Targeted therapy for HM1.24 (CD317) on multiple myeloma cells

CD317 maintains proteostasis and cell survival in response to proteasome inhibitors by targeting calnexin for RACK1-mediated autophagic degradation

Unbalanced protein homeostasis (proteostasis) networks are frequently linked to tumorigenesis, making cancer cells more susceptible to treatments that target proteostasis regulators. Proteasome inhibition is the first licensed proteostasis-targeting therapeutic strategy, and has been proven effective in hematological malignancy patients. However, drug resistance almost inevitably develops, pressing for a better understanding of the mechanisms that preserve proteostasis in tumor cells. Here we report that CD317, a tumor-targeting antigen with a unique topology, was upregulated in hematological malignancies and preserved proteostasis and cell viability in response to proteasome inhibitors (PIs). Knocking down CD317 lowered Ca²⁺ levels in the endoplasmic reticulum (ER), promoting PIs-induced proteostasis failure and cell death. Mechanistically, CD317 interacted with calnexin (CNX), an ER chaperone protein that limits calcium refilling via the Ca²⁺ pump SERCA, thereby subjecting CNX to RACK1-mediated autophagic degradation. As a result, CD317 decreased the level of CNX protein, coordinating Ca²⁺ uptake and thus favoring protein folding and quality control in the ER lumen. Our findings reveal a previously unrecognized role of CD317 in proteostasis control and imply that CD317 could be a promising target for resolving PIs resistance in the clinic.

PD-1 Blockade Reinvigorates Bone Marrow CD8+ T Cells from Patients with Multiple Myeloma in the Presence of TGFβ Inhibitors

PURPOSE

Immune-checkpoint inhibitors have shown therapeutic efficacy in various malignant diseases. However, anti-programmed death (PD)-1 therapy has not shown clinical efficacy in multiple myeloma.

EXPERIMENTAL DESIGN

Bone marrow (BM) mononuclear cells were obtained from 77 newly diagnosed multiple myeloma patients. We examined the expression of immune-checkpoint receptors in BM CD8⁺ T cells and their functional restoration by ex vivo treatment with anti-PD-1 and TGFβ inhibitors.

RESULTS

We confirmed the upregulation of PD-1 and PD-L1 expression in CD8⁺ T cells and myeloma cells, respectively, from the BM of multiple myeloma patients. PD-1-expressing CD8⁺ T cells from the BM of multiple myeloma patients coexpressed other checkpoint inhibitory receptors and exhibited a terminally differentiated phenotype. These results were also observed in BM CD8⁺ T cells specific to myeloma antigens NY-ESO-1 and HM1.24. BM CD8⁺ T cells from multiple myeloma patients exhibited reduced proliferation and cytokine production upon T-cell receptor stimulation. However, anti-PD-1 did not increase the proliferation of BM CD8⁺ T cells from multiple myeloma patients, indicating that T-cell exhaustion in multiple myeloma is hardly reversed by PD-1 blockade alone. Intriguingly, anti-PD-1 significantly increased the proliferation of BM CD8⁺ T cells from multiple myeloma patients in the presence of inhibitors of TGFβ, which was overexpressed by myeloma cells.

CONCLUSIONS

Our findings indicate that combined blockade of PD-1 and TGFβ may be useful for the treatment of multiple myeloma.

CD317 Activates EGFR by Regulating Its Association with Lipid Rafts

EGFR regulates various fundamental cellular processes, and its constitutive activation is a common driver for cancer. Anti-EGFR therapies have shown benefit in cancer patients, yet drug resistance almost inevitably develops, emphasizing the need for a better understanding of the mechanisms that govern EGFR activation. Here we report that CD317, a surface molecule with a unique topology, activated EGFR in hepatocellular carcinoma (HCC) cells by regulating its localization on the plasma membrane. CD317 was upregulated in HCC cells, promoting cell-cycle progression and enhancing tumorigenic potential in a manner dependent on EGFR. Mechanistically, CD317 associated with lipid rafts and released EGFR from these ordered membrane domains, facilitating the activation of EGFR and the initiation of downstream signaling pathways, including the Ras-Raf-MEK-ERK and JAK-STAT pathways. Moreover, in HCC mouse models and patient samples, upregulation of CD317 correlated with EGFR activation. These results reveal a previously unrecognized mode of regulation for EGFR and suggest CD317 as an alternative target for treating EGFR-driven malignancies. SIGNIFICANCE: Activation of EGFR by CD317 in hepatocellular carcinoma cells suggests CD317 as an alternative target for treating EGFR-dependent tumors.

