title: Yeast screens identify the RNA polymerase II CTD and SPT5 as relevant targets of BRCA1 interaction.
abstract: BRCA1 has been implicated in numerous DNA repair pathways that maintain genome integrity, however the function responsible for its tumor suppressor activity in breast cancer remains obscure. To identify the most highly conserved of the many BRCA1 functions, we screened the evolutionarily distant eukaryote Saccharomyces cerevisiae for mutants that suppressed the G1 checkpoint arrest and lethality induced following heterologous BRCA1 expression. A genome-wide screen in the diploid deletion collection combined with a screen of ionizing radiation sensitive gene deletions identified mutants that permit growth in the presence of BRCA1. These genes delineate a metabolic mRNA pathway that temporally links transcription elongation (SPT4, SPT5, CTK1, DEF1) to nucleopore-mediated mRNA export (ASM4, MLP1, MLP2, NUP2, NUP53, NUP120, NUP133, NUP170, NUP188, POM34) and cytoplasmic mRNA decay at P-bodies (CCR4, DHH1). Strikingly, BRCA1 interacted with the phosphorylated RNA polymerase II (RNAPII) carboxy terminal domain (P-CTD), phosphorylated in the pattern specified by the CTDK-I kinase, to induce DEF1-dependent cleavage and accumulation of a RNAPII fragment containing the P-CTD. Significantly, breast cancer associated BRCT domain defects in BRCA1 that suppressed P-CTD cleavage and lethality in yeast also suppressed the physical interaction of BRCA1 with human SPT5 in breast epithelial cells, thus confirming SPT5 as a relevant target of BRCA1 interaction. Furthermore, enhanced P-CTD cleavage was observed in both yeast and human breast cells following UV-irradiation indicating a conserved eukaryotic damage response. Moreover, P-CTD cleavage in breast epithelial cells was BRCA1-dependent since damage-induced P-CTD cleavage was only observed in the mutant BRCA1 cell line HCC1937 following ectopic expression of wild type BRCA1. Finally, BRCA1, SPT5 and hyperphosphorylated RPB1 form a complex that was rapidly degraded following MMS treatment in wild type but not BRCA1 mutant breast cells. These results extend the mechanistic links between BRCA1 and transcriptional consequences in response to DNA damage and suggest an important role for RNAPII P-CTD cleavage in BRCA1-mediated cancer suppression.
authors.affiliation: Department of Surgery, Duke University Medical Center, Durham, North Carolina, United States of America. benne048@mc.duke.edu
authors.forename: Craig B
authors.initials: CB
authors.lastname: Bennett
authors.forename: Tammy J
authors.initials: TJ
authors.lastname: Westmoreland
authors.forename: Carmel S
authors.initials: CS
authors.lastname: Verrier
authors.forename: Carrie A B
authors.initials: CA
authors.lastname: Blanchette
authors.forename: Tiffany L
authors.initials: TL
authors.lastname: Sabin
authors.forename: Hemali P
authors.initials: HP
authors.lastname: Phatnani
authors.forename: Yuliya V
authors.initials: YV
authors.lastname: Mishina
authors.forename: Gudrun
authors.initials: G
authors.lastname: Huper
authors.forename: Alice L
authors.initials: AL
authors.lastname: Selim
authors.forename: Ernest R
authors.initials: ER
authors.lastname: Madison
authors.forename: Dominique D
authors.initials: DD
authors.lastname: Bailey
authors.forename: Adebola I
authors.initials: AI
authors.lastname: Falae
authors.forename: Alvaro
authors.initials: A
authors.lastname: Galli
authors.forename: John A
authors.initials: JA
authors.lastname: Olson
authors.forename: Arno L
authors.initials: AL
authors.lastname: Greenleaf
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Marks
mesh_terms: D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D004249:DNA Damage; D005804:Genes, Lethal; D042822:Genomic Instability; D006801:Humans; D006868:Hydrolysis; D012319:RNA Polymerase II / Q000378:metabolism*; D035602:Transcriptional Elongation Factors / Q000378:metabolism*
chemical_list: D019313:BRCA1 Protein; D002868:Chromosomal Proteins, Non-Histone; D035602:Transcriptional Elongation Factors; C069940:SPT5 transcriptional elongation factor; D012319:RNA Polymerase II