Campbell-Walsh Urology, 11th Edition

PART IV

Molecular and Cellular Biology

19

Molecular Genetics and Cancer Biology

Mark L. Gonzalgo; Karen S. Sfanos; Alan K. Meeker

Questions

  1. DNA is composed of all of the following elements EXCEPT:
  2. a base, either a purine or a pyrimidine.
  3. a sugar, called ribose.
  4. a phosphate.
  5. two complementary strands.
  6. hydrogen bonds.
  7. The physical chemistry of DNA bases requires:
  8. uracil to form hydrogen bonds with guanine.
  9. a purine to form hydrogen bonds with another purine.
  10. a pyrimidine to form hydrogen bonds with a purine.
  11. adenine to form hydrogen bonds with cytosine.
  12. thymine to form hydrogen bonds with guanine.
  13. Which of the following does DNA gene expression require?
  14. Linear DNA to be converted into linear RNA, a process called translation
  15. Conversion of linear RNA into a linear set of amino acids, a process called transcription
  16. Protein synthesis exclusively within the nucleus
  17. Mitosis
  18. A mechanism to bridge the gap between the genetic code and protein synthesis
  19. Which of the following statements about transcriptional regulation is FALSE?
  20. The two general components involved in transcriptional regulation are specific sequences in the RNA and proteins that interact with those sequences.
  21. In addition to the genetic information carried within the nucleotide sequence of DNA, it provides specific docking sites for proteins that enhance the activity of the transcriptional machinery.
  22. Specific sequences within the promoter or enhancer region of a gene are called response elements.
  23. DNA sequences, often referred to as consensus sequences, are found in many genes and respond in a coordinated manner to a specific signal.
  24. It is an important mechanism to ensure coordinated gene expression.
  25. What is alternative splicing?
  26. A form of protein modification occurring after a mature polypeptide is produced
  27. A modification to DNA during meiosis
  28. A process of including or excluding certain exons in an mRNA transcript
  29. A process in which novel RNA sequences are randomly inserted into a transcript
  30. A method of RNA degradation
  31. Which of the following statements is TRUE regarding the nuclear matrix?
  32. It has the same protein composition in every tissue type.
  33. It is the site of mRNA transcription.
  34. It has the same protein composition whether a cell is proliferating or undergoing differentiation.
  35. It provides a mechanism to trace the cell type of origin for a cancer, because the nuclear matrix is identical within tissue types.
  36. It is a form of DNA.
  37. What happens in the process of translation?
  38. The RNA message of four parts (the nucleotides A, U, C, G) is converted into 20 amino acids by using a functional group of three adjacent nucleotides called a codon.
  39. Each amino acid is encoded by only one codon.
  40. Shifts in the reading frame are of no consequence in the production of the polypeptide chain because of the fidelity of template DNA.
  41. Single-base substitutions always encode for the identical amino acid, known as a polymorphism.
  42. Transfer of genetic information from the DNA to the RNA occurs.
  43. Which of the following statements about ubiquitination is NOT true?
  44. Ubiquitination is an important regulatory mechanism of a cell, used in the efficient disposal of proteins.
  45. A small protein called ubiquitin is linked to a protein, tagging it for destruction.
  46. The proteosome is the site of protein-ubiquitin complex degradation.
  47. The proteosome has a cylindrical shape.
  48. The targeted inhibition of proteosome function appears to enhance cancer progression.
  49. Which of the following statements about oncogenes is TRUE?
  50. They are mutated forms of abnormal genes, known as proto-oncogenes.
  51. They can be produced by an inactivating mutation of a proto-oncogene, resulting in the silencing of the gene.
  52. They can be produced by gene amplification, resulting in many copies of the gene, or by chromosomal rearrangement.
  53. They are always due to retroviruses, capable of inducing malignant transformation of normal cells.
  54. They are endogenous cancer-fighting genes.
  55. Which of the following statements about hypermethylation is TRUE?
  56. It is a direct change to the DNA sequence, similar to a mutation which alters the normal base-pairing.
  57. It occurs exclusively on cytosine nucleotides in the dinucleotide sequence CG.
  58. Somatic methylation of CpG dinucleotides in the regulatory regions of genes is very often associated with increased transcriptional activity, leading to increased expression of that gene.
  59. In cancer, hypermethylation is associated with enhanced activity of oncogenes, and demethylation may be an effective strategy for the treatment of cancer.
