Proximal promoter of the murine syndecan-1 gene is not sufficient for the developmental pattern of syndecan expression in B lineage cells.

Syndecan-1 (CD138) is a cell membrane proteoglycan that binds extracellular matrix components and various growth factors. The role of syndecan-1 in the control of cell growth and morphology has been illustrated by its altered expression in hematological malignancies such as multiple myeloma as well as some solid tumors. It has been reported that the expression of syndecan-1 in cells of the B lineage is developmentally regulated such that pre-B cells and plasma cells express syndecan-1 while mature B cells do not. Thus, we investigated whether the proximal promoter region of the murine syndecan-1 promoter was able to confer the observed on-off-on expression of syndecan-1 in cells of the B lineage as they develop from pre-B cells to plasma cells. Experiments carried out using deletion mutants of the proximal promoter cloned upstream of the CAT reporter gene transfected into murine cell lines, representing the above stages of B-cell development, such as BA/F3 (pro-B cell), 70Z/3 (pre-B cell), 2PK3 (late mature B cell), and MPC-11 (plasma cell), showed detectable levels of CAT expression. The WEHI-231 (mature B cell) cell lines did not show detectable levels of CAT reporter activity. The strong levels of expression were observed with a fragment of the proximal promoter spanning the region from -365 to -95 (from the translation start point). However, Northern analysis of RNA obtained from the five murine B-cell lines, representing various stages of B-cell development, showed that the 70Z/3, MPC-11 but not BA/F3, and 2PK3 cells expressed detectable levels of syndecan-1 mRNA. By FACS analysis, using a rat anti mouse syndecan-1 antibody, syndecan-1 expression on the cell surface was found to correlate with the observed mRNA expression patterns in these cell lines. Our results indicate that the proximal promoter of the murine syndecan-1 promoter is not sufficient for the observed developmental pattern of syndecan expression in B cells.