Shwachman-Diamond syndrome (SDS; OMIM 260400) is an autosomal recessive disorder with clinical features that include pancreatic exocrine insufficiency, hematological dysfunction and skeletal abnormalities. Here, we report identification of disease-associated mutations in an uncharacterized gene, SBDS, in the interval of 1.9 cM at 7q11 previously shown to be associated with the disease. We report that SBDS has a 1.6-kb transcript and encodes a predicted protein of 250 amino acids. A pseudogene copy (SBDSP) with 97% nucleotide sequence identity resides in a locally duplicated genomic segment of 305 kb. We found recurring mutations resulting from gene conversion in 89% of unrelated individuals with SDS (141 of 158), with 60% (95 of 158) carrying two converted alleles. Converted segments consistently included at least one of two pseudogene-like sequence changes that result in protein truncation. SDBS is a member of a highly conserved protein family of unknown function with putative orthologs in diverse species including archaea and eukaryotes. Archaeal orthologs are located within highly conserved operons that include homologs of RNA-processing genes, suggesting that SDS may be caused by a deficiency in an aspect of RNA metabolism that is essential for development of the exocrine pancreas, hematopoiesis and chrondrogenesis.

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The effects of 1␣,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] on gene expression and function were studied in Caco-2 cells. Microarray analyses, real-time quantitative polymerase chain reactions, and Western blotting were used to determine the mRNA and protein expression of transporters and enzymes after 1,25(OH) 2 D 3 or vehicle (0.1% ethanol) treatment for 1, 3, 6, and 10 days. The mRNA and protein expressions of the apical sodium-dependent bile acid transporter, oligopeptide transporter 1, multidrug resistance-associated protein (MRP) 3, and sulfotransferase 1E1 remained unchanged with 1,25(OH) 2 D 3 treatment, whereas those for CYP3A4, multidrug resistance protein 1, and MRP2 were significantly increased (P Ͻ 0.05). 1,25(OH) 2 D 3 treatment significantly enhanced MRP4 protein expression by increasing protein stability without affecting mRNA expression, as confirmed in cycloheximide experiments. Marked increase in 6␤-hydroxylation of testosterone by CYP3A4 was also observed in the 6-day 1,25(OH) 2 D 3 -treated (100 nM) cell lysate. The transport of [ 3 H]digoxin, the P-glycoprotein (P-gp) substrate, after treatment with 100 nM 1,25(OH) 2 D 3 for 3 days revealed a higher apparent permeability (P app ) value in the basal (B)-to-apical (A) direction over that of vehicle treatment (15.1 Ϯ 0.53 ϫ 10 Ϫ6 versus 11.8 Ϯ 0.58 ϫ 10 Ϫ6 cm/s; P Ͻ 0.05), whereas the P app in the A-to-B direction was unchanged; the efflux ratio was increased (from 5.8 to 8.0). Reduced cellular retention of 5-(and-6)-carboxy-2Ј,7Ј-dichlorofluorescein, suggestive of higher MRP2 activity, was observed in the 3-day 100 nM 1,25(OH) 2 D 3 -treated cells over controls. Higher protein expression of CYP3A4, MRP2, P-gp, and MRP4 was also observed after a 6-day treatment with other vitamin D analogs (100 nM 1␣-hydroxyvitamin D 3 , 1␣-hydroxyvitamin D 2 or Hectorol, and 25-hydroxyvitamin D 3 ) in Caco-2 cells, suggesting a role of 1,25(OH) 2 D 3 and analogs in the activation of enzymes and transporters via the vitamin D receptor.The intestine plays an important role in the absorption of orally administered drugs. The expression and proximity of metabolic enzymes and efflux transporters in the enterocyte contribute to intestinal first-pass removal and delimit the tissue accumulation of endo-and xenobiotics. In the small intestine, cytochrome P450 3A4 (CYP3A4) accounts for approximately 70% of total cytochrome P450 content and is responsible for the metabolism of approximately 50% of drugs currently in use (Pelkonen et al., 2008). The ATPdependent drug efflux P-glycoprotein (P-gp), encoded by the multidrug resistance 1 gene (MDR1) located in the apical membrane of the enterocyte, is involved in the active excretion of a variety of lipophilic, cationic drugs from the intestine ). The multidrug resistance-associated proteins (MRPs), another important subfamily of Article, publication date, and citation information can be found at