Increased Ras expression and caspase-independent neuroblastoma cell death: possible mechanism of spontaneous neuroblastoma regression.
BACKGROUND
Neuroblastoma undergoes spontaneous regression frequently during its natural course. Although programmed cell death (PCD) has been implicated in this process, accumulating evidence suggests that apoptosis, a form of PCD that is regulated by caspases, may not play a major role. We examined the mechanism(s) of spontaneous regression of neuroblastoma, focusing on the role of Ras, a favorable prognostic marker of neuroblastoma.


METHODS
Tumor tissues were analyzed by light microscopy, electron microscopy, and immunohistochemistry to examine cell degeneration and expression of Ras and several indicators of PCD. Cell degeneration was also studied in vitro in neuroblastoma cells transfected with the H-ras gene. All statistical tests were two-sided.


RESULTS
Immunohistochemical analyses revealed that Ras expression was increased in areas of cellular degeneration lacking apoptotic characteristics. The degenerating cells were fragmented without nuclear condensation and, essentially, lacked caspase-3 activation and apoptotic DNA fragmentation. These cells had ultrastructural features of autophagic degeneration, another form of PCD that is distinct from apoptosis. Focal areas of degeneration associated with Ras expression were seen more frequently in tumors from patients detected in a mass-screening program (53 [60.9%] of 87) than in tumors from clinically detected, advanced-stage patients over 1 year of age (7 [29.2%] of 24) (P =.006; chi-square test), suggesting a positive relationship between Ras-associated degeneration and probability of spontaneous regression/favorable prognosis. The characteristic features of Ras-associated nonapoptotic degeneration observed in tumor samples were recapitulated in vitro by transfection-mediated Ras expression, and Ras-mediated degeneration was augmented by TrkA, another favorable prognostic marker.


CONCLUSIONS
High-level expression of H-Ras in neuroblastoma cells is associated with caspase cascade-independent, nonapoptotic PCD. This Ras-mediated nonapoptotic tumor cell death may play a key role in spontaneous regression of neuroblastoma.
Kitanaka
Chifumi
C
Biophysics Division, National Cancer Center Research Institute, Chuo-ku, Tokyo, Japan. ckitanak@ncc.go.jp
Kato
Keisuke
K
Ijiri
Rieko
R
Sakurada
Kaori
K
Tomiyama
Arata
A
Noguchi
Kohji
K
Nagashima
Yohji
Y
Nakagawara
Akira
A
Momoi
Takashi
T
Toyoda
Yasunori
Y
Kigasawa
Hisato
H
Nishi
Toshiji
T
Shirouzu
Mikako
M
Yokoyama
Shigeyuki
S
Tanaka
Yukichi
Y
Kuchino
Yoshiyuki
Y
D017209:Apoptosis; D014408:Biomarkers, Tumor / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D004273:DNA, Neoplasm / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D011905:Genes, ras / Q000235:genetics*; D006801:Humans; D007124:Immunoenzyme Techniques; D066298:In Vitro Techniques; D007223:Infant; D008565:Membrane Proteins / Q000378:metabolism; D008854:Microscopy, Electron; D009365:Neoplasm Regression, Spontaneous; D009447:Neuroblastoma / Q000378:metabolism* / Q000473:pathology*; D011237:Predictive Value of Tests; D011379:Prognosis; D020917:Receptor, trkA; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured; D015854:Up-Regulation; D018631:ras Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
D014408:Biomarkers, Tumor; D002352:Carrier Proteins; D004273:DNA, Neoplasm; D008565:Membrane Proteins; D020917:Receptor, trkA; D020169:Caspases; D018631:ras Proteins