Transcription elongation factor ELL2 directs immunoglobulin secretion in plasma cells by stimulating altered RNA processing

Abstract

Immunoglobulin secretion is modulated by a competition between use of a weak promoter proximal poly(A) site and a non-consensus splice site in the last secretory-specific exon of the heavy chain pre-mRNA. RNA polymerase II transcription elongation factor ELL2, induced in plasma cells, enhanced both polyadenylation and exon skipping with the Igh gene and reporter constructs. Lowering ELL2 expression by hnRNP F transfection or siRNA reduced secretory-specific forms of IgH mRNA. ELL2 and polyadenylation factor CstF-64 co-tracked with RNA polymerase II across the Igh mu and gamma gene segments; association of both factors was blocked by ELL2 siRNA. Thus loading of ELL2 and CstF-64 on RNAP-II was linked, causative for enhanced proximal poly(A) site use and necessary for IgH mRNA processing.

Hide and Go Seek: Activation of the Secretory-Specific Poly (A) Site of Igh by Transcription Elongation Factors

“…Yeast sub1 has been shown to interact with all the CTD kinases and it may have multiple actions throughout the transcription cycle (Garcia, Rosonina et al 2010). Surprisingly, our experiments did not show a role for PC4/ sub1 in directing alternative Igh mRNA expression (Martincic, Alkan et al 2009) and below.…”

“…The CCNC complex of cyclin C and cdk8 along with PC4/ sub1 are induced by IRF4 in multiple myeloma a tumor of the plasma cells (Shaffer, Emre et al 2008) and could act on the Igh gene to regulate transcription. We re-examined the micro-array data on gene expression in B versus plasma cells that we published previously (Martincic, Alkan et al 2009) to concentrate on transcription elongation factors. The data are shown Table 1.…”

“…We showed that treatment of plasma cells with DRB inhibits ser-2 phosphorylation and causes the unmodified RNAP-II on the Ig heavy chain in plasma cells to stall near the 5'-end of the Ig gene (Shell, Martincic et al 2007) and Figure 3. DRB also causes the decreased association of ELL2, PC4 and the polyadenylation factor CstF-64, suggesting that their binding to RNAP-II require the ser-5 and ser-2 (Shell, Martincic et al 2007), normal and DRB treatment and siell2 data (Martincic, Alkan et al 2009). The error bars and statistics showing significance are detailed in those publications and omitted here for clarity.…”

“…Changes in the level of rate-limiting, trans acting factors, like CstF-64 following lipopolysaccharide stimulation in B-cells (Takagaki, Seipelt et al 1996) or macrophages (Shell, Hesse et al 2005) or in the cell cycle (Martincic, Campbell et al 1998), can also increase mRNA polyadenylation (Getz, Elder et al 1976). Changes in the level of ELL2, a transcription elongation factor, increase use of the first poly(A) site in the Igh gene (Martincic, Alkan et al 2009), an important step for plasma cell development. Therefore, the throughput of initiated transcripts to polyadenylated, mature mRNA is limited by a.)…”

Ending the message: poly(A) signals then and now

“…This process is regulated by levels of CStF-64, which are more limited in pre-B cells than in mature B cells (Takagaki et al 1996;Takagaki and Manley 1998). Also, Pol II elongation factors may act to modulate this PAS switch (Martincic et al 2009). A similar type of APA regulation exists for the calcitonin gene.…”