Cellular Oncogenes “Oncogene” is the general term given to genes that are involved in cancer causation. Normal versions of these trans forming genes are present in normal cells and have been designated proto-oncogenes.

The discovery of cellular oncogenes came from studies with acutely transforming retroviruses. It was found that normal cells contained highly related (but not identical) copies of various retrovirus transforming genes; cellular sequences had been captured and incorporated into the retrovirus genomes. Transduction of the cellular genes was probably an accident, as the presence of the cellular sequences is of no benefit to the viruses. Many other known cellular oncogenes that have not been segregated into retrovirus vectors have been detected using molecular methods.

Cellular oncogenes are partly responsible for the molecular basis of human cancer. They represent individual com ponents of complicated pathways responsible for regulating cell proliferation, division, and differentiation and for maintaining the integrity of the genome. Incorrect expression of any component might interrupt that regulation, resulting in uncontrolled growth of cells (cancer). Examples exist of tyrosine-specific protein kinases (eg, src), growth factors (sis is similar to human platelet-derived growth factor, a potent mitogen for cells of connective tissue origin), mutated growth factor receptors (erb-B is a truncated epidermal growth factor receptor), GTP-binding proteins (Ha-ras), and nuclear transcription factors (myc, jun).

The molecular mechanisms responsible for activating a benign proto-oncogene and converting it into a cancer gene vary—but all involve genetic damage. The gene may be over expressed, and a dosage effect of the overproduced oncogene product may be important in cellular growth changes. These mechanisms might result in constitutive activity (loss of nor mal regulation), so that the gene is expressed at the wrong time during the cell cycle or in inappropriate tissue types. Mutations might alter the carefully regulated interaction of a proto-oncogene protein with other proteins or nucleic acids. Insertion of a retroviral promoter adjacent to a cellular oncogene may result in enhanced expression of that gene (ie, “promoter-insertion oncogenesis”). Expression of a cellular gene also may be increased through the action of nearby viral “enhancer” sequences.

Tumor Suppressor Genes

A second class of human cancer genes is involved in tumor development. These are the negative regulators of cell growth, tumor suppressor genes. They were identified because they form complexes with oncoproteins of certain DNA tumor viruses. The inactivation or functional loss of both alleles of such a gene is required for tumor formation—in contrast to the activation that occurs with cellular oncogenes. The prototype of this inhibitory class of genes is the retinoblastoma (Rb) gene. The Rb protein inhibits entry of cells into S phase by binding to key transcription factors that regulate expression of S-phase genes. The function of normal Rb protein is regulated by phosphorylation. The loss of Rb gene function is causally related to the development of retinoblastoma—a rare ocular tumor of children—and other human tumors.

Another crucial tumor suppressor gene is the p53 gene. It also blocks cell cycle progression; p53 acts as a transcription factor and regulates the synthesis of a protein that inhibits the function of certain cell cycle kinases. It also causes cells with DNA damage to undergo apoptosis. The loss of p53 function allows cells with damaged DNA to progress through the cell cycle, leading to the eventual accumulation of genetic mutations. The p53 gene is mutated in over half of all human cancers.

اخر الاخبار

اخبار العتبة العباسية المقدسة

شعبة الشهداء والجرحى تباشر مرحلة التدقيق الشامل لأكثر من 10 آلاف إضبارة مؤرشفة

قسم الشؤون الفكرية يصدر كتابًا تخصصيًّا في إعراب الصحيفة السجادية وبيانها

أكاديمية التطوير الإداري تنظم ورشة عن الإتيكيت الوظيفي لطلبتها

سماحة السيد الصافي يزور معهد الكفيل للنطق والتأهيل المدرسي ويشيد بالدور الإنساني والتربوي لملاكاته

المزيد

الآخبار الصحية

العلاج بالماء البارد.. باحثون يكشفون فوائده الصحية

من دون صالة رياضية.. عادة بسيطة لتحسين الصحة وخسارة الوزن

لصحة القلب وتفادي السرطان.. استهلك هذا النوع من الطعام

دراسة تحذر من خطر شرب القهوة في أكواب البلاستيك

المزيد

الآخبار التكنلوجية

إنجاز طبي تاريخي.. جراحة قلب بلا شق في الصدر

اليابان.. مراحيض توفر فحص للحالة الصحية عبر "تحليل البراز" !

اختراق واسع لمنصة "إنستغرام".. ونشر بيانات على "الدارك ويب"

علماء يحذرون: هكذا سيفنى كوكب الأرض

المزيد

مواضيع ذات صلة

Chronic Myeloid Leukemia, BCR-ABL Gene, and Disease Monitoring

Application of Liquid Biopsy to Non-small- Cell Lung Cancer Lung

Circulating Tumor DNA

Biomarkers in the Blood and in Tissues: A Complementary Approach

Biomarkers in Oncology: An Evolving Concept

Clinical Development of Venetoclax for Acute Myeloid Leukemia

Clinical Development of Oblimersen for Acute Myeloid Leukemia

Modalities for treating cancer

Tumor markers

Proto-oncogenes

Cancer-Predisposing Genes

Stages of Carcinogenesis