วัตถุประสงค์ สามารถอธิบายกลไกการเปลี่ยน proto-oncogenes ไปเป็น สามารถอธิบายกลไกการเปลี่ยน proto-oncogenes ไปเป็น oncogenes ได้ oncogenes ได้ สามารถยกตัวอย่าง oncogenes และอธิบายกลไกในการก่อ สามารถยกตัวอย่าง oncogenes และอธิบายกลไกในการก่อ มะเร็งของ oncogenes ได้ มะเร็งของ oncogenes ได้ 7. อองโคยีน (Oncogenes) 7.1 How cellular oncogenes arise เนื้อหา 7.2 Proteins produced by Oncogenes

7. ONCOGENES  Oncogenes are genes whose presence can contribute to uncontrolled cell proliferation and cancer. 7.1 How cellular oncogenes arise  Oncogenes can arise inside cells in two fundamentally different ways. 1. A mechanism involves the participation of viruses that introduce oncogenes into the cells they infect. 2. A series of mechanisms that convert normal cellular genes into oncogenes, often as a result of exposure to carcinogenic agents.

7.1.1 Cellular oncogenes arise from Proto- oncogenes  Proto-oncogenes are normal cellular genes - can be converted into oncogenes - contribute to the regulation of cell proliferation and survival  The mutations of proto-oncogenes can cause cancer. - gain-of-function mutations can induce tumor formation Cellular oncogenes were initially detected in gene transferred experiment  Transfection with tumor cell DNA  The DNA of bladder cancer cells contains genetic information, not present in normal DNA, that is capable of causing cancer (early 1980s, Robert Weinberg and Geoffrey Cooper).

Inducing cancer by DNA transfection. Kleinsmith LJ. Principles of cancer biology. Pearson International Edition. Benjamin Cummings, San Francisco p.37.  RAS oncogene was the first human oncogene to be identified. - DNA sequence is related to v- ras oncogene - ras ---> ”rat sarcoma”  RAS proto-oncogene produces a protein involved in a normal pathway for stimulating cell proliferation.  Oncogenes cannot always be detected using DNA transfection techniques.

 The mechanisms by which cellular oncogenes arise can be grouped into 5 basic categories: 1. point mutation 2. gene amplification 3. chromosomal translocation 4. DNA rearrangement 5. insertional mutagenesis Mechanism 1: Point mutations can convert proto- oncogenes into oncogenes Kleinsmith LJ. Principles of cancer biology. Pearson International Edition. Benjamin Cummings, San Francisco p.160.

 RAS oncogenes produced by point mutation have been detected in many types of cancers. ----> cancers of bladder, lung, colon, pancreas, and thyroid.  Carcinogens such as asbestos, vinyl chloride, and dimethylbenzanthracene each trigger mutations at different locations within the RAS gene Mechanism 2: Gene Amplification can convert proto-oncogenes into oncogenes  DNA located in a specific chromosomal region is replicated numerous time in succession. ----> creating dozens, hundreds, or thousands of copies of the same stretch of DNA.  Chromosome regions containing amplified genes often exhibit a distinctive, abnormal appearance that can be recognized when chromosomes are examined by light microscopy. ----> homogeneously staining regions (HSRs) and double minutes (DMs).

Appearance of chromosome regions containing Amplified DNA  Gene amplification typically yields oncogenes that produce normal proteins but in excessive quantities.  Members of MYC gene family, MYC, MYCL, and MYCN, are among the most commonly encountered oncogenes to arise by gene amplification in human cancers. MYC ----> detected in cancers of the breast, ovary, uterine cervix, lung, and esophagus. MYCN ----> detected in neuroblastoma Kleinsmith LJ. Principles of cancer biology. Pearson International Edition. Benjamin Cummings, San Francisco p.161.

 Tumor with higher copy numbers of the amplified oncogenes tend to exhibit poorer survival rates. ----> more likely to invade and metastasize

7.1.5 Mechanism 3: Chromosomal translocation can convert proto-oncogenes into oncogenes  A piece of one chromosome is broken off and moved to another chromosome. ---> Philadelphia chromosome is associated with 90% of all cases of chronic myelogenous leukemia (CML).  Chromosomal translocations contribute to cancer development by; 1) fusing two gene together to form an oncogene coding for a fusion protein Tyrosine Kinase activity  ABL= Abelson murine leukemia viral oncogene homolog BCR= Breakpoint cluster region

---> Burkitt’s lymphoma; the entire MYC proto-oncogene is moved from chromosome 8 to 14. Highly active antibody genes 2) activating the expression of a proto-oncogene by placing it near a highly active gene

7.1.6 Mechanism 4: Local DNA rearrangements can convert proto-oncogenes into oncogenes  DNA rearrangements disrupt the expression or structure of a proto- oncogene located in that region.  Types of DNA rearrangements; 1) Deletion 2) Insertion 3) Transposition 4) Inversion  DNA rearrangements are frequently detected in human tumor cells, especially in certain types of cancer. ----> thyroid cancers (nearly 50%)

 The TRK oncogene is a fusion gene created by a chromosomal inversion that brings together segments of two genes, TMP3 and NTRK1, residing on the same chromosome.  The fusion protein forms a permanent dimer and its tyrosine kinase is permanently activated.  The fusion protein acts as a permanently activated receptor that continually stimulates cell proliferation, regardless of whether its growth factor is present.

7.1.7 Mechanism 5: Insertional mutagenesis can convert proto-oncogenes into oncogenes  Retrovirus randomly inserts its genes near a proto-oncogene.  The retroviral LTRs may stimulate transcription of the proto- oncogene and trigger overproduction of a normal cellular protein that can contribute to cancer development.

