Antagonistic effects of the SRp30c protein and cryptic 5' splice sites on the alternative splicing of the apoptotic regulator Bcl-x.
Alternative 5' splice site selection allows Bcl-x to produce two isoforms with opposite effects on apoptosis. The pro-apoptotic Bcl-x(S) variant is up-regulated by ceramide and down-regulated by protein kinase C through specific cis-acting exonic elements, one of which is bound by SAP155. Splicing to the Bcl-x(S) 5' splice site is also enforced by heterogeneous nuclear ribonucleoprotein (hnRNP) F/H proteins and by Sam68 in cooperation with hnRNP A1. Here, we have characterized exon elements that influence splicing to the 5' splice site of the anti-apoptotic Bcl-x(L) isoform. Within a 86-nucleotide region (B3) located immediately upstream of the Bcl-x(L) donor site we have identified two elements (ML2 and AM2) that stimulate splicing to the Bcl-x(L) 5' splice site. SRp30c binds to these elements and can shift splicing to the 5' splice site of Bcl-x(L) in an ML2/AM2-dependent manner in vitro and in vivo. The B3 region also contains an element that represses the use of Bcl-x(L). This element is bound by U1 small nuclear ribonucleoprotein and contains two 5' splice sites that can be used when the Bcl-x(L) 5' splice site is mutated or the ML2/AM2 elements are deleted. Conversely, mutating the cryptic 5' splice sites stimulates splicing to the Bcl-x(L) site. Thus, SRp30c stimulates splicing to the downstream 5' splice site of Bcl-x(L), thereby attenuating the repressive effect of upstream U1 snRNP binding sites.
Cloutier
Philippe
P
RNA/RNP Group, Département de Microbiologie et d'Infectiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada.
Toutant
Johanne
J
Shkreta
Lulzim
L
Goekjian
Serge
S
Revil
Timothée
T
Chabot
Benoit
B
D017398:Alternative Splicing; D017209:Apoptosis; D001483:Base Sequence; D001665:Binding Sites; D005091:Exons; D006801:Humans; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D000068103:Serine-Arginine Splicing Factors; D051020:bcl-X Protein / Q000378:metabolism*
D009687:Nuclear Proteins; D020033:Protein Isoforms; D016601:RNA-Binding Proteins; D017412:Ribonucleoprotein, U1 Small Nuclear; D051020:bcl-X Protein; D000068103:Serine-Arginine Splicing Factors