  60. It marks cells for ubiquitination.
  61. Von Hippel-Lindau disease predisposes patients to:
  62. epididymal carcinoma.
  63. clear cell renal carcinoma.
  64. papillary renal cell carcinoma.
  65. adrenocortical carcinoma.
  66. all of the above.
  67. Hereditary prostate cancer genes that have been proven to cause prostate carcinoma include:
  68. ELAC2.
  69. MSR1.
  70. RNASEL.
  71. none of the above.
  72. all of the above.
  73. Which of the following hereditary tumor syndromes are associated with genitourinary tumors?
  74. Von-Hippel-Lindau syndrome
  75. Birt-Hogg-Dube syndrome
  76. Beckwith-Wiedemann syndrome
  77. None of the above
  78. All of the above
  79. Which of the following cancer-associated chromosomal abnormalities would be most likely to be associated with inactivation of a tumor suppressor gene?
  80. Inversion
  81. Tetraploidy
  82. Amplification
  83. Deletion
  84. Double minutes
  85. The two main points of control in the cell cycle are:
  86. S and G0.
  87. S and the G2M boundary.
  88. M and the G1S boundary.
  89. G1S and G2M boundaries.
  90. G2and M.
  91. The TP53 tumor suppressor gene plays a critical role in which of the following processes?
  92. Apoptosis
  93. Angiogenesis
  94. DNA replication
  95. Signal transduction
  96. All of the above
  97. INK4 family members inhibit the activity of:
  98. cyclin D/cdk4.
  99. cyclin E/cdk2.
  100. cyclin A/cdk2.
  101. cyclin B/cdc2.
  102. all of the above.
  103. Cyclin-cdk complexes primarily function at the G1S boundary by:
  104. dephosphorylation of RB1.
  105. phosphorylation of MDM2.
  106. dephosphorylation of E2F.
  107. phosphorylation of E2F.
  108. phosphorylation of RB1.
  109. The regulatory proteins at the G2M checkpoint primarily respond to:
  110. hypoxia.
  111. nutrient-poor environment.
  112. DNA damage.
  113. cytokines.
  114. all of the above.
  115. Nucleotide excision repair primarily protects the cell from DNA damage caused by:
  116. reactive oxygen species.
  117. DNA polymerase errors.
  118. double-strand breaks.
  119. ultraviolet light.
  120. all of the above.
  121. Which of the following repair pathways is responsible for repairing double-strand DNA breaks?
  122. MSH2/MSH6
  123. Homologous recombination
  124. Nucleotide excision repair
  125. Mismatch repair
  126. None of the above
  127. Which of the following genes has been linked to double-strand break repair?
  128. TP53
  129. VHL
  130. BRCA1
  131. RB1
  132. PTEN
  133. Procaspases are activated by which of the following?
  134. Phosphorylation
  135. Ubiquitination
  136. Dimerization
  137. Mitochondrial import
  138. Proteolytic cleavage
  139. Ligand-dependent apoptosis is an attractive therapeutic target because activation is:
  140. independent of TP53.
  141. dependent on TP53.
  142. independent of caspases.
  143. dependent on caspases.
  144. dependent on RB1.
  145. The TP53-induced apoptosis is mediated through:
  146. APAF-1/caspase 9.
  147. CD95 receptor.
  148. TRAIL.
  149. Bcl-2.
  150. CDKN1A (p21cip).
  151. Proapoptotic bcl-2 family members function by:
  152. digesting the mitochondria.
  153. increasing the cellular membrane permeability.
  154. increasing the mitochondrial membrane permeability.
  155. directly activating executioner caspases.
  156. increasing nuclear membrane permeability.
  157. The enzyme telomerase immortalizes cells by:
  158. protecting the cells from DNA damage.
  159. stabilizing TP53.
  160. allowing the cell to grow in a nutrient-poor environment.
  161. inhibiting apoptosis.
  162. maintaining chromosomal length.
  163. Telomere loss can lead to all of the following EXCEPT:
  164. irreversible cell cycle exit termed senescence.
  165. apoptosis.
  166. DNA hypomethylation.
  167. chromosomal instability.
  168. increased tumor initiation.
  169. Which of the following chromosomal rearrangements is NOT typically associated with a genitourinary malignancy?
  170. Fusion of BCR to Abl via chromosome translocation
  171. Fusion of TMPRSS2 to ERG via intra-chromosomal deletion
  172. Fusion of MiTF/TFEgene family members via chromosome translocation
  173. Isochromosome 8q
  174. Loss of chromosome 9
  175. An isochromosome of 12p has been identified in which genitourinary carcinoma?
  176. Testis
  177. Prostate
  178. Renal
  179. Bladder
  180. Penile
  181. Which of the following has been most consistently implicated in prostate cancer risk from GWAS studies?
  182. The 8q24 chromosomal region
  183. MSR1
  184. RNASEL
  185. TMPRSS2-ERGfusions
  186. None of the above
  187. What type of genetic alteration in cancer could be identified using next-generation RNA sequencing (RNA-seq)?
  188. MicroRNAs associated with cancer
  189. Noncoding RNAs associated with cancer
  190. Gene fusions
  191. mRNA overexpression in cancer
  192. All of the above