7.1.8 Summary: Cellular oncogenes arise from proto- oncogenes by mechanisms that alter gene structure or expression.

7.2 Proteins produced by Oncogenes  More than 100 oncogenes have been identified to date.  Most of the proteins produced by oncogenes are components of signaling pathways that promote cell proliferation and survival.  Oncogenes disrupt normal signaling mechanisms and foster the excessive proliferation and inappropriate survival of cancer cells by producing abnormal versions or excessive quantities of proteins involved in these pathways.  Proteins produced by oncogenes fall into a variety of categories, including; 1) growth factors 2) receptors 3) enzymes that catalyze protein phosphorylation 4) proteins that bind to and regulate the activity of DNA or other proteins

Kleinsmith LJ. Principles of cancer biology. Pearson International Edition. Benjamin Cummings, San Francisco p.166.

7.2.1 Oncogenes typically code for components of signaling pathways that activate cell proliferation  Growth factor triggers proliferation by activating signaling pathways involving dozens of molecules within the targeted cell. Ras-MAPK Pathway (ERK)

Grb2=growth-factor-receptor-binding protein 2 SOS = ‘son of sevenless’ KSR = kinase suppressor of Ras MEK = MAPK/ERK kinase ERK = extracellular-signal-regulated kinase PAK = p21 rac/cdc42 -activated kinase MAPK = Mitogen-Activated Protein Kinase PP2A = protein phosphatase 2A

7.2.2 Some oncogenes produce growth factors  No growth factor ----> progression through the cell cycle is halted during G1 (at the restriction point) and cell proliferation ceases.  PDGF (platelet-derived growth factor) ----> produced by blood platelets ----> stimulates the proliferation of connective tissue cells  EGF (epidermal growth factor) ----> widely distributed in normal tissues ----> acts on a variety of cell types, mainly (but not exclusively) of epithelial origin  Growth factors stimulate the cell proliferation that is required during events such as embryonic development, tissue regeneration, and wound repair.  Oncogenes v-sis ----> PDGF, simian sarcoma virus, sarcomas (monkeys) COL1A1-PDGFB ----> PDGF, chromosomal translocation, fibrosarcoma

7.2.3 Some oncogenes produce receptor proteins  membrane receptor ----> acts as a protein kinase Examples: ----> v-erb-b ----> RET ----> TRK Examples:----> ERBB2 (member of EGF receptor family) Mutant receptor Amplified receptor

7.2.4 Some Oncogenes produce plasma membrane G proteins  Ras protein----> a member of G proteins  Human RAS ----> HRAS, KRAS, NRAS  RAS mutations are detected in roughly 30% of all human cancers ----> the most commonly encountered type of human oncogene  KRAS ----> the most frequently mutated in human cancers ----> 30% of lung cancers, 50% of colon cancers, 90% of pancreatic cancers  NRAS ----> 25% of acute leukemias  HRAS ----> 10% of bladder cancers

7.2.5 Some Oncogenes produce intracellular protein kinases  Serine/threonine kinases ----> Raf (A-Raf, B-Raf, C-Raf) ----> MEK (MEK1, MEK2) ----> MAPK or ERK  Nonreceptor tyrosine kinases ----> Src kinase: intracellular : SRC mutation (certain colon cancer) : interacts with many growth factor receptors ----> Jak kinase: Jak-Stat signaling pathway : TEL-JAK2 --- translocation chromosome 9 & 12 (certain leukemias) ----> Abl kinase: a cytoplasmic and nuclear protein tyrosine kinase : implicated in processes of cell differentiation, cell division, cell adhesion, and stress response.  contribute to cancer development by stimulating pathways that activate cell proliferation, promote cell survival, or both.

STAT=Signal Transducers and Activators of Transcription v-mpl ---> receptor for Thrombopoietin

7.2.6 Some Oncogenes produce Transcription factors  Transcription factors = proteins that bind to DNA and alter the expression of specific genes.  Jun, Ets ----> stimulate the transcription of early genes that code for other transcription factors (Myc, Fos, and Jun)  Myc, Fos, and Jun ----> stimulate the transcription of delayed genes  E2F ----> one of delayed-gene products  Myc ----> the most common oncoprotein detected in many human and animal cancers. : Burkitt’s lymphoma (chromosomal translocation) ---MYC : small cell lung cancers (gene amplification) --- MYC, MYCN, MYCL : breast and ovarian cancers (gene amplification) --- MYC : neuroblastomas and glioblastomas (gene amplification) --- MYCN  viral oncogenes : c-fos, v-jun, v-myb, v-ets, and v-erb-a

7.2.7 Some Oncogenes produce Cell cycle or Cell death regulators  Cell cycle regulator genes coding for proteins involved in cell proliferation. : cyclin-dependent kinases (Cdks) ---> CDK4 (gene amplification in certain sarcomas and glioblastomas) : cyclins ---> CYCD1 (gene amplification in breast cancers and chromosomal translocation in some lymphomas) : such oncogenes cause the production of excessive amounts or hyperactive versions of Cdk-cyclin complexes, which then stimulate progression through the cell cycle.  Cell death regulator genes coding for proteins involved in cell death. ---> BCL2 (chromosomal translocation in non-Hodgkin’s lymphomas) --- excessive amounts of Bcl2 ---> MDM2 (gene amplification in some human sarcomas) :BCL2 and MDM2 helps cancer cells evade the apoptotic pathways