title: Anti-proliferative and pro-apoptotic actions of a novel human and mouse ovarian tumor-associated gene OTAG-12: downregulation, alternative splicing and drug sensitization.
abstract: In studying the age dependence and chronology of ovarian tumors in follicle stimulating hormone receptor knockout mice, we identified a novel ovarian tumor associated gene-12 (OTAG-12), which is progressively downregulated and maps to Chr. 8B3.3. OTAG-12 protein overexpression in mouse ovarian and mammary tumor cells suggested powerful anti-proliferative effects. In human epithelial ovarian cancers (OCs) and OC cell lines, OTAG-12 mRNA expression is downregulated in comparison with normal ovaries. Cloning and identification revealed that human OTAG-12 mapping to gene-rich Chr. 19p13.12 is expressed in three spliced forms: hOTAG-12a, hOTAG-12b and hOTAG-12c, of which b is predominant in the normal ovary. Functionally active hOTAG-12b is a simple protein with no disulfide bonds and a nuclear localization signal is present in all variants. Transfection of OTAG-12 variants in OC and tumorigenic HEK293 cells confirmed nuclear localization. hOTAG-12b overexpression in OC and HEK293 cells effectively suppressed cell growth, anchorage-dependent and independent colony formation followed by apoptosis, whereas hOTAG-12a and hOTAG-12c had no such effects. Deletion mutants identified the critical importance of carboxyl terminus for hOTAG-12b function. Doxycycline-inducible growth inhibition of HEK293 cells by hOTAG-12a was associated with effects on G2 cell cycle arrest and apoptosis induction. hOTAG-12b expression rendered tumorigenic cells more sensitive to four apoptotic stimuli including etoposide-a topoisomerase-II inhibitor. Doxycycline-induced hOTAG-12b expression blocked xenograft tumor growth in nude mice, whereas hOTAG-12a was ineffective. Although p53-pathway-dependent apoptotic agents could upregulate endogenous hOTAG-12b and p53 in UCI-101/107 OC cells, hOTAG-12b could also induce apoptosis in p53-null and platinum-resistant SKOV3 OC cells and Doxycycline-induced hOTAG-12b did not alter p53. Further study showed that hOTAG-12b increases mRNAs of pro-apoptotic genes such as BAD, GADD45α and CIEDB, while inhibiting anti-apoptotic NAIP and Akt1 expression, suggesting that hOTAG-12b-induced apoptosis might be p53-independent. These results indicate that hOTAG-12b is a putative ovarian tumor suppressor gene warranting further studies.
authors.affiliation: Molecular Endocrinology Laboratory, Clinical Research Institute of Montreal, Montreal, Québec, Canada.
authors.forename: X
authors.initials: X
authors.lastname: Chen
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: J P
authors.initials: JP
authors.lastname: Aravindakshan
authors.forename: W H
authors.initials: WH
authors.lastname: Gotlieb
authors.forename: M R
authors.initials: MR
authors.lastname: Sairam
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003001:Cloning, Molecular; D015536:Down-Regulation; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009857:Oncogenes; D010051:Ovarian Neoplasms / Q000235:genetics* / Q000473:pathology; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000737:chemistry / Q000235:genetics*
chemical_list: C560875:FAM32A protein, human; C560876:OTAG-12 protein, mouse; D025521:Tumor Suppressor Proteins