Answers

  1. b. A sugar, called ribose. Ribose is an element of RNA, not DNA.In a rudimentary form, DNA is the fusion of three different elements: a base (either a pyrimidine or a purine), a sugar (in the case of DNA called 2-deoxyribose; for RNA called ribose), and a phosphate (which links individual nucleotides). The repeating connections between the phosphates and the sugars provide the backbone from which the information-carrying bases protrude. In its "resting" or nonreplicating form, this chain of elements forms a helix of two complementary strands; this double helix is held together by the hydrogen bonds.
  2. c. A pyrimidine to form hydrogen bonds with a purine. The double helix is held together by the formation of hydrogen bonds between the pyrimidine on one strand and the purine base on the other.Uracil is in RNA, not DNA. Purines do not form bases with purines. The purine adenine (A) always forms two hydrogen bonds to the pyrimidine thymine (T), and the purine guanine (G) always forms three hydrogen bonds to the pyrimidine cytosine (C), one consequence being that A-T bonding is weaker than G-C bonding.
  3. e. A mechanism to bridge the gap between the genetic code and protein synthesis.The physical locations of DNA and its genetic code and protein synthesis and the manifestation of that code are separate: DNA is in the nucleus, and protein synthesis is cytoplasmic. The DNA message must be converted into mRNA by a process called transcription in the nucleus. The mRNA is transferred into the cytoplasm where the mRNA is converted into a protein by a process called translation.
  4. a. The two general components involved in transcriptional regulation are specific sequences in the RNA and proteins that interact with those sequences. Specific sequences in the DNA called response elements bind to the nuclear proteins that control transcription.Importantly, this provides a mechanism to coordinate gene expression by providing similar docking sites for genes that need to be expressed at specific time points. Although mRNA transcription, stability, transport, and translation are all highly regulated, they are not controlled by the transcriptional machinery binding to specific mRNA sequences.
  5. c. A process of including or excluding certain exons in an mRNA transcript. A specific gene may have multiple similar (not identical) forms (isoforms). This is accomplished by having specific exons included or excluded from the final mRNA transcript. This allows one DNA sequence to produce several protein products that have different functions.It is not a random process but is very tightly regulated to ensure that the correct mRNA transcript is produced in the correct cell at the correct point in time.
  6. b. It is the site of mRNA transcription.
  7. a. The RNA message of four parts (the nucleotides A, U, C, G) is converted into 20 amino acids by using a functional group of three adjacent nucleotides called a codon. There is significant redundancy with several codons encoding for each amino acid.As a result, the RNA sequence between individuals can be different and yet still encode the same amino acid sequence (a polymorphism). However, some polymorphisms do result in amino acid changes. Shifts in reading frame are the most deleterious mutations because they result in a change in all the codons after the insertion/deletion and, as a result, a dramatic change in the amino acid sequence.
  8. e. The targeted inhibition of proteosome function appears to enhance cancer progression.Degradation of proteins in the cell is an active, not passive, process. Ubiquitination is the process by which proteins are tagged for transport to the proteosome for destruction. Perturbation of this process is often found in cancer, and therefore inhibition of ubiquitination is a promising therapy for cancer.
  9. c. They can be produced by gene amplification, resulting in many copies of the gene, or by chromosomal rearrangement. There are at least three ways a proto-oncogene can be converted into an oncogene. First, a mutation can occur within the coding sequence, producing a permanently activated form of the gene. A second mechanism converting a proto-oncogene into an oncogene is through gene amplification. A third mechanism of oncogene formation is through chromosomal rearrangement.
