The Types of Endometrial Cancer - Essay Example

Endometrial cancer is one of the most common female gynecologic malignancies with recently increasing mortality rate, is reported over the world. In the United States, endometrial cancer is the first common female malignancy and it is showing the second common female cancer in UK. Even though the endometrial cancer is accompanied with high risk of death, the molecular mechanisms of endometrial carcinogenesis are poorly clarified yet. It is developed when the alteration of cells, which are located in the endometrium and the lining of the uterus, is initiated by several genetic aberrations including allelic deletion, mutation of tumour suppressor genes and activation of oncogenes. The most common type of endometrial cancer is endometrioid adenocarcinoma. It is developed in cells that form glands of the endometrium and shows specific features under the microscope. Endometrioid endometrial cancer (EEC) is the most common type of endometrial cancer, which compromises about 75% to 80% of endometrial cancer and usually occurs at the time of, or one to two decades after menopause, and shows most common symptoms with vaginal bleeding. Its clinical behaviour and grade depend on the degree of differentiation. High grade of tumour development are associated with more advanced stage of disease. Endometrial subtype of endometrial cancer (EEC) is estrogen related. It is already well defined that high level of estrogen in patients lead to increase the risk of endometrial adenocarcinoma as estrogen hormone sustains to promote the growth of endometrial cancer cells. That is, the risk of tumour development is associated with an increase in uncontrolled estrogen activity. According to the study of classic model regarding endometrial cancer and breast cancer, estrogen modulates the expression of estrogen responsive downstream effectors by binding to estrogen receptor and induces subsequent reactions through the action of estrogen receptor at the transcriptional level. The second most common form is papillary serous adenocarcinoma, which is composed of about 10% of all endometrial cancers and another form is clear cell adenocarcinoma, which compromises about 4-5% of all endometrial carcinomas. Both papillary serous and clear cell adenocarcinomas show more aggressiveness than endometrioid adenocarcinomas, and can be often detected at advanced stages. Estrogen hormone functions on cell growth and differentiation, mainly in tissues of reproductive system including mammary glands, uterus, vagina and ovaries in female and testis, epididymis and prostate in male. In addition, estrogen acts as maintaining bone density and protecting against osteoporosis. Also, there is evidence that estrogen affects on blood lipids, so it could have effect on cardiac disease. Furthermore, in brain estrogen regulates destructive process, which finally causes dementia. It regulates the gene expression positively or negatively depending on cell types and environmental background. Binding to estrogen receptor that has a role as a nuclear receptor protein, transcription factors, which control the expression of estrogen responsive genes and activate all these estrogen effects. Estrogen affects the expression of genes and cellular phenotypic changes by mainly two ways. One is by diffusing into the cells directly as a non-genomic mechanism and another is by binding to estrogen receptors in the nucleus as a genomic mechanism. Estrogen receptor has two types of isoform. Both estrogen receptors subtypes are members of nuclear receptor super family and acts as ligand inducible transcriptional activator by interacting with specific cis-acting enhancer sequences, so that it is called as estrogen responsive elements (EREs). The activity of binding between estrogen and estrogen receptor activates the dimerisation of estrogen receptors, which sequentially lead to interact between receptor dimmers and promoter regions in DNA of target genes directly to switch on or off the transcription. This reaction is the classic genomic pathway of estrogen effect. Two types of estrogen receptor isoforms a and b share common characteristics both structurally and functionally. Human estrogen receptor α contains 595 amino acids. It has a molecular functional structure consisting of several separable domains, which are able to function independently. From the picture of structure of estrogen receptor α, a central DNA binding domain equivalent to region C and a carboxy-terminal hormone binding domain, which indicates region E, are mostly highly conserved regions to act specific independent transcriptional activation function. ER α stimulates transcription on binding to estrogen response elements within the promoters of estrogen-regulated genes. DNA-binding domain located at N-terminal 180 amino acids, contains transcription activation function AF-1. In addition, ligand-binding domain (hormone binding domain) contains a ligand activated transcription activation function AF-2 sequences required for ligand dependent dimerisation. Both transcription activation functions are able to act independently. It regulates cell proliferation, that is a reason why estrogen receptor α acts as a major role in breast cancer and endometrial cancer progression. Recently, another estrogen receptor subtype, estrogen receptor b, has been identified. Estrogen receptor b has respectively shorter amino acids than estrogen receptor a and DNA binding domain region is highly conserved (95%) between estrogen receptor a and estrogen receptor b. However, the rest of domains between estrogen receptor a and receptor b are less conserved. In contrast with the genomic action of estrogen hormone, a non-genomic estrogen action leads to very rapid response of the intracellular signalling pathway through protein-protein interactions. From the previous studies in which the mechanisms of non-genomic estrogen effect have been described with several mammalian cells, estrogen is considered to activate several intracellular signalling pathways through the estrogen receptor a independent mechanisms, such as protein kinase A (PKA), mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3 kinase (PI3K), which is cascaded to AKT signalling pathway.  