radioresistance and provides a new research direction and theoretical basis for addressing the radioresistance of NPC.

Pro-survival autophagy and cancer cell resistance to therapy

Resistance to therapy is one of the prime causes for treatment failure in cancer and recurrent disease. In recent years, autophagy has emerged as an important cell survival mechanism in response to different stress conditions that are associated with cancer treatment and aging. Autophagy is an evolutionary conserved catabolic process through which damaged cellular contents are degraded after uptake into autophagosomes that subsequently fuse with lysosomes for cargo degradation, thereby alleviating stress. In addition, autophagy serves to maintain cellular homeostasis by enriching nutrient pools. Although autophagy can act as a double-edged sword at the interface of cell survival and cell death, increasing evidence suggest that in the context of cancer therapy-induced stress responses, it predominantly functions as a cell survival mechanism. Here, we provide an up-to-date overview on our current knowledge of the role of pro-survival autophagy in cancer therapy at the preclinical and clinical stages and delineate the molecular mechanisms of autophagy regulation in response to therapy-related stress conditions. A better understanding of the interplay of cancer therapy and autophagy may allow to unveil new targets and avenues for an improved treatment of therapy-resistant tumors in the foreseeable future.

LAPTM4B facilitates tumor growth and induces autophagy in hepatocellular carcinoma

Background: Hepatocellular carcinoma (HCC) is one of the most frequent cancers and the third leading cause of cancer-related deaths. It has been reported that lysosomal associated transmembrane protein LAPTM4B expression is significantly upregulated in human cancers and closely associated with tumor initiation and progression.

Purpose: We aimed to reveal the relevance of LAPTM4B and the pathogenesis of HCC. Methods: Cell viability assessment, colony formation assay, in vivo xenograrft model, microarray, real-time PCR, immunofluorescence and western blot analysis were applied.

Results: Our results demonstrated that LAPTM4B promoted HCC cell proliferation in vitro and tumorigenesis in vivo. Additionally, upon starvation conditions, LAPTM4B facilitated cell survival, inhibited apoptosis and induced autophagic flux. Expression profiling coupled with gene ontology (GO) analysis revealed that 159 gene downregulated by LAPTM4B silencing was significantly enriched in response to nutrient and some metabolic processes. Moreover, LAPTM4B activated ATG3 transcription to modulate HCC cell apoptosis and autophagy.

Conclusion: Our findings demonstrate that LAPTM4B acts as an oncogene that promotes HCC tumorigenesis and autophagy, and indicate that LAPTM4B may be used as a novel therapeutic target for HCC treatment.

Co-expression of HIF-1α, MDR1 and LAPTM4B in peripheral blood of solid tumors

The hypoxic tumor microenvironment is the major contributor of chemotherapy resistance in solid tumors. One of the key regulators of hypoxic responses within the cell is the hypoxia inducible factor-1α (HIF-1α) that is involved in transcription of genes promoting cell survival and chemotherapy resistance. Multidrug resistance gene-1 (MDR1) and Lysosome-associated protein transmembrane 4B-35 (LAPTM4B-35) are among those notable players which augment their responses to cellular hypoxia. MDR1 is the hypoxia responsive gene involved in multidrug resistance phenotype while LAPTM4B-35 is involved in chemotherapy resistance by stabilizing HIF-1α and overexpressing MDR1. Overexpression of HIF-1α, MDR1 and LAPTM4B has been associated with poor disease outcome in many cancers when studied individually at tissue level. However, accessibility of the tissues following the course of chemotherapy for ascertaining chemotherapy resistance is difficult and sometimes not clinically feasible. Therefore, indication of hypoxic biomarkers in patient’s blood can significantly alter the clinical outcome. Hence there is a need to identify a blood based marker to understand the disease progression. In the current study the expression of hypoxia associated chemotherapy resistance genes were studied in the peripheral blood lymphocytes of solid tumor patients and any potential correlation with disease progression were explored. The expression of HIF-1α, MDR1 and LAPTM4B was studied in blood of 72 breast, 42 ovarian, 32 colon and 21 prostate cancer patients through real time PCR analysis using delta cycle threshold method. The statistical scrutiny was executed through Fisher’s Exact test and the Spearman correlation method. There was 12–13 fold increased in expression of HIF-1α, two fold increased in MDR1 and 13–14 fold increased in LAPTM4B mRNA level in peripheral blood of breast, ovarian, prostate and colon cancer patients. In the current study there was an association of HIF-1α, MDR1 and LAPTM4B expression with advanced tumor stage, metastasis and chemotherapy treated group in breast, ovarian, prostate and colon cancer patients. The Spearman analysis also revealed a positive linear association among HIF-1α, MDR1 and LAPTM4B in all the studied cancer patients. The elevated expression of HIF-1α, MDR1 and LAPTM4B in peripheral blood of solid tumor patients can be a predictor of metastasis, disease progression and treatment response in these cancers. However, larger studies are needed to further strengthen their role as a potential biomarker for cancer prognosis.

