Lecture 10 - Cell Cycle, Oncogenes, Apoptosis

What is the fundamental method by which all living things are propagated?

Cell Division or Cell Cycle

An adult human must generate many millions of new cells per second simply to maintain _________ and the status quo.

homeostasis

What are the three universal requirements of the cell cycle?

1. Faithful replication of the DNA

2. Equal segregation of replicated chromosomes into two separate daughter cells

3. complex set of cytoplasmic & nuclear processes have to be coordinated with one another

True or False? The current focus of the cell cycle revolves around chromosomes and centromeres

False - this was the focus in the past

The ____ _____________ system is the chain of proteins that control the cell cycle and encompasses the current focus of cell cycle understanding

cell cycle-control

What are the fours phases of the cell cycle?

1. G1

2. S

3. G2

4. M

Cell cycle typically lasts for about ________ in mammalian cells, of which the M-phase takes __________

24 hours; about an hour

Which three phases of the cell cycle comprise interphase and what general activity take place during this time?

G1, S, and G2; preparation for cell division

This phase is the interval between completion of mitosis and the beginning of DNA synthesis in which cells prepare to duplicate their chromosomes

G1 (first gap) Phase

During the S phase, what four core actions take place to prepare the cell for division

1. Nucleosomes disassemble as the replication forks advance

2. Synthesis of histones and other proteins associated with DNA is increased

3. The amounts of DNA and histones double as chromosomes are duplicated

4. Histones complex with DNA = nucleosomes are formed

During ______ phase, cells prepare to divide and synthesize tubulin for construction of the microtubules of the spindle apparatus.

G2

What important processes takes place during M phase of the cell cycle?

Mitosis and Cytokinesis

What are the three fates of cells leaving M-phase

1. re-enter G1 phase

2. leave the cell cycle never to divide again

3. enter G0 phase (extended G1 phase) in which they remain for long periods of time

____________ are points in the cell cycle at which the cycle can be arrested if previous events have not been completed

checkpoints

What are the three major checkpoints of the cell cycle?

1. G1 checkpoint

2. G2 checkpoint

3. Metaphase checkpoint

The ____ checkpoint, or ___________ point, ensures that the cell is large enough to divide, and that enough nutrients are available to support the resulting daughter cells prior to __ phase.

G1; restriction; S

The ____ checkpoint ensures that DNA replication in S phase has been completed successfully prior to __ phase

G2; M

The ___ checkpoint ensures that all of the chromosomes are attached to the mitotic spindle by a kinetochore

metaphase

The functional consequence of failure to "satisfy" the requirements of a cell-cycle checkpoint is usually ___________.

death by apoptosis (programmed cell death).

Match the following Cyclins and CdKs with their respective phase in the cell cycle. Answer choices may be used multiple times or not at all

Bank

Cyclin A / Cyclin B / Cyclin D / Cyclin E

Cdk1 / Cdk2 / Cdk4 / Cdk6 / Cdk7

G1 phase / S phase / G2 Phase / M phase

Cyclin E / Cdk2 / G1,S phase

Cyclin A / Cdk2, 7 / S phase

Cyclin B / Cdk1 / G2,M phase

Cyclin D / Cdk4, 6 / G1 phase

The family of protein kinases that control the cell cycle are called ___________________

cyclin-dependent kinases (Cdks)

What causes the activity of Cdks to rise and fall throughout the cell cycle?

level of cyclins

The oscillations of cyclin levels lead to cyclical changes in the ____________ of ___________ __________ that regulate the major events of the cell cycle (DNA replication, mitosis, and cytokinesis)

phosphorylation; intracellular proteins

_________ are proteins that exist within an array of other proteins and enzymes to control the _________ changes in Cdk activity

Cyclins; cyclical

(please note: Cdk activity is cyclical and follows Cyclin concentration, but not Cdk concentration)

True or False? Cdks can perform their protein kinase activity at any time, but do so at different rates during the cell cycle

False - unless tightly bound to a cyclin, they have no protein kinase activity

What is the primary drive for the advance of the cell cycle?

Formation of Cyclin - Cdk complexes

True or False? Cdk levels remain relatively constant throughout the cell cycle

True

What causes the assembly and activation of cyclin-cdk complexes? What does this result in?

Cyclical changes in cystolic cyclin concentration; triggers cell-cycle events

True or False? Unique combinations of cyclins and CDKs control different stages of cell cycle each

True

The 1st step in G1 checkpoint activation starts with ______ ______ stimulation of quiescent cells to induce the production of ________

Growth factor; Cyclin D

In the 2nd step of G1 checkpoint activation, Cyclin __ binds to Cdk ____ and activates them

D; 4 & 6

In the 3rd step of G1 checkpoint activation, The __________ complex p_____________ the _____________ gene product

Cyclin D-cdk4/6; phosphorylates; retinoblastoma (Rb protein)

In the 4th step of G1 checkpoint activation, phosphorylation Rb causes what?

releases it from the transcription factor E2F (normally inactive as it is masked by Rb).

