Leonard Hayflick - Why are cancer cells immortal? (169/187)

To hear more of Leonard Hayflick’s stories, go to the playlist:    • Leonard Hayflick - Childhood in Pennsylvan...  

Born in 1928, Leonard Hayflick is known for his research in cell biology, virus vaccine development, and mycoplasmology. His discovery that human cells divide for a limited number of times in vitro has been named after him as the Hayflick limit. [Listener: Christopher Sykes; date recorded: 2011]

TRANSCRIPT: The convergence of these three fields, these three disparate fields, about which workers in each of the three knew nothing about the work of the other two, came together in the ways... the way that I mentioned; quite by accident, as you now can realise. It came very close to resolving all the questions that I was pursuing. We had reached a point where, first of all, we knew there was a counter – not a clock but a counter – and we knew that it was located in the nucleus – we had done experiments that located a nucleus – and it was at that point that Calvin Harley and Carol Greider met, and... and as I've recited it, essentially discovered the molecular basis for what I had found.

But there still is one very important remaining question, and that is that as I had discovered, unlike normal cells, cancer cells are immortal. How do cancer cells avoid this... this shortening-of-telomere problem and therefore stop dividing themselves? That was answered when Carol and Liz Blackburn discovered an enzyme called telomerase, a very unusual enzyme with strange and novel behaviour that I won't discuss, it's quite detailed, but what it does in principal is to do the following.

As telomeres are lost at each round of division in a cancer cell, this enzyme telomerase is expressed, activated, and what it does is to lay on the missing pieces of telomeres. Telomeres are composed of four chemicals, and these four chemicals are reattached to the DNA molecule at each round of division. When these four chemicals should be lost, it reattaches them, essentially, and consequently maintains the telomere length more or less constant, although actually there are some telomeres that are lost but they're never lost to the extent in cancer cells as they're lost in normal cells.

Consequently, a cancer cell is immortal because this magic enzyme telomerase is expressed and maintains telomere length essentially constant. So that answered the final question: how do cancer cells circumvent the inevitably of finitude if their telomeres have become shortened, which they do not, as I just explained. So these were phenomenal findings and they resulted, actually, in the year 2009 in the award of the Nobel Prize in Physiology or Medicine to Liz Blackburn, Carol Greider, and John Szostak for discovering the molecular basis for what I had discovered and also for discovering how chromosomes are protected at their ends by these telomeres.

So this was quite an astounding finding. It made headlines even in lay newspapers and of course in the scientific literature. And it finally gave final proof, I suppose you would say, or the final bit of evidence that persuaded scientists to believe what I had found, because there were... it took several decades before there were even a handful of scientists who believed what I had discovered because of the previous 60-year dogma that said that when you put cells in culture, they divided forever unless you made some technical mistake.