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                                      9/25/90

                    7. UNRAVELING THE BIOLOGY OF CELLULAR AGING

       We grow old  because  our cells grow old -- a process we think of as
       inevitable and immutable.

       Cancer cells, however,  seem to escape  the  process  of  aging  and
       become "immortal."  This review of recent research sheds some light
       on the cellular aging process and suggests a connection  between the
       biology of cellular aging and the biology of cancer.

       Investigators have observed  that  a human diploid fibroblast placed
       in a cell  culture goes through a  limited,  predictable  number  of
       replications before it stops dividing.

       Moreover, the replicative life span of an animal's  fibroblasts  has
       been shown to  correlate  with the life span of the species.  When a
       fibroblast becomes senescent, its  growth is stopped at a particular
       part of the cell cycle (the G1/S boundary) and it ceases  to respond
       to certain growth factors.

       Certain growth-inducing proto-oncogenes seem to be turned off, while
       concentrations of possibly  growth-retarding  proteins  seem  to  be
       increased.

       Researchers speculate that cancer cells circumvent the mechanisms of
       senescence, and experiments  have   shown  that  specific  molecular
       manipulations can cause a senescent cell to begin dividing again.

       It remains to  be  shown whether further understanding  of  cellular
       aging will have  implications for the control of aging in plants and
       animals, but the prospect is exciting.  -- ALK.

       Goldstein S.

       Replicative senescence: the human fibroblast comes of age.

       Science 1990 Sep 7; 249:1129-33



























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