HnRNP G and Tra2beta: opposite effects on splicing matched by antagonism in RNA binding.
The hnRNP G family comprises three closely related proteins, hnRNP G, RBMY and hnRNP G-T. We showed previously that they interact with splicing activator proteins, particularly hTra2beta, and suggested that they were involved in regulating Tra2-dependent splicing. We show here that hnRNP G and hTra2beta have opposite effects upon the incorporation of several exons, both being able to act as either an activator or a repressor. HnRNP G acts via a specific sequence to repress the skeletal muscle-specific exon (SK) of human slow skeletal alpha-tropomyosin, TPM3, and stimulates inclusion of the alternative non-muscle exon. The binding of hnRNP G to the exon is antagonized by hTra2beta. The two proteins also have opposite effects upon a dystrophin pseudo-exon. This exon is incorporated in a patient to a higher level in heart muscle than skeletal muscle, causing X-linked dilated cardiomyopathy. It is included to a higher level after transfection of a mini-gene into rodent cardiac myoblasts than into skeletal muscle myoblasts. Co-transfection with hnRNP G represses incorporation in cardiac myoblasts, whereas hTra2beta increases it in skeletal myoblasts. Both the cell specificity and the protein responses depend upon exon sequences. Since the ratio of hnRNP G to Tra2beta mRNA in humans is higher in skeletal muscle than in heart muscle, we propose that the hnRNP G/Tra2beta ratio contributes to the cellular splicing preferences and that the higher proportion of hnRNP G in skeletal muscle plays a role in preventing the incorporation of the pseudo-exon and thus in preventing skeletal muscle dystrophy.
Nasim
M Talat
MT
Department of Biochemistry, University of Leicester, Leicester LE1 7RH, UK.
Chernova
Tatyana K
TK
Chowdhury
Hasnin M
HM
Yue
Bai-Gong
BG
Eperon
Ian C
IC
D001483:Base Sequence; D002311:Cardiomyopathy, Dilated / Q000235:genetics; D002478:Cells, Cultured; D029721:Drosophila Proteins; D016189:Dystrophin / Q000235:genetics / Q000378:metabolism; D005091:Exons; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology; D032386:Myoblasts, Cardiac / Q000502:physiology; D009928:Organ Specificity; D011544:Pseudogenes; D012313:RNA / Q000378:metabolism*; D012326:RNA Splicing; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D014335:Tropomyosin / Q000235:genetics / Q000378:metabolism
D029721:Drosophila Proteins; D016189:Dystrophin; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D012261:Ribonucleoproteins; C498783:TPM3 protein, human; D014335:Tropomyosin; C066174:tra2 protein, Drosophila; D012313:RNA