3.3 Cumulus complex

[40]. This effect was apparently not consistent with previous observations regarding ATP actions in GLC, but it could be explained by the differential sensitivity of distinct P2 receptors [41]. It is possible that extracellular concentration of ATP and the expression of P2 receptor determine the specific effect of purinergic

Recently it was described that the P2X7 receptor is expressed in mouse luteal cells. Its activation with ATP or BzATP induced an antiproliferative effect by regulating the expression of cyclin D2 and cyclin E2, as well as the phosphorylation of mitogen-activated protein kinase p38 [42]. The result suggests a role for the P2X7

The purinergic system is well represented in GLC. A set of purinergic receptors can modulate basic cellular processes such as proliferation, apoptosis, and steroidogenesis. Growing evidence indicates that purines are important regulators of GLC, but further studies are necessary to reinforce their role in ovarian physiology.

The theca cell layer is an enclosure of cells that surrounds the oocyte during folliculogenesis. It is crucial for maintaining the structural integrity of the follicle as well as for regulating nutrient influx to the avascular GCL [43, 44]. Theca is also the site for the synthesis of steroid hormones, specifically androgens (testosterone and dihydrotestosterone), from acetate or cholesterol into estrogens by granulosa cells in an LH-dependent manner [3]. In addition, theca is the only component of the follicle that is innervated by sympathetic and parasympathetic nervous systems, implicating that this layer functions as a complex integrator of endocrine and neural

When a primary follicle has one or two layers of granulosa cells, an outer granulosa cell layer differentiates into theca cells and, together with recruited theca precursor cells from the stroma, forms the theca cell layer surrounding the oocyte [44, 46]. Some pathophysiological reproduction-related conditions such as infertility or polycystic ovarian syndrome are often the result of dysfunctional activity of

The theca cell layer contacts the rich microvasculature system surrounding each follicle and integrates signals from autonomic innervation [49]. It has been demonstrated that ATP can be co-released with noradrenaline from terminals of the peripheral nervous system [50] and as a result of mechanical stress and changes in cell volume in the oocyte [51]; thus, ATP is a relevant modulator of cellular com-

Purinergic signaling has been described in female reproductive organs, and evidence has shown that ATP in the extracellular space participates in the physiological regulation of the ovary [52]. The first characterization of purinergic signaling in theca cells showed the functional expression, and activation of P2X7 receptors induced cell death, an important mechanism for the onset and physiological progression of follicle atresia [53]. P2X7 receptors have also been associated with the inhibition of luteal cell survival and proliferation, pointedly in small luteal cells,

On the other hand, there is also evidence of the expression of uridine triphosphate (UTP)-sensitive P2Y receptors in theca cells P2Y2 and P2Y6, but not P2Y4 [54]. In this system, stimulation of the expressed P2Y receptors with UTP in cultured theca cells induces the activation of mitogenic-signaling pathways that promote cell proliferation [54]. This finding is a relevant pathophysiological indication, since a slow but maintained proliferation takes place in polycystic ovarian syn-

theca cells during ovulation and follicle development [47, 48].

which have been suggested as theca-derived luteal cells [42].

munication between the theca cell layer and surrounding oocyte cells.

stimulation.

3.2 Theca cells

information [45].

drome [47].

32

receptor in luteal body function.

Adenosine Triphosphate in Health and Disease

The organized structure of the cumulus-enclosed oocyte (CEO) complex corresponds to a specialized GLC surrounding the oocyte. Cumulus cells secrete factors to regulate oocyte maturation and maintain meiotic arrest [56]. It was reported that porcine and murine follicular fluid contains purine compounds that presumably participate in CEO functions, suggesting that it could be an important signal to trigger physiological events [57, 56]. Until recently, purinergic receptors were identified and characterized in CEO, indicating that purinergic signaling participates in CEO physiology [58, 59].

When Eppig et al. discovered that the main components of follicular fluid were nucleotide-derived metabolites [60] and established a relationship with follicle maturation [56, 57], they hypothesized that the local purinergic metabolism in the ovarian fluid can be involved in oocyte maturation or may participate in other aspects of follicular functions.

In these studies, the concentration of nucleotide compounds in murine follicular fluid was determined using high-performance liquid chromatography (HPLC). They identified two purine compounds: hypoxanthine and ADO, with concentrations in ranges of 2–4 and 0.3–0.7 mM, respectively. They also showed that these purines affected the CEO by maintaining the meiotic arrest [56].

