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The Rac activator Tiam1 is required for (alpha)3(beta)1-mediated laminin-5 deposition, cell spreading, and cell migration.

Hamelers IH, Olivo C, Mertens AE, Pegtel DM, van der Kammen RA, Sonnenberg A, Collard JG - J. Cell Biol. (2005)

Bottom Line: Both Tiam1 and V12Rac1 can rescue the defects of Tiam1-/- keratinocytes, indicating that these deficiencies are caused by impaired Tiam1-mediated Rac activation.Moreover, Tiam1 deficiency impairs keratinocyte migration in vitro and reepithelialization of excision wounds in mouse skin.Our studies indicate that Tiam1 is a key molecule in alpha3beta1-mediated activation of Rac, which is essential for proper production and secretion of LN5, a requirement for the spreading and migration of keratinocytes.

View Article: PubMed Central - PubMed

Affiliation: Division of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.

ABSTRACT
The Rho-like guanosine triphosphatase Rac1 regulates various signaling pathways, including integrin-mediated adhesion and migration of cells. However, the mechanisms by which integrins signal toward Rac are poorly understood. We show that the Rac-specific guanine nucleotide exchange factor Tiam1 (T-lymphoma invasion and metastasis 1) is required for the integrin-mediated laminin (LN)-5 deposition, spreading, and migration of keratinocytes. In contrast to wild-type keratinocytes, Tiam1-deficient (Tiam1-/-) keratinocytes are unable to adhere to and spread on a glass substrate because they are unable to deposit their own LN5 substrate. Both Tiam1 and V12Rac1 can rescue the defects of Tiam1-/- keratinocytes, indicating that these deficiencies are caused by impaired Tiam1-mediated Rac activation. Tiam1-/- cells are unable to activate Rac upon alpha3beta1-mediated adhesion to an exogenous LN5 substrate. Moreover, Tiam1 deficiency impairs keratinocyte migration in vitro and reepithelialization of excision wounds in mouse skin. Our studies indicate that Tiam1 is a key molecule in alpha3beta1-mediated activation of Rac, which is essential for proper production and secretion of LN5, a requirement for the spreading and migration of keratinocytes.

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Tiam1 deficiency delays wound repair in vivo. (A) Examples of cross sections from 3-d-old wounds from WT and Tiam1−/− mice stained for LN5 (top) and of cross sections from paraffin-embedded 4-d-old wounds stained with hematoxylin and eosin (HE; bottom). Arrows and drawings indicate the position of the advancing epithelial edges. Bar, 250 μm. (B) Histograms of wound diameters (in micrometers ± SEM) measured from 12 wounds in the skin of three mice per group at each time point. *, P < 0.01; **, P < 0.005.
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fig9: Tiam1 deficiency delays wound repair in vivo. (A) Examples of cross sections from 3-d-old wounds from WT and Tiam1−/− mice stained for LN5 (top) and of cross sections from paraffin-embedded 4-d-old wounds stained with hematoxylin and eosin (HE; bottom). Arrows and drawings indicate the position of the advancing epithelial edges. Bar, 250 μm. (B) Histograms of wound diameters (in micrometers ± SEM) measured from 12 wounds in the skin of three mice per group at each time point. *, P < 0.01; **, P < 0.005.

Mentions: In mouse skin, Tiam1 is strongly expressed in basal and suprabasal keratinocytes of the interfollicular epidermis and in hair follicles. Tiam1−/− mice show no major skin phenotype, but are resistant to Ras-induced skin tumors (Malliri et al., 2002). Because of the effect of Tiam1 deficiency in LN5 production and secretion in keratinocytes, we wondered whether defects in the skin of Tiam1−/− mice could be found by a more detailed analysis of intact and wounded skin. Analysis of intact skin revealed no differences in the deposition and processing of LN5, the expression of the α3 and β4 integrins, and the components of the basal lamina between WT and Tiam1−/− mice (Fig. S3, available at http://www.jcb.org/cgi/content/full/jcb.200509172/DC1, and not depicted). Subsequently, we generated full-thickness excision wounds in the skin of WT and Tiam1−/− mice, and wound closure was monitored over time. The repair of such excision wounds is achieved by clot formation followed by extensive migration and hyperproliferation of keratinocytes at the wound rim, which is partly dependent on LN5 secretion. Immunological and histological analysis revealed that the closure of the wound margins was significantly delayed in the Tiam1−/− mice when compared with WT mice (Fig. 9). The reepithelialization process was completed in ∼5–6 d in both WT and Tiam1−/− mice. Although these data do not exclude the possibility that Tiam1 may also influence wound repair by other mechanisms, the delayed reepithelialization of the wounds in the skin of Tiam1−/− mice supports our in vitro findings that Tiam1 plays a role in LN5 deposition that is required for the spreading and migration of keratinocytes.


