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The coupling of alpha6beta4 integrin to Ras-MAP kinase pathways mediated by Shc controls keratinocyte proliferation
F Mainiero1, C Murgia, K K Wary
1Department of Pathology, New York University School of Medicine, New York 10016, USA.
Abstract:
The signaling pathways linking integrins to nuclear events are incompletely understood. We have examined intracellular signaling by the alpha6beta4 integrin, a laminin receptor expressed in basal keratinocytes and other cells. Ligation of alpha6beta4 in primary human keratinocytes caused tyrosine phosphorylation of Shc, recruitment of Grb2, activation of Ras and stimulation of the MAP kinases Erk and Jnk. In contrast, ligation of the laminin- and collagen-binding integrins alpha3beta1 and alpha2beta1 did not cause these events. While the stimulation of Erk by alpha6beta4 was suppressed by dominant-negative Shc, Ras and RhoA, the activation of Jnk was inhibited by dominant-negative Ras and Rac1 and by the phosphoinositide 3-kinase inhibitor Wortmannin. Adhesion mediated by alpha6beta4 induced transcription from the Fos serum response element and promoted cell cycle progression in response to mitogens. In contrast, alpha3beta1- and alpha2beta1-dependent adhesion did not induce these events. These findings suggest that the coupling of alpha6beta4 integrin to the control of cell cycle progression mediated by Shc regulates the proliferation of basal keratinocytes and possibly other cells which are in contact with the basement membrane in vivo.
Insights
The alpha6beta4 integrin activates Shc, Ras, and MAP kinases, promoting keratinocyte proliferation. This integrin signaling pathway is crucial for regulating cell cycle progression in basal keratinocytes.
Area of Science:
- Cell Biology
- Molecular Biology
- Dermatology
Background:
- Integrins mediate cell adhesion and signal transduction.
- Signaling pathways connecting integrins to nuclear events require further elucidation.
- The alpha6beta4 integrin is a key laminin receptor in basal keratinocytes.
Purpose of the Study:
- To investigate the intracellular signaling pathways activated by the alpha6beta4 integrin.
- To determine how alpha6beta4 integrin ligation influences cellular events like proliferation.
- To compare alpha6beta4 signaling with that of other integrins (alpha3beta1, alpha2beta1).
Main Methods:
- Primary human keratinocyte culture.
- Integrin ligation assays.
- Analysis of protein phosphorylation (e.g., Shc tyrosine phosphorylation).
- Assessment of signaling molecule activation (Ras, MAP kinases Erk and Jnk).
- Use of dominant-negative constructs and kinase inhibitors (Wortmannin).
- Reporter gene assays (Fos serum response element).
- Cell cycle progression analysis.
Main Results:
- Alpha6beta4 integrin ligation induced Shc phosphorylation, Grb2 recruitment, Ras activation, and MAP kinase (Erk, Jnk) stimulation.
- Other integrins (alpha3beta1, alpha2beta1) did not trigger these specific signaling events.
- Erk activation was dependent on Shc, Ras, and RhoA; Jnk activation involved Ras, Rac1, and PI3K.
- Alpha6beta4-mediated adhesion promoted transcription from the Fos serum response element and cell cycle progression.
- Alpha3beta1- and alpha2beta1-dependent adhesion did not induce these nuclear events.
Conclusions:
- The alpha6beta4 integrin couples to Shc-mediated signaling pathways.
- This coupling regulates cell cycle progression and proliferation in basal keratinocytes.
- Alpha6beta4 integrin signaling is distinct from that of alpha3beta1 and alpha2beta1 integrins.
- The findings highlight the role of alpha6beta4 in maintaining keratinocyte proliferation at the basement membrane.