Eppig et al. also analyzed the same compounds in porcine follicular fluid; they identified that hypoxanthine at 1.4 mM is the major inhibitory component producing a transient inhibition [61]. This observation contrasted with that of other laboratories which had failed to detect inhibitory activity in follicular fluid.

On the other hand, the cellular effects of purinergic ligands were studied by Ca2+ imaging and electrophysiological approaches. In 2002, two reports elucidated which purinergic receptor was expressed in CEO cells. The first report of P2Y expression in CEO began with an interesting observation that ATP could stimulate an intracellular Ca+2 transient. Experiments using the CEO complex and applying ATP or UTP to the extracellular solution induced a wave of Ca+2 mobilization from cumulus cells to the oocyte through gap junctions, suggesting that ATP was involved in oocyte maturation; moreover, they showed that the response involved the P2Y2 receptor. Since gonadotropin hormones, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) had no effect on Ca+2 changes [59], the authors concluded that ATP was the specific messenger to mediate calcium signals involved in oocyte maturation in the CEO complex.

In another report, the responses generated by a putative purinergic receptor expressed in the CEO were identified and characterized. Employing the voltage clamp technique with two electrodes, the authors observed depolarization responses when extracellular ATP was applied. RT-PCR analysis revealed a product correspondent to the P2Y2 receptor, suggesting that calcium mobilization is dependent on this receptor. A detailed description of distinct currents generated from several ionic channels, such as Ca+2-dependent Cl current, voltage-dependent K<sup>+</sup> currents, and a cationic current mainly driven by Na<sup>+</sup> , was provided. The authors concluded that both purinergic receptors and ionic channels were located in CEO

cells that transmitted their electrical signals to the oocyte via gap junctions [58]. These data support the idea that P2Y2 is an important element in paracrine signaling in regulating CEO complex physiology. Future studies are required to determine the mechanisms involved in CEO functions and oocyte maturation by ATP stimulation.

Ovarian cancer (OC) is considered the most lethal gynecological malignancy, as it is usually diagnosed by the time the tumor has spread to other regions [71]. OC is the seventh most common type of cancer in women, and patients have a low survival rate [72]. Early detection of the disease proves difficult due to unspecific symptoms such as abdominal pain and bloating, whereas advanced stages are confused with gastrointestinal illnesses [73]. Although OC can arise from any of the cells located in the ovary (germ, stroma, and the epithelium), it is acknowledged that almost 90% of OC is derived from the OSE. According to histological characteristics, epithelial ovarian cancer (EOC) is classified in serous, endometrioid, and

Ovarian tumors frequently show disseminated metastasis through ascites in the peritoneal cavity. OC cells are exfoliated from the primary tumor surface to the peritoneal fluid, where they survive as single cells or multicellular aggregates. These cells acquire resistance to anoikis, have stem cell properties, and are plastic in terms of switching between epithelial and mesenchymal phenotypes. In addition to cancer cells, the malignant ascite microenvironment has normal cell types, such as platelets, associated fibroblast, and immune cells, which support and assist cancer cells [75, 76]. This distinctive tumor microenvironment (TME) has paracrine and autocrine signals that support cancer cell proliferation, death evasion, dissemination, and invasion to peritoneal organs. Therefore, understanding cellular and molecular

Purinergic signaling has emerged as an important regulator of tumor growth [77]. The following facts support this assertion: (1) cancer cells increase in metabolic rate [78]; (2) ATP and ADO levels increase in the tumor interstitium [79, 80]; (3) purinergic receptors are expressed in tumor cells [77]; and (4) high CD73 ectonucleotidase expression is a prognosis factor for several types of cancer [81]. Early studies of purinergic signaling in ovarian carcinoma-derived cells (OCDC)

In other OCDC lines (EFO-21 and EFO-27), the presence of P2Y2 receptor was described, and ATP response was monitored through intracellular Ca2+ mobilization and phospholipase D (PLD) activation. In addition, ATP downregulated basal cell proliferation and the proliferation induced by fetal calf serum (FCS) [84]. However, in IOSE-29 (preneoplastic) and IOSE-29EC (neoplastic) cell lines, which also express P2Y2, ATP-stimulated cell growth through the MAPK/ERK kinase activation [85]. These findings showed that ATP effects differ across cell lines, which

