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The Sos1 and Sos2 Ras-specific exchange factors: differences in placental expression and signaling properties
Abstract:
Targeted disruption of both alleles of mouse sos1, which encodes a Ras-specific exchange factor, conferred mid-gestational embryonic lethality that was secondary to impaired placental development and was associated with very low placental ERK activity. The trophoblastic layers of sos1(-/-) embryos were poorly developed, correlating with high sos1 expression in wild-type trophoblasts. A sos1(-/-) cell line, which expressed readily detectable levels of the closely related Sos2 protein, formed complexes between Sos2, epidermal growth factor receptor (EGFR) and Shc efficiently, gave normal Ras.GTP and ERK responses when treated with EGF for < or =10 min and was transformed readily by activated Ras. However, the sos1(-/-) cells were resistant to transformation by v-Src or by overexpressed EGFR and continuous EGF treatment, unlike sos1(+/-) or wild-type cells. This correlated with Sos2 binding less efficiently than Sos1 to EGFR and Shc in cells treated with EGF for > or =90 min or to v-Src and Shc in v-Src-expressing cells, and with less ERK activity. We conclude that Sos1 participates in both short- and long-term signaling, while Sos2-dependent signals are predominantly short-term.
Insights
Targeted disruption of the mouse sos1 gene caused embryonic lethality due to poor placental development. Sos1 protein is crucial for both short- and long-term cellular signaling pathways.
Area of Science:
- Molecular Biology
- Developmental Biology
- Cell Signaling
Background:
- The Son of Sevenless (Sos) proteins are guanine nucleotide exchange factors (GEFs) that activate Ras.
- Sos1 is a key mediator in signaling pathways initiated by receptor tyrosine kinases like EGFR.
- The specific roles of Sos1 versus Sos2 in embryonic development and cellular signaling remain incompletely understood.
Purpose of the Study:
- To investigate the function of Sos1 during mouse embryonic development.
- To elucidate the distinct roles of Sos1 and Sos2 in cellular signaling pathways.
- To determine the contribution of Sos1 to placental development and embryonic viability.
Main Methods:
- Generation of mice with targeted disruption of both alleles of the sos1 gene (sos1(-/-)).
- Analysis of embryonic development, placental morphology, and ERK activity in sos1(-/-) embryos.
- Establishment and characterization of a sos1(-/-) cell line expressing Sos2.
- Assessment of Ras.GTP and ERK activation in response to epidermal growth factor (EGF) and v-Src in wild-type, sos1(+/-), and sos1(-/-) cells.
Main Results:
- Targeted disruption of sos1 resulted in mid-gestational embryonic lethality, linked to impaired placental development and reduced ERK activity.
- sos1(-/-) embryos exhibited poorly developed trophoblastic layers, correlating with high sos1 expression in wild-type trophoblasts.
- sos1(-/-) cells expressing Sos2 showed normal short-term Ras.GTP and ERK responses to EGF but were resistant to long-term EGF stimulation or v-Src transformation.
- Sos2 exhibited less efficient binding to EGFR, Shc, and v-Src compared to Sos1, leading to diminished long-term ERK activity.
Conclusions:
- Sos1 plays a critical role in both short- and long-term cellular signaling, essential for embryonic development and placental function.
- Sos2 primarily mediates short-term signaling events, with limited contribution to long-term signaling pathways.
- Differential binding efficiencies of Sos1 and Sos2 to signaling partners underlie their distinct roles in cellular responses.