Beta-cell expression of 65-kDa heat-shock protein mRNA is function- and age-dependent

This study examined the expression of mRNA coding for the 65-kDa heat-shock protein (HSP) in rat islet cells of different functional states and different ages. In addition, beta cells and non-beta cells purified by fluorescence-activated cell sorting were studied. Total RNA from islet cells and insulin-producing RINm5F cells was isolated and analyzed by Northern blotting using a cDNA probe coding for the human homologue to the mycobacterial 65-kDa HSP, after which blots were quantified by densitometric scanning. Isolated beta cells were found to express 65-kDa HSP mRNA. The expression was increased in Lewis islet cells exposed to heat shock or high glucose concentration, four- and three-fold, respectively (p < 0.01). In isolated beta cells cultured at high glucose concentration a doubling in the content of 65-kDa HSP mRNA was seen compared with islets cultured at low glucose concentration (p < 0.05). In islets from Lewis rats fasted for 24 h, the content of 65-kDa HSP mRNA was 42% lower than in islets isolated from normally fed Lewis rats (p < 0.01). Both in BB rats and Wistar Furth rats the content of 65-kDa HSP mRNA was found to be higher in the 30- and the 60-day-old rats compared with the neonatal animals (p < 0.01). The expression of 65-kDa HSP mRNA was increased in RINm5F cells following heat shock, while no induction was seen after stimulation with glucose, TPA or IBMX. It is concluded that the 65-kDa heat-shock protein belongs to the family of inducible functional antigens in beta cells, which strengthens the interest in 65-kDa HSP as an antigen possibly involved in the initiation of autoimmune beta-cell destruction.