Regarding the expression of P2X receptors in OCDC lines, some of the first reports evaluated P2X7 expression in OC biopsies as in SKOV-3 and OVCAR-3 cells. P2X7 expression in human ovaries is confined to the OSE, whereas in EOC biopsies, its expression is wider and localized in transformed zones [86, 87]. Additionally, receptor functionality was evaluated in cell lines, and it was demonstrated that its stimulation induces ERK and AKT phosphorylation, whereas its inhibition reduces cell viability [87]. The latter result was surprising due to previous findings that

could be associated with the activated intracellular mechanism.

associated P2X7 receptor activation with apoptosis.

evaluated the effects of ATP on [Ca2+]i mobilization. It was demonstrated in OVCAR-3 and SKOV-3 cell lines that stimulation with ATP in a μM range induced a biphasic response that consisted in a rapid peak followed by a smaller and sustained plateau phase. In addition, chelation of Ca2+ abrogated the slower response induced by ATP, while the rapid response was maintained. Furthermore, low concentrations of ATP induced SKOV-3 and OVCAR-3 cell proliferation [82, 83]. These pioneer works indicated that OCA cells were responsive to ATP. Furthermore, the biphasic response induced by ATP suggested that these cells could express two types of purinergic receptors: channels operated by ligands and G protein-coupled receptors

mechanisms that promote progression of the disease is very relevant.

clear cells and in mucinous carcinomas [74].

Purinergic Signaling: A New Regulator of Ovarian Function

DOI: http://dx.doi.org/10.5772/intechopen.80756

(GPCRs).

35

### 3.4 Ovarian surface epithelium

Ovarian surface epithelium (OSE) is a monolayer surrounding the ovary. It is composed of a single flat layer of squamous-to-cuboidal epithelial cells featuring distinguished epithelial and mesenchymal markers. OSE is essential during ovulation to promote follicular rupture and release the oocyte [62] and for postovulatory repair of the ovary [63].

Initial and important studies were led by Nelly Auersperg to characterize and identify epithelial and mesenchymal markers, hormonal and growth factor receptors, and physiopathological role, with the idea that OSE is determinant in the onset of ovarian carcinoma [64]. During ovulation, the OSE is involved in three main phases: apex formation, rupture, and repair [65].

The initial phase starts with the actions of luteinizing hormone (LH) and triggers apex formation at the rupture site of the ovarian surface [66]. In the second phase, OSE cells initiate a lytic cascade [62, 67, 68], releasing proteolytic enzymes to degrade the basal lamina, the tunica albuginea, and ovarian cells of the mature follicle. The digested matrix, follicular wall disintegration, and peeling of OSE cells create a wound stigma that facilitates oocyte release. Finally, the repair phase consists in wound closure by postovulatory cell proliferation and migration [69].

Nevertheless, the signaling involved in these phases during ovulation in the OSE is unclear. Purinergic signaling was suggested as a part of intraovarian modulation due to a certain purinergic receptor expressed in the OSE committed in physiological processes. Recently, Vazquez-Cuevas et al. demonstrated the expression of ligand-activated ion channel P2X7 in OSE. In primary cultures of mouse OSE, they observed that BzATP induced a non-desensitizing increment of [Ca+2]I, and this response was blocked with A438079, a selective antagonist of the P2X7 receptor. The functional role of P2X7 was investigated in situ by TUNEL assay. P2X7 stimulation with BzATP induced apoptosis in OSE cells and was differential throughout the oestrous cycle; DNA fragmentation was greater during proestrous [70]. These findings contribute to the idea that local factors, such as ATP, may participate in a proposed cyclic proliferation-death equilibrium of the OSE cell layer in the ovulatory process.

Understanding purinergic signaling and receptor expression in the OSE will help to decipher the mechanisms underlying ovary physiology and pathology. However, more studies need to contribute evidence related to homeostasis and postovulatory repair. Some studies regarding OSE-derived cancer cells will be discussed in the next section.

### 4. Purinergic signaling in ovarian cancer

Although the specific roles for purinergic signaling in ovarian physiology are not completely understood, significant advances have been made in deciphering the role of purines in cancer. Plenty of information supports that purinergic system elements have a role in cancer progression, and this implicates that they are potential therapeutic targets. Here we will address the relevance of the purinergic system in ovarian cancer (OC).

