Localization and characterization of stannin: relationship to cellular sensitivity to organotin compounds

The cDNA encoding the protein stannin was isolated previously via subtractive hybridization, using differential expression after trimethyltin (TMT) intoxication, as a basis for isolating mRNA which may be expressed in TMT-sensitive cells. Initial characterization revealed a novel gene product which was differentially expressed in several tissues sensitive to TMT. In the current study, biochemical and molecular techniques were used to quantitate stannin expression at the cellular and subcellular levels. Northern blot analysis showed that the stannin 3.0 kb mRNA transcript was present, in decreasing amounts, in: spleen, hippocampus, neocortex, cerebellum, striatum, midbrain, kidney and lung. Liver, heart, skeletal muscle and testis showed no detectable expression of stannin mRNA. Immunoblot analysis using antipeptide antisera raised against stannin indicated a high level of expression in spleen, followed by brain and kidney. Stannin mRNA was present during early brain development and consolidated by post-natal day (PND) 20 to patterns and levels seen in adults. In situ hybridization studies showed widespread neuronal expression of stannin mRNA at PND 1, which shifted to a restricted pattern of expression in specific regions by PND 20. Stannin was partially purified from rodent brain and spleen using cation exchange, sizing and hydrophobic interaction chromatography. It behaved as a monomer throughout purification. Stannin was also expressed in a baculovirus system, using a series of constructs containing the entire cDNA, 1.0 kb of DNA flanking the open reading frame, and a 400 bp open reading frame minimal construct. While all constructs expressed stannin, the best expression was seen with the entire cDNA. Based on current findings, we suggest that stannin expression is necessary but not sufficient for TMT toxicity.