The protooncogene
The ectonucleoside triphosphate diphosphohydrolase 5 (NTPDase5; EC: 3.6.1.6), also known as CD39L4 (
The
In the first studies, it was not possible to conclude whether the PCPH had nucleotide degrading activity, since it shares the apyrase conserved regions [
The
The major functional difference between the normal NTPDase5 and the mt-PCPH oncoprotein is that the former provides lower levels of protection against apoptotic agents, including chemotherapeutic drugs, and radiation than the latter. This role of mt-PCPH seems to be mediated by its ability to promote a Ras-independent sustained activation of the ERK pathway [
The aim of this work is to provide an overview, in a systematic review format, of the expression profile of the NTPDase5 and mt-PCPH in cancer cell lines and tumor samples, in comparison to healthy tissues, and describe the proposed mechanisms by which the mutated and WT proteins act in the neoplastic development.
This review describes a “literature overview” about PCPH/NTPDase5 in all types of cancer.
We performed an electronic search on January, 2014, for papers indexed in PubMed and Scopus database. The search strategy comprised only the medical subject heading (MeSH) term “ENTPD5 or NTPDase5.” For inclusion in this review, papers had to describe any relation of PCPH/NTPDase5 to cancer. No language restriction was applied. By this search strategy, 55 papers were identified. After reviewing their abstracts, 14 eligible papers were chosen and three citations retrieved from manual search were included, providing 17 papers that examined PCPH/NTPDase5 expression status in cancer (Figure
Methodological flow chart of the search strategy in PubMed and Scopus databases.
Data were extracted from each original study about PCPH/NTPDase5 gene or protein expression in normal and pathological state as well as its isoform expression patterns in tissues and tumor cells.
Thus, it is possible to conclude that the expression of ENTPD5/mt-PCPH in tumors studied so far is highly variable, as described in Tables
NTPDase5 profile expression in tumor cell lines.
Author; |
Tumor cell line | Control group | Methods | NTPDase5 expression | mt-PCPH expression |
---|---|---|---|---|---|
Beckenkamp et al., 2014 [ |
Cervical cancer cell lines SiHa, HeLa, and C33A | Normal immortalized keratinocytes (HaCaT cells) | RT-PCR | Expressed in all cell lines with higher levels in SiHa cells than HeLa, C33A, and HaCaT cells | Not described |
Zadran et al., 2012 [ |
Human brain tumor cell lines U87 and U87vIII | Not described | WB | Expressed in U87 and at higher levels in U87vIII | Not described |
Villar et al., 2007 [ |
Human prostate tumor cells lines LNCaP, C42, and PC3 | Nonneoplastic human prostatic epithelial cells (RWPE-1) | RT-PCR and WB | Not detected in RWPE-1 but it was highly detected in LNCaP and in both C42 and PC3 was expressed at lower levels | Not described |
Regadera et al., 2006 [ |
Testicular germ cell tumors NCCIT (mutant Tp53) and NT2/D1 (wild-type Tp53) | Not described | WB | Both cell lines expressed several NTPDase5-immunorelated polypeptides (ranged 20–90 KDa) | Low molecular-size polypeptides were less abundant in NT2/D1 than NCCIT cells |
Blánquez et al., 2004 [ |
Human benign and malignant neoplastic breast samples | Normal human breast tissue samples | WB | Both normal tissue and benign and malignant breast tumors samples showed the expression of the NTPDase5 protein | Only the more aggressive breast tumor samples expressed the mt-PCPH |
Blánquez et al., 2002 [ |
Cell lines cultured from explants of laryngeal tumors (SCC) at stages II, III, and IV | Primary laryngeal epithelial cells (LECs) from the normal margin of surgical specimens | WB | Expression related directly to the evolution of the three grades of laryngeal dysplasia, characterized by increments of cell proliferation in parallel with changes in epithelial differentiation | LECs expressed more mt-PCPH than normal NTPDase5 and SCCs presented a loss in the mt-NTPDase5 |
Rouzaut et al., 2001 [ |
20 mammary tumor derived cell lines | Not described | WB | Detectable in 8 of the 20 cells lines | The mt-PCPH, after prolonged exposures, was detectable in all but two cell lines |
Rouzaut et al., 2001 [ |
18 tumor cell lines derived from the central or peripheral nervous system | Not described | WB | Absent in 13 cell lines and barely detectable in 4 cell lines | Expressed in 13 cell lines |
Rouzaut et al., 2001 [ |
6 colon tumor cell lines | Not described | WB | Expressed highly in all six cell lines | Expressed in 4 cell lines |
Rouzaut et al., 2001 [ |
5 lung tumor cell lines | Not described | WB | Detectable at low levels in all five cell lines | Detectable at low levels in 4 cell lines |
Rouzaut et al., 2001 [ |
1 pancreas tumor cell line | Not described | WB | Highly expressed | Detectable at low levels |
Legend: U87vII: U87 glioblastoma cells transduced to express the epidermal growth factor receptor vIII; WB: Western blot.
