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Ebook The biology of cancer (2/E): Part 2

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Ebook The biology of cancer (2/E): Part 2

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2rei)i. 1831T ere cannot however be the least doubt, that the higher organisms, as they are now constructed, contain within themselves the germs of dea

th.August Weissmann, philosopher of biology. 1889Metazoan organisms have a vital interest in eliminating defective or malfunctioning cells from their Ebook The biology of cancer (2/E): Part 2

tissues. Responding to this need, mammals have implanted a loyal watchman in their cells. Within almost all cells in mammalian tissues, the p53 protei

Ebook The biology of cancer (2/E): Part 2

n serves as the local representative ofthe organisms interests, p53 is present onsite to ensure that the cell keeps its household in order.If p53 rece

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2 and. at the same tune, orchestrate localized responses in that cell to facilitate the repair of damage. If p53 learns that metabolic derangement or d

amage to the genome IS too severe to be cured. It may decide to emit signals that awaken the cell s normally latent suicide program—apoptosis. T e con Ebook The biology of cancer (2/E): Part 2

sequence IS the rapid death of the cell. T is results in the elimination of a cell whose continued growth and division might otherwise pose a threat t

Ebook The biology of cancer (2/E): Part 2

o the organism s health and viability.T e apoptotic program that may be activated by p53 is built into rhe control circuitry of most cells throughout

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2in an hour of its initial activation T e continued presence of a latent but intact apoptotic machinery represents an ongoing threat to an incipient ca

ncer cell, sinceMovies in this chapter9.1p53 Structure9.2Apoptosis331332 Chapter 9: p53 and Apoptosis: Master Guardian and ExecutionerFigure 9.1 Large Ebook The biology of cancer (2/E): Part 2

T antigen in SV40-transformed cells Antibodies that bind the SV40 large T (LT) antgen can be used to detect LT in the nuclei of SV40-transformed tumo

Ebook The biology of cancer (2/E): Part 2

r cells. In the present case, such antibodies were used to stain human mammary epithelial cells (MECs) that were transformed by introduction of the SV

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2 by linking these antibody molecules to peroxidase enzyme, which generated the dark brown spots In this image of a tumor xenograft, the transformed ME

Cs form ducts (seen in cross section), which are surrounded by normal stromal cells {light blue nuclei). (Courtesy of T.A. Ince.)this machinery is poi Ebook The biology of cancer (2/E): Part 2

sed to eliminate cells that are en route to becoming neoplastic. T is explains why p53 function must be disabled before a clone of pre-malignant cells

Ebook The biology of cancer (2/E): Part 2

cams a sure and stable foothold within a tissue. Without a clear description of p53 function and apoptosis, we have no hope of understanding a fundam

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2ine cells that have been transformed by the SV40 DNA tumor virus are injected into a mouse of identical genetic background (that IS. a syngeneic host)

, the immune system of the host reacts by mounting a strong response: antibodies are made that react with a nuclear protein that is present in the vir Ebook The biology of cancer (2/E): Part 2

us-transformed cells and is otherwise undetectable in normal mouse cells (Figure 9.1). T is protein, the large tumorflarge T. LT) antigen, is encoded

Ebook The biology of cancer (2/E): Part 2

by a region of the viral genome that is also expressed when this virus infects and multiplies within monkey kidney cells—host cells that permit a full

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2 of distinct regulatory circuits within infected and transformed cells. Indeed, large T was cited in the previous chapter because of its ability to bi

nd and thus functionally inactivate pRb (see Section 8.5). Anti-large T sera harvested from mice and hamsters bearing SV40-induced tumors were used in Ebook The biology of cancer (2/E): Part 2

1979 to analyze the proteins in SV40-transformed cells. T e resulting immunoprecipitates contained both large T and an associated protein that exhibi

Ebook The biology of cancer (2/E): Part 2

ted an apparent molecular weight of 53 to 54 kilodaltons (Figure 9.2A). Antisera reactive with the p53 protein were found to detect this protein in mo

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2tibodies that recognized only large T immunoprecipitated the 53- to 54-kD protein in virus-infected but not in uninfected cells.Taken together, these

observations indicated that the large T protein expressed in SV40-transformed cells was tightly bound to a novel protein, which came to be called p53 Ebook The biology of cancer (2/E): Part 2

(see Figure 9.2B). Antisera that reacted with both large T and p53 detected p53 in certain uninfected cells, notably tumor cells that were transformed

Ebook The biology of cancer (2/E): Part 2

by non-viral mechanisms, such as the F9 embryonal carcinoma cells analyzed in Figure 9.2A. T e latter observations indicated that p53 was of cellular

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2inogen also expressed p53.T esc various lines of evidence suggested that the large T oncoprotein functions, at least in part, by targeting host-cell p

roteins for binding ( T e discovery that largePapovaviruses leaa (O me discovery 01-'-S-ST antigen is also able to bind pRb. the retinoblastoma protei Ebook The biology of cancer (2/E): Part 2

n, came seven years later.) In the years since these 1979 discoveries, a number of other DNA viruses and at least one RNA virus have been found to spe

Ebook The biology of cancer (2/E): Part 2

cify oncoproteins that associate with p53 or per-turb its function (Table 9.1). (As we will discuss later in this chapter, and as is apparent from thi

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2Viral protein targeting pRbViral protein targeting p53Viral protein targeting apoptosisSV40large T (LTV*large T(LT)aAdenovirusE1AE1B55KE1B19KbHPVE7E6P

olyomaviruslarge Tlarge T?middle T (MT)'Herpesvirus saimiriV cyclin'*v-Bcl-2®HHV-8 (KSHV)K cyclin'1LANA-2v-Bcl-2/ V-FLIP'Human cytomegalovirus (HCMV)I Ebook The biology of cancer (2/E): Part 2

E72OIE86vICA? PUL37'HTLV-ITaxiTaxEpstein-BarrEBNA3CEBNA-1*LMP1“Figure 9.2 The discovery of p53 and its association with SV40 large T (A) Normal BALB/c

Ebook The biology of cancer (2/E): Part 2

3T3 mouse fibroblasts (3T3) transformed by SV40, as well as F9 mouse embryonal carcinoma cells, were exposed to 35S-metlx>mne. and resulting cell lys

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2mmunopreopitated a protein of 94 kD from virus-infected but not uninfected 3T3 cells. In addition, a second protein running slightly ahead of the 54-k

D marker was immunoprecipitated from 5V40-transformed 3T3 cells but not from normal 3T3 cells. Moreover, this same protein could be immunoprecipitated Ebook The biology of cancer (2/E): Part 2

from F9 cells, whether or not they had been exposed to SV40 (arrow). These particular data, on their own, did not prove a physical association of SV4

Ebook The biology of cancer (2/E): Part 2

0 large T (the 94-kD protein) with pS3. but they did show that p53 was a cellular protein that was present in elevated amounts in two types of transfo

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

Ebook The biology of cancer (2/E): Part 2une response against both large T and the hamster's own p53. (Bl As revealed by x-ray crystallography.SV40 large T molecules assemble into homohexamer

s. each subunit of which binds and thereby sequesters a single molecule of pS3. (A, from D.l. Linzer and AJ. Levine. Cefl 17:43-52.1979 8. from D b et Ebook The biology of cancer (2/E): Part 2

al.. Nature 423:512-518, 2003.)

Chapter 9p53 and Apoptosis: Master Guardian and ExecutionerTo examine rhe causes of life, we must fret have recourse to death,Mary Shelley. Ff

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