Expression signature of lysosomal-associated transmembrane protein 4B in hepatitis C virus-induced hepatocellular carcinoma

INTRODUCTION

Hepatocellular carcinoma is a lethal disease worldwide and therefore the establishment of novel diagnostic biomarkers is imperative. In this study, it was hypothesized that an abnormal expression of the lysosomal-associated protein transmembrane 4 beta ( LAPTM4B) gene is crucial in the pathogenesis of hepatitis C virus-mediated hepatocellular carcinoma; hence we investigated the expression profile of LAPTM4B in hepatitis C virus-induced hepatocellular carcinoma.

METHODS

A group of 189 consecutive patients (hepatitis C virus-related hepatocellular carcinoma as tumor cases; n=93, hepatitis C virus-related cirrhotics as disease controls; n=96) opting for living donor liver transplantation as a therapeutic surgical regimen were recruited with informed consent. Additionally, paired adjacent non-tumorous tissues (n=93) obtained from cases were also included. Serum LAPTM4B protein concentrations were assessed by third-generation enzyme-linked immunosorbent assay and LAPTM4B mRNA, and protein expressions at tissue level were determined by quantitative real time reverse transcription-polymerase chain reaction (qRT-PCR) and immunohistochemistry techniques, respectively.

RESULTS

LAPTM4B protein concentrations in sera of patients were higher ( p<0.001) in tumor cases (1.25±0.25 ng/ml) compared to disease controls (0.53±0.28 ng/ml). Our study also depicts positive clinicopathological correlations between alpha-fetoprotein titers (b=0.65; p<0.001), quantitative hepatitis C virus RNA copies (b=0.33; p<0.001), and LAPTM4B protein concentrations, all in sera of patients. In addition, qRT-PCR and immunohistochemistry analyses revealed a significantly higher ( p<0.05) tissue LAPTM4B mRNA and protein expression, respectively, in tumor cases rather than in non-tumorous tissues and disease controls.

CONCLUSIONS

Together, our results illustrate the LAPTM4B gene as a diagnostic biomarker in patients with hepatocellular carcinoma having documented evidence of chronic hepatitis C virus infection.

A Ceramide-Regulated Element in the Late Endosomal Protein LAPTM4B Controls Amino Acid Transporter Interaction

Membrane proteins are functionally regulated by the composition of the surrounding lipid bilayer. The late endosomal compartment is a central site for the generation of ceramide, a bioactive sphingolipid, which regulates responses to cell stress. The molecular interactions between ceramide and late endosomal transmembrane proteins are unknown. Here, we uncover in atomistic detail the ceramide interaction of Lysosome Associated Protein Transmembrane 4B (LAPTM4B), implicated in ceramide-dependent cell death and autophagy, and its functional relevance in lysosomal nutrient signaling. The ceramide-mediated regulation of LAPTM4B depends on a sphingolipid interaction motif and an adjacent aspartate residue in the protein's third transmembrane (TM3) helix. The interaction motif provides the preferred contact points for ceramide while the neighboring membrane-embedded acidic residue confers flexibility that is subject to ceramide-induced conformational changes, reducing TM3 bending. This facilitates the interaction between LAPTM4B and the amino acid transporter heavy chain 4F2hc, thereby controlling mTORC signaling. These findings provide mechanistic insights into how transmembrane proteins sense and respond to ceramide.

Autophagy, Cell Viability, and Chemoresistance Are Regulated By miR-489 in Breast Cancer

It is postulated that the complexity and heterogeneity in cancer may hinder most efforts that target a single pathway. Thus, discovery of novel therapeutic agents targeting multiple pathways, such as miRNAs, holds promise for future cancer therapy. One such miRNA, miR-489, is downregulated in a majority of breast cancer cells and several drug-resistant breast cancer cell lines, but its role and underlying mechanism for tumor suppression and drug resistance needs further investigation. The current study identifies autophagy as a novel pathway targeted by miR-489 and reports Unc-51 like autophagy activating kinase 1 (ULK1) and lysosomal protein transmembrane 4 beta (LAPTM4B) to be direct targets of miR-489. Furthermore, the data demonstrate autophagy inhibition and LAPTM4B downregulation as a major mechanism responsible for miR-489-mediated doxorubicin sensitization. Finally, miR-489 and LAPTM4B levels were inversely correlated in human tumor clinical specimens, and more importantly, miR-489 expression levels predict overall survival in patients with 8q22 amplification (the region in which LAPTM4B resides).Implications: These findings expand the understanding of miR-489-mediated tumor suppression and chemosensitization in and suggest a strategy for using miR-489 as a therapeutic sensitizer in a defined subgroup of resistant breast cancer patients. Mol Cancer Res; 16(9); 1348-60. ©2018 AACR.