NTPDase5/mt-PCPH profile expression in clinical samples.
Author; |
Tissue study | Methods | Sampling size | Control group | NTPDase5 expression | mt-PCPH expression |
---|---|---|---|---|---|---|
Zadran et al., 2012 [ |
Primary glioblastoma multiforme (GBMs) | Tissue microarrays, IHC, and WB | 140 patients | Adjacent normal brain | Elevated levels were observed in GBM cores when compared to adjacent normal tissues | Not described |
Mikula et al., 2010 [ |
Adenocarcinomas and colonic adenomas | Mass spectrometry and qRT-PCR | 5 adenocarcinomas; 12 colonic adenomas; 4 normal mucosas | Normal mucosa | Continuously downregulated in a progression from normal mucosa to adenocarcinoma | Not described |
Villar et al., 2007 [ |
Prostate normal, hyperplasic, and tumor cells | IHC | 63 patients | Normal human prostate | Not detected in normal prostate, detected slightly in HPB, and elevated in PIN and prostate carcinoma (samples with a |
Not described |
Regadera et al., 2006 [ |
Testicular tumors | IHC | 54 patients | Normal testicular tissue | Increased expression in testicular tumors relative to normal tissue; present in well-differentiated squamous epithelia and lost in dedifferentiated squamous cells | Not described |
Blánquez et al., 2002 [ |
Laryngeal mild, moderate, and severe stages dysplastic lesions | IHC | 59 patients | Normal laryngeal mucosa | Expressed at lower levels in severe than in mild dysplastic cases and at much lower levels than in the normal tissue | Not described |
Blánquez et al., 2004 [ |
Human breast tumors | IHC and WB | 54 patients | Normal human breast samples | Undetectable in normal and benign samples and increase in carcinoma |
Absent in benign human breast and low molecular weight polypeptides in ductal and lobular carcinoma |
Solanas et al., 2002 [ |
Rat mammary benign and malignant tumors induced | IHC and WB | 35 malignant tumors; 19 benign tumors | Normal rat mammary gland | Tumor samples showed higher levels and were more expressed in the malignant tumors | Tumor samples showed decrease in the mt-NTPDase5 expression when compared with the normal tissue |
Legend: HPB: hyperplasia prostate benign; PIN: prostatic intraepithelial neoplasia; IHC: immunohistochemistry; WB: Western blot.
Breast tumors induced in mice exhibited increased expression of the normal NTPDase5 and decreased expression of the mt-PCPH when compared with healthy mammary gland, and this difference was more evident in malignant tumors in comparison to benign tumors [
Testicular germ tumor cell lines NCCIT and NT2/D1 also presented high levels of NTPDase5 and very low levels of mt-PCPH [
Immunohistochemical analysis also identified that, in cases of laryngeal cancer and testicular germ tumor cells, the concentration of NTPDase5 is higher in areas of differentiation and neoplastic transformation, with low proliferation, than in areas with high proliferation rates, raising the hypothesis that this protein acts more in the initial processes of cancer than in well-advanced, malignant neoplastic phenotypes [
Studies with clinical specimens of prostate cancer and prostate tumor cell lines RWPE-1, LNCaP, C4-2, and PC-3 demonstrated that NTPDase5 is not significantly expressed in healthy prostate tissue but is present in cases of benign hyperplasia and is more pronouncedly expressed in tumor samples. Also, this protein was not detected in the tumor cell line PC-3 but was expressed in LNCaP cell line. In addition, a positive relationship between the level of NTPDase5 expression, and especially mt-PCPH expression, and the invasiveness of prostate cancer was found, thus associating the expression of the NTPDase5 more with cancer motility than with its proliferation [
Clinical samples of glioblastoma multiforme (GBMs) showed a higher level of NTPDase5 expression when compared to adjacent normal tissues [
When an increase in either the NTPDase5 or the mt-PCPH expression was present, this was observed as early as nonneoplastic lesions, suggesting that the deregulation of these proteins is involved in the initial stages of neoplastic development. Thus, it is possible to consider the use of the NTPDase5 as a tool for early identification of various neoplastic cells [
Recently, cervical human cancer cells SiHa (HPV 16-positive), HeLa (HPV 18-positive), and C33A (HPV-negative) were shown to present different levels of
The neoplastic transforming activity is the role of the mt-PCPH that represents the major functional difference between the normal protooncogene and mutated active oncogene. It is supposed that this activity is due to the ability of this protein to cause a Ras-independent sustained activation of ERK1 [
Although the normal NTPDase5 lacks the transforming ability, it is suggested that the NTPDase5 and especially the mt-PCPH confer resistance to cells subjected to stress conditions [
