Patients with SDS express variable levels of SBDS protein. (A) Schematic diagram of SBDS mutations. The locations of the SBDS mutations identified in our patient series are diagramed (not drawn to scale). The SBDS gene is composed of 5 exons (depicted with boxes). The translated mRNA regions are shaded gray. (B) SBDS expression in fibroblasts. Bone marrow fibroblast protein lysates were analyzed by immunoblotting for SBDS protein (top). The SBDS genotypes of each cell line are indicated in parentheses. The blot was also probed for tubulin to ascertain equivalent protein loading (bottom). DF259 and DF307 harbored SBDS mutations predicted to lead to premature translation termination. The wild-type (WT) control (NMF-100) is a marrow fibroblast cell line derived from a healthy control patient. (C) SBDS expression in lymphoblasts. Lymphoblast protein lysates were analyzed by immunoblotting for SBDS protein (top) and tubulin (bottom). DF250, DF259, and DF260 carried SBDS mutations predicted to lead to premature translation termination. SD101 carried a missense (R169C) mutation on 1 SBDS allele. DF269 is derived from a patient with SDS who lacked any identified SBDS mutations. (D) Retroviral transduction of the SBDS cDNA restores SBDS protein expression. A lymphoblast (DF277.L) or fibroblast (DF259.F) SDS cell line was infected with a pBabe retrovirus containing a wild-type SBDS cDNA (lanes 3 and 5) or empty vector (lanes 2 and 4). Cell lysates were immunoblotted for SBDS protein. A normal lymphoblast control cell line (DF213) was run in lane 1 (WT control). (E) SBDS protein is expressed in a variety of tissues. Lysates from the indicated human cell lines were immunoblotted for SBDS protein expression. Caco2 indicates intestinal epithelial cell line; HepG2, hepatocellular carcinoma cell line; HL-60, myeloid leukemia cell line; U2OS, osteosarcoma cell line; CAPAN-1, pancreatic adenocarcinoma cell line.