Neonatal murine epidermal cells express a functional multidrug-resistant pump.
Phospho-glycoproteins are members of the ABC transporter family encoded by the multidrug-resistant genes. These proteins are highly expressed in many tumor cells derived from patients undergoing treatment with anti-cancer drugs. Phospho-glycoproteins are large 12 transmembrane spanning molecules of 170 kDa, involved in adenosine-5'-triphosphate-dependent efflux of molecules out of the cell, known currently as multidrug-resistant pumps. Expression analysis of phospho-glycoproteins in mice and humans indicates widespread distribution in a number of organs, such as brain and testis. We have analyzed skin, and more particularly keratinocytes, to determine whether they express phospho-glycoproteins and express the multidrug-resistant phenotype. Immunofluorescent staining of skin showed that keratinocytes located in the basal layer of the epidermis preferentially expressed phospho-glycoproteins, as did the outer root sheath cells of hair follicles. Phospho-glycoprotein expression on the basal cells was restricted to the cell surface. Polymerase chain reaction analysis of first strand cDNA from keratinocytes identified the phospho-glycoproteins to be mdr1b. Using beta1 integrin expression and density gradient centrifugation we were able to enrich and identify the basal cell compartment by flow cytometric analysis and assay this subset of cells for phospho-glycoprotein activity. Basal cells loaded with rhodamine 123, a substrate for multidrug-resistant pumps, effluxed the molecule from the cells in a time-dependent manner. This study shows that basal layer keratinocytes express functional phospho-glycoproteins. We speculate that phospho-glycoproteins may play a role in regulating the level of environmental toxins and differentiation factors, as has been suggested for other progenitor cell compartments.
Sleeman
M A
MA
Genesis Research and Development Corporation Limited, Auckland, New Zealand. m.sleeman@genesis.co.nz
Watson
J D
JD
Murison
J G
JG
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000276:immunology; D000818:Animals; D000906:Antibodies / Q000032:analysis; D001483:Base Sequence; D018432:Drug Resistance, Multiple / Q000235:genetics*; D019450:Genes, MDR; D007150:Immunohistochemistry; D019012:Integrin beta1 / Q000096:biosynthesis; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D020112:Rhodamine 123 / Q000378:metabolism; D012867:Skin / Q000166:cytology / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000906:Antibodies; D019012:Integrin beta1; D020112:Rhodamine 123