Genetics of Cancer Lecture 34 Alterations in different kinds of Genes cause Cancer Oncogenes dominant gain-of-function mutations promote cell transformation Tumor suppressor genes recessive, loss-of-function mutations promote cell transformation Mutator genes Usually recessive, loss-of-function mutations that increase spontaneous and environmentally induced mutation rates Most of the mutations that contribute to cancer occur in somatic cells – but germ line mutations can also contribute egg sperm zygote endoderm colon growth and differentiation mitotic divisions mitotic divisions 2 meiotic divisions gametes (eggs or sperm) Most of the mutations that contribute to cancer occur in somatic cells – but germ line mutations can also contribute egg sperm zygote endoderm colon growth and differentiation mitotic divisions mitotic divisions 2 meiotic divisions gametes (eggs or sperm) germ line Cytoplasmic signal transduction proteins Nuclear proteins Growth Factor Genes Signal Transduction and Growth Regulation Cytoplasmic signal transduction proteins Nuclear proteins Growth Factor Genes Great Targets for Dominant Acting Oncogenes Secreted Growth factors, e.g. EGF, PDGF Specific Receptors for Growth factors e.g., RET, EGFR G-proteins, kinases and their targets e.g., RAS, ABL, (RB) Transcription factors, e.g., MYC, JUN, FOS Receptor Tyrosine Kinases (RTKs) Extracellular domain Cytoplasmic domain Exterior Cytoplasm Kinase active site Transmembrane domain Figure by MIT OCW. Receptor Tyrosine Kinases (RTKs) Images removed due to copyright reasons. Extracellular Growth factor Engages with and dimerizes specific receptors on cell surface Dimerized Receptor activates cascade of molecular events Machinery for increased cell proliferation is mobilized Images removed due to copyright reasons. Please see Figure 1 in Zwick, E., J. Bange and A. Ullrich. Trends Mol Med. 8, no.1 (Jan 2002): 17-23. "Receptor Tyrosine Kinases as Targets for Anticancer Drugs." Receptor Tyrosine Kinases (RTKs) Kinases Trans- cription Factors Images removed due to copyright reasons. Constitutive Activation converts RTKs to Dominant Acting Oncogenes Images removed due to copyright reasons. Please see Figure 2 in Zwick, E., J. Bange and A. Ullrich. Trends Mol Med. 8, no. 1 (Jan 2002):17-23. "Receptor Tyrosine Kinases as Targets for Anticancer Drugs." Genetic alterations leading to Constitutive Activation of RTKs ? Deletion of extracellular domain ? Mutations that stimulate dimerization without ligand binding ? Mutations of Kinase domain ?Overexpression of Ligand ?Overexpression of Receptor Two Classic Examples Her2 receptor EGF receptor Her2 = Human Epidermal growth factor receptor 2 EGFR = Epidermal growth factor receptor Images removed due to copyright reasons. Please see Lodish, Harvey, et. al. Molecular Cell Biology. 5th ed. New York : W.H. Freeman and Company, 2004. EGF Receptors signal through the RAS G-protein Images removed due to copyright reasons. Please see Lodish, Harvey, et. al. Molecular Cell Biology. 5th ed. New York : W.H. Freeman and Company, 2004. Cytoplasmic signal transduction proteins Nuclear proteins Growth Factor Genes Signal Transduction and Growth Regulation Secreted Growth factors, e.g. EGF, PDGF Specific Receptors for Growth factors e.g., RET, EGFR G-proteins and kinases, e.g., RAS, ABL, RB Transcription factors, e.g., MYC, JUN, FOS G-proteins, kinases and their targets e.g., RAS, ABL, RB cABL – A non-receptor, cytoplasmic tyrosine kinase that can be converted into an oncoprotein ? cABL proto-oncogene product signals to many of the same molecules as the RTKs ? Signals cell cycle progression and cell proliferation The Philadelphia Chromosome and Chronic Myeloid Leukemia Images removed due to copyright reasons. Human Chromosome Spread – G-banding Karyotype Images removed due to copyright reasons. Human Chromosome Spread – G-banding Karyotype Images removed due to copyright reasons. The Philadelphia Chromosome created by a Translocation between Chrs 9 and 22 Chronic Myeloid Leukemia Images removed due to copyright reasons. The Philadelphia Chromosome and Chronic Myeloid Leukemia Images removed due to copyright reasons. The Philadelphia Chromosome and Chronic Myeloid Leukemia Images removed due to copyright reasons. Please see Lodish, Harvey, et. al. Molecular Cell Biology. 5th ed. New York : W.H. Freeman and Company, 2004. Fusion Protein Uncontrolled ABL Kinase Activity and Signal Transduction Chronic Myeloid Leukemia Images removed due to copyright reasons. Please see Lodish, Harvey, et. al. Molecular Cell Biology. 