Evidence that taurine modulates osmoregulation by modification of osmolarity sensor protein ENVZ - expression

Although the involvement of taurine in osmoregulation is well-documented an d widely accepted, no detailed mechanism for this function has been reporte d so far. We used subtractive hybridization to study mRNA steady state levels of gene s up- or downregulated by taurine. Rats were fed taurine 100 mg/kg body wei ght per day for a period of three days and hearts (total ventricular tissue ) of experimental animals and controls were pooled and used for mRNA extrac tion, mRNAs from two groups were used for subtractive hybridization. Clones of the subtractive library were sequenced and the obtained sequences were identified by gen bank assignment. Two clones were found to contain sequences which could be assigned to the o smolarity sensor protein envZ, showing homologies of 61 and 65%. EnvZ is an inner membrane protein in bacteria, important for osmosensing and required for porine gene regulation. It undergoes autophosphorylation and subsequen tly phosphorylates OmpR, which in turn binds to the porine (outer membrane protein) promoters to regulate the expression of OmpF and OmpC, major outer membrane porines. This is the first report of an osmosensing mechanism in the mammalian syste m, which was described in bacteria only. Furthermore, we are assigning a te ntative role for taurine in the osmoregulatory process by modifying the exp ression of the osmoregulatory sensor protein ENVZ.