Hypoxia selects for high-metastatic Lewis lung carcinoma cells overexpressing Mcl-1 and exhibiting reduced apoptotic potential in solid tumors.
Low oxygen tension (hypoxia) is a common feature of solid tumors and stimulates the expressions of a variety of genes including those related to angiogenesis, apoptosis and endoplasmic reticulum (ER) stress response. Here we show a close correlation between metastatic potential and the resistance to hypoxia- and ER stress-induced apoptosis among the cell lines with differing metastatic potential derived from Lewis lung carcinoma. An apoptosis-specific expression profiling and immunoblot analyses revealed that the expression of antiapoptotic Mcl-1 increased as the resistance to apoptosis increased. Downregulation of the Mcl-1 expression in the high-metastatic cells by Mcl-1 small interfering RNA increased the sensitivity to hypoxia-induced apoptosis and decreased the metastatic ability. The hypoxia-induced apoptosis was not associated with p53 accumulation, although at present it is not possible to conclude that apoptosis-induced apoptosis is p53-independent. There was no correlation between the expression levels of ER stress-response proteins GADD153, GRP78 and ORP150 and the resistance to hypoxia or ER stresses. In vitro, small numbers of the high-metastatic cells overtook the low-metastatic cells after exposure to several rounds of hypoxia and reoxygenation. In solid tumors initially established from equal mixtures, the proportion of the high-metastatic cells to low-metastatic cells was significantly higher in hypoxic areas. Moreover, the high-metastatic cells were overtaking the low-metastatic cells in some of the tumors. Thus, tumor hypoxia and ER stress may provide a physiological selective pressure for the expansion of the high-metastatic cells overexpressing Mcl-1 and exhibiting reduced apoptotic potential in solid tumors.
Koshikawa
N
N
Division of Chemotherapy, Chiba Cancer Center Research Institute, Chuoh-ku, Chiba, Japan.
Maejima
C
C
Miyazaki
K
K
Nakagawara
A
A
Takenaga
K
K
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D018827:Carcinoma, Lewis Lung / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism
C497250:Ddit3 protein, mouse; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; C579094:Mcl1 protein, mouse; D018832:Molecular Chaperones; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; C050087:oxygen-regulated proteins; D051742:Transcription Factor CHOP