Except for early response genes, Myc universally upregulates gene expression. Furthermore, the upregulation is nonlinear. Genes whose expression is already significantly upregulated in the absence of Myc are strongly boosted in the presence of Myc, whereas genes whose expression is low in the absence Myc get only a small boost when Myc is present.[14]
Inactivation of SUMO-activating enzyme (SAE1 / SAE2) in the presence of Myc hyperactivation results in mitotic catastrophe and cell death in cancer cells. Hence inhibitors of SUMOylation may be a possible treatment for cancer.[15]
Amplification of the MYC gene was found in a significant number of epithelial ovarian cancer cases.[16] In TCGA datasets, the amplification of Myc occurs in several cancer types, including breast, colorectal, pancreatic, gastric, and uterine cancers.[17]
In the experimental transformation process of normal cells into cancer cells, the MYC gene can cooperate with the RAS gene.[18][19]
Expression of Myc is highly dependent on BRD4 function in some cancers.[20][21] BET inhibitors have been used to successfully block Myc function in pre-clinical cancer models and are currently being evaluated in clinical trials.[22][23]
Animal Models
During the discovery of Myc gene, it was realized that chromosomes that reciprocally translocate to chromosome 8 contained immunoglobulin genes at the break-point. Enhancers that normally drive expression of immunoglobin genes now lead to overexpression of Myc proto-oncogene in lymphoma cells. To study the mechanism of tumorigenesis in Burkitt lymphoma by mimicking expression pattern of Myc in these cancer cells, transgenic mouse models were developed. Myc gene placed under the control of IgM heavy chain enhancer in transgenic mice gives rise to mainly lymphomas. Later on, in order to study effects of Myc in other types of cancer, transgenic mice that overexpress Myc in different tissues (liver, breast) were also made. In all these mouse models overexpression of Myc causes tumorigenesis, illustrating the potency of Myc oncogene. In a study with mice, reduced expression of Myc was shown to induce longevity, with significantly extended median and maximum lifespans in both sexes and a reduced mortality rate across all ages, better health, cancer progression was slower, better metabolism and they had smaller bodies. Also, Less TOR, AKT, S6K and other changes in energy and metabolic pathways (such as AMPK, more oxygen consumption, more body movements, etc). The study by John M. Sedivy and others used Cre-Loxp -recombinase to knockout one copy of Myc and this resulted in a “Haplo-insufficient” genotype noted as Myc+/-. The phenotypes seen oppose the effects of normal aging and are shared with many other long-lived mouse models such as CR (calorie restriction) ames dwarf, rapamycin, metformin and resveratrol. One study found that Myc and p53 genes were key to the survival of Chronic Myeloid Leukaemia (CML) cells. Targeting Myc and p53 proteins with drugs gave positive results on mice with CML.
SRY (sex determining region Y)-box 2, also known as SOX2, is a transcription factor that is essential for maintaining self-renewal, or pluripotency, of undifferentiated embryonic stem cells. Sox2 has a critical role in maintenance of embryonic and neural stem cells.[3]
Sox2 is a member of the Sox family of transcription factors, which have been shown to play key roles in many stages of mammalian development. This protein family shares highly conserved DNA binding domains known as HMG (High-mobility group) box domains containing approximately 80 amino acids.[3]
Sox2 holds great promise in research involving induced pluripotency, an emerging and very promising field of regenerative medicine
However, a group of researchers concluded that the primary role of Sox2 in embryonic stem cells is controlling Oct4 expression, and they both perpetuate their own expression when expressed concurrently.
In an experiment involving mouse embryonic stem cells, it was discovered that Sox2 in conjunction with Oct4, c-Myc and Klf4 were sufficient for producing induced pluripotent stem cells. The discovery that expression of only four transcription factors was necessary to induce pluripotency allowed future regenerative medicine research to be conducted considering minor manipulations.