LAPTM4B gene copy number gain is associated with inferior response to anthracycline-based chemotherapy in hormone receptor negative breast carcinomas

PURPOSE

To determine the associations between lysosomal-associated transmembrane protein 4b (LAPTM4B) gene copy number and response to different chemotherapy regimens in hormone receptor negative (HR-) primary breast carcinomas.

PATIENTS AND METHODS

Two cohorts were analyzed: (1) 69 core biopsies from HR-breast carcinomas treated with neoadjuvant chemotherapy (anthracycline based in 72.5% of patients and non-anthracycline based in 27.5% of patients). (2) Tissue microarray (TMA) of 74 HR-breast carcinomas treated with adjuvant therapy (77.0% of the patients received anthracycline, 17.6% of the patients non-anthracycline-based therapy, and in 5.4% of the cases, no treatment data are available). Interphase FISH technique was applied on pretreatment core biopsies (cohort I) and on TMAs (cohort II) using custom-made dual-labelled FISH probes (LAPTM4B/CEN8q FISH probe Abnova Corp.).

RESULTS

In the neoadjuvant cohort in the anthracycline-treated group, we observed a significant difference (p = 0.029) of average LAPTM4B copy number between the non-responder and pathological complete responder groups (4.1 ± 1.1 vs. 2.6 ± 0.1). In the adjuvant setting, the anthracycline-treated group of metastatic breast carcinomas was characterized by higher LAPTM4B copy number comparing to the non-metastatic ones (p = 0.046). In contrast, in the non-anthracycline-treated group of patients, we did not find any LAPTM4B gene copy number differences between responder vs. non-responder groups or between metastatic vs. non-metastatic groups.

CONCLUSION

Our results confirm the possible role of the LAPTM4B gene in anthracycline resistance in HR- breast cancer. Analyzing LAPTM4B copy number pattern may support future treatment decision.

Long Noncoding RNA HCAL Facilitates the Growth and Metastasis of Hepatocellular Carcinoma by Acting as a ceRNA of LAPTM4B

Long noncoding RNAs (lncRNAs) are a new class of regulatory noncoding RNAs. Emerging evidences indicate that lncRNAs play a critical role in the development of hepatocellular carcinoma (HCC). Although several lncRNAs have been annotated, the association of most lncRNAs with HCC is unknown. In this study, we investigated lncRNA alterations in HCC by performing lncRNA microarray analysis. We identified a novel lncRNA called HCC-associated lncRNA (HCAL) that was highly expressed in HCC tissues. HCAL upregulation was clinically associated with poor differentiation, intravascular cancer embolus, and decreased survival of patients with HCC. HCAL silencing significantly inhibited the growth and metastasis of HCC cells both in vitro and in vivo. Interestingly, transcriptome-sequencing analysis of HCAL-knockdown cells showed alterations in some cancer-related pathways. Mechanistically, HCAL directly interacted with and functioned as a sponge for microRNAs such as miR-15a, miR-196a, and miR-196b to modulate LAPTM4B expression. Taken together, our findings suggest the presence of a novel lncRNA-miRNA-mRNA regulatory network, i.e., the HCAL-miR-15a/miR-196a/miR-196b-LAPTM4B network, in HCC and indicate that HCAL may be a potential target for treating HCC.

Lysosome-associated protein transmembrane4β is involved in multidrug resistance processes of colorectal cancer

Colorectal cancer (CRC) is one of the most common reasons for cancer-associated mortality worldwide. The present study aimed to investigate the drug resistance mechanism of the oxaliplatin (OXA)-resistant HT-29 cell line (HT-29/L-OHP) and examine the expression of lysosome-associated protein transmembrane 4β (LAPTM4β), a drug resistance-associated gene. In the present study, a drug concentration gradient method was used to establish the drug-resistant HT-29/L-OHP cell line. Cell apoptosis was analyzed by flow cytometry. LAPTM4β mRNA expression was examined by reverse transcription-quantitative polymerase chain reaction analysis and LAPTM4β-35 expression was examined by western blot analysis. Cell morphology of the HT-29/L-OHP drug-resistant cell line was examined. The results indicated that the intercellular space among HT-29 cells was small, with aggregative growth while the intercellular space among HT-29/L-OHP cells was large, with scattered growth. The apoptotic rate in HT-29/L-OHP cells (11.7%) was significantly lower compared with that in HT-29 cells (17.7%) (P<0.05). LAPTM4β mRNA expression in HT-29/L-OHP cells was significantly increased compared with that in HT-29 cells (P<0.05). The relative expression of LAPTM4β-35 protein in HT-29/L-OHP cells was significantly higher compared with that inHT-29 cells (P<0.05). In conclusion, LAPTM4β may be involved in the multidrug resistance processes of CRC. Therefore, LAPTM4β may serve as a novel biomarker for drug resistance of CRC.

