2002 Global Researcher Conference Proceeding

April 26 - 28, 2002

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Conference: 2002 Global Researcher Conference
Title: High proportion of ROMK processing defects underlying hyperprostaglandin E syndrome/antenatal Bartter syndrome
Authors: Konrad, Martin; Peters, Melanie; Seyberth, M.D., Hannsjorg W.
Institutions: Philipps University, University Children's Hospital, Philipps University Marburg
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Konrad

Mutations in the renal inwardly rectifying K+ channel ROMK cause autosomal recessive hyperprostaglandin E syndrome/ antenatal Bartter syndrome (HPS/aBS), a severe salt-losing tubular disorder leading to extensive salt- and water wasting.

Numerous mutations distributed all over the protein have been identified in HPS/aBS patients. Until now, most of the missense mutations have been clustered in two regions: (i) the channel core region (amino acids 84-180), and (ii) the pH sensor built up from the amino acid residues Arg/Lys/Arg at positions 41, 80, and 311. Mutations in the channel core region are thought to lead to defective K+ conductance due to conformational changes, whereas mutations affecting the Arg/Lys/Arg triad shift the pH gating off the neutral range to more alkaline pH values. However, many ROMK mutations are not located in these two regions and thus other pathogenic mechanisms are conceivable, e.g. sorting or processing defects. In the present study, we evaluated the underlying pathogenic mechanisms of 18 naturally occurring ROMK mutations by heterologous expression in Xenopus oocytes and a human kidney cell line. ROMK mutations were functionally analyzed by electrophysiological methods in oocytes and immunofluorescence in oocytes and HEK-cells. We identified a high proportion of ROMK mutants (14/18) that did not reach the cell surface revealing defective processing. High expression levels rescued 6/14 ROMK mutants leading to significant potassium currents in the two electrode voltage clamp analysis.

In conclusion, this study revealed that defective ROMK processing might be the predominant pathogenic mechanism leading to HPS/aBS and this might enable the development of new therapeutic strategies directed at the restoration of channel function as already shown for other diseases caused by processing defects, such as cystic fibrosis or NDI.

ROMK is a membrane protein that allows the movement of potassium ion through the apical cell wall in renal tubular epithelia. Mutant ROMK cause a disease known as autosomal recessive hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS). Many different mutations of ROMK have been identified that result in HPS/aBS. Konrad, et al., analyzed 18 of these mutants to determine how they functioned. The researchers found 14 out of the 18 did not reach the cell membrane, which indicated they were not properly processed. Six out of 18 of these mutants could be made to function properly in laboratory cell cultures if the researchers ensured there were enough of the mutants in the cultures. The researchers concluded that defective ROMK processing might be the primary reason that leads to HPS/aBS.