# MECHANISMS OF TUMOR PROMOTION IN VITRO

> **NIH NIH R01** · OREGON HEALTH & SCIENCE UNIVERSITY · 1988 · $210,446

## Abstract

Phorbol ester tumor promoters induce the expression of certain
proliferation-associated genes by a pathway that involves activation of the
Ca2+ and phospholipid-dependent protein kinase C.  We have shown that
activation of protein kinase C by the phorbol ester TPA induces the
expression of VL30, a proliferation-associated gene which can also be
induced by EGF.  Structurally, VL30 resembles both retroviruses and
eukaryotic transposable elements in the possession of long terminal repeats
(LTR) which appear to be required for the insertional mutagenesis caused by
integration of retroviruses.

Retroviral LTRs contain sequences which function as promoters and enhancers
of gene transcription.  Activation of cellular oncogenes following the
insertion of retroviruses may reflect the replacement of normal cellular
regulatory elements with the retroviral control elements.  A major goal of
this proposal is the characterization of the putative regulatory elements
within the VL30 LTR, particularly in identifying those sequences within the
VL30 LTR which respond to protein kinase C activation.  This will be
accomplished by detailed study of two cell lines subcloned from Rat-1 cells
which had been infected with VL30-containing psuedovirions.  Both cell
lines express VL30 RNA in response to TPA treatment.  Structural techniques
will be used to identify the VL30 sequences which have become integrated in
these subclones, and the ability of these sequences to act as
transcriptional promoters or enhancers will be studied by inserting these
sequences into expression vectors.  Once these sequences have been
identified, we will attempt to identify proteins in nuclear extracts which
bind to these DNA sequences.  It will be particularly relevant to our
understanding of carcinogenesis if can identify DNA-binding proteins whose
abundance or activity are modified by treatment with phorbol ester tumor
promoters.

Expression of retroviral genes has been correlated with increased rates of
transposition in other systems.  We will alter the expression of VL30RNA by
a variety of means, including long-term exposure to TPA or EGF or
transfection of cells with known oncogenes in order to determine the
relationship between gene expression and translocation in this system.  We
will also investigate the oncogenic potential of VL30 elements by
monitoring the transformation rate in cells which have been infected with
VL30.  We will simultaneously monitor the translocation of VL30 elements by
using specific probes derived from our structural studies of the VL30
integrants and the flanking host sequences.  These studies will allow us to
determine whether transposition and transformation are correlated in the
VL30 system, and whether agents which increase VL30 expression can act as
carcinogens.

## Key facts

- **NIH application ID:** 3178224
- **Project number:** 5R01CA039360-05
- **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:** 1988
- **Award amount:** $210,446
- **Award type:** 5
- **Project period:** 1984-07-01 → 1991-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/3178224

## Citation

> US National Institutes of Health, RePORTER application 3178224, MECHANISMS OF TUMOR PROMOTION IN VITRO (5R01CA039360-05). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/3178224. Licensed CC0.

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