Expression of Kell blood group protein in nonerythroid tissues

The Kell blood group protein is a zinc endopeptidase that yields endothelin -3, a potent bioactive peptide, by cleavage of big endothelin-3, a larger i ntermediate precursor. On red cells, Kell protein is linked by a single dis ulfide bond to XK, a protein that traverses the membrane 10 times and whose absence, as occurs in the McLeod phenotype, is associated with a set of cl inical symptoms that include nerve and muscle disorders and red cell acanth ocytosis. Previous studies Indicated that Kell is primarily expressed in er ythroid tissues, whereas XK has a wider tissue distribution. The tissue dis tribution of Kelt protein has been further investigated by Northern blot an alysis, PCR-screening of tissue complementary DNAs (cDNAs), and Western imm unoblots. Screening of an RNA dot-blot panel confirmed that Kell is primari ly expressed in erythroid tissues but is also expressed in a near equal amo unt in testis, with weaker expression in a large number of other tissues. P CR-screening of cDNAs from different tissues and DNA sequencing of the prod ucts gave similar results. In 2 of the nonerythroid tissues tested, testis end skeletal muscle, Kell protein was detected by Western immunoblotting. I n skeletal muscle, isolation of XK with a specific antibody coisolated Kell protein. These studies demonstrate that Kell is expressed in both erythroi d and nonerythroid tissues and is associated with XK. (Blood. 2000;96:340-3 46) (C) 2000 by The American Society of Hematology.