Extracellular matrix and nuclear localization of beta ig-h3 in human bladder smooth muscle and fibroblast cells

The extracellular matrix (ECM) plays an essential role in bladder structure and function. In this study, expression of beta ig-h3, a recently identifi ed extracellular matrix protein, was investigated in human bladder tissue, and human bladder smooth-muscle (SMC) and fibroblast cells in vitro. SMCs s ecreted greater than three times the level of this protein compared with fi broblasts. The relative levels of beta ig-h3 mRNA in the two cell types ref lected the protein expression. Immunohistochemical analysis demonstrated pr otein deposition in the ECM as well as cytoplasmic localization and, unexpe ctedly, nuclei. Anti-beta ig-h3 antibodies also stained the matrix surround ing the detrusor SMCs and nuclei of bladder fibroblasts, SMCs, and urotheli um in intact bladder tissue. Western blot analyses of medium and matrix fra ctions obtained from cells in vitro revealed protein of similar to 70-74 kD a, whereas nuclear extracts contained a 65-kDa reactive protein band. We pr opose that although this protein is a structural component of bladder ECM, its nuclear localization suggests that it has other regulatory and/or struc tural functions, (C) 2000 Wiley-Liss, Inc.