Galangin suppresses human laryngeal carcinoma via modulation of caspase-3 and AKT signaling pathways

Laryngeal cancers are mostly squamous cell carcinomas. Although targeting radio-resistant cancer cells is important for improving the treatmental efficiency, the signaling pathway- and therapeutic strategy-related to laryngeal carcinoma still require further study. Galangin is an active pharmacological ingredient, isolated from propolis and Alpinia officinarum Hance, and has been reported to have anticancer and anti-oxidative properties through regulation of cell cycle, resulting in angiogenesis, apoptosis, invasion and migration without triggering any toxicity in normal cells. PI3K/AKT and p38 are important signaling pathways to modulate cancer cell apoptosis and proliferation through caspase-3, NF-κB and mTOR signal pathways. Autophagy is also enhanced by activating LC3s and Beclin 1. In the present study, galangin was found to suppress laryngeal cancer cell proliferation. Also, flow cytometry, immunohistochemical and western blot analysis indicated that cell apoptosis was induced for galangin administration, promoting caspase-3 expression through regulating PI3K/AKT/NF-κB. Furthermore, galangin inhibited laryngeal cancer cell proliferation, related to p38 inactivation by galangin treatment. Additionally, mTOR activation regulated by PI3K/AKT was reduced by galangin, suppressing cancer cell transcription and proliferation. Our data also indicated that the tumor volume and weight in nude mice were reduced for galangin use in vivo accompanied by Ki-67 decrease and TUNEL increase in tumor tissues. Together, our data indicated that galangin has a potential role in suppressing human laryngeal cancer via inhibiting tumor cell proliferation, activating apoptosis and autophagy, which were regulated by p38 and AKT/NF-κB/mTOR pathways, providing a therapeutic strategy for human laryngeal cancer treatment.

Increased autophagic response in a population of metastatic breast cancer cells

Breast cancer cells are heterogeneous in their ability to invade and fully metastasize, and thus also in their capacity to survive the numerous stresses encountered throughout the multiple steps of the metastatic cascade. Considering the role of autophagy as a survival response to stress, the present study hypothesized that distinct populations of breast cancer cells may possess an altered autophagic capacity that influences their metastatic potential. It was observed that a metastatic breast cancer cell line, MDA-MB-231, that was sensitive to autophagic induction additionally possessed the ability to proliferate following nutrient deprivation. Furthermore, a selected subpopulation of these cells that survived multiple exposures to starvation conditions demonstrated a heightened response to autophagic induction compared to their parent cells. Although this subpopulation maintained a more grape-like pattern in three-dimensional culture compared to the extended spikes of the parent population, autophagic induction in this subpopulation elicited an invasive phenotype with extended spikes. Taken together, these results suggest that autophagic induction may contribute to the ability of distinct breast cancer cell populations to survive and invade.

Cross-cancer profiling of molecular alterations within the human autophagy interaction network

Aberrant activation or disruption of autophagy promotes tumorigenesis in various preclinical models of cancer, but whether the autophagy pathway is a target for recurrent molecular alteration in human cancer patient samples is unknown. To address this outstanding question, we surveyed 211 human autophagy-associated genes for tumor-related alterations to DNA sequence and RNA expression levels and examined their association with patient survival outcomes in multiple cancer types with sequence data from The Cancer Genome Atlas consortium. We found 3 (RB1CC1/FIP200, ULK4, WDR45/WIPI4) and one (ATG7) core autophagy genes to be under positive selection for somatic mutations in endometrial carcinoma and clear cell renal carcinoma, respectively, while 29 autophagy regulators and pathway interactors, including previously identified KEAP1, NFE2L2, and MTOR, were significantly mutated in 6 of the 11 cancer types examined. Gene expression analyses revealed that GABARAPL1 and MAP1LC3C/LC3C transcripts were less abundant in breast cancer and non-small cell lung cancers than in matched normal tissue controls; ATG4D transcripts were increased in lung squamous cell carcinoma, as were ATG16L2 transcripts in kidney cancer. Unsupervised clustering of autophagy-associated mRNA levels in tumors stratified patient overall survival in 3 of 9 cancer types (acute myeloid leukemia, clear cell renal carcinoma, and head and neck cancer). These analyses provide the first comprehensive resource of recurrently altered autophagy-associated genes in human tumors, and highlight cancer types and subtypes where perturbed autophagy may be relevant to patient overall survival.