### Purinergic Signaling: A New Regulator of Ovarian Function DOI: http://dx.doi.org/10.5772/intechopen.80756

cells that transmitted their electrical signals to the oocyte via gap junctions [58]. These data support the idea that P2Y2 is an important element in paracrine signaling in regulating CEO complex physiology. Future studies are required to determine the mechanisms involved in CEO functions and oocyte maturation by ATP stimulation.

Ovarian surface epithelium (OSE) is a monolayer surrounding the ovary. It is composed of a single flat layer of squamous-to-cuboidal epithelial cells featuring distinguished epithelial and mesenchymal markers. OSE is essential during ovulation to promote follicular rupture and release the oocyte [62] and for postovulatory

Initial and important studies were led by Nelly Auersperg to characterize and identify epithelial and mesenchymal markers, hormonal and growth factor receptors, and physiopathological role, with the idea that OSE is determinant in the onset of ovarian carcinoma [64]. During ovulation, the OSE is involved in three main

The initial phase starts with the actions of luteinizing hormone (LH) and triggers apex formation at the rupture site of the ovarian surface [66]. In the second phase, OSE cells initiate a lytic cascade [62, 67, 68], releasing proteolytic enzymes to degrade the basal lamina, the tunica albuginea, and ovarian cells of the mature follicle. The digested matrix, follicular wall disintegration, and peeling of OSE cells create a wound stigma that facilitates oocyte release. Finally, the repair phase consists in wound closure by postovulatory cell proliferation and migration [69]. Nevertheless, the signaling involved in these phases during ovulation in the OSE is unclear. Purinergic signaling was suggested as a part of intraovarian modulation due to a certain purinergic receptor expressed in the OSE committed in physiological processes. Recently, Vazquez-Cuevas et al. demonstrated the expression of ligand-activated ion channel P2X7 in OSE. In primary cultures of mouse OSE, they observed that BzATP induced a non-desensitizing increment of [Ca+2]I, and this response was blocked with A438079, a selective antagonist of the P2X7 receptor. The functional role of P2X7 was investigated in situ by TUNEL assay. P2X7 stimulation with BzATP induced apoptosis in OSE cells and was differential throughout the oestrous cycle; DNA fragmentation was greater during proestrous [70]. These findings contribute to the idea that local factors, such as ATP, may participate in a proposed cyclic proliferation-death equilibrium of the OSE cell layer in the ovula-

Understanding purinergic signaling and receptor expression in the OSE will help to decipher the mechanisms underlying ovary physiology and pathology. However, more studies need to contribute evidence related to homeostasis and postovulatory repair. Some studies regarding OSE-derived cancer cells will be discussed in the

Although the specific roles for purinergic signaling in ovarian physiology are not completely understood, significant advances have been made in deciphering the role of purines in cancer. Plenty of information supports that purinergic system elements have a role in cancer progression, and this implicates that they are potential therapeutic targets. Here we will address the relevance of the purinergic system

3.4 Ovarian surface epithelium

Adenosine Triphosphate in Health and Disease

phases: apex formation, rupture, and repair [65].

4. Purinergic signaling in ovarian cancer

repair of the ovary [63].

tory process.

next section.

in ovarian cancer (OC).

34

Ovarian cancer (OC) is considered the most lethal gynecological malignancy, as it is usually diagnosed by the time the tumor has spread to other regions [71]. OC is the seventh most common type of cancer in women, and patients have a low survival rate [72]. Early detection of the disease proves difficult due to unspecific symptoms such as abdominal pain and bloating, whereas advanced stages are confused with gastrointestinal illnesses [73]. Although OC can arise from any of the cells located in the ovary (germ, stroma, and the epithelium), it is acknowledged that almost 90% of OC is derived from the OSE. According to histological characteristics, epithelial ovarian cancer (EOC) is classified in serous, endometrioid, and clear cells and in mucinous carcinomas [74].

Ovarian tumors frequently show disseminated metastasis through ascites in the peritoneal cavity. OC cells are exfoliated from the primary tumor surface to the peritoneal fluid, where they survive as single cells or multicellular aggregates. These cells acquire resistance to anoikis, have stem cell properties, and are plastic in terms of switching between epithelial and mesenchymal phenotypes. In addition to cancer cells, the malignant ascite microenvironment has normal cell types, such as platelets, associated fibroblast, and immune cells, which support and assist cancer cells [75, 76]. This distinctive tumor microenvironment (TME) has paracrine and autocrine signals that support cancer cell proliferation, death evasion, dissemination, and invasion to peritoneal organs. Therefore, understanding cellular and molecular mechanisms that promote progression of the disease is very relevant.

