p53 (26 page)

‘This meant that a very small group of people originally from the same city became, within about 15 years, the seed of all the white population of that area. I believe one of them had the
mutation, and through intermarriage it reached a high prevalence in the community from very early on. These very particular historical and demographic circumstances could explain how the mutation
got so firmly established despite having a negative effect.’

By the middle of the 18th century the road stretched in a continuous track from Sorocaba, inland from São Paolo, to Porto Alegre, and soon became a busy trading route. Trade consisted
largely of cattle being taken to market in Sorocaba from the south, and goods of all sorts being brought down by mule on the return journey. It was a round trip of some six months for the
tropeiros,
who would have had many stops, and likely liaisons, along the way – perfect conditions for spreading a genetic mutation.

Again, the theory cannot be proved and Patricia Prolla, for one, is wary of all possible explanations advanced thus far for the high prevalence of the mutation in Brazil: they leave too many
questions unanswered, she believes. But Hainaut remains intrigued. When the road reached the escarpment, it branched north to São Paulo and Rio de Janeiro, and south towards the small
settlement that grew eventually into Porto Alegre. The leader of the team that drove south was Francisco de Brito Peixoto, a famous figure who appears in history books as the first explorer of Rio
Grande do Sul, the southernmost state in today’s Brazil, and the founder with his father of the coastal city of Laguna. He died in 1735 and is said to be buried beneath the altar of a small
chapel in Laguna; Hainaut dreams of getting permission one day to disinter his bones and to sample his DNA as the possible first carrier of p53 with the 337 mutation.

AN UNUSUAL PATTERN OF DISEASE

A mutation that kills people prematurely usually dies out within a few generations as it inhibits child-bearing and thus the passing on of the faulty gene. It’s one of
the ironies of the Brazilian form of LFS that it is more persistent and widespread than the classic syndrome because the 337 mutation is somewhat ‘weaker’. Carriers of this mutant have
a lifetime risk of developing tumours of around 60 per cent and they tend to get sick later in life. Thus around one in four carriers of the Brazilian mutant remains cancer-free until at least
their 30th birthday, whereas the comparable figure for those with classic LFS mutations is only one in two. The spectrum of tumour types is somewhat different also, with leukaemia and sarcomas
being less common among Brazilian patients, but ACC and a tumour of the central nervous system called choroid plexus carcinoma being more prevalent in young children.

Two remarkable observations may hold clues to why the pressures of natural selection have failed to eliminate 337, as they would be expected to do. One is that those carriers in Brazil who
don’t get cancer are likely to go on to a healthy and vigorous old age, perhaps well into their nineties, suggesting that there are some counterbalancing advantages to having the mutant.
Another is that carriers of the 337 mutant do not get the cancers associated with viral infection, such as cervical cancer or Hepatitis B-associated liver cancer. Perhaps the mutation protects
carriers from viral infection or from some other disease that plagued the early Portuguese settlers, giving them a survival advantage, suggested Hainaut. This is just wild speculation at the
moment, but unlike the theories about the mutant’s origins, at least it is testable in the lab.

If the prevalence rates of the 337 mutation found in the screening programmes of newborn babies in Paraná and women attending mammography services in Porto Alegre are truly
representative, several hundred thousand people in southern Brazil are living with mutant p53 and are at high risk of developing multiple cancers. Precious few are within reach of the specialist
genetic counselling and treatment services of São Paulo’s A C Camargo and the Hospital de Clinicas de Porto Alegre. For some of those who are, however, the regular check-ups put their
minds at rest and allow them to live normal lives. Others are unable to shake off the spectre of cancer.

