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Effect of ras-gene transformation on the inhibition of NIH3T3 cell growth by pertussis toxin
J D Hildebrandt1, L Lederman, D L Steffen
1Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01545.
Abstract:
To investigate the relationship between the effects of a pertussis toxin-inhibitable class of G-proteins and the ras family of protooncogenes on cell growth, we isolated multiple cell lines transformed by oncogenic Hras or Nras genes and measured the ability of pertussis toxin to inhibit their growth rate. Although all of the cell lines were morphologically transformed and could grow in agar suspension, there was considerable variability in their resistance to pertussis toxin, ranging from cell lines completely resistant to pertussis toxin to cell lines as sensitive to pertussis toxin as the parental cells from which they derived. For those lines resistant to pertussis toxin, this resistance is not due to an inability of pertussis toxin to reach or react with its intracellular target; pertussis toxin could be shown to ADP-ribosylate the endogenous G-proteins of all lines tested regardless of whether it affected their growth rate. There was a strong correlation between the level of active ras protein expressed in the different lines and the degree of resistance to pertussis toxin (r = 0.80). Although the Hras-transformed cell lines were more resistant to pertussis toxin as a group than the Nras-transformed cell lines, we believe that this is not a primary difference between Nras and Hras, but, rather, is due to a higher average level of expression of ras in the cell lines receiving Hras. We suggest that the consequences of ras transformation vary with the concentration of oncogenic ras present in the cell, and that different assays or different properties of transformation show different sensitivities to the level of ras expression.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Oncogenic ras proteins influence cell growth by affecting pertussis toxin-sensitive G-proteins. Higher ras levels correlate with increased resistance to pertussis toxin, impacting cell growth regulation.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- G-proteins mediate cellular signaling pathways.
- Ras proto-oncogenes are critical regulators of cell growth and differentiation.
- Pertussis toxin inhibits specific G-protein functions.
Purpose of the Study:
- To investigate the interplay between G-protein signaling and ras oncogenes in cell growth.
- To determine how oncogenic ras expression affects sensitivity to pertussis toxin.
Main Methods:
- Isolated cell lines expressing oncogenic Hras or Nras.
- Measured cell growth rates in the presence of pertussis toxin.
- Assessed pertussis toxin's ability to ADP-ribosylate G-proteins.
- Correlated active ras protein levels with toxin resistance.
Main Results:
- Variable resistance to pertussis toxin observed in ras-transformed cell lines.
- Pertussis toxin effectively ADP-ribosylated G-proteins in all tested lines.
- Strong positive correlation (r=0.80) found between active ras protein levels and pertussis toxin resistance.
- Hras-transformed lines showed higher resistance than Nras lines, likely due to higher ras expression.
Conclusions:
- Cellular response to oncogenic ras transformation is concentration-dependent.
- Ras protein levels modulate sensitivity to G-protein-targeted inhibitors like pertussis toxin.
- This suggests varying sensitivities of cellular processes to ras oncogene activity.