Purinergic signaling has emerged as an important regulator of tumor growth [77]. The following facts support this assertion: (1) cancer cells increase in metabolic rate [78]; (2) ATP and ADO levels increase in the tumor interstitium [79, 80]; (3) purinergic receptors are expressed in tumor cells [77]; and (4) high CD73 ectonucleotidase expression is a prognosis factor for several types of cancer [81].

Early studies of purinergic signaling in ovarian carcinoma-derived cells (OCDC) evaluated the effects of ATP on [Ca2+]i mobilization. It was demonstrated in OVCAR-3 and SKOV-3 cell lines that stimulation with ATP in a μM range induced a biphasic response that consisted in a rapid peak followed by a smaller and sustained plateau phase. In addition, chelation of Ca2+ abrogated the slower response induced by ATP, while the rapid response was maintained. Furthermore, low concentrations of ATP induced SKOV-3 and OVCAR-3 cell proliferation [82, 83]. These pioneer works indicated that OCA cells were responsive to ATP. Furthermore, the biphasic response induced by ATP suggested that these cells could express two types of purinergic receptors: channels operated by ligands and G protein-coupled receptors (GPCRs).

In other OCDC lines (EFO-21 and EFO-27), the presence of P2Y2 receptor was described, and ATP response was monitored through intracellular Ca2+ mobilization and phospholipase D (PLD) activation. In addition, ATP downregulated basal cell proliferation and the proliferation induced by fetal calf serum (FCS) [84]. However, in IOSE-29 (preneoplastic) and IOSE-29EC (neoplastic) cell lines, which also express P2Y2, ATP-stimulated cell growth through the MAPK/ERK kinase activation [85]. These findings showed that ATP effects differ across cell lines, which could be associated with the activated intracellular mechanism.

Regarding the expression of P2X receptors in OCDC lines, some of the first reports evaluated P2X7 expression in OC biopsies as in SKOV-3 and OVCAR-3 cells. P2X7 expression in human ovaries is confined to the OSE, whereas in EOC biopsies, its expression is wider and localized in transformed zones [86, 87]. Additionally, receptor functionality was evaluated in cell lines, and it was demonstrated that its stimulation induces ERK and AKT phosphorylation, whereas its inhibition reduces cell viability [87]. The latter result was surprising due to previous findings that associated P2X7 receptor activation with apoptosis.

An important feature of cancer cells is their ability to migrate and invade secondary organs. One process that allows OC cells to dissociate from primary tumors and survive in peritoneal fluid is the EMT, in which cells switch from an epithelial to a mesenchymal phenotype. Even though this process was first described in embryonic development, today its role in cancer is well accepted. The involvement of purines in EMT has recently been reviewed [9]. It has been proven that P2Y2 stimulation promotes SKOV-3 cell migration, and this effect is associated with epithelial growth factor receptor (EGFR) transactivation. Moreover, expression of EMT inductors such as SNAIL and TWIST was promoted in response to UTP; in addition, the intermediate filament vimentin was augmented by this pharmacological stimulus. Interestingly, addition of apyrase (Apy) to cell medium, with the aim of removing extracellular ATP, decreased cell migration and favored an epitheliallike phenotype due to the relocation of E-cadherin to SKOV-3 cellular junctions [88]. The authors concluded that products obtained by ATP hydrolysis (i.e., ADO) promoted an epithelial phenotype, while P2Y2 activation by ATP analogues promoted a mesenchymal one.

cytoskeleton rearrangement increased [10]. Regarding ADORA2 expression, it has been proven that the addition of NECA reduces cell viability and promotes apoptosis in CAOV-4 and OVCAR-3 cell lines [92]. Activation of ADORA3 in OCA-derived cell lines is associated with apoptosis induction and G1 phase cell cycle arrest [94]. Altogether, the evidence highlights purinergic signaling as an important regulator in

Since Geoffrey Burnstock proposed his purinergic hypothesis in the early 1970s, enormous advances have been achieved in describing the molecular elements that conform the purinergic system and in our understanding of a complex system that is constituted as a continuous metabolic network together with the dynamic events in extracellular signaling. Indeed, the specific actions of purinergic signaling in each system are still being discovered, and its study is a growing field of knowledge. In this chapter, we summarize current knowledge of purinergic signaling in the ovary, where an extensive and specialized expression of purinergic receptors and purinehandling enzymes are observed. The accumulated evidence depicts an emergent and complex system, and at the same time, it raises important questions with deep

This work was funded by PAPIIT-UNAM, number IN201017 to F.G.V.-C. and IN201618 to M.D.-M. and CONACyT number 284-557 to M.D.-M. We thank Jessica

The authors declare that there is no conflict of interest regarding the publication

González Norris for editing the English version of this manuscript.

