TI  - Functional significance of  <prot>CD9</prot>  association with  beta 1 integrins  in human
      epidermal keratinocytes.
PG  - 297-305
AB  - <prot>CD9</prot> is a member of the tetraspan (TM4) family of proteins and is
      abundantly expressed in the epidermis. As  <prot>CD9</prot>  forms complexes with  beta 1
      integrins  and the integrins are known to regulate keratinocyte behaviour,
      we investigated <prot>CD9</prot> expression and function in human epidermal
      keratinocytes. <prot>CD9</prot> was present in all the living layers of the epidermis,
      whereas the beta 1 integrins were largely confined to the basal layer; the
      same relative distribution was found in stratified cultures of
      keratinocytes. There was extensive co-localisation of <prot>CD9</prot> and beta 1
      integrins on microvilli and at cell-cell borders of basal keratinocytes;
      however, in contrast to the integrins, <prot>CD9</prot> was not found in focal
      adhesions. <prot>CD9</prot> was detected in beta 1 integrin immunoprecipitates and also
      in immunoprecipitates of <prot>CD44</prot> and <prot>syndecan</prot>, but not of cadherins.  <prot>CD9</prot>  was
      associated with  alpha 3 beta 1  but not alpha 5 beta 1; small amounts of
      <prot>CD9</prot> also co-immunoprecipitated with antibodies to alpha 2 beta 1 and alpha
      6 beta 4. Antibodies to <prot>CD9</prot> did not affect the proportion of keratinocytes
      that adhered to <prot>laminin 1</prot>, <prot>type IV collagen</prot> and <prot>fibronectin</prot>, but did
      inhibit motility of keratinocytes on tissue culture plastic. Like
      antibodies to the <prot>beta 1 integrin</prot> subunit, anti-<prot>CD9</prot> inhibited
      suspension-induced terminal differentiation. These results suggest that
      <prot>CD9</prot> may play a role in regulating keartinocyte motility and
      differentiation.
AD  - Keratinocyte Laboratory, Imperial Cancer Research Fund, London.
