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J. Cell Biol.,
Volume 142, Number 1, July 13, 1998 271-284
4 Integrin
Subunit, Requires Complex Formation of
4 and
HD1/Plectin, and Involves a Direct Interaction between
4 and the Bullous Pemphigoid Antigen 180

* Division of Cell Biology, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands; Hemidesmosomes (HDs) are stable anchoring
structures that mediate the link between the intermediate
filament cytoskeleton and the cell substratum. We investigated the contribution of various segments of the
Department of
Dermatology, University of Geneva, CH-1211 Geneva, Switzerland; and § Department of Pathology, University Hospital
Vrije Universiteit, 1081 HV Amsterdam, The Netherlands
4 integrin cytoplasmic domain in the formation of HDs in
transient transfection studies using immortalized keratinocytes derived from an epidermolysis bullosa patient
deficient in
4 expression. We found that the expression
of wild-type
4 restored the ability of the
4-deficient
cells to form HDs and that distinct domains in the NH2-
and COOH-terminal regions of the
4 cytoplasmic domain are required for the localization of HD1/plectin and
the bullous pemphigoid antigens 180 (BP180) and 230 (BP230) in these HDs. The tyrosine activation motif located in the connecting segment (CS) of the
4 cytoplasmic domain was dispensable for HD formation, although
it may be involved in the efficient localization of BP180. Using the yeast two-hybrid system, we could demonstrate
a direct interaction between
4 and BP180 which involves
sequences within the COOH-terminal part of the CS and
the third fibronectin type III (FNIII) repeat. Immunoprecipitation studies using COS-7 cells transfected with
cDNAs for
6 and
4 and a mutant BP180 which lacks
the collagenous extracellular domain confirmed the interaction of
4 with BP180. Nevertheless,
4 mutants which
contained the BP180-binding region, but lacked
sequences required for the localization of HD1/plectin,
failed to localize BP180 in HDs. Additional yeast two-
hybrid assays indicated that the 85 COOH-terminal residues of
4 can interact with the first NH2-terminal pair of
FNIII repeats and the CS, suggesting that the cytoplasmic
domain of
4 is folded back upon itself. Unfolding of the
cytoplasmic domain may be part of a mechanism by
which the interaction of
4 with other hemidesmosomal components, e.g., BP180, is regulated.
6
4 integrin
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