# MECHANISMS OF TUMOR PROMOTION IN VITRO AND IN VIVO

> **NIH NIH R01** · OREGON HEALTH & SCIENCE UNIVERSITY · 1992 · $234,466

## Abstract

Tumor promoters act by stimulating the clonal selection and outgrowth of
initiated cell populations.  This process involves the activation of
cellular signalling pathways normally involved in the regulation of cell
proliferation.  Several distinct tumor promoters are known to exert
specific-effects on these signaling pathpromoters such as
12-O-tetradecanoyl 13-phorbol acetate (TPA) can substitute for endogenous
diacylglycerols in the activation of protein kinase C (pkC).  Okadaic acid
is a specific and potent inhibitor of the protein phosphatase 1 and 2A.
Thapsigargin causes an elevation of intra-cellular Ca(2+) levels subsequent
to inhibition of the Ca(2+)-ATPase responsible for sequestering Ca(2+) in
intracellular stores. We have obtained data indicating that these disparate
tumor promoters are capable of interacting both additively and
synergistically to stimulate the expression of several genes, including
VL30.  VL30 is an endogenous murine retrovirus which is abundantly
expressed in response to either transformation or proliferative stimuli.
We have shown that a single VL30 element, transferred from the mouse genome
to Rat-1 fibroblasts by pseudovirion-mediated transfection, is capable of
responding transcriptionally to a number of agonists, including TPA and
EGF.  At least two independent signaling pathways, one involving pkC and
the other increased intracellular Ca(2+), are involved in the regulation of
VL30 expression.  Deletional mutagenesis studies have implicated a triple
repeat unit present in the VL30 LTR as an enhancer element capable of
mediating responsiveness to TPA and EGF.  The ability of thapsigargin and
okadaic acid to interact positively with TPA in stimulating gene expression
also maps to this repeat unit, and to an AP-1-like element present in this
repeat.  The initial goal of this proposal is to determine the role of
other putative response elements, primarily a CArG element, in this
regulation, and to identify and characterize the DNA binding proteins
involved in transcriptional regulation from these elements.  Once the
functional response element has been full defined, we propose to produce
transgenic mice containing the tumor promoter-responsive element linked to
a lacZ reporter gene.  A major goal of this proposal is to determine the
effects of the three tumor promoters on gene expression in vivo, by
monitoring lacZ expression in these transgenic mice in response to topical
applications of TPA, thapsigargin, and okadaic-acid, alone and in
combination.  These experiments will indicate whether the observed
interactions between the signaling pathways responding to these tumor
promoters in vitro also function in vivo.  We will determine whether
cell-type- or tissue-specific changes in lacZ reporter gene expression are
associated with the growth of tumors.  We will use primary cell lines
established from these transgenic mice to study the effect of targeted
disruptions of specific signaling pathways and DNA-protein interac...

## Key facts

- **NIH application ID:** 3178219
- **Project number:** 2R01CA039360-09
- **Recipient organization:** OREGON HEALTH & SCIENCE UNIVERSITY
- **SAM.gov UEI:** NPSNT86JKN51
- **Principal Investigator:** BRUCE E. MAGUN
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 1992
- **Award amount:** $234,466
- **Award type:** 2
- **Project period:** 1984-07-01 → 1996-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/3178219

## Citation

> US National Institutes of Health, RePORTER application 3178219, MECHANISMS OF TUMOR PROMOTION IN VITRO AND IN VIVO (2R01CA039360-09). Retrieved via MORVS 2026-10-24 from https://api.morvs.ai/grant/nih/3178219. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*