LAPTM4B: an oncogene in various solid tumors and its functions

The oncogene Lysosome-associated protein transmembrane-4β (LAPTM4B) gene was identified, and the polymorphism region in the 5′-UTR of this gene was certified to be associated with tumor susceptibility. LAPTM4B-35 protein was found to be highly expressed in various solid tumors and could be a poor prognosis marker. The functions of LAPTM4B in solid tumors were also explored. It is suggested that LAPTM4B could promote the proliferation of tumor cells, boost invasion and metastasis, resist apoptosis, initiate autophagy and assist drug resistance.

A potent betulinic acid analogue ascertains an antagonistic mechanism between autophagy and proteasomal degradation pathway in HT-29 cells

Background

Betulinic acid (BA), a member of pentacyclic triterpenes has shown important biological activities like anti-bacterial, anti-malarial, anti-inflammatory and most interestingly anticancer property. To overcome its poor aqueous solubility and low bioavailability, structural modifications of its functional groups are made to generate novel lead(s) having better efficacy and less toxicity than the parent compound. BA analogue, 2c was found most potent inhibitor of colon cancer cell line, HT-29 cells with IC₅₀ value 14.9 μM which is significantly lower than standard drug 5-fluorouracil as well as parent compound, Betulinic acid. We have studied another mode of PCD, autophagy which is one of the important constituent of cellular catabolic system as well as we also studied proteasomal degradation pathway to investigate whole catabolic pathway after exploration of 2c on HT-29 cells.

Methods

Mechanism of autophagic cell death was studied using fluorescent dye like acridine orange (AO) and monodansylcadaverin (MDC) staining by using fluorescence microscopy. Various autophagic protein expression levels were determined by Western Blotting, qRT-PCR and Immunostaining. Confocal Laser Scanning Microscopy (CLSM) was used to study the colocalization of various autophagic proteins. These were accompanied by formation of autophagic vacuoles as revealed by FACS and transmission electron microscopy (TEM). Proteasomal degradation pathway was studied by proteasome-Glo™ assay systems using luminometer.

Results

The formation of autophagic vacuoles in HT-29 cells after 2c treatment was determined by fluorescence staining – confirming the occurrence of autophagy. In addition, 2c was found to alter expression levels of different autophagic proteins like Beclin-1, Atg 5, Atg 7, Atg 5-Atg 12, LC3B and autophagic adapter protein, p62. Furthermore we found the formation of autophagolysosome by colocalization of LAMP-1 with LC3B, LC3B with Lysosome, p62 with lysosome. Finally, as proteasomal degradation pathway downregulated after 2c treatment colocalization of ubiquitin with lysosome and LC3B with p62 was studied to confirm that protein degradation in autophagy induced HT-29 cells follows autolysosomal pathway.

Conclusions

In summary, betulinic acid analogue, 2c was able to induce autophagy in HT-29 cells and as proteasomal degradation pathway downregulated after 2c treatment so protein degradation in autophagy induced HT-29 cells follows autolysosomal pathway.

A genome-wide association study on amyotrophic lateral sclerosis in the Taiwanese Han population

Identification of mutations in patients with amyotrophic lateral sclerosis (ALS) in a genome-wide association study can reveal possible biomarkers of such a rapidly progressive and fatal neurodegenerative disease. It was observed that significant single nucleotide polymorphisms vary when the tested population changes from one ethnic group to another. To identify new loci associated with ALS susceptibility in the Taiwanese Han population, we performed a genome-wide association study on 94 patients with sporadic ALS and 376 matched controls. We uncovered two new susceptibility loci at 13q14.3 (rs2785946) and 11q25 (rs11224052). In addition, we analyzed the functions of all the associated genes among 54 significant single nucleotide polymorphisms using Gene Ontology annotations, and the results showed several statistically significant neural- and muscle-related Gene Ontology terms and the associated diseases.

Emerging roles of PtdIns(4,5)P2--beyond the plasma membrane

Phosphoinositides are a collection of lipid messengers that regulate most subcellular processes. Amongst the seven phosphoinositide species, the roles for phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] at the plasma membrane, such as in endocytosis, exocytosis, actin polymerization and focal adhesion assembly, have been extensively studied. Recent studies have argued for the existence of PtdIns(4,5)P2 at multiple intracellular compartments, including the nucleus, endosomes, lysosomes, autolysosomes, autophagic precursor membranes, ER, mitochondria and the Golgi complex. Although the generation, regulation and functions of PtdIns(4,5)P2 are less well-defined in most other intracellular compartments, accumulating evidence demonstrates crucial roles for PtdIns(4,5)P2 in endolysosomal trafficking, endosomal recycling, as well as autophagosomal pathways, which are the focus of this Commentary. We summarize and discuss how phosphatidylinositol phosphate kinases, PtdIns(4,5)P2 and PtdIns(4,5)P2-effectors regulate these intracellular protein and membrane trafficking events.

