Lecture 6 Tissue Renewal 2

Question 1

Cell cycle

Answer 1

G0 quiescence
G1 cells with chromosomes in the nucleus
S DNA synthesis chromosome duplication
G2 cells with duplicated chromosome, preparation of mitotic spindle
M mitosis chromosome separation and cell division

Question 2

Ki57

Answer 2

Expressed at all phases of the active cell cycle but not in G0 resting cells

Question 3

BrdU

Answer 3

DNA can incorporate labeled nucleotides in S phase

Question 4

General

Signal transduction

Answer 4

EGFR, Wnt, notch, BMP

Question 5

Restriction point

Answer 5

If quiescent cells are exposed to the correct GFs m, they can enter G1, activate growth pathways and pass through the restriction point (G1-S) boundary
Having passed the RO growth factor availability has no effect on progression
Controlled by retinoblastoma protein pRb

Question 6

Retinoblastoma protein (pRB)

Answer 6

Classic tumor suppressor protein
Controls the passage through the restriction point
Loss of function mutations causes retinoblastoma–autosomal dominant trait
pRB represses E2F transcription factors that regulate genes necessary for cell cycle progression but are inhibited when bound to pRB
When pRB is phosphorylated by specific kinase, it changes shape and releases E2Fs which can then activate expression of target genes and drive cell cycle

Question 7

E2F target genes

Answer 7

DNA polymerase alpha
Thymidylate reductase 
CDK1
CyclinE
CyclinA 

All promote either DNA synthesis or cell cycle progression

Question 8

PRB is regulated by

Answer 8

Cyclin dependent kinase (CDK) complexes
CDKs are activated by cyclins and phosphorylated pRB

Cyclin d levels are low in quiescent cells but rise rapidly in response to GF signaling, gradually phosphorylating pRB and pushing cell toward restriction point

Question 9

CyclinD CDK4/6

CyclinE CDK2

Answer 9

Hyperphosphorylate pRB committing to cell division
D early and mid G1
E late G1

Question 10

Regulation of cyclin CDK complexes

Answer 10

Targeted degradation of cyclin subunits through ubiquitin mediated proteolysis
Cyclins have redundancy

Question 11

Negative regulation of cyclin CDK activity

Answer 11

CKI Inhibutors
Some are specific INK4s inhibit CDK4

Others p22, p27, p57 inhibit multiple

Question 12

P16

Answer 12

Lost in many human cancers

Question 13

Cancer results when balance between positive and negative reg factors is lost

Answer 13

Positive factors : cyclin D, CDk 4/6, cyclin E
Over expression of cyclin D1 carcinoma
CDK4 over expression in sarcomas and gliomas

Loss of negative factors:
Rb loss failure of restriction point
CIP KIP family p21,27,57
G1 specific: INK4 family p15,16,18,19

Pink 16 is lost or silenced in cancer

Question 14

Apoptosis

Answer 14

Withdrawal of appropriate GFs removes life preserving signals
Highly ordered ATP dependent process , su cellular components destroyed by proteases (caspases) and nucleases

Question 15

Senescence

Answer 15

Permanent cell cycle arrest
Increased expression of cell cycle inhibitors p16, p21, p27 and senescence associated beta galaxtosidase (SABG)

Flattened morphology
Senescence can be induced by the loss of telomeric sequences on the ends of chromosomes or by elevated oncogenic signaling in transformed cells

Question 16

Moles

Answer 16

Activating mutations in melon octet GF signaling protein BRAF leads to aberrant cell division triggering a protective cell cycle arrest p16
Senescence
BRAF activation increases the expression of p15