One of the cell protection mechanisms against apoptosis afforded by NTPDase5 is through inhibition of mTOR. After cellular exposure to ionizing radiation, mTOR plays a proapoptotic role and this role is antagonized by the expression of mt-PCPH protein or by the overexpression of the normal protein NTPDase5. They are responsible for blocking the activation of mTOR and its translocation from the cytoplasm to the nucleus, preventing the phosphorylation of p53 at Ser18. Phosphorylation of p53 mediates the release of cytochrome c by mitochondria and the subsequent activation of caspase 9/3, inducing the apoptosis [
Integration of the proposed pathways by which the NTPDase5/mt-PCPH acts on the neoplastic progression. Due to the lack of information about the role of these proteins in cancer development and progression, this scheme presents all data published so far, not taking into consideration in which cell the proposed mechanisms were studied although it is possible that some of the contradictions presented may be a direct consequence of this fact. The figure demonstrates how the loss of the tumor suppressor PTEN possibly causes an increase in NTPDase5 expression and an overactive PI3K/AKT pathway. AKT and mTOR regulate cell growth and survival, such as Bcl-2 gene leading to an increase in apoptotic resistance. Furthermore it is also suggested that the NTPDase5 interacts with PKC
It was also observed that the overexpression of the NTPDase5 protein and more significantly the mt-PCPH actually decreases the intracellular concentration of ATP and confers resistance not only to stress-induced apoptosis but also to those induced by chemotherapy. The overexpression of these enzymes increased resistance of prostate tumor cells when in contact with cisplatin and of colorectal carcinoma cells when in contact with oxaliplatin [
The proposed mechanism by which NTPDase5/mt-PCPH increases the neoplastic cell resistance to cisplatin is due to the ability of this protein to prevent the dephosphorylation of the kinase PKC
Fang et al. [
NTPDase5, by activating AKT, also plays a critical role in triggering the Warburg effect, leading to an increase in anaerobic glycolysis even in the presence of oxygen, increasing the levels of lactate and production of important macromolecules for cell proliferation, promoting angiogenesis and metastasis [
In addition to participating in the PI3K/PTEN signaling pathway, which is overactive in approximately 90% of GBMs, NTPDase5 also plays an important role in the development of this cancer. This protein plays a modulatory role in the bioenergetics of this malignancy, increasing the catabolic efficiency of the aerobic glycolysis. In addition, when
Tumors of the respiratory system have a heterogeneity in what concerns the activation of Akt and PTEN inhibition. Those with this signaling pathway being active, however, are more resistant to treatments that involve starvation [
Finally, overexpression of
In most of the types of cancers studied, the NTPDase5/mt-PCPH shows a change in its expression levels even in precursors of the malignant and benign lesions, which makes this protein a potential tool for early diagnosis of tumorigenesis. This enzyme has also been identified as a key element in a number of pathways known to be frequently activated in neoplastic processes and which give tumor cells a survival advantage when compared to healthy cells. In most cases, the participation of the NTPDase5/mt-PCPH occurs with a change in the intracellular ATP concentration and with participation of this enzyme in the phosphorylation and activation processes of proteins with antiapoptotic activity, conferring to the tumor cells resistance against apoptosis by stress or by chemotherapy treatments. The two main pathways related to the NTPDase5/mt-PCPH activity are the mTOR and the PI3K/PTEN signaling pathways, which are directly related, since the inhibition of PTEN results in a PI3K and consequent AKT overactivation, which in turn regulates the growth of tumor cells by different signaling pathways, one being its effect on mTOR (Figure
This review included all the data published so far regarding the role of the proteins NTPDase5/mt-PCPH in cancer development and progression. Due to the scarcity of studies with NTPDase5/mt-PCPH, it is difficult to establish tissue- or cell-type-specific functions. However, it seems relatively well established that
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors thank Dr. Guido Lenz (Laboratório de Sinalização e Plasticidade Celular, UFRGS) for the critical revision of the paper and valuable corrections. Paula Andreghetto Bracco was a recipient of a Master fellowship from CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior); Márcia Rosângela Wink is recipient of research fellowship from CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico); Ana Paula Santin Bertoni is recipient of CAPES-PNPD fellowship. This study was supported by the Pronem-FAPERGS (Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul 11/2072-2), the CNPq (475882/2012-1), and the PROBITEC-CAPES (004/2012).