Tau Tubulin Kinase TTBK2 Sensitivity of Glutamate Receptor GluK2.
OBJECTIVE
Inherited, autosomal dominant spinocerebellar ataxia type 11 (SCA11) is caused by loss of function mutations of TTBK2 (tau tubulin kinase 2). Mutations observed in patients with SCA11 include truncated TTBK2(450). The present study explored the possibility that TTBK2 influences the function of the glutamate receptor GluK2.


METHODS
GluK2 was expressed in Xenopus oocytes without and with additional expression of wild type TTBK2, the truncated mutant TTBK2(450), or the kinase dead mutants TTBK2(KD) and TTBK2(450/KD). GluK2 current was determined by dual electrode voltage clamp and GluK2 protein abundance in the cell membrane utilizing confocal microscopy.


RESULTS
Glutamate exposure of GluK2 expressing oocytes generated a current, which was significantly lower in oocytes expressing GluK2 together with TTBK2 wt or TTBK2(KD) than in oocytes expressing GluK2 alone or together with either TTBK2(450) or TTBK2(450/KD). According to confocal microscopy of EGFP-tagged GluK2, TTBK2 wt decreased the GluK2 protein abundance in the cell membrane. Overexpression of an inactive RAB5(N133I) mutant but not RAB5wt could reverse the TTBK2 effect on GluK2 suggesting that RAB5 function is required for the effect.


CONCLUSIONS
TTBK2 down-regulates GluK2 activity by decreasing the receptor protein abundance in the cell membrane via RAB5-dependent endocytosis, an effect that may protect against neuroexcitotoxicity.
Department of Cardiovascular Medicine, Institute for Genetics of Heart Diseases (IfGH), University Hospital Muenster, Muenster, Germany.
Kristina
K
Nieding
Veronika
V
Matschke
Sven G
SG
Meuth
Florian
F
Lang
Guiscard
G
Seebohm
Nathalie
N
Strutz-Seebohm
D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D004705:Endocytosis; D005786:Gene Expression Regulation; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D008845:Microinjections; D009154:Mutation; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D000072417:Protein Domains; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D018092:Kainic Acid Receptors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D019076:Transgenes; D014982:Xenopus laevis; D020696:rab5 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D018698:Glutamic Acid; D010455:Peptides; D017346:Protein Serine-Threonine Kinases; D018092:Kainic Acid Receptors; D020696:rab5 GTP-Binding Proteins; C095903:tau-tubulin kinase; C427755:RAB5C protein, human