Loss of PTEN gene is the earliest detectable genetic indication in the multi-step process leading to endometrioid endometrial cancer. PTEN (Phosphatase and Tensin homologue deleted from chromosome 10), also known as MMAC1 (Mutated in Multiple Advanced Cancers) or TEP1 (TGF β-regulated and Epithelial cell-enriched Phosphatase) is originally identified as a candidate tumour suppressor gene on chromosome 10q23. According to the previous studies, PTEN tumour suppressor gene plays an important role of cell cycle arrest and programmed cell apoptosis as well as regulation of cell adhesion, migration and differentiation. Somatic deletion or mutation on a genomic region of PTEN tumour suppressor gene has been shown in most of human tumour developments including glioblastomas, endometrial, breast and advanced prostate cancers. Understanding of PTEN tumour suppressor gene and the specific well defined signalling pathways in which mutation of PTEN causes the tumour growth reactions may be helpful for predicting factors for tumour aggressiveness and therapy resistance. PTEN gene contains the protein tyrosin phosphatase (PTPs) domain as well as homology of tensin, a cytoskeletal protein. The protein encoded by PTEN tumour suppressor gene, is a member of dual specificity protein phosphatases (DSPs), which function to dephosphorylate serine, threonine and tyrosine residues. The phosphatase domain of PTEN gene is charged of important function in PTEN, which is proved by the fact that most of the point mutations in PTEN tumour suppressor gene detected in very early stage of tumours and in cell lines are confined to exon 5 of PTEN, which encodes this phosphatase domain. However, PTEN gene is very active on highly acidic substrate Phosphatidylinositol-triphosphate (PIP3), which is the main in vivo PTEN substrate. PTEN tumour suppressor gene specifically functions to keep the level of PIP3 very low by cleaving D3 phosphate of PIP3 and transforming PIP3 to PIP2. Usually in the inactive condition of cells, the levels of PIP3 are kept very low but the levels of PIP3 are rapidly increased by the stimulation of growth factor, which is induced by the activation of PI3 kinase. Once PIP3 is accumulated at the membrane, it reactivates proteins containing a pleckstrin homology domain, which binds PIP3. Upon the membrane recruitment, AKT, which is a downstream effector of PI3K, is phosphorylated to be activated. Activated AKT is a well-known survival factor, which has a critical role in controlling cell survival and apoptosis by regulating the amount of release of cytochrome c from mitochondria. In addition, AKT inhibits programmed cell death by phosphorylating and inactivating the proapoptotic factor BAD, Forkhead transcription factors (FKHR) and caspase 9 that appears to be an AKT substrate only in human cells. Overexpression of AKT is strongly associated with tumour development and progression. This is supported by the previous studies in which mutated and deleted PTEN tumour suppressor gene shows many charges in activated PI3K-AKT signalling pathway and human cancer development. AKT has 3 isoforms, such as AKT1, AKT2 and AKT3. AKT1 is a predominant subform in most of tissues. AKT2 shows the highest expression in insulin-responsive tissues. Furthermore, amplification of AKT2 gene has been found in some cases of ovarian cancer, breast cancer and pancreatic cancer.  Activation of AKT component is occurred at mainly two residues, which are at Thr308 by phospholipid binding and activation loop phosphorylation by PDK1 and at Ser472 by phosphorylatioin within carboxy terminus. Recently, many studies have reported the processes between ER α-medicated signals and growth factor-mediated signals. For example, AF-1 transcription activation of estrogen receptor α is enhanced by Mitogen-Activated Protein Kinase, which is rapidly induced by estrogen, especially on the site of serine 118 of ER α. Regarding of endometrial carcinoma, recent studies suggest that estrogen can activate PI3K/AKT pathway by ligand-independent mechanism, which is non-transcriptional in normal endometrial cells. Mitogen Activated Protein Kinases are a family of serine-threonine kinases activated by phosphorylation, which is caused by various mitogen signals. Mitogen Activated Protein Kinase signalling cascade has a major role in modulating signal transduction in eukaryotic cells, such as progression of mitogen-induced cell cycle through the G1 phase, control of embryonic development, programmed cell death and cellular differentiation. This sequential cascade toward estrogen receptor a activation is composed of three kinds of components MAP Kinase, an activator of MAP Kinase (MAP Kinase Kinase or MEK) and a MAP Kinase Kinase Kinase (MEKK). In addition, in mammalian cells three kinds of distinct Mitogen Activated Protein Kinase signal transduction pathways are occurred including extracellular signal-regulated kinases, which is known as ERK or p42/p44 MAPK, stress-activated protein kinases-1 (SAPK 1), which is known as c-jun N-terminal kinase (JNK) and p38 kinases, which is known as SAPK2/RK. ERK1 and ERK2 activated by mitogen are identified as major signalling transducers in cell proliferation. However, SAPKs/JNKs and p38 MAPK are strongly activated by cellular stress inducers and rarely activated by mitogen. After mitogen or stress inducers respectively activate these components, cytosolic proteins are translocated to the nucleus to the activated target proteins and/or transcription factors. Mitogen-Activated Protein Kinases are turned on in the response of dual phosphorylation from the extracellular stimuli. Dual phosphorylation is occurred in activation domain of MAP Kinases at threonine and tyrosine residues. It is turned on in order by dual specificity MAP kinase kinase, which is activated by MAP kinase kinase kinase. There are two kinds of major roles in these regulatory cascades. In the pathways, the information from the upstream components is carried to the targeting effectors and all incoming information is coordinated with the parallel signalling pathways. Moreover, Mitogen-Activated Protein Kinase pathway allows the signal to be amplified and a threshold subject to be generated to keep the multiple activation cascades. (Paul DM, et al., Mitogen Activated Protein Kinase signal transduction pathways in the prostate, Cell Communication and Signalling, 2:5 2004) In general, the processes between MAP Kinase and MAP kinase kinase are highly specific. For example, p42/p44 MAP kinases are activated by MAP/ERK kinases (MEK) 1&2, and p38 MAP kinase is selectively phosphorylated by MAPKK 3&6. Additionally, in usual conditions MAPK 7&4 activate JNK. However, when MAPK 4 is overexpressed, MAPK 4 can activate p38 MAPK. In contrast, the processes, which are occurred downstream of MAP kinase kinase kinase are less clearly identified. In mammalian cells, growth factor and nerve growth factor (NGF) stimulated ERK1 & ERK2, and MAPKK1 & MAPKK2 through receptor tyrosine kinase (RTKs), heterotrimeric G protein-coupled receptor or cytokine receptors. Mitogen-Activated Protein Kinase signalling transduction cascades involve ERK/MAPK superfamily enzymes and are controlled by activities of protein phosphotases. Understanding of pathway for Mitogen-Activated Protein Kinase signalling transduction has a lot of potential to provide rapid improvement on the control of cellular events by growth factors and stresses. Overexpression of different growth factor receptors, such as insulin like growth factor receptor or members of epidermal growth factor family makes cells less sensitive to drugs, so that uncontrolled cell cycles are retained. Insulin like growth factor receptor or erbB2, which is one of epidermal growth factor receptors, utilise several types of signalling pathway. One of them is Mitogen Activated Protein Kinase pathway, which is one of the major routines of the endometrial cancer. And other receptor signals are transmitted by PI3K-AKT pathway, which is clearly identified above. Inhibiting any steps in both pathways such as Mitogen Activated Protein Kinase and PI3K-AKT pathway can cause cell apoptosis and increase the sensitivity to cytotoxic drugs. In addition, any proteins from any step of both pathways can be therapeutic candidates for treating endometrial cancer. According to the recent decade’s studies and trials, the investigation that certain ligands, such as natural compounds or synthetic drugs as well as estrogen, and pathways are able to alter the activities of estrogen receptor in different ways gives us many clues that new drugs having selective and specific effects on estrogen receptor functions can be developed. In addition, drug development can offer the effective therapy for treatment menopausal symptoms, improvement postmenopausal bone loss and perhaps decrease of the risk of cardiac disease providing the way of optimal replacement of hormone as well as endometrial cancer treatment. This project hypotheses that endometrioid adenocarcinoma of uterus sustains specific phosphorylation procedures on estrogen receptor α that describe ligand independent activation by events on AKT, PI3K and ERa in the status of PTEN tumour suppressor gene and specific proteins from every single step of cascades may provide opportunities for therapeutic development in endometrial cancer. The aim of this investigation is to identify the expression of AKT and its upstream and downstream components especially induced by estrogen by non-transcriptional effect in well or poorly differentiated endometrioid endometrial cancer cell lines and figure out the ability of specific drug triciribine and ICI182,780 to modify the status of proliferation and survival in endometrial cancer cell lines. T riciribine is targeted inhibitors of AKT cascade inducing cell apoptosis and growth arrest in cancer cells with aberrant AKT activity. And ICI182,780, which is called faslodex as well, acts as a potent inhibitor of transcription of estrogen-regulated genes blocking estrogen receptor transactivation coming from both AF-1 and AF-2 domains. In addition, it degrades estrogen receptor with obvious decrease in cellular concentration of estrogen receptor. Furthermore, even though it is very early stage of understanding how drugs like triciribine and faslodex can affect gene expression in endometrial tumour tissues, this investigation may be helpful for predicting factors for tumour aggressiveness and therapy resistance. in addition, other signal pathways, which are occurred on estrogen receptor α, such as PI3K-AKT and MAPK pathway should be considered to understand different functions of estrogen receptors in endometrial cancer or breast cancer. Read More