G.H.,cancer, & oncogenes

lappel at eagle.wesleyan.edu lappel at eagle.wesleyan.edu
Tue Feb 15 17:05:08 EST 1994

In article <94043.1652533RJP8 at QUCDN.QueensU.CA>, <3RJP8 at QUCDN.QueensU.CA> writes:
> In some preliminary research on the role of growth hormone with respect to
> its effects on cancerous cells, is it correct to assume that oncogenes, the
>  so-called "cancer-causing" gene is a growth hormone stimulant?  If not, how
> is there a connection between growth hormone and cancer???  I have heard
> conflicting studies, and they seem to tie glucose into the process...where does
>  this sugar come into play (other than the fact that the cell needs glucose's
>  energy to divide in the first place.)  Thanks for any help you may be able to
>  give me...
	I can't tell what level you are asking this question from, so I will
take the risk of insulting your intelligence and give you a
cancer-for-non-scientists answer, to use as it fits:
	As an adult, you are not doing a lot of growth and differentiation. 
You are pretty much maintaining yourself as you are.  But at other times in
your life, particularly during enbryogenesis, you had to grow very rapidly, and
differentiate new cell types.  Therefore, you must have genes capable of
directing such growth and differentiation.  Because you never lose genetic
information from your cells (let's skip the immune system for now), those genes
must still be around in all of your cells.  But they must somehow be turned off
so that you don't grow exponentially like an infant!
	Now imagine that something goes wrong in the regulatory system that
keeps those embryonic-growth genes off, and they turn on at the wrong place and
time.  That, in its simplest form, is cancer: cells dividing without proper
regulation.  Those genes that were initially responsible for growth, but if 
turned back on inadvertently in the wrong situation can cause tumors, are 
called proto-oncogenes.  Once the proto-oncogene actually gets turned back on,
 it is called an oncogene.
	That vocabulary established, what does this have to do with growth
hormones and other sorts of factors?  Well, genes involved in growth tend to
operate through, or be regulated by, growth factors.  So one can imagine all
sorts of points along a regulatory cascade or network involving a growth
hormone, that a gene could function as an oncogene if misregulated. But not
every oncogene need be associated with growth hormone -- some could be on
different regulatory or signalling pathways.
	And where does this misregulation come from?  The simplest case to
imagine is a spontaneous mutation that turns a gene from off to on.  Say a
blast of sunshine to a cell causes damage to its DNA, that when repaired
incorporates a error in the critical sequence for keeping the gene off.  Bingo
-- you've got cancer. (Let's ignore dominant/recesssive for now, and keep
things simple.)
	Here concludes oncogenes 101. Hope it helps -- if not the questioner,
then someone else.

Laurel F. Appel     (LAPPEL at EAGLE.WESLEYAN.EDU)
Genetics Group
Biology Dept.
Wesleyan University
Middletown, CT 06459

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