  10. b. It occurs exclusively on cytosine nucleotides in the dinucleotide sequence CG. Hypermethylation is a normal process by which DNA is modified by the addition of a methyl group to a cytosine nucleotide in a CpG DNA sequence. There is no change in DNA sequence. Methylation results in gene silencing,that is, decreased expression of the gene. As a result, hypermethylation in cancer is associated with decreased transcription and, therefore, reduces expression of tumor suppressor genes. Ubiquitination decreases levels of proteins but does so by increasing the degradation of the protein. Although alterations in ubiquitination occur in cancer, they are not directly related to methylation.
  11. b. Clear cell renal carcinoma.VHL is a hereditary tumor syndrome that predisposes patients to clear cell renal carcinoma, retinal angiomas, pheochromocytomas, hemangiomas of the central nervous system, epididymal cystadenomas, and pancreatic islet cell tumors. It is not associated with epididymal, papillary renal cell, or adrenocortical carcinomas.
  12. d. None of the above. All of the genes listed have been linked to prostate cancerby linkage studies examining families with a strong predisposition to prostate cancer and, in some cases, by case control studies examining polymorphisms within these genes. However, no data have conclusively demonstrated that these genes cause prostate cancer.
  13. e. All of the above.Each of these syndromes includes increased risk of specific genitourinary malignancies among their spectra of pathologies.
  14. d. Deletion. A common mechanism of tumor suppressor gene inactivation is through deletion of the gene or a chromosomal region containing the gene.The other abnormalities listed produce either no net loss of genetic material or lead to a gain of genetic material, a finding often associated with increased oncogene activity due to increased copy number of the oncogene.
  15. d. G1S and G2M boundaries.
  16. a. Apoptosis. Active TP53 binds to the promoter region of TP53-responsive genes and stimulates the transcription of genes responsible for cell cycle arrest, repair of DNA damage, and apoptosis.TP53 responds to DNA damage by inducing cell cycle arrest through CDKN1A (p21cip1) and then transcriptionally activating DNA repair enzymes. If the cell cannot arrest growth and/or repair the DNA, TP53 induces apoptosis. Although angiogenesis, DNA replication, and signal transduction are all critical cellular processes, TP53 does not directly influence any of them.
  17. a. Cyclin D/cdk4.The INK4 family of cdk inhibitors directly inhibits the assembly of cyclin D with cdk4 and cdk6 by blocking the phosphorylation of the cyclin D-cdk4/6 complex. This phosphorylation is necessary for activation of the complex.
  18. e. Phosphorylation of RB1.Phosphorylation is the attachment of a phosphate to a protein. It alters the conformation of the protein and therefore is an excellent method of regulating gene function. Cyclin-cdk complexes phosphorylate RB1 or its family members, p107 and p130. Phosphorylated RB1 can no longer bind to members of the E2F family of transcription factors. Free E2F heterodimerizes with DP1 or DP2 and transcriptionally activates genes important in DNA replication, such as DNA polymerase-A, and in the cell cycle, such as E2F-1. Dephosphorylation of RB has the opposite effect. E2F regulation does not occur directly though phosphorylation or dephosphorylation. MDM2 regulates TP53 and is not directly affected by cyclin-cdk complexes.
  19. c. DNA damage.Hypoxia, nutrient-poor environment, and cytokines are all signals to the cell that it is not in an environment that is conducive to cellular division. These signals influence the cell before it invests its energy in replicating the DNA—that is, it is a G1S checkpoint. If DNA damage occurs, it is critical that the errors be repaired before cellular division. Therefore, DNA damage can lead to cell cycle arrest at both the G1S and G2M checkpoints.
