Rama Pai,
Brian Soreghan, Imre L. Szabo,
Meredith Pavelka, Dolgor Baatar & Andrzej S. Tarnawski
Medical Service, Department of
Veterans Affairs Medical
Center, Long Beach, California, and the Department of Medicine, University of
California, Irvine, California, USA
Correspondence
should be addressed to
Andrzej S. Tarnawski andrzej.tarnawski@med.va.gov
Prostaglandins (PGs), bioactive lipid molecules produced by
cyclooxygenase enzymes (COX-1 and COX-2), have diverse biological activities,
including growth-promoting actions on gastrointestinal mucosa1, 2, 3, 4, 5.
They are also implicated in the growth of colonic polyps and cancers6.
However, the precise mechanisms of these trophic actions of PGs remain unclear.
As activation of the epidermal growth factor receptor (EGFR) triggers mitogenic
signaling in gastrointestinal mucosa, and its expression is also upregulated in
colonic cancers and most neoplasms7, 8, 9, we investigated whether
PGs transactivate EGFR. Here we provide evidence that prostaglandin E2
(PGE2) rapidly phosphorylates EGFR and triggers the extracellular
signal-regulated kinase 2 (ERK2)−mitogenic signaling pathway in normal gastric
epithelial (RGM1) and colon cancer (Caco-2, LoVo and HT-29) cell lines.
Inactivation of EGFR kinase with selective inhibitors significantly reduces PGE2-induced
ERK2 activation, c-fos mRNA expression and cell proliferation. Inhibition of
matrix metalloproteinases (MMPs), transforming growth factor-
(TGF-
) or c-Src blocked
PGE2-mediated EGFR transactivation and downstream signaling
indicating that PGE2-induced EGFR transactivation involves signaling
transduced via TGF-
, an EGFR ligand,
likely released by c-Src-activated MMP(s). Our findings that PGE2
transactivates EGFR reveal a previously unknown mechanism by which PGE2
mediates trophic actions resulting in gastric and intestinal hypertrophy as
well as growth of colonic polyps and cancers.

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NSAIDs block prostaglandin synthesis,
a growth factor frequently
overexpress in cancer tumors.
Anti-Cancer Drugs:
February 2002 - Volume
13 - Issue 2 - pp 127-137
http://journals.lww.com/anti-cancerdrugs/Abstract/2002/02000/COX_2_inhibitors_in_cancer_treatment_and.3.aspx
COX-2 inhibitors
in cancer treatment and prevention, a recent
development
Abstract
Epidemiological
and experimental studies have demonstrated the effect of non-steroidal anti-inflammatory
drugs (NSAIDs) in the prevention of human cancers. NSAIDs block endogenous prostaglandin synthesis through inhibition
of cyclooxygenase (COX) enzymatic activity. COX-2, a key isoenzyme in
conversion of arachidonic acid to prostaglandins, is inducible
by various agents such as growth factors and tumor promoters, and is frequently
overexpressed in various tumors. The contribution of COX-2 to carcinogenesis
and the malignant phenotype of tumor cells has been thought to be related to
its abilities to (i) increase production of prostaglandins, (ii) convert
procarcinogens to carcinogens, (iii) inhibit apoptosis, (iv) promote
angiogenesis, (v) modulate inflammation and immune function, and (vi) increase
tumor cell invasiveness, although some studies indicated that NSAIDs have
COX-2-independent effects. A number of clinical trials using COX-2 inhibitors
are in progress, and the results from these studies will increase our
understanding of COX-2 inhibition in both cancer treatment and prevention. The
combination of COX-2 inhibitors with radiation or other anti-cancer or cancer
prevention drugs may reduce their side effects in future cancer prevention and
treatment. Recent progress in the treatment and prevention of cancers of the
colon, esophagus, lung, bladder, breast and prostate with NSAIDs, especially
COX-2 inhibitors, is also discussed
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
NSAIDs inhibit the proliferation rate, alter the cell cycle
distribution, and induce apoptosis in colon cancer cell lines
Biochemical Pharmacology
Volume 52, Issue 2,
26 July 1996, Pages 237–245
Effects of nonsteroidal anti-inflammatory drugs on proliferation
and on induction of apoptosis in colon cancer cells by a
prostaglandin-independent pathway
Nonsteroidal anti-inflammatory drugs (NSAIDs) decrease the
incidence of and mortality from colon cancer. We observed that NSAIDs inhibit the
proliferation rate, alter the cell cycle distribution, and induce apoptosis in
colon cancer cell lines. We evaluated
whether the inhibition by NSAIDs of prostaglandin (PG) synthesis is required
for their effects
on colon cancer cells by studying two human colon cancer cell lines: HCT-15 and
HT-29. HCT-15, which lacks cyclooxygenase transcripts, does not produce PGs
even when exogenously stimulated, whereas HT-29 produces PGE2, PGF2α, and PGI2. HCT-15 and HT-29 cells, when treated for up to
72 hr with 200 μM sulindac sulfide (an active metabolite of sulindac) or 900 μM
piroxicam, showed changes in proliferation, cell cycle phase distribution, and
apoptosis. Treatment with PGE2, PGF2α, and PGI2, following a variety of protocols, and at
concentrations between 10−6 and 10−11 M, failed to reverse the effects of NSAIDs on these three
parameters of cell growth. We concluded that NSAIDs inhibit the
proliferation rate of the two colon cancer cell lines independent of their
ability to inhibit PG synthesis. Thus,
alternative mechanisms for their activity on tumor cell growth must be
entertained. These observations may be relevant to the mechanism of colon tumor
inhibition by NSAIDs. two colon cancer cell lines independent of their
ability to inhibit PG synthesis. Thus, alternative mechanisms for their
activity on tumor cell growth must be entertained. These observations may be
relevant to the mechanism of colon tumor inhibition by NSAIDs.
Aspirin
induces necrosis factor for abnormal cell death. Detailed article at http://www.fasebj.org/content/15/7/1273.full