Zz. Nie et al., C-terminus of desmoyokin/AHNAK protein is responsible for its translocation between the nucleus and cytoplasm, J INVES DER, 114(5), 2000, pp. 1044-1049
We previously demonstrated that desmoyokin gene is identical to AHNAK gene,
which is downregulated in neuroblastomas. Whereas desmoyokin/AHNAK protein
is distributed in the nucleus and cytoplasm in nonepithelial tissues, it i
s distributed in the cell membrane in epithelial tissues. It is present dif
fusely in the cytoplasm and nucleus of epithelial cell lines cultured in lo
w calcium condition. Low to normal calcium shift translocates it to the cel
l boundary. In this study, we investigated which domain(s) of desmoyokin/AH
NAK protein are responsible for its different distribution. We constructed
three different eukaryotic expression plasmids, pN-DY, pM-DY, and pC-DY, wh
ich expressed N-terminus, central domain, and C-terminus of this molecule,
respectively, when transfected into COS-7 cells, normal human keratinocytes
, and HeLa cells. In normal calcium medium, whereas N-terminus and central
domain of desmoyokin/AHNAK protein were present mainly in the cytoplasm, C-
terminus was present in the nucleus, cytoplasm, and weakly in the cell memb
rane. In low calcium medium, C-terminus was present exclusively in the nucl
eus, and a part of the molecules translocated from the nucleus to the cytop
lasm, 3 h after the shift to normal calcium medium or 3 h after addition of
protein kinase C activator, 12-O-tetradecanoylphorbol-13-acetate in low ca
lcium medium. Calcium shift showed no effects on the distribution of N-term
inus and central domain. These results suggested that C-terminus, but neith
er N-terminus nor central domain, is responsible for the translocation of t
his protein into the nucleus. This study may also suggest that C-terminus p
lay a role in the translocation to the cell membrane, although further evid
ence is necessary.