The tumor suppressor activity of MDA-7/IL-24 is mediated by intracellular protein expression in NSCLC cells.
mda-7/IL-24 (HGMW-approved symbol IL24) is a tumor suppressor gene whose expression is lost during tumor progression. Gene transfer using adenoviral mda-7/IL-24 (Ad-mda7) exhibits minimal toxicity on normal cells while inducing potent apoptosis in a variety of cancer cell lines. Ad-mda7-transduced cells express high levels of MDA-7 protein intracellularly and also secrete a soluble form of MDA-7 protein. In this study, we sought to determine whether the intracellular or secreted MDA-7 protein was responsible for anti-tumor activity in H1299 lung tumor cells. Ad-mda7 transduction of lung tumor cells increased expression of stress-related proteins, including BiP, GADD34, PP2A, caspases 7 and 12, and XBP-1, consistent with activation of the UPR pathway, a key sensor of endoplasmic reticulum (ER)-mediated stress. Blocking secretion of MDA-7 did not inhibit apoptosis, demonstrating that intracellular MDA-7 was responsible for cytotoxicity. Consistent with this result, when applied directly to lung cancer cells, soluble MDA-7 protein exhibited minimal cytotoxic effect. We then generated mda-7 expression constructs using vectors that target the expressed protein to various subcellular compartments, including cytoplasm, nucleus, and ER. Only full-length and ER-targeted MDA-7 elicited cell death in tumor cells. Thus in lung cancer cells, Ad-mda7 activates the UPR stress pathway and induces apoptosis via intracellular MDA-7 expression in the secretory pathway.
Sieger
Kerry A
KA
Introgen Therapeutics, Inc., Houston, TX 77030, USA.
Mhashilkar
Abner M
AM
Stewart
Alexis
A
Sutton
R Bryan
RB
Strube
Randall W
RW
Chen
Si Yi
SY
Pataer
Abujiang
A
Swisher
Stephen G
SG
Grimm
Elizabeth A
EA
Ramesh
Rajagopal
R
Chada
Sunil
S
D000256:Adenoviridae / Q000235:genetics; D000943:Antigens, Differentiation; D017209:Apoptosis; D015153:Blotting, Western; D020126:Brefeldin A / Q000494:pharmacology; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics*; D053454:Caspase 12; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D018797:Cell Cycle Proteins; D002460:Cell Line; D045744:Cell Line, Tumor; D002469:Cell Separation; D002470:Cell Survival; D016207:Cytokines / Q000235:genetics*; D018450:Disease Progression; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D005434:Flow Cytometry; D018014:Gene Transfer Techniques; D016147:Genes, Tumor Suppressor; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007378:Interleukins / Q000235:genetics*; D008175:Lung Neoplasms / Q000235:genetics*; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D018832:Molecular Chaperones / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D017510:Protein Folding; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D011506:Proteins / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology; D000099180:Interleukin-24
D000943:Antigens, Differentiation; D020126:Brefeldin A; D053454:Caspase 12; D053179:Caspase 7; D020169:Caspases; D018797:Cell Cycle Proteins; D016207:Cytokines; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D007378:Interleukins; D018832:Molecular Chaperones; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D011506:Proteins; D014415:Tunicamycin; D000099180:Interleukin-24; C431904:Il24 protein, mouse; C432785:PPP2R1B protein, human; C087519:PPP1R15A protein, human; C513256:Ppp1r15a protein, mouse; C506444:CASP12 protein, human; C505520:CASP7 protein, human; C506440:Casp12 protein, mouse; C505524:Casp7 protein, mouse