LAPTM4B is associated with poor prognosis in NSCLC and promotes the NRF2-mediated stress response pathway in lung cancer cells

We recently demonstrated that lysosomal protein transmembrane 4 beta (LAPTM4B) is elevated in non-small cell lung cancers (NSCLCs) and in the surrounding premalignant airway field of cancerization. In the present study, we sought to begin to understand the relevance of LAPTM4B expression and signaling to NSCLC pathogenesis. In situ hybridization analysis of LAPTM4B transcript in tissue microarrays comprised of 368 NSCLCs demonstrated that LAPTM4B expression was significantly increased in smoker compared to non-smoker lung adenocarcinoma tumors (P < 0.001) and was significantly associated with poor overall survival (P < 0.05) in adenocarcinoma patients. Knockdown of LAPTM4B expression inhibited cell growth, induced cellular apoptosis and decreased cellular autophagy in serum starved lung cancer cells. Expression profiling coupled with pathways analysis revealed decreased activation of the nuclear factor erythroid 2-like 2 (NRF2) stress response pathway following LAPTM4B knockdown. Further analysis demonstrated that LAPTM4B augmented the expression and nuclear translocation of the NRF2 transcription factor following serum deprivation as well as increased the expression of NRF2 target genes such as heme oxygenase 1/HMOX1). Our study points to the relevance of LAPTM4B expression to NSCLC pathogenesis as well as to the probable role of LAPTM4B/NRF2 signaling in promoting lung cancer cell survival.

Lentivirus-mediated RNA Interference Targeting LAPTM4B Inhibits Human Ovarian Cancer Cell Invasion In Vitro

LAPTM4B (lysosome-associated protein transmembrane 4 beta) play an important role in several human carcinomas. We examines the effects of RNA interference mediated downregulation of human lysosomal-associated protein transmembrane 4 beta expression on the biological behavior of the human serous adenocarcinoma cell line NIH:OVCAR3. This study investigated the expression level of lysosomal-associated protein transmembrane 4 beta in several ovarian cancer cell lines. RNA interference mediated by recombinant lentiviral vectors expressing an artificial lysosomal-associated protein transmembrane 4 beta miRNA was used to induce long-lasting downregulation of lysosomal-associated protein transmembrane 4 beta gene expression in NIH:OVCAR3 cells. Lysosomal-associated protein transmembrane 4 beta expression as well as the motility, migration potential, and proliferation of the tumor cells was measured by flow cytometry, real-time polymerase chain reaction, Western blot analysis, transwell migration assays, wound healing assays, and cell counting kit-8 assays. In addition, the cell cycle analysis utilized fluorescence-activated cell sorting. Four recombinant plasmid expression vectors encoding premiRNAs against lysosomal-associated protein transmembrane 4 beta (pcDNA-LAPTM4B-miR-1, -2, -3, and-4) were constructed and transfected into 293T cells, which overexpress lysosomal-associated protein transmembrane 4 beta. The recombinant lentiviral vector for lysosomal-associated protein transmembrane 4 beta RNA interference was packaged with pcDNA-LAPTM4B-miR-3, which had the highest interfering efficiency, thereby successfully generating stable transfectants. Compared with the control cells, the LAPTM4B-miRNA-transfected NIH:OVCAR3 cells exhibited significant decreases in cell motility and invasion. Furthermore, LAPTM4B depletion resulted in a significant decrease in proliferating cell nuclear antigen, vascular endothelial growth factor, MMP2, MMP9, and CDK12 expression. We propose that lysosomal-associated protein transmembrane 4 beta expression may be an oncogene-inducing feature of invasive ovarian cancer cells and may be a potential therapeutic target for ovarian cancer treatment.