5th ed. New York : W.H. Freeman and Company, 2004. Cytoplasmic signal transduction proteins Nuclear proteins Growth Factor Genes Signal Transduction and Growth Regulation Secreted Growth factors, e.g. EGF, PDGF Specific Receptors for Growth factors e.g., RET, EGFR G-proteins and kinases, e.g., RAS, ABL, RB Transcription factors, e.g., MYC, JUN, FOS G-proteins, kinases and their targets e.g., RAS, ABL, RB Burkitt’s Lymphoma: A chromosome translocation cMYC to be expressed inappropriately in B-cells cMYC drives cells from G1 to S c-myc IgH 14 8 Figure by MIT OCW. Another way that oncogenic transcription factors can be up-regulated: Gene Amplification Chromosome from a TUMOR Blue –staining of all chromosomes Red – staining of chromosome 4 Green – staining of the N-MYC gene (N-MYC and cMYC share many similar proerties) Images removed due to copyright reasons. Please see Lodish, Harvey, et. al. Molecular Cell Biology. 5th ed. New York : W.H. Freeman and Company, 2004. One more example – with an interesting twist A translocation between Chr 14 and Chr 18 to put the BCL2 gene under the strong IgH promoter The BCL2 protein PREVENTS programmed cell death, B cells live longer than normal leading to B-cell Lymphomas lgH enhancer Chromosome 14 Chromosome 18 Translocation 4;18 Breakpoint Breakpoint Rejoining of breakpoints Immunoglobulin heavy chain gene (lgH) Not active in B lymphocytes bcl2 gene Active in B lymphocytes Figure by MIT OCW. What chromosomal events convert proto- oncogenes to dominantly acting oncogenes ? Point mutations (e.g., RAS) ? Deletion mutations (e.g., RTKs) ?Chromosomal translocations that produce novel fusion proteins (e.g., Bcr-Abl) ? Chromosomal translocation to juxtapose a strong promoter upstream and the proto- oncogene such that it is inappropriately expressed (e.g., Bcl2) ? Gene amplification resulting in overexpression (e.g., N-Myc) Cytoplasmic signal transduction proteins Nuclear proteins Growth Factor Genes Signal Transduction and Growth Regulation Secreted Growth factors, e.g. EGF, PDGF Specific Receptors for Growth factors e.g., RET, EGFR Transcription factors, e.g., MYC, JUN, FOS G-proteins, kinases and their targets e.g., RAS, ABL, RB RB – the Retinoblastoma Gene – was the first example of a Tumor Repressor Gene (aka a Recessive Oncogene) Loss of Function Mutations in both RB genes lead to malignant tumors of the retina during the first few years of life Images removed due to copyright reasons. RB prevents cells from leaving G1 to enter S-phase, until the appropriate time Extracellular growth control signals Intracellular quality control checks (DNA synthesis) S Daughter cells M (Mitosis) G 1 G 0 G 2 Figure by MIT OCW. Phosphorylation of RB at the appropriate time in G1 allows release of the E2F Transcription Factor E2F RB RB E2F P P P Cell cycle Kinase Must lose function of both RB alleles in order to lose cell cycle control Transcribes genes for replication and cell proliferation Two ways to get retinal tumors due to loss of RB function Germline mutation Mendelian Sporadic Normal gene Somatic mutation Multiple tumors Bilateral Early-onset Single tumors Unilateral Later-onset Somatic mutation Somatic mutation Figure by MIT OCW. ? In order to lose cell cycle control MUST lose function of both alleles ? But, for Mendelian inheritance of RB, children need only inherit only one non-functional allele ? To explain this the “TWO HIT” hypthesis was proposed ?During development of the retina a second mutation is almost certain to occur ?RB is one of the very few cancers that seems to require defects in only one gene (but in both alleles The Retinoblastoma disease behaves as an autosomal dominant mutation Germline mutation Somatic mutation Multiple tumors Bilateral Early-onset Figure by MIT OCW. How is the second RB allele rendered non-functional? Loss of Heterozygosity LOH This can happen is several ways Mutant RBwt Rb Heterozygous for RB mutation Point Mutation Non-Disjunction Chromosome loss & duplication Chromosome loss Recombination Deletion Interchromosomal Recombination Gene ConversionTranslocation Mutant Rb wt Rb Cytoplasmic signal transduction proteins Nuclear proteins Growth Factor Genes Signal Transduction and Growth Regulation Secreted Growth factors, e.g. EGF, PDGF Specific Receptors for Growth factors e.g., RET, EGFR G-proteins and kinases, e.g., RAS, ABL, RB Transcription factors, e.g., MYC, JUN, FOS G-proteins, kinases and their targets e.g., RAS, ABL, RB Alterations in different kinds of Genes cause Cancer Oncogenes dominant gain-of-function mutations promote cell transformation Tumor suppressor genes recessive, loss-of-function mutations promote cell transformation Mutator genes Usually recessive, loss-of-function mutations that increase spontaneous and environmentally induced mutation rates