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.
Department of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA.
Rachel Wilson
RW
Goehe
Jacqueline C
JC
Shultz
Charuta
C
Murudkar
Sanja
S
Usanovic
Nadia F
NF
Lamour
Davis H
DH
Massey
Lian
L
Zhang
D Ross
DR
Camidge
Jerry W
JW
Shay
John D
JD
Minna
Charles E
CE
Chalfant
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