ELKS, a protein structurally related to the active zone protein CAST, is involved in Ca2+-dependent exocytosis from PC12 cells.
The active zone protein CAST binds directly to the other active zone proteins RIM, Bassoon and Piccolo, and it has been suggested that these protein-protein interactions play an important role in neurotransmitter release. To further elucidate the molecular mechanism, we attempted to examine the function of CAST using PC12 cells as a model system. Although PC12 cells do not express CAST, they do express ELKS, a protein structurally related to CAST. Endogenous and exogenously expressed ELKS, RIM2 and Bassoon were colocalized in punctate signals in PC12 cells. Over-expression of full-length ELKS resulted in a significant increase in stimulated exocytosis of human growth hormone (hGH) from PC12 cells, similar to the effect of full-length RIM2. This increase was not observed following over-expression of deletion constructs of ELKS that lacked either the last three amino acids (IWA) required for binding to RIM2 or a central region necessary for binding to Bassoon. Moreover, over-expression of the NH(2)-terminal RIM2-binding domain of Munc13-1, which is known to inhibit the binding between RIM and Munc13-1, inhibited the stimulated increase in hGH secretion by full-length RIM2. Furthermore, this construct also inhibited the stimulated increase in hGH secretion induced by full-length ELKS. These results suggest that ELKS is involved in Ca(2+)-dependent exocytosis from PC12 cells at least partly via the RIM2-Munc13-1 pathway.
Inoue
Eiji
E
KAN Research Institute, Kyoto 600-8815, Japan.
Deguchi-Tawarada
Maki
M
Takao-Rikitsu
Etsuko
E
Inoue
Marie
M
Kitajima
Isao
I
Ohtsuka
Toshihisa
T
Takai
Yoshimi
Y
D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005089:Exocytosis / Q000502:physiology*; D019382:Human Growth Hormone / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins / Q000378:metabolism; D016716:PC12 Cells / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction
D048868:Adaptor Proteins, Signal Transducing; C113688:Bsn protein, rat; C479909:ERC1 protein, rat; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins; C484282:Rims2 protein, rat; C103912:Unc13a protein, rat; D019382:Human Growth Hormone; D002118:Calcium