Subcellular localization and tumor-suppressive functions of 15-lipoxygenase 2 (15-LOX2) and its splice variants.
15-Lipoxygenase 2 (15-LOX2), the most abundant arachidonate (AA)-metabolizing enzyme expressed in adult human prostate, is a negative cell-cycle regulator in normal human prostate epithelial cells. Here we study the subcellular distribution of 15-LOX2 and report its tumor-suppressive functions. Immunocytochemistry and biochemical fractionation reveal that 15-LOX2 is expressed at multiple subcellular locations, including cytoplasm, cytoskeleton, cell-cell border, and nucleus. Surprisingly, the three splice variants of 15-LOX2 we previously cloned, i.e. 15-LOX2sv-a/b/c, are mostly excluded from the nucleus. A potential bi-partite nuclear localization signal (NLS),203RKGLWRSLNEMKRIFNFRR221, is identified in the N terminus of 15-LOX2, which is retained in all splice variants. Site-directed mutagenesis reveals that this putative NLS is only partially involved in the nuclear import of 15-LOX2. To elucidate the relationship between nuclear localization, enzymatic activity, and tumor suppressive functions, we established PCa cell clones stably expressing 15-LOX2 or 15-LOX2sv-b. The 15-LOX2 clones express 15-LOX2 in the nuclei and possess robust enzymatic activity, whereas 15-LOX2sv-b clones show neither nuclear protein localization nor AA-metabolizing activity. To our surprise, both 15-LOX2- and 15-LOX2sv-b-stable clones proliferate much slower in vitro when compared with control clones. More importantly, when orthotopically implanted in nude mouse prostate, both 15-LOX2 and 15-LOX2sv-b suppress PC3 tumor growth in vivo. Together, these results suggest that both 15-LOX2 and 15-LOX2sv-b suppress prostate tumor development, and the tumor-suppressive functions apparently do not necessarily depend on AA-metabolizing activity and nuclear localization.
Bhatia
Bobby
B
Department of Carcinogenesis, the University of Texas M. D. Anderson Cancer Center, Science Park Research Division, Smithville 78957, USA.
Maldonado
Carlos J
CJ
Tang
Shaohua
S
Chandra
Dhyan
D
Klein
Russell D
RD
Chopra
Dharam
D
Shappell
Scott B
SB
Yang
Peiying
P
Newman
Robert A
RA
Tang
Dean G
DG
D001093:Arachidonate 15-Lipoxygenase / Q000235:genetics / Q000378:metabolism*; D016147:Genes, Tumor Suppressor; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008297:Male; D011467:Prostate / Q000201:enzymology*; D011471:Prostatic Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D012326:RNA Splicing
D007527:Isoenzymes; C458528:ALOX15B protein, human; D001093:Arachidonate 15-Lipoxygenase