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Simian virus 40 large tumor antigen is unable to transform mouse embryonic fibroblasts lacking type 1 insulin-like
1Jefferson Cancer Institute, Thomas Jefferson University, Philadelphia, PA 19107-5541.
Abstract:
Fibroblast cell lines were established from mouse embryos homozygous for a targeted disruption of the Igf1r gene, encoding the type 1 receptor for insulin-like growth factor I (IGF-I) and from their wild-type littermates. The cells from the wild-type embryos (W cells) grow in serum-free medium supplemented with platelet-derived growth factor, epidermal growth factor, and IGF-I, whereas the cells from Igf1r(-/-) embryos (R- cells) do not, although they grow at a reduced rate in 10% fetal calf serum. The simian virus 40 (SV40) large T antigen, expressed from a transfected plasmid, can transform W cells, which form foci in monolayer cultures and colonies in soft agar (anchorage-independent growth). In contrast, the SV40 large tumor antigen, although normally expressed from the transfected template, is unable to transform R- cells, which remain contact-inhibited and fail to grow in soft agar. The transformed phenotype is restored if the R- cells carrying the SV40 large tumor antigen are stably transfected with a plasmid expressing the human IGF-I receptor. These results demonstrate that signaling via the IGF-I receptor is an indispensable component of the SV40 transformation pathway. This conclusion is further supported from the results of antisense RNA experiments with tumor cell lines showing that interference with the function of the IGF-I receptor has a profound effect on anchorage-independent growth, even under conditions that only modestly affect growth in monolayers.
Insights
Signaling via the insulin-like growth factor I receptor (IGF-IR) is essential for simian virus 40 (SV40) transformation. Loss of IGF-IR signaling prevents SV40-induced anchorage-independent growth, highlighting IGF-IR
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- The insulin-like growth factor I receptor (IGF-IR) plays a crucial role in cell growth and survival.
- Simian virus 40 (SV40) large T antigen is a potent oncogene capable of inducing cellular transformation.
- The precise role of IGF-IR signaling in SV40-mediated transformation is not fully understood.
Purpose of the Study:
- To investigate the necessity of IGF-IR signaling in SV40-induced cellular transformation.
- To determine if IGF-IR is a critical component of the SV40 transformation pathway.
Main Methods:
- Establishment of mouse embryonic fibroblast cell lines with and without functional Igf1r gene.
- Transfection with SV40 large T antigen.
- Assessment of transformation phenotypes, including focus formation and anchorage-independent growth.
- Restoration of transformation by reintroducing human IGF-IR.
Main Results:
- Fibroblasts lacking functional IGF-IR (R- cells) failed to undergo SV40-induced transformation, exhibiting contact inhibition and inability to grow in soft agar.
- Wild-type fibroblasts (W cells) transformed readily upon SV40 expression, displaying foci formation and anchorage-independent growth.
- Reintroduction of human IGF-IR into R- cells restored the transformed phenotype, enabling anchorage-independent growth.
- Antisense RNA experiments confirmed the critical role of IGF-IR in anchorage-independent growth.
Conclusions:
- IGF-IR signaling is indispensable for SV40-mediated cellular transformation.
- The IGF-IR pathway is a critical determinant of anchorage-independent growth induced by SV40.
- Targeting IGF-IR signaling may represent a therapeutic strategy against SV40-associated oncogenesis.