hnRNP L regulates the tumorigenic capacity of lung cancer xenografts in mice via caspase-9 pre-mRNA processing.
Caspase-9 is involved in the intrinsic apoptotic pathway and suggested to play a role as a tumor suppressor. Little is known about the mechanisms governing caspase-9 expression, but post-transcriptional pre-mRNA processing generates 2 splice variants from the caspase-9 gene, pro-apoptotic caspase-9a and anti-apoptotic caspase-9b. Here we demonstrate that the ratio of caspase-9 splice variants is dysregulated in non-small cell lung cancer (NSCLC) tumors. Mechanistic analysis revealed that an exonic splicing silencer (ESS) regulated caspase-9 pre-mRNA processing in NSCLC cells. Heterogeneous nuclear ribonucleoprotein L (hnRNP L) interacted with this ESS, and downregulation of hnRNP L expression induced an increase in the caspase-9a/9b ratio. Although expression of hnRNP L lowered the caspase-9a/9b ratio in NSCLC cells, expression of hnRNP L produced the opposite effect in non-transformed cells, suggesting a post-translational modification specific for NSCLC cells. Indeed, Ser52 was identified as a critical modification regulating the caspase-9a/9b ratio. Importantly, in a mouse xenograft model, downregulation of hnRNP L in NSCLC cells induced a complete loss of tumorigenic capacity that was due to the changes in caspase-9 pre-mRNA processing. This study therefore identifies a cancer-specific mechanism of hnRNP L phosphorylation and subsequent lowering of the caspase-9a/9b ratio, which is required for the tumorigenic capacity of NSCLC cells.
Goehe
Rachel Wilson
RW
Department of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA.
Shultz
Jacqueline C
JC
Murudkar
Charuta
C
Usanovic
Sanja
S
Lamour
Nadia F
NF
Massey
Davis H
DH
Zhang
Lian
L
Camidge
D Ross
DR
Shay
Jerry W
JW
Minna
John D
JD
Chalfant
Charles E
CE
D017398:Alternative Splicing; D000818:Animals; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D005091:Exons; D034664:Heterogeneous-Nuclear Ribonucleoprotein L / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008175:Lung Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D008297:Male; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D037941:Silencer Elements, Transcriptional; D014183:Transplantation, Heterologous
D034664:Heterogeneous-Nuclear Ribonucleoprotein L; D007527:Isoenzymes; D012322:RNA Precursors; D034741:RNA, Small Interfering; D053453:Caspase 9