B. Li et al., PRK, A CYTOKINE-INDUCIBLE HUMAN PROTEIN SERINE THREONINE KINASE WHOSEEXPRESSION APPEARS TO BE DOWN-REGULATED IN LUNG CARCINOMAS/, The Journal of biological chemistry, 271(32), 1996, pp. 19402-19408
We have cloned and characterized a putative protein serine/threonine k
inase termed prk through a combination of polymerase chain reaction an
d conventional cDNA library screening approaches. There are apparently
two distinct domains within pll protein deduced from its nucleotide s
equences. The amino-terminal portion has the feature of the catalytic
domain of a serine/threonine kinase and shows strong homology to mouse
fnk and other polo family kinases including mouse snk, human and muri
ne plk, Drosophila polo, and yeast Cdc5, The carboxyl-terminal portion
, presumably the regulatory domain, shares extensive homology to mouse
fnk, Northern blotting analyses reveal that prk expression is restric
ted to a very limited number of tissues with placenta, ovaries, and lu
ng containing detectable amounts of prk mRNA. prk mRNA expression is a
lso detected at a low level in the megakaryocytic cell line Dami, MO7e
, and three brain glioma cell lines, In addition, refeeding of serum-d
eprived MO7e, Dami, and K562 cells of hematopoietic origin and GMOO637
D of lung fibroblasts rapidly activates prk, mRNA expression with its
peak induction around 2 h after serum addition, pl-fi gene activation
by the serum requires no new protein synthesis, The recombinant cytoki
nes such as interleukin-3 and thrombopoietin also activate prk mRNA ex
pression in MO7e cells, Furthermore, a survey of RNAs isolated from th
e tumor and the uninvolved tissues from 18 lung cancer patients reveal
s that prk mRNA expression is significantly down-regulated in tumor ti
ssues, Southern blotting analysis indicates that the pl h gene is pres
ent in a single copy in the genome of tumors and normal cells, Taken t
ogether, these results suggest that prk expression may be restricted t
o proliferating cells and involved in the regulation of cell cycle pro
gression, The molecular cloning- of prk cDNA will facilitate the study
of its biological role as well as its potential role in tumorigenesis
.