The calcium (Ca²⁺)-dependent membrane-binding Annexin A6 (AnxA6), is a multifunctional, predominantly intracellular scaffolding protein, now known to play relevant roles in different cancer types through diverse, often cell-type-specific mechanisms. AnxA6 is differentially expressed in various stages/subtypes of several cancers, and its expression in certain tumor cells is also induced by a variety of pharmacological drugs. Together with the secretion of AnxA6 as a component of extracellular vesicles, this suggests that AnxA6 mediates distinct tumor progression patterns via extracellular and/or intracellular activities. Although it lacks enzymatic activity, some of the AnxA6-mediated functions involving membrane, nucleotide and cholesterol binding as well as the scaffolding of specific proteins or multifactorial protein complexes, suggest its potential utility in the diagnosis, prognosis and therapeutic strategies for various cancers. In breast cancer, the low AnxA6 expression levels in the more aggressive basal-like triple-negative breast cancer (TNBC) subtype correlate with its tumor suppressor activity and the poor overall survival of basal-like TNBC patients. In this review, we highlight the potential tumor suppressor function of AnxA6 in TNBC progression and metastasis, the relevance of AnxA6 in the diagnosis and prognosis of several cancers and discuss the concept of therapy-induced expression of AnxA6 as a novel mechanism for acquired resistance of TNBC to tyrosine kinase inhibitors.

The present studies were conducted to evaluate key serum proteins and other components that mediate anchorage-independent growth (3-D growth) of LNCaP prostate cancer cells as spheroids. The cells were cultured on ultra-low attachment plates in the absence and presence of fetuin-A and with or without extracellular vesicles. The data show that fetuin-A (alpha 2HS glycoprotein) is the serum protein that mediates 3-D growth in these cells. It does so by sequestering extracellular vesicles of various sizes on the surfaces of rounded cells that grow as spheroids. These vesicles in turn transmit growth signals such as the activation of AKT and MAP kinases in a pattern that differs from the activation of these key growth signaling pathways in adherent and spread cells growing in 2-D. In the process of orchestrating the movement and disposition of extracellular vesicles on these cells, fetuin-A is readily internalized in adhered and spread cells but remains on the surfaces of non-adherent cells. Taken together, our studies suggest the presence of distinct signaling domains or scaffolding platforms on the surfaces of prostate tumor cells growing in 3-D compared to 2-D.

Background: Polybacterial infections associated with periodontitis are increasingly linked to systemic vascular complications, yet the underlying endothelial mechanisms remain unclear. This study investigated how a consortium of red-complex bacteria (Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola) and orange complex (Fusobacterium nucleatum) affects oxidative stress, inflammation, metabolism, and apoptosis in endothelial cells, and whether L-Sepiapterin [a tetrahydrobiopterin (BH4) precursor via salvage pathway] or bardoxolone methyl (CDDO-Me) [a potent nuclear factor erythroid 2-related factor 2 (Nrf2) activator)] could provide protection. Methods: Human umbilical vein endothelial cells (HUVECs) were infected for 12–72 h and treated with L-Sepiapterin or CDDO-Me. Nitric oxide (NO), BH4, and reactive oxygen species (ROS) levels were quantified, and mRNA expression of key genes regulating nitric oxide synthase activity, antioxidant defense, inflammation (TLR4/NF-κB, cytokines), metabolism (PI3K-AKT-PEA-15), and apoptosis (FAS–caspase pathway) was analyzed. Results: Infection markedly reduced NO and BH4, elevated ROS, activated TLR4/NF-κB and proinflammatory cytokines, disrupted PI3K/AKT signaling, and triggered endothelial apoptosis. Treatments with L-Sepiapterin and CDDO-Me restored NO bioavailability, reduced oxidative and inflammatory responses, normalized metabolic gene expression, and attenuated apoptosis, with CDDO-Me showing more promising effects. This study provides the mechanistic insight linking periodontal polybacterial infection to endothelial dysfunction and metabolic impairment such as diabetes, suggesting that redox-modulating strategies such as L-Sepiapterin and CDDO-Me may help prevent vascular damage associated with periodontal disease.

