The Transcription Elongation Factor CA150 Interacts with RNA Polymerase II and the Pre-mRNA Splicing Factor SF1

Abstract

CA150 represses RNA polymerase II (RNAPII) transcription by inhibiting the elongation of transcripts. The FF repeat domains of CA150 bind directly to the phosphorylated carboxyl-terminal domain of the largest subunit of RNAPII. We determined that this interaction is required for efficient CA150-mediated repression of transcription from the ␣ 4 -integrin promoter. Additional functional determinants, namely, the WW1 and WW2 domains of CA150, were also required for efficient repression. A protein that interacted directly with CA150 WW1 and WW2 was identified as the splicing-transcription factor SF1. Previous studies have demonstrated a role for SF1 in transcription repression, and we found that binding of the CA150 WW1 and WW2 domains to SF1 correlated exactly with the functional contribution of these domains for repression. The binding specificity of the CA150 WW domains was found to be unique in comparison to known classes of WW domains. Furthermore, the CA150 binding site, within the carboxyl-terminal half of SF1, contains a novel type of proline-rich motif that may be recognized by the CA150 WW1 and WW2 domains. These results support a model for the recruitment of CA150 to repress transcription elongation. In this model, CA150 binds to the phosphorylated CTD of elongating RNAPII and SF1 targets the nascent transcript.A complex array of general transcription factors, DNA binding activators and repressors, and a multitude of coregulators mediate transcription in eukaryotes (32,48,49). Regulation of the frequency of transcription initiation is a well-documented means of controlling gene expression (32,48,64), but many genes are also controlled by modulation of the ability of RNA polymerase II (RNAPII) to elongate transcripts (11, 15-17, 37, 53, 82, 93). Although the mechanisms controlling RNAPII elongation efficiency are not completely understood, it is clear that the interplay of multiple protein factors regulates RNAPII elongation efficiency (21,70,75). Some of these elongation factors have been identified, and they belong to two classes: positive transcription elongation factors (P-TEFs), such as positive elongation factor b (P-TEFb) (38,47,67,68), and negative transcription elongation factors (N-TEFs), such as DRB sensitivity-inducing factor (DSIF) and negative elongation factor (NELF) (28,84,90). In addition to trans-acting elongation factors, nucleic acid sequences in the template and transcript can modulate elongation (11,44,82). A topic central to elongation control is the role of the carboxyl-terminal domain (CTD) of the largest subunit of RNAPII (25). The CTD contains 52 repeats of a 7-amino-acid sequence with the consensus YSPTSPS and is the substrate for several kinases, including P-TEFb (25,68,99). Phosphorylation of the CTD occurs during a transitional step of the transcription cycle, the switch from the initiation phase to the elongation phase. Hypophosphorylated RNAPII (designated RNAPIIA) is preferentially recruited to a promoter and initiates transcription. Subsequently, the RNAPII becomes hyper...

Transcription Elongation Regulator 1 Is a Co-integrator of the Cell Fate Determination Factor Dachshund Homolog 1

“…TCERG1 expression enhanced DACH1-mediated trans-repression. It has been reported previously that the carboxyl-terminal and amino-terminal halves of TCERG1, containing FF repeats and WW domains, respectively, are required for efficient repression of the ␣4-integrin gene expression (24). We included two mutants of TCERG1 representing the FF domain (FF2-6) deletion and amino-terminal deletion (591-1098) in DACH1 trans-repression assays.…”

“…The carboxyl-terminal deletion of TCERG1 (1-715) defective for DACH1 binding failed to enhance DACH1 repression, although the WW domain deletion has no effect on TCERG1 function as a co-repressor of DACH1. Through multiple WW domains in its amino terminus, TCERG1 associates with splicing factor 1 (SF1) (24), a protein that functions in the assembly of a pre-RNA splicing complex. We failed to observe synergistic repression of DACH1 and SF1 binding domain of TCERG1 (data not shown).…”

“…IP-WB analysis demonstrated the co-precipitation of TCERG1 with DACH1. The WW domain binds to the SF1 splicing factor (24). Deletion of all three WW domains did not affect DACH1 binding (Fig.…”

The RNA polymerase C-terminal domain

“…For example, the spliceosome-associated protein TCERG1 (formerly known as CA150) interacts with the phosphorylated CTD through FF domains, 30 while interacting with other splicing factors, such as SF1, through its WW domains. 31 Based on these observations, an appealing hypothesis is that proteins such as TCERG1 provide a link between the CTD and factors that play a central role in spliceosome assembly, although direct evidence to support this idea is still lacking. In addition, the RNA binding proteins PSF and p54 nrb , also implicated in rates, it is possible that increased recruitment of splicing factors, such as U2AF65, to the more highly phosphorylated CTD can influence AS decisions.…”

Untitled

“…WW1 and WW2 functional domains are also found in CA150 near the FF domains and appear to fine-tune the repression of transcription through their association with the ubiquitous splicing-transcription factor SF1. At present, CA150 is believed to bind to the phosphorylated C-terminal repeat domain of RNA polymerase II of the elongating RNAPII with SF1 targeting the nascent transcripts [51]. CA150 also has been found by DD to be up-regulated in all-trans retinoic acid (ATRA)-induced apoptosis of H9 and SR-786 T cell lymphoma cell lines [52] and to be significantly increased in striatal and cortical brain tissue from individuals with the neurodegenerative disorder Huntington's disease (HD) [53].…”