[Thymic cyst with elevated SLX levels in serum and cystic fluid].

A 24-year-old man was admitted to our hospital in June 1996 with complaints of anterior chest discomfort. Chest X-ray films on admission showed an abnormal mediastinal shadow with well-defined margin. Chest X-ray examinations about 6 weeks earlier had not detected any abnormalities. Laboratory tests on admission showed a high serum concentration of Siaryl Lewis X-i antigen (SLX). A computed tomographic scan of the chest showed a large (6 x 6 x 12 cm) homogeneous mass in the right anterior mediastinum. The mass was removed completely and histologically diagnosed as a thymic cyst. Biochemical analysis of fluid from the cyst revealed remarkably high levels of SLX, CA 19-9, and CEA. In immunohistochemical studies, epithelial cells from the cystic walls stained positive for SLX, CA 19-9, and CEA. After the operation, the level of serum SLX returned almost to normal.

Activity and expression of murine small Maf family protein MafK.

Transcription factor NF-E2 is believed to be crucial for the regulation of erythroid-specific gene transcription. The three small Maf family proteins (MafF, MafG, and MafK), which are closely related to c-Maf proto-oncoprotein, constitute half of NF-E2 activity by virtue of forming heterodimers with the large, tissue-restricted subunit of NF-E2 (p45). We isolated cDNA clones encoding the murine small Maf family protein MafK and characterized the structure, activity, and expression profile of MafK mRNA. Functional analyses demonstrate that MafK binds to consensus NF-E2 sites in the absence of p45 in vitro and represses transcription of NF-E2 site-dependent reporter genes in transient transfection assays, while p45 introduced into cells alone does not effectively bind to DNA and does not affect transcription. In the presence of p45, MafK confers site-specific DNA binding activity to p45, and p45 in turn mediates transcriptional activation with its amino-terminal proline-rich domain. mRNA for MafK is expressed in fractions enriched for hematopoietic stem cells as well as erythroid cells, suggesting that MafK plays an important regulatory role in hematopoiesis.