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Integrin alpha 6 beta 4 forms a complex with the cytoskeletal protein HD1 and induces its redistribution in

C M Niessen1, E H Hulsman, E S Rots

  • 1Division of Cell Biology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.

Molecular Biology of the Cell
|April 1, 1997
PubMed

Insights

The integrin alpha 6 beta 4 directly binds to HD1, a key hemidesmosome protein. This interaction, mediated by beta 4

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Integrin alpha 6 beta 4 is a crucial component of hemidesmosomes, mediating cell adhesion and linking to intermediate filaments.
  • The precise mechanism by which beta 4 interacts with keratin filaments within hemidesmosomes remains unclear.
  • Understanding these interactions is vital for comprehending hemidesmosome assembly and function.

Purpose of the Study:

  • To investigate the direct interaction between the beta 4 cytoplasmic domain and other cellular proteins.
  • To identify the specific protein(s) that interact with the beta 4 subunit within hemidesmosomes.
  • To elucidate the role of the beta 4 cytoplasmic domain in the localization and assembly of hemidesmosomal components.

Main Methods:

  • Used glutathione S-transferase (GST) fusion proteins of the beta 4 cytoplasmic domain (beta 4A and beta 4B) to pull down interacting proteins from cell lysates.
  • Performed immunoblot analysis using specific antibodies to identify the pulled-down proteins.
  • Utilized COS-7 cells, a cell line lacking endogenous hemidesmosomal components, for transfection studies to assess protein localization and complex formation.
  • Generated and expressed mutant beta 4 subunits lacking specific domains to determine the regions critical for HD1 interaction and localization.

Main Results:

  • A fragment of the beta 4A cytoplasmic domain, containing fibronectin type III repeats, specifically bound a 500-kDa protein identified as HD1.
  • The cytoplasmic domain of beta 4 (both beta 4A and beta 4B variants) is essential for the formation of a complex with HD1.
  • Expression of integrin alpha 6 beta 4 in COS-7 cells led to the colocalization of HD1 with the integrin at the basal cell side, independent of other cytoskeletal networks.
  • A mutant beta 4 subunit lacking fibronectin type III repeats and the connecting segment failed to alter HD1 distribution, confirming the importance of this region for interaction.

Conclusions:

  • The cytoplasmic domain of integrin beta 4 directly interacts with the hemidesmosomal plaque protein HD1.
  • This direct association between beta 4 and HD1 is crucial for the proper localization of HD1 and likely plays a key role in hemidesmosome assembly.
  • The findings provide new insights into the molecular mechanisms underlying hemidesmosome formation and stability.

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