Subcellular localization and characterization of interleukin-1 alpha produced by rat bladder cancer cells

A rat bladder cancer cell line BC31ad, previously reported to constitutively release tumor necrosis factor alpha (TNF alpha), was found to produce an interleukin (IL)-1-like factor inducing proliferation of murine thymocytes in a standard costimulation assay (LAF activity). IL-1-like factor was partially purified by DEAE-Sephacel, Sephacryl S-200 and MonoQ-FPLC chromatographies from the serum-free conditioned medium of a BC31 adderived clone, C19, to the specific activity of 3.2 x 10(6) U/mg and characterized as a protein of molecular weight 17 kDa with isoelectric point 5.2. LAF activity of IL-1-like factor was specifically neutralized with anti-rat IL-1 alpha but not with anti-rat IL-1 beta. These findings show that the IL-1-like factor is rat IL-1 alpha, although the precise molecular relationship with monocyte IL-1 alpha is unclear. Furthermore, IL-1 alpha was shown to be primarily located in the cytosol and plasma membrane without spontaneous release. A kinetics study indicated that it was leaked into the medium late in culture resulting from cell destruction, in contrast to TNF alpha which was released as the cell number was increased. We discussed the possible role of IL-1 alpha as an autocrine or paracrine growth regulator.