N-glycosylation determines the abundance of the transient receptor potential channel TRPP2 [Glycobiology and Extracellular Matrices]

April 10th, 2014 by Hofherr, A., Wagner, C., Fedeles, S., Somlo, S., Kottgen, M.

Glycosylation plays a critical role for the biogenesis and function of membrane proteins. Transient receptor potential channel TRPP2 is a nonselective cation channel that is mutated in autosomal dominant polycystic kidney disease (ADPKD). TRPP2 has been shown to be heavily N-glycosylated, but the glycosylation sites and the biological role of N-linked glycosylation have not been investigated. Here, we show that native TRPP2 is glycosylated at five asparagines in the first extracellular loop using a combination of mass spectrometry and biochemical approaches. Glycosylation is required for efficient biogenesis of TRPP2 as mutations of the glycosylated asparagines result in strongly decreased protein expression of the ion channel. Wild-type and N-glycosylation-deficient TRPP2 are degraded in lysosomes as shown by increased TRPP2 protein levels upon chemical inhibition of lysosomal degradation. In addition, we demonstrate that glucosidase II (GII) mediates glycan trimming of TRPP2 using pharmacological and genetic approaches. The non-catalytic β-subunit of glucosidase II (GIIβ) is encoded by PRKCSH, one of the genes causing autosomal dominant polycystic liver disease (ADPLD). The impaired GIIβ-dependent glucose trimming of TRPP2 glycosylation in ADPLD may explain decreased TRPP2 protein expression in Prkcsh-/- mice and the genetic interaction observed between TRPP2 and PRKCSH in ADPLD. These results highlight the biological importance of N-linked glycosylation and GII-mediated glycan trimming in the control of biogenesis and stability of TRPP2.