BST-2 promotes survival in circulation and pulmonary metastatic seeding of breast cancer cells

Bone marrow stromal antigen 2 (BST-2) mediates various facets of cancer progression and metastasis. Here, we show that BST-2 is linked to poor survival in invasive breast cancer patients as its expression positively correlates with disease severity. However, the mechanisms that drive the pro‐metastatic functions of BST-2 are not fully understood. Correlation of BST-2 expression and tumor aggressiveness was analyzed in human tissue samples. Migration, invasion, and competitive experimental metastasis assays were used to measure the cellular responses after silencing BST-2 expression. Using a mouse model of breast cancer, we show that BST-2 promotes metastasis independent of the primary tumor. Additional experiments show that suppression of BST-2 renders non-adherent cancer cells non-viable by sensitizing cells to anoikis. Embedment of cancer cells in basement membrane matrix reveals that silencing BTS-2 expression inhibits invadopodia formation, extracellular matrix degradation, and subsequent cell invasion. Competitive experimental pulmonary metastasis shows that silencing BST-2 reduces the numbers of viable circulating tumor cells (CTCs) and decreases the efficiency of lung colonization. Our data define a previously unknown function for BST-2 in the i) formation of invadopodia, ii) degradation of extracellular matrix, and iii) protection of CTCs from hemodynamic stress. We believe that physical (tractional forces) and biochemical (ECM type/composition) cues may control BST-2’s role in cell survival and invadopodia formation. Collectively, our findings highlight BST-2 as a key factor that allows cancer cells to invade, survive in circulation, and at the metastatic site.

BST2 promotes cell proliferation, migration and induces NF-κB activation in gastric cancer

OBJECTIVES

To investigate the functional roles of bone marrow stromal cell antigen 2 (BST2) in gastric cancer (GC) cells and its implications in the development of GC patients.

RESULTS

BST2 was frequently overexpressed in GC tissues compared with the adjacent non-tumorous tissues, and high BST2 expression was correlated with tumor stage and lymphatic metastasis. Furthermore, in vitro experiments demonstrated that knockdown of BST2 by siRNA inhibited cell proliferation, induced apoptosis and repressed cell motility in GC cells. In addition, the pro-tumor function of BST2 in GC was mediated partly through the NF-κB signaling.

CONCLUSION

BST2 possesses the oncogenic potential in GC by regulating the proliferation, apoptosis, and migratory ability of GC cells, thereby BST2 could be a potential therapeutic target for the treatment of GC.

Overexpression of the transmembrane protein BST-2 induces Akt and Erk phosphorylation in bladder cancer

Bladder cancer, the majority of which is urothelial carcinoma (UC), is a common malignancy worldwide. Genes encoding transmembrane/secretory proteins expressed specifically in certain cancers may be ideal biomarkers for cancer diagnosis and may represent therapeutic targets. In the present study, the expression and function of the bone marrow stromal cell antigen 2 (BST2) gene was analyzed in UC. Reverse transcription-quantitative polymerase chain reaction demonstrated that expression of BST2 in normal tissue samples was the highest in liver tissue. However, expression of BST2 in UC tissue samples was higher than in normal liver. Immunohistochemical analysis revealed weak or no staining of BST-2 in non-neoplastic mucosa, whereas UC tissue exhibited stronger and more extensive staining compared with non-neoplastic mucosa. BST-2 staining was observed mainly on UC cell membranes. In total, 28 (41%) of 69 UC cases were positive for BST-2. UC cases positive for BST-2 were more frequently T2/3/4 cases [so-called muscle-invasive bladder cancer (MIBC)] than Ta/is/1 cases (P=0.0001). However, Kaplan-Meier analysis demonstrated no association between BST-2 expression and survival. BST2 small interfering RNA (siRNA)-transfected T24 cells exhibited significantly reduced cell growth relative to negative control siRNA-transfected T24 cells. The levels of phosphorylated Akt and extracellular signal-regulated kinase were lower in BST2 siRNA-transfected T24 cells than in control cells. These results suggest the involvement of BST-2 in the pathogenesis of UC. Since BST-2 is expressed on the cell membrane, BST-2 may be a good therapeutic target for MIBC.