EOC progression.

5. Conclusion

physiological and pathological implications.

Purinergic Signaling: A New Regulator of Ovarian Function

DOI: http://dx.doi.org/10.5772/intechopen.80756

AC adenylate cyclase ADO adenosine

AMPK AMP kinase Apy apyrase

egr-1 early growth-1

ADP adenosine diphosphate AMP adenosine monophosphate

ATP adenosine triphosphate

CEO cumulus-enclosed oocyte EGFR epithelial growth factor receptor

EOC epithelial ovarian cancer

[Ca2+]i intracellular concentration of Ca2+

EMT epithelial to mesenchymal transition ENPP ectonucleotide pyrophosphatase

ENTPD/CD39 ectonucleoside triphosphate diphosphohydrolase

Acknowledgements

Conflict of interest

of this article.

Abbreviations

37

As previously mentioned, ATP and ADO concentrations increase in cancer. Although ATP is within a low nM range in the healthy interstitium, it increases to μM concentrations (800 μM) near the tumor. This new evidence is relevant because extracellular ATP was monitored in vivo in tumors induced with OVCAR-3 cells in nude mice [80]. Given that extracellular ATP can be hydrolyzed by membrane ectonucleotidases (CD39 breaks ATP into ADP and AMP, and CD73 hydrolyzes AMP to ADO), it could be assumed that the increase in extracellular ATP is directly correlated with the increase in ADO. Even though extracellular ADO has not been measured in tumors in vivo, there is evidence that ADO levels increase in tumor microdialysates and are more abundant at the core of the tumor [79]. In vitro studies have also indicated that OCDC-derived cell lines release ATP to the cell medium [10, 89].

Correspondingly, ADO function has been evaluated in several types of cancer, and an immunosuppressive role has been proposed for this molecule through ADORA2A receptor activation. Specifically, in OCDC cell lines, it has been demonstrated that ADO inhibits antitumor activity of T and natural killer (NK) cells. Moreover, OC biopsies, OC-derived primary cultures, and cell lines express functional CD39 and CD73 [89]. Therefore, strategies such as CD39 and CD73 inhibition with the aim of reducing extracellular ADO concentrations have been performed, and an improved immune response was described using antibodies against these enzymes [89]. CD73 expression has also been associated with poor prognosis in high-grade serous ovarian carcinoma (HGSOC) [90]. Recent evidence demonstrated that CD73 expression in primary-derived OC promotes stemness and tumor growth and proved that this enzyme acts as an EMT promoter [91], allowing us to recognize CD73 as a promising target for OC.

Eventually, ADO in the extracellular milieu activates ADORA receptors (also known as P1), whose expression has also been characterized in different OCDC lines (e.g., in SKOV-3, CAOV-4, and OVCAR-3). Transcript and protein presence of the four ADORA receptors has been described in the previously mentioned cell lines, with ADORA2B and ADORA3 expression being more abundant; their functionality was demonstrated through cAMP measurement in response to specific agonists [92, 93].

SKOV-3 cell incubation with Apy, ADO, or NECA, an ADORA2 receptor agonist, decreases cell migration. A transcriptional study using a microarray demonstrated that treatment with ADO reduced expression of WNT2, WNT6, WNT10B, and FGF-18, all of which activate signaling pathways involved in EMT in OC [10]. On the other hand, expression of ARPC4 and RAPGEG1 transcripts associated with cytoskeleton rearrangement increased [10]. Regarding ADORA2 expression, it has been proven that the addition of NECA reduces cell viability and promotes apoptosis in CAOV-4 and OVCAR-3 cell lines [92]. Activation of ADORA3 in OCA-derived cell lines is associated with apoptosis induction and G1 phase cell cycle arrest [94]. Altogether, the evidence highlights purinergic signaling as an important regulator in EOC progression.