Fernanda (her name has been changed to protect the family’s identity) was one of the young women in the Ibiuna family present at the first meeting with Achatz and her colleagues round the
kitchen table. I met her myself on a visit to the small town, reached just as the sprawl of São Paulo begins to fizzle out into tentative countryside. Blonde, pretty, athletic and tanned,
Fernanda sat on the settee with her long legs tucked under her and told me how hard she had been hit by the news that her test result was positive – that she was a carrier of mutant p53
– and how much she dreads the biannual screening trips to A C Camargo. She finds walking through the hospital’s bright, crowded cancer clinic on her way to Maria Isabel’s
consulting rooms, past so many people who are extremely sick, particularly disturbing, she said. That’s the fate that awaits herself and her loved ones, she thinks, and memories of her
mother’s long battle with the disease, and of the frequent visits to hospital, flood her mind.

In Porto Alegre, a man who saw his wife and 11-year-old daughter die from cancer within weeks of each other struggles to cope with the fact that his small son too is a carrier of the faulty
gene. He feels the ground has been dug from under his feet and there are no certainties in life any more, said his sister-in-law Margarete; she has taken on responsibility for bringing the child
for his check-ups because his father’s fears for him are overwhelming. A glamorous, buxom woman in early middle age with large dark eyes, glossy black hair and heavy silver rings on her
fingers, she agreed to meet me in a small room off the clinic where Patricia Prolla was seeing patients and their families.

Margarete’s face crumpled and her eyes brimmed as she explained that this was her first visit to the hospital since her niece had died of a brain tumour a few months previously. She had
sat with the girl for the last 20 days of her life, mostly just holding her hand, as the doctors tried to control the pain. Margarete was thankful she could do something to protect her nephew from
cancer, but has not been tested herself for the mutant gene. She shrugged and looked away. She’s happier not knowing her status. ‘What will be, will be,’ she said, drawing
irrational comfort from the fact that she looks more like her father, who was not the carrier of the mutant gene, than like her mother, who was.

Until the Brazilian authorities decide how to deal with the public-health crisis posed by the mutant p53, fatalism and grasping at small straws are the only real options for people living with
the faulty gene in their families. Meanwhile, LFS is offering insights that might help to resolve one of the longest-running controversies of p53 research – whether or not mutant p53 does
indeed act like an oncogene, driving the process of tumour formation under certain circumstances rather than simply knocking out the function of the wild-type allele.

***

When, 10 years after it was discovered, normal p53 was found to be a tumour suppressor not an oncogene (or tumour ‘driver’), many people lost interest in the
mutants they had been inadvertently studying for so long. Instead, they began to focus their full attention on the wild-type protein, which was a much more exciting prospect. In doing so they chose
to ignore what they had observed with the mutants. The few who said hang on a minute, the mutants may indeed be doing something to drive these tumours – something
more
than simply
losing their ability to stop the cells running amok – became lone voices talking to empty rooms. ‘It was kind of a reaction to the fact that these mutant p53 clones had misled the field
and caused us to draw the wrong conclusion,’ commented Moshe Oren. ‘They were a sore point in our history, and many people just wanted to forget about them.’

Not Varda Rotter. You will remember meeting her back in
Chapter 7
in relation to the revolutionary discoveries that led to the recognition of p53 as a tumour suppressor. In 1979–80, her
experiments with the Abelson cancer virus had led to malignant blood cells that had no p53 protein at all – a completely different result from that of most of her colleagues, who were finding
an over-abundance of p53 protein in their tumour cells. The virus, Rotter discovered, was disabling the gene by inserting a bit of its own genetic material into p53 so that it could not produce any
protein.

Curious to see what effect the loss of p53 had on these malignant blood cells, she injected them into laboratory mice, where she found that they caused small tumours to develop that soon
regressed. Next she took some of these same malignant blood cells and, using some technical wizardry, replaced the crippled p53 with a functional copy of a mutant p53 gene – that is, a mutant
that was able to produce its protein. She then injected these engineered cells into her mice, and this time she found they produced extremely aggressive tumours that were eventually fatal. She
published her findings in
Cell
in 1984.

