Timothy Hughes responds to my view that cellular senescence is a protection
against tumours with two common counter-arguments.
He suggests that there is immune surveillance of tumours; this idea has been
considered and investigated for many decades. At the moment the conclusion
is very unclear. While it seems that some tumours may be immunogenic,
it appears that most tumours are bvery poorly immunogenic. In addition,
as I read the literature there is very little hard evidence for immune
surveillance of tumours as a major protective function.
The second point is the large proliferative capacity of fibroblasts in
vitro. While this appears to be a serious obstacle to the idea, Timothy
himself points out that in general tumours never (?) senesce. The fact
is that an extended life-span or immortalization is the most universal
common phenotype in tumours; there is an almost perfect correllation
between "natural" tumours and immortalization. Of course, it has been
frequently pointed out that immortalization of a cell clone may be a
necessary requirement for a tumour, but it is clearly not a sufficient
condition. Additional morphological and "malignant" alterations are also
required.
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Sydney SHALL,
Laboratory of Cell and Molecular Biology,
Biology Building,
University of Sussex,
Brighton,
East Sussex BN1 9QG,
ENGLAND.
Telephone: +44.273.67.83.03
FAX: +44.273.67.83.33
E-Mail:
Janet: BAFA1 at uk.ac.sussex.central
Elsewhere: BAFA1 at central.sussex.ac.uk
EARN/BITNET: BAFA1%sussex.central at ukacrl
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