Signaling and Cell Cycle Control

During the Eukaryotic cell cycle what occurs in nearly every tissue during devlopment

cell division

what is cell division

specific events required to ensure every cell has eveything it needs to live

After passing M phase and into G1, what 2 things can a cell do?

• continues through another division

• enters G0

what happens in G0

differentiated cells stop dividing and enter this phase

what is G0 phase also known as

quiescent

what does quiescent mean

being in a state of quiet, inactivity, stillness, or dormancy

what does uinregulated cell division lead to?

cancer development

What type of development is primarily post-natal

mammary gland development

Mammary gland development is primarily post-natal

• The ductal tree develops as an invagination of ectoderm.

• At birth, a rudimentary “ductal tree” structure is already

present.

• Very limited development occurs until the onset of puberty

In relation to signals and receptors in pro-growth cell signals , what type of protein molecules require a cell membrane receptor

protein signaling molecules

What type of signaling molecule use nuclear receptors

hydrophobic signaling molecules

what is an example of a hydrophobic signaling molecule that uses nuclear receptors

steroid hormones

What is significant about these things:

• altered gene expression

• increased translation

• increased nutrient uptake and metabolic rat e

• altered morphology

these are all the possible changes that a cell growing to divide may face

what nuclear hormone receptor binding induces estrogen receptor (ER) dimerization

estrogen

As nuclear hormone receptor:

Estrogen binding induces estrogen receptor (ER) dimerization.

What is the first step in this process

the estrogen receptor is translocated to the nucleus

As nuclear hormone receptor:

Estrogen binding induces estrogen receptor (ER) dimerization.

What is the second step in this process?

binds to genes containing an estrogen response element (ERE)

As nuclear hormone receptor:

Estrogen binding induces estrogen receptor (ER) dimerization.

What is the last step in this process

ER interacts with coactivator proteins for the recruitment of transcription machinery

what does ER effects in combination with other transcription factors determine

the level of ecpression for each gene in the cell

What is an estrogen antagonist that competes with estrogen for binding to ER

Tamoxifen

What type of activation is it when:

peptide binding to RTKs (receptor tyrosine kinases) stimulates autophosphorylation

RAS- Dependent Activation

During RAS- Dependent Pathway Activation

What peptide binding stimulates autophosphorylation

Peptide binding to RTKs (receptor tyrosine kinases)

During RAS- Dependent Pathway Activation

• Peptide binding to RTKs (receptor tyrosine kinases) stimulates autophosphorylation

How is this done?

GRB2, an adaptor protein, uses its SH2 domain to bind these phosphotyrosines, recruiting the GEF SOS to the membrane. SOS then activates Ras by catalyzing the exchange of GDP for GTP.

What results in GDP/GTP exchange by RAS

SOS activity

How is RAS signaling turned off

GTPase activating protein (GAP)

The RAS dependent pathway is activated by RTKs for many growth factors, such as IGF-1, EGF, and PDGF

How does RAS-GTP activate its protein kinase activity

RAF-GTP interacts with RAF

RAS-GTP interacts with RAF activating its protein kinase activity

Whats the first thing that happens in this cascade

RAF phosphorylates MEK

RAS-GTP interacts with RAF activating its protein kinase activity:

RAF phosphorylates MEK

Whats the next thing that happens in this cascade

MEK phosphorylates ERK

RAS-GTP interacts with RAF activating its protein kinase activity:

• RAF phosphorylates MEK

• MEK phosphorylates ERK\

• _____________

Whats the next thing that happens in this cascade

ERK phosphorylates transcription factors in the nucleus

RAS-GTP interacts with RAF activating its protein kinase activity:

• RAF phosphorylates MEK

• MEK phosphorylates ERK\

• ERK phosphorylates transcription factors in the nucleus

Whats the next thing that happens in this cascade

ELK-1 binds Serum Response Element (SRE) located in

pro-growth genes to activate their transcription

RAS-GTP interacts with RAF activating its protein kinase activity:

• RAF phosphorylates MEK

• MEK phosphorylates ERK\

• ERK phosphorylates transcription factors in the nucleus

• ELK-1 binds Serum Response Element (SRE) located in

  pro-growth genes to activate their transcription

What is one of these pro-growth genes?

FOS

In thew RAS- Dependent pathway what does this sequential activation of protein kinases result in

signal amplification and diversification

what is another word for signal amplification and diversification

signaling cascade

In RAS-Dependent pathways how is the phosphorylation and activity of target proteins (signal cascade) reversed

protein phosphatases

What are JUN and FOS

activating protein-1 (AP-1)

JUN and FOS are activating protein- 1, what is their significance?

binds the TRE cis-acting element, regulating many genes needed for progression through the cell cycle

What is an activatr of proliferation genes

Myc/Max

what is a repressor of pro-growth genes

Mad/Max

What is a complex that is an activator of many pro-growth genes and stimulates RNA Poll activity

Myc/Max

What kick starts the cell cycel in relation ot the activator of proliferation genes

upregulation of cyclin D (a pro growth gene)

What controls cell cycel timing

family of kinases

A family of kinases controls cell cycle timing. What does each active kinase have?

• one catalytic subunit

• one regulatory subunit

what is in one catalytic subnit of an active kinase

cyclin dependent kinase (CDK)

what is an example of a regulatory subunit

cyclin

Family of kinases controls cell cycle timing with each active kinase having one catalytic subunit ( cyclin dependent kinase (CDK) and one regulatory subunit (cyclin).

