THE SUBCELLULAR-DISTRIBUTION OF THE HIGH-MOLECULAR-MASS PROTEIN, HD1,IS DETERMINED BY THE CYTOPLASMIC DOMAIN OF THE INTEGRIN BETA-4 SUBUNIT

The high molecular mass protein, HD1, is a structural protein present in hemidesmosomes as well as in distinct adhesion structures termed ty pe II hemidesmosomes. We have studied the distribution and expression of HD1 in the GD25 cells, derived from murine embryonal stem cells def icient for the beta 1 integrin subunit. We report here that these cell s possess HD1 but not BP230 or BP180, two other hemidesmosomal constit uents, and express only traces of the alpha 6 beta 4 integrin. By immu nofluorescence and interference reflection microscopy HD1 was found to gether with vinculin at the end of actin filaments in focal contacts. In OVCAR-4 cells, derived from a human ovarian carcinoma which, like G D25 cells, only weakly express alpha 6 beta 4, HD1 was also localized in focal contacts, Upon transfection of both GD25 and OVCAR-4 cells wi th cDNA for the human beta 4 subunit the subcellular distribution of H D1 changed significantly, HD1 is then no longer present in focal conta cts but in other structures at cell-substrate contacts, colocalized wi th alpha 6 beta 4. These junctional complexes are probably the equival ent of the type II hemidesmosomes. Transfection of GD25 cells with bet a 1 cDNA did not affect the distribution of HD1, which indicates that the localization of HD1 in focal contacts was not due to the absence o f beta 1. Moreover, in GD25 cells transfected with cDNA encoding a bet a 4/beta 1 chimera, in which the cytoplasmic domain of beta 4 was repl aced by that of beta 1, the distribution of HD1 was unaffected. Our fi ndings indicate that the cytoplasmic domain of beta 4 determines the s ubcellular distribution of HD1 and emphasize the important role of alp ha 6 beta 4 in the assembly of hemidesmosomes and other junctional adh esive complexes containing HD1.