CD317 Promotes the survival of cancer cells through apoptosis-inducing factor

BACKGROUND

Low nutrient environment is a major obstacle to solid tumor growth. However, many tumors have developed adaptive mechanisms to circumvent the requirement for exogenous growth factors.

METHODS

Here we used siRNA interference or plasmid transfection techniques to knockdown or enhance CD317 expression respectively, in mammalian cancer cells, and subjected these CD317-manipulated cells to serum deprivation to study the role of CD317 on stress-induced apoptosis and the underlying mechanism.

RESULTS

We report that CD317, an innate immune gene overexpressed in human cancers, protected cancer cells against serum deprivation-induced apoptosis. In tumor cells, loss of CD317 markedly enhanced their susceptibility to serum deprivation-induced apoptosis with no effect on autophagy or caspase activation, indicating an autophagy- and caspase-independent mechanism of CD317 function. Importantly, CD317 knockdown in serum-deprived tumor cells impaired mitochondria function and subsequently promoted apoptosis-inducing factor (AIF) release and nuclear translocation but had little effect on mitochondrial and cytoplasmic distributions of cytochrome C, a pro-apoptotic factor released from mitochondria that initiates caspase processing in response to death stimuli. Furthermore, overexpression of CD317 in HEK293T cells inhibits serum deprivation-induced apoptosis as well as the release and nuclear accumulation of AIF.

CONCLUSION

Our data suggest that CD317 functions as an anti-apoptotic factor through the mitochondria-AIF axis in malnourished condition and may serve as a potential drug target for cancer therapy.

Overexpression of Transmembrane Protein BST2 is Associated with Poor Survival of Patients with Esophageal, Gastric, or Colorectal Cancer

BACKGROUND

Gastrointestinal (GI) cancer, including gastric cancer (GC), colorectal cancer (CRC), and esophageal squamous cell carcinoma (ESCC), is the most common malignancy worldwide. To identify genes that encode transmembrane proteins present in GI cancer, Escherichia coli ampicillin secretion trap libraries were generated from MKN-74 GC cells, and BST2 was identified as overexpressed in GC. This study analyzed the expression and function of the BST2 gene in human GI cancers and examined the relationship between bone marrow stromal antigen-2 (BST-2) expression and GI patient clinicopathologic characteristics.

METHODS

Expression and distribution of BST-2 protein was analyzed by immunohistochemistry in 180 GC cases, 140 CRC cases, and 132 ESCC cases. Cell growth was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

RESULTS

Immunohistochemical analysis of BST-2 in GC tissues showed that 65 (36 %) of 180 GC cases were positive for BST-2. Uni- and multivariate analyses demonstrated that BST-2 expression is an independent prognostic classifier of GC patients. Immunohistochemical analysis showed that 46 % of 140 CRC cases and 27 % of 132 ESCC cases were positive for BST-2. In ESCC, BST-2 expression was an independent prognostic predictor for survival. The growth of BST2 small interfering RNA (siRNA)-transfected GC cells was significantly slower than the growth of negative control siRNA-transfected GC cells. The levels of phosphorylated epidermal growth factor receptor, extracellular signal-regulated kinase, and Akt were lower in BST2 siRNA-transfected GC cells than in control cells.

CONCLUSIONS

The results suggest that BST-2 is involved in tumor progression and serves as an independent prognostic classifier for patients with GC. Because BST-2 is expressed on the cell membrane, BST-2 could be a therapeutic target for GC, CRC, and ESCC.

The role of BST-2/Tetherin in host protection and disease manifestation

Host cells respond to viral infections by activating immune response genes that are not only involved in inflammation, but may also predispose cells to cancerous transformation. One such gene is BST‐2, a type II transmembrane protein with a unique topology that endows it tethering and signaling potential. Through this ability to tether and signal, BST‐2 regulates host response to viral infection either by inhibiting release of nascent viral particles or in some models inhibiting viral dissemination. However, despite its antiviral functions, BST‐2 is involved in disease manifestation, a function linked to the ability of BST‐2 to promote cell‐to‐cell interaction. Therefore, modulating BST‐2 expression and/or activity has the potential to influence course of disease.