PKD1 and cyst: Our previous report showed that the mRNA and protein expression of CD74 were upregulated in Pkd1 mutant renal epithelial cells, including Pkd1 null mouse embryonic kidney (MEK) cells and postnatal Pkd1 homozygous PN24 cells, and its expression was also increased in cyst lining epithelial cells in human ADPKD kidneys compared with normal kidneys [16].