In the 5th step of G1 checkpoint activation, ___ activates the _______________ of genes required for S-phase

E2F; transcription

In the 6th step of the G1 checkpoint, What are the 4 mechanisms of the Cyclin D-Cdk4/6 inactivation?

1. Binding of cyclin-dependent kinase inhibitor (CDKI)

2. Phosphorylation of cdk and targeted for degradation by proteosome

3. Ubiquitin-mediated degradation

4. Changes in the transcription of genes encoding Cdk regulators

Loss of function or disruption of Retinoblastoma protein can cause what disease?

Unilateral advanced Retinoblastoma (cancer)

In _____ cells, cell cycle checkpoints are often deregulated

tumor (cancerous)

How do genetic defects in cancerous cells deregulate the cell cycle?

genetic defects can raise and/or lower the abundance of the cyclin-CdK complexes

What are the three places in genes that cancerous mutations can occur?

1. In the genes encoding the Cyclins or CDKs

2. In genes encoding the proteins that respond to specific Cyclin/CDK complexes

3. In genes encoding proteins that regulate the abundance of these complexes

What are the 2 types of genes that are commonly mutated to cause cancer?

1. Tumor suppressor genes

2. Oncogenes

_____________ genes encode proteins that inhibit the cell cycle

Tumor suppressor

_________ are genes that promote the progression of the cell cycle

Oncogenes

True or False? Dysregulation of tumor suppressors, oncogenes, or both is uncommon

False

What are the three gene manipulation mechanisms through which dysregulation of the cell cycle occurs?

1. point mutations,

2. changes in expression levels

3. deletion of the entire gene

A ____ __ ________ mutation in tumor suppressor genes causes dysregulation leading to cancer

loss of function

A ____ __ ________ mutation in oncogenes causes dysregulation leading to cancer

gain of function

Mutations in tumor suppressor genes ______ its action and leads to _________ progression through the cell cycle while mutations in oncogenes _________ its action and leads to _______ progression through the cell cycle

blocks; unchecked; upregulates; favored

An _________ is a gene whose product is involved either in transforming cells in culture or in inducing cancer in animals

Oncogene

_______________ are normal genes involved in the control of cell growth or division that may mutate into oncogenes

proto-oncogenes

True or False? Most oncogenes are mutant forms of normal genes

True

Conversion/activation, of a proto-oncogene into an oncogene generally involves a ________________ mutation

gain-of-function

Mutations to Oncogenes are ________ and require ________ copy(s) of the mutant allele to produce the cancerous phenotype

dominant; only one

What are the three mechanisms that can produce oncogenes from corresponding proto-oncogenes?

1. Point mutations

2. Gene amplification

3. Gene (chromosomal) translocation

How do point mutations cause proto-oncogenes to become cancerous?

causes protein products to act constitutively (acts/forms products continuously regardless of need)

How does gene amplification cause proto-oncogenes to become cancerous?

localized reduplication of a DNA segment leads to overexpression of the encoded protein

How does gene (chromosome) translocation cause proto-oncogenes to become cancerous?

growth-regulatory genes are brought under the control of a different promoter and that causes inappropriate expression of the gene

What are the common regulatory molecules encoded by proto-oncogenes that may become cancerous

1. growth factors

2. growth factor receptors

3. signal transduction proteins

4. transcription factors

5. cell cycle regulators

6. regulators of apoptosis

_______ ________ is a classic example of a gene translocation involving chromosomes 8 and 14 that causes a cancerous phenotype

Burkitt's lymphoma

In Burkitt's lymphoma, gene translocation places the ____________ from chromosome __ under the control of the powerful _____________________ on chromosome __

MYC proto-oncogene; 8; immunoglobin heavy chain (IGH) promoter; 14

Gene translocation in Burkitt's lymphoma causes _____ levels of MYC ______-expression in lymphoid cells, where the IGH promoter is normally active

high; over

The MYC protein, important in Burkitt's lymphoma, normally signals for cell _____________ and when overexpressed, causes ___________ ______________.

proliferation (division/replication); enhanced proliferation

What are the two methods in which gene translocation mutations can act?

1. relocation of a coding sequence of one gene to the regulatory sequence of another

2. fusion of coding sequences of two genes to generate fusion genes (potent oncogenes)

The ____________ ____________ is a gene translocation product of a reciprocal translocation involving chromosomes 9 and 22

Philadelphia chromosome

The Philadelphia chromosome translocation fuses the coding sequence of the _________________ gene on chromosome 22 with the coding sequence of the __________ on chromosome 9

BCR (breakpoint cluster region); ABL gene

True or False? Both Burkitt's lymphoma and the Philadelphia chromosome are caused by the fusion of two coding sequences

False - Burkitt's lymphoma is caused by the fusion of a regulatory sequence and coding sequence

The BCR-ABL fusion protein encoded by the chimeric Philadelphia gene is a _______ _________ _______ that constitutively activates signaling pathways involved in ____ ______ and _____________.

protein tyrosine kinase; cell growth; proliferation

Oncogenic RAS mutations cause cells to ____________ upstream signaling, and _____________ the downstream signaling pathways leading to ______________ proliferation and ___________ cell survival

bypass/skip the requirement of; constitutively activate; uncontrolled; enhanced

Tumor-suppressor genes generally encode proteins that _________ cell proliferation

inhibit

True or False? Tumor suppressor genes are like "brakes" of which the loss of one or more can contribute to the development of cancers

True

Tumor-suppressor genes generally encode for what 5 classes of proteins?