The productive replication of human immunodeficiency virus type 1 (HIV-1) involves intricate interactions between viral proteins and host cell machinery. However, the contributions of the lysosomal pathways for HIV-1 replication are not fully understood. The goal of this study was to determine the impact of lysosome-targeting compounds on HIV-1 replication and identify the cellular changes that are linked to HIV-1 inhibition using cell culture models of HIV-1 infection. Here, we demonstrate that the treatment of cells with various pharmacological agents known to inhibit lysosomal functions interfere with HIV-1 replication. The vacuolar ATPase (V-ATPase) inhibitor bafilomycin A1 exerted a potent inhibition of HIV-1 replication. Bafilomycin A1 inhibition of HIV-1 was independent of coreceptor tropism of HIV-1. Our data suggest that bafilomycin A1 inhibits HIV-1 at the post-integration steps of the virus life cycle, which include viral gene expression, virus assembly, and/or egress. Analysis of the cellular alterations following bafilomycin A1 treatment indicates that bafilomycin A1 causes a disruption in lysosome structure and functions. Treatment of cells with bafilomycin A1 caused an accumulation of unesterified cholesterol in lysosomes along with the expansion of the lysosomal compartments. Interestingly, the overexpression of the lysosomal cholesterol transporter Niemann–Pick type C 1 (NPC1) partially relieved bafilomycin A1 inhibition of HIV-1. Collectively, our data suggest that bafilomycin A1 inhibits HIV-1 replication in part by disrupting the lysosomal cholesterol trafficking pathway.

Triple-negative breast cancer (TNBC) tumors are typically heterogeneous, predominantly epithelial tissues with discrete patches of mesenchymal-like TNBC cells that differ in their invasiveness, proliferation potential and response to treatment. However, the impact of mesenchymal-like and epithelial TNBC cells on the persistence of chemotherapy-resistant disease remains poorly understood. Mesenchymal-like and epithelial TNBC cell types were detected by multiplex fluorescent immunohistochemistry using antibodies against vimentin, Ki67, and Annexin A6 (AnxA6). Chemotherapy drug-resistant mesenchymal-like and epithelial TNBC cell populations were established by pulse exposure and stepwise dose escalation and validated by 3D cultures and unbiased antibody arrays. Analysis of the response of TNBC tumors treated with six common chemotherapy regimens resulted in 36% complete response and 64% partial response with residual tumor sizes ranging from 0.5 to 37.0 mm. Treatment of TNBC cells with chemotherapy agents led to distinct resistance signatures including downregulation of survivin and upregulation of M-CSF and CXCL8/IL-8 in the model mesenchymal-like TNBC cells, and upregulation of CCL2/MCP-1, CTSS and DKK-1 in model epithelial TNBC cells. The inhibitory phosphorylation of GSK-3β (p-S9) increased in paclitaxel-resistant epithelial cells but decreased in resistant mesenchymal-like TNBC cells. Finally, chemotherapy resistance also activated p90 ribosomal S6 kinases (RSK1/2) in both cell types, while activation of mitogen- and stress-activated kinases (MSK1/2) was only observed in chemotherapy-resistant epithelial TNBC cells. These data reveal that chemotherapy resistance of epithelial and mesenchymal-like TNBC cellular subsets led to distinct profiles of proinflammatory and immune cell chemotactic cytokines and modulated the activities of GSK-3β, p90 RSK1/2 and the related MSK1/2. Targeting these factors and/or the associated signaling pathways may help overcome chemotherapy resistance in TNBC.

Annexin A6 (AnxA6) is a predominantly intracellular calcium-dependent membrane-binding multifunctional protein that is also detected extracellularly and in small extracellular vesicles (exosomes). We previously demonstrated that lapatinib resistance in triple-negative breast cancer (TNBC) cells is associated with AnxA6 upregulation and accumulation of cholesterol in late endosomes. Here, we investigated the fate of AnxA6 and cholesterol in lapatinib-resistant (LAP-R) cells and whether extracellular AnxA6 influences TNBC cell survival. We demonstrate that reduced expression of AnxA6 in LAP-R cells decreased the secretion of MCP-1/CCL2, CCL8/IL-8, DKK1, TSP-1, and OPN by antibody arrays. The secretion of exosomes was also markedly reduced in AnxA6-depleted LAP-R cells, while AnxA6 upregulation stimulated the release of MCP-1 and exosomes. Compared to the respective controls, exosome-associated AnxA6, Rab7, and cholesterol levels were increased in exosomes isolated from AnxA6-expressing LAP-R cells. Mechanistically, we demonstrated by co-immunoprecipitation, GST pulldown, and proximity ligation assays that AnxA6 interacts with SNAP23, a component of the membrane fusion machinery. Finally, blocking extracellular AnxA6 with neutralizing antibodies reduced the viability of AnxA6-low TNBC cells but had little effect on AnxA6-high cells. These findings suggest that extracellular AnxA6 is critical for the survival of highly proliferative AnxA6-low basal-like breast cancer cells and that AnxA6 influences TNBC progression by facilitating the secretion of pro-inflammatory cytokines and cholesterol-enriched exosomes.