Clathrin-dependent endocytosis of claudin-2 by DFYSP peptide causes lysosomal damage in lung adenocarcinoma A549 cells

Claudins are tight junctional proteins and comprise a family of over 20 members. Abnormal expression of claudins is reported to be involved in tumor progression. Claudin-2 is highly expressed in lung adenocarcinoma tissues and increases cell proliferation, whereas it is not expressed in normal tissues. Claudin-2-targeting molecules such as peptides and small molecules may be novel anti-cancer drugs. The short peptide with the sequence DFYSP, which mimics the second extracellular loop of claudin-2, decreased claudin-2 content in the cytoplasmic fraction of A549 cells. In contrast, it did not affect the content in the nuclear fraction. The decrease in claudin-2 content was inhibited by chloroquine (CQ), a lysosomal inhibitor, but not by MG-132, a proteasome inhibitor. In the presence of DFYSP peptide and CQ, claudin-2 was co-localized with LAMP-1, a lysosomal marker. The DFYSP peptide-induced decrease in claudin-2 content was inhibited by monodancylcadaverine (MDC), an inhibitor of clathrin-dependent endocytosis. DFYSP peptide increased lysosome content and cathepsin B release, and induced cellular injury, which were inhibited by MDC. Cellular injury induced by DFYSP peptide was inhibited by necrostatin-1, an inhibitor of necrotic cell death, but not by Z-VAD-FMK, an inhibitor of apoptotic cell death. Our data indicate that DFYSP peptide increases the accumulation of the peptide and claudin-2 into the lysosome, resulting in lysosomal damage. Claudin-2 may be a new target for lung cancer therapy.

Lysosomal proteins in cell death and autophagy

Nearly 60 years ago, lysosomes were first described in the laboratory of Christian de Duve, a discovery that significantly contributed to him being awarded a share of the 1974 Nobel Prize in Physiology or Medicine for elucidating 'the structural and functional organization of the cell'. Initially thought of as a simple waste degradation facility of the cell, these organelles recently emerged as signalling centres with connections to major cellular processes. This review provides an overview of the many roles of lysosomal proteins in two of these processes: cell death and autophagy. We discuss both resident lysosomal proteins as well those that temporarily associate with lysosomes to influence autophagy and cell death pathways. Particular focus is given to studies in mammalian cells and in vivo systems.

Lysosome-associated protein transmembrane-4β-35 is a novel independent prognostic factor in small cell lung cancer

The lysosome-associated protein transmembrane-4β-35 (LAPTM4B-35) protein has been indicated to be involved in solid tumors, while its role in small cell lung cancer (SCLC) remains unknown. The aim of this study is to investigate the LAPTM4B-35 protein expression and its clinical and prognostic role in SCLC patients. A total of 88 SCLC patients who underwent radical surgery between 2002 and 2010 were enrolled in the study. The level of messenger RNA (mRNA) and protein was detected from the fresh paired tumor specimens and adjacent normal tissues. The clinicopathological and survival data were collected. And the relationship between LAPTM4B-35 and clinicopathological features was analyzed. The prognostic value of LAPTM4B-35 for SCLC was investigated by univariate and multivariate analyses. The LAPTM4B-35 was overexpressed significantly in SCLC cancer tissues. The elevated protein expression was correlated strongly with clinical stage (p = 0.012) and tumor recurrence (p = 0.023). The 5-year overall survival and disease-free survival (DFS) were significantly worse in the patients with high LAPTM4B-35 level. Multivariate Cox analysis indicated that high LAPTM4B-35 expression was an independent prognostic factor for overall survival (OS) and DFS (p = 0.017 vs p = 0.011). LAPTM4B-35 overexpression was an independent factor in SCLC prognosis, which may be considered a potential useful marker in defining the SCLC prognosis.

The relationship between LAPTM4B polymorphisms and cancer risk in Chinese Han population: a meta-analysis

LAPTM4B is a newly cloned gene that shows an active role in many solid tumors progression in substantial researches, mainly through the autophage function. Accumulated studies have been conducted to determine the association of LAPTM4B polymorphism with cancer risk. While the results are inconsistent, we conducted the meta-analysis to determine the strength of the relationship. Results showed that allele*2 carriers exhibited a significantly increased risk of cancer development with comparison to allele*1 homozygote (for *1/2, OR = 1.55, 95% CI 1.367-1.758; for *2/2, OR = 2.093, 95%CI 1.666-2.629; for *1/2 + *2/2, OR = 1.806, 95%CI 1.527-2.137). We also observed a significant association between *2/2 homozygote and cancer risk with comparison to allele*1 containing genotypes (OR = 1.714, 95%CI 1.408-2.088). Allele*2 is a risk factor for cancer risk (OR = 1.487, 95%CI 1.339-1.651). Stratified analysis by tumor type exhibits the significant association of this genetic variants with various cancers. In conclusion, LAPTM4B polymorphism is associated with cancer risk and allele*2 is a risk factor.