Loss of pluripotency is regulated by hypermethylation of some Sox2 and Oct4 binding sites in male germ cells and post-transcriptional suppression of Sox2 by miR134.
Varying levels of Sox2 affect embryonic stem cells’ fate of differentiation. Sox2 inhibits differentiation into the mesendoderm germ layer and promotes differentiation into neural ectoderm germ layer. Npm1/Sox2 complexes are sustained when differentiation is induced along the ectodermal lineage, emphasizing an important functional role for Sox2 in ectodermal differentiation.
A study conducted in Milano, Italy showed, through the development of a knockout model, that deficiency of Sox2 results in neural malformities and eventually fetal death, further underlining Sox2’s vital role in embryonic development.
Neural stem cells
In neurogenesis, Sox2 is expressed throughout developing cells in the neural tube as well as in proliferating central nervous system progenitors. However, Sox2 is downregulated during progenitors’ final cell cycle during differentiation when they become post mitotic. Cells expressing Sox2 are capable of both producing cells identical to themselves and differentiated neural cell types, two necessary hallmarks of stem cells. Proliferation of Sox2+ neural stem cells can generate neural precursors as well as Sox2+ neural stem cell population.
Induced pluripotency is possible using adult neural stem cells, which express higher levels of Sox2 and c-Myc than embryonic stem cells. Therefore, only two exogenous factors, one of which is necessarily Oct4, are sufficient for inducing pluripotent cells from neural stem cells, lessening the complications and risks associated with introducing multiple factors to induce pluripotency.
Eye deformities
Mutations in this gene have been linked with bilateral anophthalmia, a severe structural eye deformity.
Cancer
In lung development, Sox2 controls the branching morphogenesis of the bronchial tree and differentiation of the epithelium of airways. Overexpression causes an increase in neuroendocrine, gastric/intestinal and basal cells. Under normal conditions, Sox2 is critical for maintaining self-renewal and appropriate proportion of basal cells in adult tracheal epithelium. However, its overexpression gives rise to extensive epithelial hyperplasia and eventually carcinoma in both developing and adult mouse lungs.
In squamous cell carcinoma, gene amplifications frequently target the 3q26.3 region. The gene for Sox2 lies within this region, which effectively characterizes Sox2 as an oncogene. Sox2 is a key upregulated factor in lung squamous cell carcinoma, directing many genes involved in tumor progression. Sox2 overexpression cooperates with loss of Lkb1 expression to promote squamous cell lung cancer in mice. Its overexpression also activates cellular migration and anchorage-independent growth.
Sox2 expression is also found in high gleason grade prostate cancer, and promotes castration-resistant prostate cancer growth.
The ectopic expression of SOX2 may be related to abnormal differentiation of colorectal cancer cells.
Sox2 has been shown to be relevant in the development of Tamoxifen resistance in breast cancer.
Regulation by thyroid hormone
There are three thyroid hormone response elements (TREs) in the region upstream of the Sox2 promoter. This region is known as the enhancer region. Studies have suggested that thyroid hormone (T3) controls Sox2 expression via the enhancer region. The expression of TRα1 (thyroid hormone receptor) is increased in proliferating and migrating neural stem cells. It has therefore been suggested that transcriptional repression of Sox2, mediated by the thyroid hormone signaling axis, allows for neural stem cell commitment and migration from the sub-ventricular zone. A deficiency of thyroid hormone, particularly during the first trimester, will lead to abnormal central nervous system development.Further supporting this conclusion is the fact that hypothyroidism during fetal development can result in a variety of neurological deficiencies, including cretinism, characterized by stunted physical development and mental retardation.
Hypothyroidism can arise from a multitude of causes, and is commonly remedied with hormone treatments such as the commonly used Levothyroxine.
Interactions
SOX2 has been shown to interact with PAX6,NPM1,and Oct4. SOX2 has been found to cooperatively regulate Rex1 with Oct3/4 .
Source: Wiki
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