  20. d. Ultraviolet light.Nucleotide excision repair (NER) is a major defense against DNA damage caused by ultraviolet radiation and chemical exposure. NER acts on a wide range of alterations that result in large local distortions in DNA by recognizing distortions in the DNA helix, excising the damaged DNA, and replacing it with the correct sequence. Base excision repair is the primary mechanism for repairing damage caused by reactive oxygen species. Mismatch repair is the primary mechanism for polymerase errors. Double-strand break repair is the primary mechanism for repairing double-strand breaks.
  21. b. Homologous recombination.Homologous recombination (HR) is one of two mechanisms for repairing DNA double strand breaks, the other being nonhomologous end joining (NHEJ). In homologous recombination, the normal undamaged sister chromatid is used as a template to repair the damaged segment of DNA.
  22. c. BRCA1. BRCA1 is associated with familial breast and ovarian cancer.It is believed that the breast cancer susceptibility gene BRCA1 (as well as BRCA2) play an important role in homologous recombination as well as sensing DNA damage. Both BRCA1 and BRCA2 are part of an enzymatic complex with RAD51- and BRCA1-associated RING domain 1 (BARD1). This complex is recruited by proliferating cell nuclear antigen (PCNA) to regions that have undergone DNA damage to repair DNA breaks.
  23. e. Proteolytic cleavage. Procaspases are the larger, inactive precursor forms of the caspase proteins.Specific proteolytic cleavage is required for their activation. The caspases themselves are proteases and, once activated, proceed to cleave and activate other caspases, thus facilitating a proteolytic cascade that serves to amplify the initial apoptotic signal.
  24. a. Independent of TP53.The identification of ligand-dependent apoptosis receptors may have a profound impact on therapy. Most cancer therapies (e.g., chemotherapy and external beam radiotherapy) depend on TP53 to induce apoptosis in the cancer cell. Because TP53 is mutated in more than half of malignancies, TP53-independent pathways for apoptosis are of great clinical interest. Because ligand-dependent apoptosis is independent of TP53, these receptors and ligands are attractive and novel treatment targets.
  25. a. APAF-1/caspase 9.The TP53-induced apoptosis is dependent on the APAF-1/caspase 9 activation pathway.
  26. c. Increasing the mitochondrial membrane permeability.Although each proapoptotic bcl-2 family member responds to different stimuli, the principal mechanism by which these family members induce cell death is by increasing mitochondrial membrane permeability.
  27. e. Maintaining chromosomal length. Telomerase immortalizes cells by maintaining the ends of the chromosomes, or telomeres, which normally shorten with each cell division.
  28. c. DNA hypomethylation. Normal cells closely monitor their telomere lengths and, should they fall below a critical threshold length, will initiate either cell senescence or apoptosis.If key players in these responses (e.g., TP53) are mutated, then chromosomal instability may result, contributing to cancer initiation. To date, no strong connection is known for telomere loss and loss of DNA methylation.
  29. a. Fusion of BCR to Abl via chromosome translocation.This particular chromosomal abnormality is typically found in chronic myelogenous leukemia patients, not in solid tumors. TMPRSS2-ERG gene fusions are found in approximately 50% of prostate cancer cases. MiTF/TFE gene family translocations have been associated with a subset of renal cell carcinomas. Isochromosome 8q is found in a subset of prostate cancers and is often associated with the loss of 8p. Loss of chromosome 9 is observed in a subset of urothelial cancers, and enumeration of this chromosome by FISH is one of the components of a molecular test used for detecting bladder cancer.
  30. a. Testis.The urologic malignancy most closely linked to a karyotypic abnormality is a testis tumor. A 12p isochromosome was first identified in a testis tumor in the 1980s, and experimentally this cytogenetic hallmark of testicular tumors has diagnostic and prognostic value.
  31. a. The 8q24 chromosomal region.Systematic review of GWAS studies in prostate cancer indicate that the 8q24 region continues to be the most implicated in prostate cancer risk and among different racial cohorts.
  32. e. All of the above.RNA-seq technologies can sequence all RNA species in a sample in an unbiased manner, with an analysis that is not limited to "annotated" sequences.

