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Modulation of nuclear proto-oncogene expression and cellular growth in myeloid leukemic cells by human interferon
A H Marshall1, D Alper, J Hiscott
1Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada.
Abstract:
To address the mechanisms that regulate expression of specific growth-related nuclear proto-oncogenes, the transcript levels of the c-fos, c-myc, (2'5')-oligoadenylate synthetase, IFN-alpha 1, and IFN-beta 1 genes have been measured in the human leukemic cell lines KG-1, U937, and HL-60 following growth stimulation by serum, induction of differentiation by tumor-promoting agents, and/or treatment of cells with exogenously supplied alpha interferon (rIFN-alpha 2). Production of fos and myc RNA was measured by S1 mapping, using fos DNA probes which identified either primary unspliced transcripts or steady-state-spliced mRNA levels, and using a myc probe which spanned the two major c-myc start sites, P1 and P2. Pretreatment of a quiescent KG-1 cell population with IFN for 18 hours before serum addition decreased the stimulation of both fos and myc RNA production. In HL-60 and U937 cells, IFN pretreatment had no inhibitory effect on serum-induced fos or myc transcription; however, in U937, rIFN-alpha 2 treatment alone stimulated fos mRNA 11-fold. Expression of 2'5'oligoadenylate synthetase was induced in IFN-treated cultures but not in cells stimulated with serum alone. No serum-induced IFN-alpha 1 or IFN-beta 1 gene expression was observed in KG-1 or U937 cells. These results demonstrate that exogenous rIFN-alpha 2 treatment of quiescent KG-1 cells can antagonize the effect of growth factors by altering expression of nuclear proto-oncogenes, but in general growth inhibition is not obligatorily coupled to inhibition of proto-oncogene transcription.
Insights
Interferon (IFN) can alter proto-oncogene expression in leukemia cells, sometimes blocking growth factor effects. However, this doesn't always mean growth inhibition is linked to reduced proto-oncogene transcription.
Area of Science:
- Molecular Biology
- Cell Biology
- Immunology
Background:
- Proto-oncogenes like c-fos and c-myc regulate cell growth.
- Interferons (IFNs) are key immune signaling molecules with potential anti-cancer effects.
- Understanding how IFNs affect proto-oncogene expression is crucial for cancer research.
Purpose of the Study:
- To investigate the regulatory mechanisms of growth-related nuclear proto-oncogenes.
- To determine the impact of serum, differentiation agents, and interferon (IFN) on proto-oncogene expression in human leukemia cell lines.
- To explore the relationship between IFN treatment and proto-oncogene transcription.
Main Methods:
- Measured transcript levels of c-fos, c-myc, (2'5')-oligoadenylate synthetase, IFN-alpha 1, and IFN-beta 1 genes.
- Utilized S1 mapping with specific DNA probes to quantify fos and myc RNA production.
- Treated human leukemic cell lines (KG-1, U937, HL-60) with serum, tumor promoters, and recombinant human interferon-alpha 2 (rIFN-alpha 2).
Main Results:
- IFN pretreatment inhibited serum-induced fos and c-myc RNA production in KG-1 cells.
- IFN pretreatment did not inhibit serum-induced fos or c-myc transcription in HL-60 and U937 cells.
- rIFN-alpha 2 alone stimulated fos mRNA in U937 cells; IFN induced (2'5')-oligoadenylate synthetase expression, but not IFN-alpha 1 or IFN-beta 1.
- Exogenous rIFN-alpha 2 antagonized growth factor effects on proto-oncogenes in KG-1 cells.
Conclusions:
- Exogenous rIFN-alpha 2 can alter proto-oncogene expression, potentially antagonizing growth factor signaling.
- Growth inhibition is not consistently coupled with the inhibition of proto-oncogene transcription by IFN.
- Leukemia cell lines exhibit differential responses to IFN and growth factors regarding proto-oncogene regulation.