1. Intracellular proteins (e.g. Cyclin-kinase inhibitor = regulate or inhibit progression through a specific stage of the cell cycle)

2. Secreted-hormone Receptors (e.g., Tumor-derived growth factor β) = function to inhibit cell proliferation

3. Checkpoint-control proteins = arrest the cell cycle if DNA is damaged or chromosomes are abnormal

4. Apoptosis promoting Proteins

5. DNA repair Enzymes

Mutations of tumor suppressor genes are ____ __ _________ mutations

loss of function

Mutations to tumor suppressor genes are ________ and require ________ copy(s) of the mutant allele to produce the cancerous phenotype

recessive; both

Loss of function mutations on tumor suppressor genes that lead to loss of tumor suppression can come in two types: __________ or _________ mutations

deletion; inactivating

What is the most commonly mutated tumor suppressor gene?

p53

What are the 8 functions p53 performs to maintain cell homeostasis?

1. Senescence

2. Angiogenesis

3. Autophagy

4. Cell-cycle arrest

5. Migration

6. Apoptosis

7. DNA repair

8. Metabolism

What are the 7 activating stressors of the p53 gene?

1. Oxidative stress

2. Nutrient deprivation

3. Hypoxia

4. DNA damage

5. Oncogene expression

6. Ribosomal dysfunction

7. Telomere attrition

______ protein is a transcription factor that is activated by various signals and regulates several cellular processes such as DNA repair, cell cycle, and most importantly _______

p53; apoptosis

The p53 protein acts as the "guardian of the genome" by halting ___________ in cells that have suffered ____ ________ and targeting unrepaired cells to ___________.

replication; DNA damage; apoptosis

True or False? Mutations of one or both p53 alleles are found in less than 50% of human tumors

False - mutations are found in more than 50% of human tumors

True or false? Two mutant p53 genes will lead to abnormal p53 proteins that drive continuous cell growth

False - abnormal p53 protein will fail to detect damaged cells which can later result in cancer, but do not promote cell proliferation directly

What 3 conditions cause a rise in the level of p53?

1. DNA-damaging mutagens

2. ionizing radiation

3. UV light

When p53 acts as a transcription factor, it stimulates the transcription of ____

CKI

CKI _______ cyclin-CDK complexes and prevents the ______________ of Rb and release of E2F proteins causing a G1 ____ ______ ______.

inhibits; phosphorylation; cell cycle arrest

What is the direct result of G1 cell cycle arrest caused by CKI?

cell is prevented from entering S-phase

DNA repair enzyme transcription is stimulated by ________

p53 protein

What two things does p53 induce when DNA repair is successful?

induces:

1. its own downregulation 2. allows the cell to enter S-phase

What does p53 induce when DNA repair is not successful?

the apoptotic pathway which causes cell death

What two mechanisms are used to regulate the number of cells in a multicellular community?

1. Rate of cell division

2. Rate of cell death

_________ is the intracellular death (suicide) program of a cell that occurs when cells are no longer needed

apoptosis

True or False? Several billions of cells die every hour, even when the vast majority of them are healthy

True

What are the two types of signaling pathways that can activate apoptosis?

1. Extrinsic pathway

2. Intrinsic pathway

In the 1st step of extrinsic apoptosis, the signaling pathway is activated by the _____ _________ through the binding of extracellular ligands

death receptors

In the 2nd step of extrinsic apoptosis, the activated death receptor binds 2 molecules of the protein ___________________

procaspase 8 or 10

In the 3rd step of extrinsic apoptosis, the procaspases ________________ cleave each other to form _______ ____________

autocatalytically; active caspases

In the 4th step of extrinsic apoptosis, the newly cleaved and active Caspases ___ and ___ activate caspases ___, ___, and ___

8 and 10; 3, 6 and 7

In the 5th step of extrinsic apoptosis, Caspase ___ cleaves a Bcl-2 protein, Bid, to a form that activates the ____________ __________ __________ to apoptosis

3; mitochondrial integrity pathway

Caspases 8 and 10 are known as __________ caspases

initiator

caspases 3, 6 and 7 are known as __________ caspases

executor

Procaspases are converted to their active Caspase (cysteine protease) forms by the proteolytic cleavage of what region of their polypeptide chain?

the inhibitory region

In the 1st step of intrinsic apoptosis, what are four intracellular signals that can begin the signal cascade?

1. DNA damage

2. growth factor withdrawal

3. cell injury

4. release of certain steroids