What cyclin- cdk complex is found in early G1

Cyclin D-CDK4-6

Family of kinases controls cell cycle timing with each active kinase having one catalytic subunit ( cyclin dependent kinase (CDK) and one regulatory subunit (cyclin).

What cyclin- cdk complex is a restriction point

Cyclin E-CDK2

Family of kinases controls cell cycle timing with each active kinase having one catalytic subunit ( cyclin dependent kinase (CDK) and one regulatory subunit (cyclin).

What cyclin- cdk complex is located in S phase?

Cyclin A-CDK2

What result in the oscillations of cyclin-CDK activity?

• CDK phosphorylation or dephosphorylation

• controlled degradation of the cyclin subunit =

  ubiquitin

• periodic synthesis of CDKs and cyclins

• the action of specific CDK-inhibiting proteins

  (CIP)

How does CDK get regulated

by phoshorylation and proteolysis

what is a regulatory protein that targets proteins for destruction

ubiquitin

what are proteolytic enzyme complexes within cdk regulation by phosphorylation and proteolysis?

proteasomes

what are destruction box recognizing proteins within cdk regulation by phosphorylation and proteolysis?

DBRP

what is a checkpoint before DNA replication

Restriction point

what is a cell considered when it passes the restriction point?

it is committed

How are Cyclin-dependent kinase activity inhibitors are expressed in this checkpoint and how are they termed?

in G1 and they are termed CDK inhibitors (CKI)

Cyclin-dependent kinase activity inhibitors are expressed in G1 termed CDK inhibitors (CKI).

What blocks cyclin D binding

Inhibitor of cdk4 (INK4) proteins

Cyclin-dependent kinase activity inhibitors are expressed in G1 termed CDK inhibitors (CKI).

What protein binds to an inhibits the activites of intact CDK-cyclin complexes

CDK interacting protein (CIP)

what is an example of CDK interacting protein (CIP)?

p21

At the restriction point, what is a corepressor that binds the activator E2F to arrest cell division

retinoblastoma protein (pRb)

What happens to cyclin D-CDK4/6 and cyclin E-CDK2 at the restriction point

hyperphosphorylate Rb releasing Rb from E2F

what is an activator of genes needed in S phase

E2F

E2F is an activator of genes needed in S phase

including:

• ______________________

cell cycle machinery genes (cyclins, cyclin-dependent kinases)

E2F is an activator of genes needed in S phase

including:

• cell cycle machinery genes (cyclins,

  cyclin-dependent kinases

• _________

pro-growth transcription factors (Myc, E2F

family)

E2F is an activator of genes needed in S phase

including:

• cell cycle machinery genes (cyclins,

  cyclin-dependent kinases

• pro-growth transcription factors (Myc, E2F

  family)

• _____________________

• components of the DNA replication

  machinery (replisome) and proteins of

  chromatin (histones

When does restriction point block progression

if dna damage is present

What happens in regards to the restriction point when there is DNA damage

p53 activation upregulates transcription of CKI genes such as p21

How does p53 upregulate transcription of CKI genes such as p21

it blocks CDK from binding ATP

What were the clinical findings in Retinoblastoma and

Cell Cycle Dysregulation

Genetic testing shows a mutation in the RB1 gene, which encodes the retinoblastoma protein (pRb), a key regulator ofthe G1/S checkpoint in the cell cycle

What is the molecular insight of retinoblastoma and cell cycle dysregulation

pRb normally binds and inhibits E2F transcription factors, preventing premature entry into S phase. When RB1 is mutated, pRb cannot restrain E2F, leading to uncontrolled transcription of genes required for DNA replication. This loss of cell cycle control results in excessive proliferation and tumor formation, characteristic of retinoblastoma. Familial cases follow the two-hit hypothesis, where one defective allele is inherited and the second is lost through somatic mutation

What does the transition to S-phase from G1 require

syntheis of cyclin A

what is a transcriptional activator of cyclin A

EF2

aside from the transition to S phase from G1 requires synthesis of cyclin A, what else does it require

sufficient active cyclin E-CDK2 to activate cyclin A-CDK2

How does Cyclin E-CDK2 drives the transition from G1→S

by phosphorylating the CDK inhibitor Sic1 (or p27 in mammals), targeting it for ubiquitination and subsequent degradation by the SCF ubiquitin ligase complex

aside from the transition to S phase from G1 requires synthesis of cyclin A, there is a requiremrnt of sufficent active cyclin cyclin E-CDK2 to activate cyclin A-CDK2.

What results from the phsophorylation of SIc1

it makes it susceptible to a ubiquitin ligase

what coordinates replication initaition?

licensing

for licensing to coordinate replication what must bind tightly to DNA in the G1 phase?

Origin of replication complexes (ORC)

what is the mechanisim after the origin of replication complexes bind tightly to DNA in G1 phase

Cell division cycle 6 (CDC6) and CDT1 join and load the helicase Mini Chromosome Maintenance (MCM)

What does MCM do?

translocates 3′→5′ along the leading strand template using ATP

for licensing to coordinate replication what happens in S-phase

replication is initiated by phosphorylation of complex proteins by cyclin A–CDK2

or licensing to coordinate replication, in the S phase or licensing to coordinate replication.

What happens after this?

The replisome is assembled, and bidirectional DNA synthesis is initiated