Chapter review

  1. Cancer cells have (1) genetic instability, (2) autonomous growth, (3) insensitivity to internal and external antiproliferative signals, (4) resistance to apoptosis, (5) unlimited cell division, (6) angiogenesis, (7) invasive behavior, and (8) the ability to evade the immune system.
  2. RNA contains coding sequences (exons) and noncoding sequences (introns).
  3. Loss of function of both alleles of a tumor suppressor gene is typically required for carcinogenesis.
  4. Tumor suppressor genes normally negatively regulate and control cellular growth. Oncogenes promote cell growth. Oncogenes are mutated forms of normal genes (proto-oncogenes)
  5. Oncogenes often exert their effects by interfering with cell cycle checkpoints and apoptotic pathways.
  6. Certain tumor suppressor genes do not follow the two-hit hypothesis and may be inhibited by one alteration on one allele that inhibits the normal protein from the unaltered allele.
  7. Cyclin-dependent kinases (CDK) are involved in synthetic activities of the cell cycle.
  8. The regulatory portion of the CDK protein is called the cyclinand may also assist in substrate specificity.
  9. The key point in the late G1cell phase at which the cell cycle becomes insensitive to extracellular signals is termed the restriction point. Loss of R-point control is typically due to inactivation of the RB1 pathway. Many cancer cells exhibit loss of R-point control.
  10. If the cell cannot arrest growth or repair DNA damage, TP53often induces apoptosis.
  11. Hypermethylation of CpG islands results in transcriptional downregulation, whereas hypomethylation of these regions increases the potential for gene activity.
  12. Many prostate cancers are thought to harbor some form of a recurrent gene fusion such as TMPRSS2 and ERG.
  13. Spontaneous mutation rate is insufficient to explain the number of mutations observed in cancers. Genetic instability is required.
  14. Family history is one of the strongest predictors of prostate cancer risk.
  15. The VHLgene is found to be mutated in over half of sporadic renal cell carcinoma cases. VHL targets HIF-1 (hypoxia-inducible factor).
  16. Telomeres are structures composed of specialized repetitive DNA complexed with telomere-specific binding proteins located at the ends of every human chromosome and serve to stabilize and protect the end.
  17. Progressive telomere shortening acts as a mitotic clock, signaling cell cycle exit (death) once telomeres reach a shortened threshold length. The majority of cancers have short telomeres but restabilize their telomeres through activation of the enzyme telomerase.
  18. Apoptosis is an orderly process in which the contents of dying cells are degraded, packaged, and then engulfed by neighboring macrophages. This activity does not produce an inflammatory response.
  19. Defects in the apoptotic cascade can profoundly influence tumor response to chemotherapy and radiotherapy.
  20. Effective chemotherapy and radiation therapy in large part are dependent on apoptosis.
  21. Apoptosis is mediated by the caspases.
  22. Large variations in chromosome number and structure are the hallmarks of most solid tumors. The greater these variations, the more aggressive the tumor.
  23. Free radical scavengers such as alpha-tocopherol, vitamin C, carotenoids, bilirubin and urate, and the enzymes superoxide dismutase, glutathione peroxidase, and glutathione transferase detoxify carcinogens.
  24. A specific gene may have multiple similar (not identical) forms (isoforms). This is accomplished by having specific exons included or excluded from the final mRNA transcript. This allows one DNA sequence to produce several protein products that have different functions.