Ovarian cancer (OC) has the highest mortality rate among all gynecologic cancers and is characterized by early peritoneal spread. The growth and development of OC are associated with the formation of ascitic fluid, creating a unique tumor microenvironment. Understanding the mechanisms of tumor progression is crucial in identifying new diagnostic biomarkers and developing novel therapeutic strategies. Exosomes, lipid bilayer vesicles measuring 30–150 nm in size, are known to establish a crucial link between malignant cells and their microenvironment. Additionally, the confirmed involvement of exosomes in carcinogenesis enables them to mediate the invasion, migration, metastasis, and angiogenesis of tumor cells. Functionally active non-coding RNAs (such as microRNAs, long non-coding RNAs, circRNAs), proteins, and lipid rafts transported within exosomes can activate numerous signaling pathways and modify gene expression.
No | Gene Symbol | Uniprot ID | Function |
---|---|---|---|
1 | CD9 | P21926 | Membrane protein. Identified on membranes of oocytes and extracellular exosomes |
2 | HSPA8 | P11142 | Chaperone protein |
3 | PDCD6IP | Q8WUM4 | Involved in sorting of cargo proteins of the MVBs for incorporation into ILVs |
4 | GAPDH | P04406 | Modulates the organization and assembly of the cytoskeleton |
5 | ACTB | P60709 | Protein that polymerizes to produce filaments |
6 | ANXA2 | P07355 | Calcium-regulated membrane-binding protein |
7 | CD63 | P08962 | Cell surface receptor for TIMP1 and plays a role in the activation of cellular signaling cascades AKT, FAK/PTK2 and MAPK |
8 | SDCBP | O00560 | Involved in the trafficking of transmembrane proteins, exosome biogenesis, and tumorigenesis |
9 | ENO1 | P06733 | Involved in glycolysis, growth control, hypoxia tolerance, and allergic responses |
10 | HSP90AA1 | P07900 | Chaperone protein |
11 | TSG101 | Q99816 | The component of the ESCRT-I complex mediates the association between the ESCRT-0 and ESCRT-I complex |
12 | PKM | P14618 | Catalyzes the final rate-limiting step of glycolysis generating ATP |
13 | LDHA | P00338 | Interconverts simultaneously and stereospecifically pyruvate and lactate with concomitant interconversion of NADH and NAD+. |
14 | EEF1A1 | P68104 | Translation elongation factor that catalyzes the GTP-dependent binding of aminoacyl-tRNA (aa-tRNA) to the A-site of ribosomes |
15 | YWHAZ | P63104 | Adapter protein implicated in the regulation of a large spectrum of signaling pathways |
16 | PGK1 | P00558 | Catalyzes one of the two ATP-producing reactions; acts as a polymerase alpha cofactor protein |
17 | EEF2 | P13639 | Catalyzes the GTP-dependent ribosomal translocation step during translation elongation |
18 | ALDOA | P04075 | Plays a key role in glycolysis and gluconeogenesis; scaffolding protein |
19 | HSP90AB1 | P08238 | Chaperone protein |
20 | ANXA5 | P08758 | Acts as an indirect inhibitor of the thromboplastin-specific complex |
Proteomic analysis of exosomes obtained from the SKOV3 and HOSEPiC cell cultures revealed 659 universal proteins out of all 1433 identified exosomal proteins [38][46]. COX2 is one of the most abundant exosomal proteins whose increased expression is associated with hypoxia. Probably, the formation of tumor spheroids and metastasis process are caused by overexpression of this protein [39][47].
Proteins implicated in carcinogenesis have been identified in the cargo of exosomes obtained from the blood plasma and ascitic fluid of OC patients. Specifically, proteins like ATF2, MTA1, ROCK1/2, and CD147 are involved in tumor angiogenesis, while GNA12, EPHA2, and COIA1 promote migration and metastasis. The Nanog protein plays a role in mediating the proliferation and invasion of tumor cells. Exosomes also contain Hsp90 and Hsc70, MHCI, and MHCII. Additionally, various enzymes have been detected in exosomes, such as phosphate isomerase, peroxiredoxins, aldehyde reductase, fatty acid synthase, and Dicer, which is involved in microRNA maturation, among others [40][41][48,49].
The important role of the PKR1 protein in the initiation of angiogenesis in vitro was demonstrated by the study of tumor-associated exosomes derived from A2780 and HO-8910 cell cultures. The PKR1 signaling pathway can be mediated by phosphorylation of STAT3. When the HUVECs cells were treated with the PKR1-positive exosomes, migration and tube formation were increased compared to controls [42][51]. It is known that ascitic fluid can be detected in small amounts even in the early stages of OC. As the tumor grows, ascites become a key component of the tumor microenvironment. Thus, proteomic analysis of exosomes derived from ascites may improve our understanding of OC dissemination as exosomes provide communication between cells and the tumor microenvironment. It has also been shown that up to 40% of the unique proteins of ascitic fluid are part of exosomes [43][52]. The formation of premetastatic niches is one of the key mechanisms of OC progression. Several studies have shown that exosomes secreted by the tumor play an important role in this process. For example, exosomes carry bioactive molecules such as TGFβ, TNFα, interleukins, MMPs, etc. that mediate EMT. Exosomes of cancer-associated fibroblasts are enriched with TGFβ and thus can activate the SMAD pathway in OC cells. This signaling pathway leads to enhanced cell migration and invasion. It’s well-documented that OC, like many other solid tumors, often occurs under hypoxic conditions. Hypoxia impacts various stages of carcinogenesis, including the formation and secretion of tumor-associated exosomes. For instance, hypoxia enhances exosome secretion by promoting the fusion of MVBs with the cell membrane [44][60]. Immunosuppression is crucial for tumor proliferation and metastasis. The ability of exosomes to influence this process in tumor cells has also been shown. For example, exosomes derived from ascitic fluid express the ganglioside GD3 on their surface. This molecule can interact with the T-cell receptor, resulting in the arrest of T cells. In addition to immunosuppressive mechanisms, the Fas ligand on the surface of the OC exosomes can suppress the T-cell receptor expression and mediate the T-cell apoptosis [40][48].In addition to proteins and lipids, exosomes carry functionally active nucleic acids. It has been shown that exosomes have DNA in their crown, but the proportion of such DNA does not exceed 0.025% of blood plasma DNA in healthy women [30][32]. It is also known that exosomes contain various types of RNA: mRNA, microRNA, long noncoding RNA, rRNA, tRNA, circRNA, etc. [45][62]. According to the Exocarta database (www.exocarta.org, accessed on 1 April 2023), exosomes are involved in the transport of more than 2838 microRNAs and 3408 mRNAs. Some researchers also consider lncRNAs and circRNAs as promising diagnostic biomarkers for liquid biopsy due to their ability to influence the carcinogenesis of tumors, including OCs.