A kinase-independent role for EGF receptor in autophagy initiation

The epidermal growth factor receptor (EGFR) is upregulated in numerous human cancers. Inhibition of EGFR signaling induces autophagy in tumor cells. Here, we report an unanticipated role for the inactive EGFR in autophagy initiation. Inactive EGFR interacts with the oncoprotein LAPTM4B that is required for the endosomal accumulation of EGFR upon serum starvation. Inactive EGFR and LAPTM4B stabilize each other at endosomes and recruit the exocyst subcomplex containing Sec5. We show that inactive EGFR, LAPTM4B, and the Sec5 subcomplex are required for basal and starvation-induced autophagy. LAPTM4B and Sec5 promote EGFR association with the autophagy inhibitor Rubicon, which in turn disassociates Beclin 1 from Rubicon to initiate autophagy. Thus, the oncoprotein LAPTM4B facilitates the role of inactive EGFR in autophagy initiation. This pathway is positioned to control tumor metabolism and promote tumor cell survival upon serum deprivation or metabolic stress.

LAPTM4B-35, a cancer-related gene, is associated with poor prognosis in TNM stages I-III gastric cancer patients

Background

Lysosome-associated transmembrane protein 4β-35 (LAPTM4B-35), a member of the mammalian 4-tetratransmembrane spanning protein superfamily, has been reported to be overexpressed in several cancers. However the expression of LAPTM4B-35 and its role in the progression of gastric cancer (GC) remains unknown. The aim of this study was to investigate LAPTM4B-35 expression in GC, its potential relevance to clinicopathologic parameters and role of LAPTM4B-35 during gastric carcinogenesis.

Methods

In the present study, paraffin-embedded specimens with GC (n = 240, including 180 paired specimens) and 24 paired fresh frozen tissues were analyzed. qRT-PCR and immunohistochemistry (IHC) were used to analyze the expression of LAPTM4B-35 in GC. The effects of LAPTM4B-35 on GC cell proliferation, migration and invasion were determined by overexpression and knockdown assays.

Results

IHC showed that LAPTM4B-35 was expressed in 68.3% (123/180) of GC tissues, while in 16.1% (29/180) of their paired adjacent noncancerous gastric tissues (P = 0.000). LAPTM4B-35 mRNA levels in GC tissues were also significantly elevated when compared with their paired adjacent noncancerous tissues (P = 0.017). Overexpression of LAPTM4B-35 was significantly associated with degree of differentiation, depth of invasion, lymphovascular invasion and lymph node metastasis (P<0.05). Kaplan-Meier survival curves revealed that patients with LAPTM4B-35 expression had a significant decrease in overall survival (OS) in stages I-III GC patients (P = 0.006). Multivariate analysis showed high expression of LAPTM4B-35 was an independent prognostic factor for OS in stage I-III GC patients (P = 0.025).

Conclusion

These findings indicate that LAPTM4B-35 overexpression may be related to GC progression and poor prognosis, and thus may serve as a new prediction marker of prognosis in GC patients.

Differential expression of lysosome-associated protein transmembrane-4 beta (LAPTM4B) in granulosa cells of ovarian follicles and in other bovine tissues

Background

LAPTM4B is a member of the lysosome-associated transmembrane protein superfamily that is differentially expressed in normal human tissues and upregulated in various types of carcinomas. These proteins are thought to be involved in the regulation of cell proliferation and survival. The objective of this study was to investigate the expression of bovine LAPTM4B during ovarian follicular development and in various bovine tissues.

Methods and results

Northern blot analysis revealed a 1.8 kb transcript, with highly variable steady state levels among tissues. RT-PCR analysis showed that LAPTM4B mRNA transcripts were low in granulosa cells of small antral follicles, increased in large dominant follicles, and decreased in ovulatory follicles following injection of human chorionic gonadotropin (hCG; P < 0.003). Ovulatory follicles collected at various times after hCG injection revealed a significant reduction of LAPTM4B mRNA starting at 18 h post-hCG (P < 0.029). Immunobloting analysis using antibodies generated against bovine LAPTM4B recognized proteins of 26.3 and 31.5 kDa in granulosa cells of developing follicles and corpus luteum. Further analyses of affinity-purified His-tag LAPTM4B overexpressed in HEK cells showed that the 31.5 kDa protein represented the ubiquinated isoform of the 26.3 kDa native protein. The 26.3 kDa protein was differentially expressed showing highest amounts in dominant follicles and lowest amounts in ovulatory follicles 24 h post-hCG. Immunohistochemical analyses of LAPTM4B showed marked heterogeneity of labeling signal among tissues, with LAPTM4B mainly localized to perinuclear vesicles, in keeping with its putative lysosomal membrane localization.

Conclusion

This study reports for the first time that bovine LAPTM4B in granulosa cells is present in both unubiquinated and ubiquinated forms, and is differentially expressed in developing ovarian follicles, suggesting a possible role in terminal follicular growth.