The Rac activator Tiam1 is required for (alpha)3(beta)1-mediated laminin-5 deposition, cell spreading, and cell migration.

Hamelers IH, Olivo C, Mertens AE, Pegtel DM, van der Kammen RA, Sonnenberg A, Collard JG - J. Cell Biol. (2005)

Tiam1 deficiency delays wound repair in vivo. (A) Examples of cross sections from 3-d-old wounds from WT and Tiam1−/− mice stained for LN5 (top) and of cross sections from paraffin-embedded 4-d-old wounds stained with hematoxylin and eosin (HE; bottom). Arrows and drawings indicate the position of the advancing epithelial edges. Bar, 250 μm. (B) Histograms of wound diameters (in micrometers ± SEM) measured from 12 wounds in the skin of three mice per group at each time point. *, P < 0.01; **, P < 0.005.
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fig9: Tiam1 deficiency delays wound repair in vivo. (A) Examples of cross sections from 3-d-old wounds from WT and Tiam1−/− mice stained for LN5 (top) and of cross sections from paraffin-embedded 4-d-old wounds stained with hematoxylin and eosin (HE; bottom). Arrows and drawings indicate the position of the advancing epithelial edges. Bar, 250 μm. (B) Histograms of wound diameters (in micrometers ± SEM) measured from 12 wounds in the skin of three mice per group at each time point. *, P < 0.01; **, P < 0.005.
Mentions: In mouse skin, Tiam1 is strongly expressed in basal and suprabasal keratinocytes of the interfollicular epidermis and in hair follicles. Tiam1−/− mice show no major skin phenotype, but are resistant to Ras-induced skin tumors (Malliri et al., 2002). Because of the effect of Tiam1 deficiency in LN5 production and secretion in keratinocytes, we wondered whether defects in the skin of Tiam1−/− mice could be found by a more detailed analysis of intact and wounded skin. Analysis of intact skin revealed no differences in the deposition and processing of LN5, the expression of the α3 and β4 integrins, and the components of the basal lamina between WT and Tiam1−/− mice (Fig. S3, available at http://www.jcb.org/cgi/content/full/jcb.200509172/DC1, and not depicted). Subsequently, we generated full-thickness excision wounds in the skin of WT and Tiam1−/− mice, and wound closure was monitored over time. The repair of such excision wounds is achieved by clot formation followed by extensive migration and hyperproliferation of keratinocytes at the wound rim, which is partly dependent on LN5 secretion. Immunological and histological analysis revealed that the closure of the wound margins was significantly delayed in the Tiam1−/− mice when compared with WT mice (Fig. 9). The reepithelialization process was completed in ∼5–6 d in both WT and Tiam1−/− mice. Although these data do not exclude the possibility that Tiam1 may also influence wound repair by other mechanisms, the delayed reepithelialization of the wounds in the skin of Tiam1−/− mice supports our in vitro findings that Tiam1 plays a role in LN5 deposition that is required for the spreading and migration of keratinocytes.

Bottom Line: Both Tiam1 and V12Rac1 can rescue the defects of Tiam1-/- keratinocytes, indicating that these deficiencies are caused by impaired Tiam1-mediated Rac activation.Moreover, Tiam1 deficiency impairs keratinocyte migration in vitro and reepithelialization of excision wounds in mouse skin.Our studies indicate that Tiam1 is a key molecule in alpha3beta1-mediated activation of Rac, which is essential for proper production and secretion of LN5, a requirement for the spreading and migration of keratinocytes.

View Article: PubMed Central - PubMed

Affiliation: Division of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.

ABSTRACT
The Rho-like guanosine triphosphatase Rac1 regulates various signaling pathways, including integrin-mediated adhesion and migration of cells. However, the mechanisms by which integrins signal toward Rac are poorly understood. We show that the Rac-specific guanine nucleotide exchange factor Tiam1 (T-lymphoma invasion and metastasis 1) is required for the integrin-mediated laminin (LN)-5 deposition, spreading, and migration of keratinocytes. In contrast to wild-type keratinocytes, Tiam1-deficient (Tiam1-/-) keratinocytes are unable to adhere to and spread on a glass substrate because they are unable to deposit their own LN5 substrate. Both Tiam1 and V12Rac1 can rescue the defects of Tiam1-/- keratinocytes, indicating that these deficiencies are caused by impaired Tiam1-mediated Rac activation. Tiam1-/- cells are unable to activate Rac upon alpha3beta1-mediated adhesion to an exogenous LN5 substrate. Moreover, Tiam1 deficiency impairs keratinocyte migration in vitro and reepithelialization of excision wounds in mouse skin. Our studies indicate that Tiam1 is a key molecule in alpha3beta1-mediated activation of Rac, which is essential for proper production and secretion of LN5, a requirement for the spreading and migration of keratinocytes.

Show MeSH
Related in: MedlinePlus