This was dramatic stuff that caught her imagination and when, five years later, normal p53 was revealed as a tumour suppressor,
not
a tumour driver, she was not about to dismiss the
aggressive behaviour of the mutant as no longer important. Rotter did not follow the herd nor change the focus of her research and she became the standard bearer of what is known as mutant
‘gain of function’, often shortened to GOF (remember the analogy in
Chapter 7
of the car with the jammed accelerator pedal or the failed brakes? GOF is the jammed accelerator).
‘What convinced me was this,’ said Rotter, rummaging through her computer images to show me an iconic slide of a thin slice of tumour tissue in which p53 protein showed up as bright
red. Clearly the cells were stuffed with it. ‘When you take almost any tumour from a human and you stain it for p53, this is what you get . . . Did you ever see anything so covered in
protein?’ she asked rhetorically. ‘I felt it can’t just be lying there for nothing.’

That is what prompted her to do the experiments with the mice and the engineered malignant blood cells – she had to prove that her hunch was right and that the abundant protein produced by
the mutant p53 gene was actively doing something in tumour cells. This makes p53 unusual among tumour suppressors, almost all of which are simply knocked out by mutation, she explained.
‘Unlike other tumour suppressors, p53 has a schizophrenic personality. You have the wild type which is very important: the guardian of the genome that takes care of DNA repair, takes care of
genomic fidelity, takes care of everything. But once this is mutated then it becomes a
monster
.’ It was this characterisation of p53 that her granddaughter sought to portray in her
picture of a devil and an angel that Rotter has framed on her office wall.

Among a field of sceptics, one person who also remained curious about the mutants was Rotter’s colleague at the Weizmann Institute, Moshe Oren. It was while he was investigating their
activity in dishes in his lab that he stumbled across the temperature-sensitive mutant when the thermostat in one of his incubators started to play up. This, you will recall, led to the discovery
that p53 can trigger apoptosis or cell suicide. But it also contributed to another equally critical discovery about the nature of p53 – that the normal, wild-type protein can change its
shape, and thereby its behaviour in cells, from a suppressor of growth to a promoter of growth, under certain conditions. Though it’s now thought likely to be a common feature of proteins
that control many others in a cell, such flexibility of shape and behaviour in a single protein was virtually unknown at the time it was discovered in p53 and, as we’ll see, it shed light on
mysteries way beyond the field of cancer biology.

AN EXTREMELY FLEXIBLE PROTEIN

The person credited with the discovery of the protein’s flexibility is Jo Milner, who developed what is known as ‘the conformational hypothesis’ of p53.
Milner, whom Oren describes as a ‘very clever and original’ scientist, traces her fascination with biology to a childhood spent in Bridlington, a seaside town on the north-east coast of
England, where she spent long happy days walking the beach, guddling in rock pools and coming home with starfish in her pockets. It was her mother who, bringing up her children alone after World
War II, nurtured a sense of curiosity and freedom of spirit in Milner and her siblings. Times were tough, she remembered, ‘but there was never any sense of hardship. We grew up in a tiny home
brimming with friends who all seemed to adopt Mum as their own.

‘One of my abiding memories is of looking out of the window from an early-morning train and seeing, across a field, a white sheet being waved from the upper floor of a large house: the
train was carrying me to London for an interview at the university; the large house was where my mother worked as a housekeeper; and the sheet was her fond farewell and good luck.’

After gaining a degree in zoology in London, Milner studied for her PhD at Cambridge University. Since then her career has taken her to Harvard, back to England for another 20 years at Cambridge
and finally to the University of York, where she was, until very recently, director of the p53 Research Unit in the Department of Biology. I took the train south from my home in Scotland to visit
her as she was busy packing up her lab on the brink of retirement and looking forward to following her still-lively curiosity as a scientist without the pressure any longer of leading a team. As we
sat in the sun room of her elegant stone house in an old village nestled in farmland outside York, the scent from an ornamental lime tree in a pot hanging delicately in the air, she talked of the
steps that led to her discovery of p53’s extraordinary flexibility – one of the rare and thrilling eureka moments in a scientist’s life.