title: Loss of giant obscurins promotes breast epithelial cell survival through apoptotic resistance.
abstract: Obscurins (∼70 - 870 kDa), encoded by the single OBSCN gene, are cytoskeletal proteins originally identified in striated muscles with structural and regulatory roles. Recently, analysis of 13,023 genes in breast and colorectal cancers identified OBSCN as one of the most frequently mutated genes, implicating it in cancer formation. Herein we studied the expression profile of obscurins in breast, colon, and skin cancer cell lines and their involvement in cell survival. Immunoblot analysis demonstrated significant reduction of obscurin proteins [corrected] in cancer cells, resulting from decreased mRNA levels and/or the presence of mutant transcripts. In normal epithelium, obscurins localize in cytoplasmic puncta, the cell membrane, and the nucleus. Accordingly, subcellular fractionation demonstrated the presence of 2 novel nuclear isoforms of ∼110 and ∼120 kDa. Nontumorigenic MCF10A breast epithelial cells stably transduced with shRNAs targeting giant obscurins exhibited increased viability (∼30%) and reduced apoptosis (∼20%) following exposure to the DNA-damaging agent etoposide. Quantitative RT-PCR further indicated that the antiapoptotic genes BAG4 and HAX1 were up-regulated (1.5- and 1.4-fold, respectively), whereas initiator caspase-9 and death caspase-3 transcripts were down-regulated (0.8- and 0.6-fold, respectively). Our findings are the first to pinpoint critical roles for obscurins in cancer development by contributing to the regulation of cell survival.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA. ako
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Perry
authors.forename: Marey
authors.initials: M
authors.lastname: Shriver
authors.forename: Marie G
authors.initials: MG
authors.lastname: Mameza
authors.forename: Bryan
authors.initials: B
authors.lastname: Grabias
authors.forename: Eric
authors.initials: E
authors.lastname: Balzer
authors.forename: Aikaterini
authors.initials: A
authors.lastname: Kontrogianni-Konstantopoulos
mesh_terms: D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D001483:Base Sequence; D001940:Breast / Q000166:cytology* / Q000378:metabolism*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival / Q000235:genetics / Q000502:physiology; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005047:Etoposide / Q000633:toxicity; D005260:Female; D015870:Gene Expression; D020662:Guanine Nucleotide Exchange Factors / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics* / Q000502:physiology*; D006801:Humans; D009124:Muscle Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics* / Q000502:physiology*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D064067:Rho Guanine Nucleotide Exchange Factors; D012878:Skin Neoplasms / Q000235:genetics / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D009124:Muscle Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D034741:RNA, Small Interfering; D064067:Rho Guanine Nucleotide Exchange Factors; D005047:Etoposide; C578224:OBSCN protein, human; D017346:Protein Serine-Threonine Kinases