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Molecular and Cellular Biology, December 2000, p. 9271-9280, Vol. 20, No. 24
Department of Molecular and Cell Biology,
University of California at Berkeley, Berkeley, California 94720
Received 5 May 2000/Returned for modification 20 June 2000/Accepted 25 September 2000
Evasion of apoptosis appears to be a necessary event in tumor
progression. Some oncogenes, such as c-myc and E1A, induce
apoptosis in the absence of survival factors. However, others, such as
bcl-2 and v-src, activate antiapoptotic
pathways. For v-Src, these antiapoptotic pathways are dependent on the
function of Ras, phosphatidylinositol (PI) 3-kinase, and Stat3. Here we
asked whether v-Src can activate a proapoptotic signal when survival
signaling is inhibited. We show that when the functions of Ras and PI
3-kinase are inhibited, v-src-transformed Rat-2 fibroblasts
undergo apoptosis, evidenced by loss of adherence, nuclear
fragmentation, and chromosomal DNA degradation. The apoptotic response
is dependent on activation of caspase 3. Under similar conditions
nontransformed Rat-2 cells undergo considerably lower levels of
apoptosis. Apoptosis induced by v-Src is accompanied by a loss of
mitochondrial membrane potential and release of cytochrome
c and is blocked by overexpression of bcl-2,
indicating that it is mediated by the mitochondrial pathway. However
apoptosis induced by v-Src is not accompanied by an increase in the
level of p53 and is not dependent on p53 function. Thus v-Src generates
a p53-independent proapoptotic signal.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
v-Src Generates a p53-Independent Apoptotic
Signal
*
Corresponding author. Mailing address: Department of
Molecular and Cell Biology, University of California at Berkeley, 401 Barker Hall #3204, Berkeley, CA 94720-3204. Phone: (510) 642-1508. Fax:
(510) 643-1729. E-mail: smartin{at}socrates.berkeley.edu.
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